Basic Track

Transcription

Basic Track

Chapter
AMERICAN RAILWAY ENGINEERING AND
MAINTENANCE OF WAY ASSOCIATION
_________________________________________
Practical Guide To Railway Engineering
Basic Track
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©2003 AREMA®
AREMA COMMITTEE 24 - EDUCATION & TRAINING
Basic Track
Joseph E. Riley P.E.
Metra
Chicago, IL 60661
[email protected]
James C. Strong P.E.
Parsons Transportation Group
Martinez, CA 94553-1845
[email protected]
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Chapter
CHAPTER 3 - BASIC TRACK
Basic Track
The engineer will frequently work from a set of standardized railway
or transit standards when making his or her selection of track
components for any given design project. However, a basic
understanding of elementary track componentry, geometry and
maintenance operations is necessary if intelligent decisions are to
be made within the options that are typically available.
3.1 Track Components
W
e begin our study with the prime component of the track – the rail.
3.1.1 Rail
Rail is the most expensive material in the track.1 Rail is steel that has been rolled into
an inverted "T" shape. The purpose of the rail is to:
•
Transfer a train's weight to cross ties.
•
Provide a smooth running surface.
•
Guide wheel flanges.
1
Canadian National Railway Track Maintainer’s Course
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The first rails were wooden.
Later iron straps were added to
the wooden rails to reduce
wear. This was followed by
cast iron rails and finally, steel
rails were rolled from an ingot.
(See Figure 3-1) Today, steel
rail is rolled in a continuous
casting process.
Over the years, the shape of rail
has also changed. However,
the "T" rail section, first rolled
in 1831, has been the standard
Figure 3-1 Rolled Rail – Photo by J. E. Riley
in North America ever since.
Rails vary in weight and shape (known as "section").
Identification of Rail
The weight of rail is based on how much the rail weighs in pounds per yard. Over the
past 200 years, increasingly heavier rail was required to handle the increased weight of
locomotives and rolling stock and traffic volume increases. The largest rail commonly
used today is 136 lb., although 140 lb. is still rolled and second-hand 152 lb. rail is
available in limited quantities. AREMA has recently recommended a new rail section
to maximize available head wear and minimize stress related failures. This section is
the 141 lb., but is not yet widely in use. A rail's weight, along with its section and other
information, is rolled as a raised character onto the web of the rail.
The rail section refers to the shape of the cross-section of a rail. For example, there are
several sections of 100 lb. rail. Rail mills identify the different shapes and types of rails
by codes rolled onto the rail's web. The section code appears right after the weight.
The section codes signify different dimension and shape standards. These codes
further represent the engineering group, which created the design plan (thus, the
standard) for that rail section. Some of the more common section codes are:
RE:
REHF:
American Railway Engineering Maintenance of Way Association
(AREMA).
AREMA “head free” section.
ARA-A: American Railway Association, “A” section.
ARA-B: American Railway Association, “B” section.
ASCE: American Society of Civil Engineers.
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The rail section base dimension is important when choosing tie plates, rail anchors and
pre-drilled timber ties and concrete ties. The height of the rail and the width of the
head of the rail are important to determine the selection of joint bars. Next, the
method of hydrogen elimination is specified. CC indicates that the rail was controlled
cooled. Controlled cooling was first utilized in the late 1930's. Rail rolled prior to this
date has a proclivity to the formation of dangerous transverse defect type fissures.
Other methods used in new rail today to eliminate hydrogen bubbles, includes
controlled cooling of blooms (BC) and Vacuum Degassing (VT). Finally, the rail
manufacturer, the year rolled and the month rolled are also indicated. On the opposite
side of the web of the rail, additional information is hot stamped indicating whether the
rail has been end hardened (CH), the heat number, rail letter designation if not
continuous cast, indicating from what part of the ingot the rail is from and if of a
special metallurgy, the designation for special alloys.
The information provided by the rail branding and stamping provides valuable insight
to the suitability for reuse of second-hand rail in a variety of situations. For example,
many railways limit the use of rail stamped as an "A" rail within the ingot to slow speed
yards and sidings because of the potential for the creation of seams in the head and
web of the rail called pipe rail or the development of vertical split heads. This does not
mean that “A” rail cannot be used in main tracks, as rail chemistry is probably a better
indicator of the proclivity of the development of such defects.
In general, rail sections smaller than 90 lb. should not be utilized for new construction,
but is available second-hand for replacing rail in trackage utilizing the given section.
Ninety lb. and 100 lb. sections are adequate for many transit and light tonnage
industrial park trackage. New trackage, exposed to 100-ton or heavier cars, should not
utilize rail sections smaller than the 11525 RE. Second-hand 11025 and 11228 RE are
comparable to the 11525 RE section, but have a proclivity to head and web separations
due to the reduced radius in the fillet between the web and the head of the rail. Good
rail in these sections is becoming increasingly more difficult to find and the engineer
may wish to give serious thought about the possibility of securing usable replacement
rail in these sections for maintenance purposes in later years. The common 5-1/2"
base sections (11525 RE and 119 RE) are commonly specified for medium tonnage
and/or commuter/passenger/transit lines. For heavy tonnage trackage, the 6" base rail
sections are preferable. These include 13225 RE, 133 RE, 136 RE, 140 RE and the
new 141 RE sections. Various 130 and 131 lb. sections are available second-hand, but
many have head and web separation related problems.
The engineer wishing to utilize second-hand rail must take into consideration the
amount of tread (top of rail) and gage wear present on the rail. Rail ends bent, kinked
or badly battered may not be suitable for jointed rail relay use. The AREMA Manual
for Railway Engineering has recommended maximum wear and alignment tolerances
that are designated by the category of track usage. If the rail is to be welded into
continuous welded rail strings (CWR), end batter and bent ends can be cropped off,
but gage and tread wear, as well as surface defects such as engine burns or bad shells,
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may make a rail unsuitable for welding. If available, the engineer should attempt to
secure the rail's defect history. The engineer should not be afraid of utilizing secondhand rail. Indeed, rail exposed earlier in its life to nothing heavier than the 70-ton car
has often become work hardened. New rail today exposed to unit train tonnage is
abraded away before it ever becomes work hardened. On the other hand, today's rail
steels possess improved rail chemistries that permit life expectancies exceeding a billion
gross tons, whereas yesterday’s rail rarely lasted more than 600 million gross tons.
Whenever possible, the engineer should specify the use of welded rail. The elimination
of the joint will reduce future maintenance costs by exponential factors. New rail is
rolled in lengths of either 39 or 80 feet in length. Construction is presently under way
to roll rail in even longer lengths. These rails are then welded in a controlled
environment into individual strings of up to 1600 feet in length for delivery to the field.
3.1.2 Ties
Ties are typically made of one of four materials:2
•
Timber
•
Concrete
•
Steel
•
Alternative materials
The purpose of the tie is to cushion and transmit the load of the train to the ballast
section as well as to maintain gage. Wood and even steel ties provide resiliency and
absorption of some impact through the tie itself. Concrete ties require pads between
the rail base and tie to provide a cushioning effect.
Timber Ties
It is recommended that all timber ties be pressure-treated with preservatives to protect
from insect and fungal attack.3 Hardwood ties are the predominate favorites for track
and switch ties. Bridge ties are often sawn from the softwood species. Hardwood ties
are designated as either track or switch ties.
Factors of first importance in the design and use of ties include durability and
resistance to crushing and abrasion. These depend, in turn, upon the type of wood,
1965 Roadmasters & Maintenance of Way Association Proceedings, Quality Track Maintenance Factors –
Their Relative Importance, W. W. Hay
2
3
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adequate seasoning, treatment with chemical preservatives, and protection against
mechanical damage. Hardwood ties provide longer life and are less susceptible to
mechanical damage.
Track Ties
Timber track ties are graded with nominal dimensions of 7" x 9" x 8'-6" or 9'-0" or
smaller ties which are 6" x 8" x 8'-0". (See Figure 3-2) The 6" x 8" x 8'-0" are typically
utilized for sidings, industry tracks and very light density trackage. An industrial grade
of both ties is also available. These ties have more wane, bark, splits or other surface
related defects than recommended under the timber grading rules. Both AREMA and
the Railway Tie Association (RTA) publish specifications and standards relating to the
grading of timber and the definitions for the above timber physical characteristics. The
cost savings may make industrial grade ties attractive for some plant trackage exposed
to infrequent and light tonnage. It is generally acknowledged that the quality of
hardwood tie available today does not meet yesteryear's standards. Thus, the additional
cost of providing gang plates, S-irons or C-irons for the tie ends may be a worthwhile
investment in extending tie life from end splitting failures. Track ties may be ordered
adzed and pre-drilled for the appropriate rail section to be used if desired. Secondhand ties, reclaimed from line abandonments, may also be available. There is wide
debate regarding the suitability and cost effectiveness of using recovered ties.
Deterioration of that part of the tie previously buried in the ballast occurs rapidly once
the tie is exposed to the air. If second-hand ties are used, do not turn the tie over, thus
providing a fresh surface for the top of the tie. These ties will deteriorate very quickly.
Better to plug the tie, adze the surface if necessary and insert the tie as it was originally
orientated. Occasionally, softwood ties may be specified for a track tie. Their use is
limited to temporary track situations such as shoe-fly's, etc., or where tonnage is very
light or hardwood species are prohibitive in cost.
For quality maintenance, ties should be not
less than 8 ft. 6 in. in length. For moderately
heavy or heavy-traffic conditions, especially
on curves of 6 degrees or more, the 9-ft. tie is
preferred, 7 in. by 9 in. in cross-section,
because of the greater stability from the larger
support and friction area. It also assists in
restraining continuous welded rail.
For lines of moderate to medium tonnage, a
tie spacing equivalent to 22 ties per 39-ft. rail Figure 3-2 Hardwood Track Ties – Photo by J. E. Riley
(21-1/4 in.) is sufficient. Heavy tonnage lines
or lines with sharp curves will find 24 ties per rail panel (19-1/2-in.) to have advantages
in holding gauge and reducing bending moment stresses in the rail.
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Switch Ties
Switch ties (Figure 3-3) are commonly
hardwood species, usually provided in either
6" or 12" increments beginning at 9'-0" up
to 23'-0" in length. Nominal cross-section
dimensions are 7" x 9", although larger ties
are specified by some railways. The primary
use for switch ties is relegated to turnouts
(thus their name). However, they are also
used in bridge approaches, crossovers, at hot
box detectors and as transition ties. Some
railways use switch ties in heavily traveled Figure 3-3 Switch Timber – Photo by Craig Kerner
road crossings and at insulated rail joints.
Switch ties ranging in length from 9'-0" to 12'-0" can also be used as "swamp" ties.
The extra length provides additional support for the track in swampy or poor-drained
areas. Some railways have utilized Azobe switch ties (an extremely dense African
wood) for high-speed turnouts. The benefits associated with reduced plate cutting and
fastener retention may be offset by the high import costs of this timber.
Softwood Ties
Softwood timber (Figure 3-4) is
more rot resistant than hardwoods,
but does not offer the resistance of
a hardwood tie to tie plate cutting,
gauge spreading and spike hole
enlargement
(spike
killing).
Softwood ties also are not as
effective in transmitting the loads to
the ballast section as the hardwood
tie. Softwood and hardwood ties
must not be mixed on the main
track except when changing from
one category to another.
Softwood ties are typically used in
open deck bridges.
Figure 3-4 Softwood Timber - Photo by J. E. Riley
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Concrete Ties
Concrete ties (Figure 3-5) are rapidly
gaining acceptance for heavy haul
mainline use, (both track and
turnouts), as well as for curvature
greater than 2°. They can be supplied
as crossties (i.e. track ties) or as switch
ties. They are made of pre-stressed
concrete containing reinforcing steel
wires. The concrete crosstie weighs
about 600 lbs. vs. the 200 lb. timber
track tie. The concrete tie utilizes a Figure 3-5 Concrete Ties – Photo by Kevin Keefe
specialized pad between the base of the
rail and the plate to cushion and absorb the load, as well as to better fasten the rail to
the tie. Failure to use this pad will cause the impact load to be transmitted directly to
the ballast section, which may cause rail and track surface defects to develop quickly.
An insulator is installed between the edge of the rail base and the shoulder of the plate
to isolate the tie (electrically). An insulator clip is also placed between the contact point
of the elastic fastener used to secure the rail to the tie and the contact point on the base
of the rail.
Steel Ties
Steel ties (Figure 3-6) are often
relegated to specialized plant
locations or areas not
favorable to the use of either
timber or concrete, such as
tunnels with limited headway
clearance. They have also
been utilized in heavy
curvature prone to gage
widening.
However, they
have not gained wide
acceptance due to problems
associated with shunting of
Figure 3-6 Steel Ties
signal current flow to ground.
Some lighter models have also experienced problems with fatigue cracking.
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Alternative Material Ties
Significant research has been done
on a number of alternative materials
used for ties. These include ties
with
constituent
components
including ground up rubber tires,
glued reconstituted ties and plastic
milk cartons. Appropriate polymers
are added to these materials to
produce a tie meeting the required
criteria. To date, there have been
only test demonstrations of these
Figure 3-7 Alternative Type Material Tie
materials or installations in light
tonnage transit properties. It remains to be seen whether any of these materials will
provide a viable alternative to the present forms of ties that have gained popularity in
use. (Figure 3-7)
3.1.3 Ballast Section
A principal purpose of the ballast section is to anchor the track and provide resistance
against lateral, longitudinal and vertical movement of ties and rail, i.e., stability.4
Additionally, the ballast section bears and distributes the applied load with diminished
unit pressure to the subgrade beneath, gives immediate drainage to the track, facilitates
maintenance and provides a necessary degree of elasticity and resilience. Good drainage
is of utmost importance to assure required stability.
Ideal qualities in ballast materials are hardness and toughness, i.e., freedom from
shattering under impact, durability or resistance to abrasion and weathering, freedom
from deleterious particles (dirt), workability, compactability, cleanability, availability,
and low first cost. The principal desired characteristic is maximum stability at minimum
over-all economic cost, including frequency of maintenance cycle, life of rails, ties and
fastenings, and the labor costs. Quality maintenance requires that more attention be
given to the quality and characteristics of ballast. The practice of buying ballast purely
because of low first cost or accessibility is clearly suspect.
The ballast sizes recommended in the AREMA Manual for Railway Engineering are
time-proven and acceptable. However, a number of AASHTO and ASTM gradations
are similar to AREMA’s and may be acceptable for use in some situations. This may be
more cost effective in locales where AREMA gradations are not readily available but
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highway rock gradations are available. The comparison chart found at the back of this
chapter cross-references various gradations.
More important factors, probably, are the shape of the ballast particle, its degree of
sharpness, angularity, and surface texture or roughness. These factors have been shown
to have a significant effect upon the stability and compactability of aggregates in
general.
The ballast types most nearly meeting the ideal requirements, in order of preference,
are granite trap rock, hard limestone, open hearth and blast furnace slags, other
limestones, prepared gravels, chat, volcanic ash, pit-run gravel and coarse sand (as a last
resort). There are other materials of local deposition that may be usefully considered,
especially for light-traffic and industrial switching tracks.
Keeping ballast in a clean, free-draining condition begins with the selection of a ballast
material that is tough, durable, not subject to abrasion, and free of clays, silts, and soft
and friable pieces. Beyond that, maintaining adequate drainage and cleaning or renewal
should be performed as needed.
Shoulder and intertrack cleaning are satisfactory until the ballast becomes cemented,
too finely abraided, or until mud and dirt have collected under the ties and in the cribs.
At this point, undercutting and cleaning, or undercutting, wasting and replacing with
new ballast is in order. Undercutting may also be a necessary alternative to raising track
during the surfacing and re-ballasting program where overhead clearances are
restrictive. (See the Appendix – Maintenance Processes for specific procedures used in
undercutting.)
The depth of ballast required is a function of the supporting capacity of the subgrade.
It should be sufficient to distribute the pressures to within the bearing capacity of the
subgrade. Uniform distribution of pressures is another factor that varies with depth.
Usually, a minimum depth of 18 to 24 inches is necessary to achieve uniform
distribution. This depth may be distributed between ballast and sub-ballast. The greater
the height of ballast around the tie, the greater is the resistance to vertical displacement.
The same holds true for shoulder and lateral displacement. A full crib of high-grade
ballast should be maintained for continuous welded rail with a ballast shoulder width of
10 to 12 in. beyond the ends of tie considered as ideal. Check individual railway
standards for designated ballast shoulder widths. Typically, 12” is required on the high
side of curves and some railways will specify as little as 6” on tangent shoulders and the
low side of curves. For jointed track, a minimum height of no more than two inches
below top of tie should be held with 6 to 8 in. of ballast shoulder outside the ends of
ties. For gravel, chat and other materials of lesser quality, the crib should be filled to the
top of tie and a 10- to 12-in. shoulder maintained beyond the tie end. The practice of
permitting the sloping of the ballast section downward at the tie ends rather than
maintaining a shoulder may reduce the lateral resistance needed for continuous welded
rail.
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3.1.4 Rail Joints
The purposes of the rail joint (made up of two joint bars or more commonly called
angle bars) are to hold the two ends of the rail in place and act as a bridge or girder
between the rail ends.5 The joint bars prevent lateral or vertical movement of the rail
ends and permit the longitudinal movement of the rails for expanding or contracting.
The joint is considered to be the weakest part of the track structure and should be
eliminated wherever possible. Joint bars are matched to the appropriate rail section.
Each rail section has a designated drilling pattern (spacing of holes from the end of the
rail as well as dimension above the base) that must be matched by the joint bars.
Although many sections utilize the same hole spacing and are even close with regard to
web height, it is essential that the right bars are used so that fishing angles and radii are
matched. Failure to do so will result in an inadequately supported joint and will
promote rail defects such as head and web separations and bolt hole breaks.
There are three basic types of rail joints (Figure 3-8)
•
Standard
•
Compromise
•
Insulated
Figure 3-8 Conventional Bar, Compromise Bar & Insulated Joint Bar –
Photo by J. E. Riley
5
Canadian National Railway, Track Maintainer’s Course
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Standard Joints
Standard joint bars connect two rails of
the same weight and section. (See Figure
3-9) They are typically 24" in length with
4-bolt holes for the smaller rail sections or
36" in length with 6-bolt holes for the
larger rail sections. Alternate holes are
elliptical in punching to accommodate the
oval necked track bolt. Temporary joints
in CWR require the use of the 36” bars in
order to permit drilling of only the two
outside holes and to comply with the FRA
Track Safety Standard’s requirement of
maintaining a minimum of two bolts in
each end of any joint in CWR.
Figure 3-9 Standard Head-Free Joint Bar – Photo by J. E.
Riley
Compromise Joints
Compromise bars connect two rails of
different weights or sections together.
(See Figure 3-10) They are constructed
such that the bars align the running
surface and gage sides of different rails
sections.
There are two kinds of
compromise joints:
•
•
Directional (Right or Left hand)
compromise bars are used where a
difference in the width of the head
between two sections requires the
offsetting of the rail to align the gage
side of the rail.
Figure 3-10 Compromise Joint Bar – Photo by J. E. Riley
Non-directional (Gage or Field Side) are used where the difference between
sections is only in the heights of the head or where the difference in width of rail
head is not more than 1/8" at the gage point. Gauge point is the spot on the gauge
side of the rail exactly 5/8" below the top of the rail.
To determine a left or right hand compromise joint:
•
Stand between the rails at the taller rail section.
•
Face the lower rail section.
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•
The joint on your right is a "right hand".
•
The joint on your left is a "left hand".
Insulated Joints
Insulated joints are used in tracks having track circuits. They prevent the electrical
current from flowing between the ends of two adjoining rails, thereby creating a track
circuit section. Insulated joints use an insulated end post between rail ends to prevent
the rail ends from shorting out.
There are three types of insulated joints:
•
Continuous
•
Non-continuous
•
Bonded
Continuous insulated joints (Figure 311) are called continuous because they
continuously support the rail base.
No metal contact exists between the
joint bars and the rails. Insulated fiber
bushings and washer plates are used to
isolate the bolts from the bars. The
joint bars are shaped to fit over the
base of the rail. This type of insulated
joint requires a special tie plate called
an "abrasion plates" to properly
support the joint.
Figure 3-11 Continuous Insulated Joint – Photo by J. E. Riley
Non-continuous insulated rail joints are called non-continuous because these joints
don't continuously support the rail base. A special insulating tie plate is required on the
center tie of a supported, non-continuous insulated joint. Metal washer plates are
placed on the outside of the joint bar to prevent the bolts from damaging the bar.
There are two common kinds of non-continuous insulated joints:
•
Glass fiber.
•
Polyurethane encapsulated bar.
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The glass fiber insulated rail joint (See the bar to the right in Figure 3-8) replaces the
joint bar with a reinforced glass filament bar. Metal washer plates are placed on the
outside of the joint bar to prevent the bolts from damaging the bar.
The polyurethane encapsulated
insulated bar (Figure 3-12) is a steel
joint bar completely encapsulated in
polyurethane over the entire joint
bar surface. The Poly joint uses
insulating bushings to insure that
track bolts do not short out the
track.
Figure 3-12 Poly Insulated Joint – Photo by J. E. Riley
Bonded insulated rail joints
(commonly called plugs or slugs)
(See Figure 3-13) are made up of
two pieces of rail, which utilize an
epoxy resin to glue the insulated
bars to the rail sections. They are
bolted together using bushings to
isolate the bar from the rail steel
itself.
The bolts maintain the
alignment of the bars and rail until
the epoxy cures. The bars are
typically of a heavier section (Dsection) to provide extra support for
the epoxy. These units can be Figure 3-13 Bonded Insulated Joint (Plug) – Photo by J. E. Riley
purchased in a variety of made up lengths. The completed assembly is then thermit
welded into the track structure. This is the preferred type of insulated joint to use in
continuous welded rail (CWR).
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3.1.5 Tie Plates
The primary purpose of a tie plate is to
provide a smooth and uniform bearing
surface between the rail and the tie.6 This
prevents the rail from cutting into the tie.
The plate also helps to maintain gauge.
Plates that are canted (typical cant is 1 in 40)
tip the rail slightly to better distribute the
wheel load to ties.
Tie plates are designated as either single
shoulder or double shoulder (Figure 3-14). Figure 3-14 7-3/4” X 14” Double Shoulder Plates –
Single shoulder plates are typically used for Photo by J. E. Riley
rail weights running from 56 lb. through 100
lb. Rail sections larger than 100 lb. generally use a double shouldered plate. Tie plates
can be ordered in a variety of sizes all the way up to 8" x 18", although the 7-3/4" x
14" plate is probably the most common new plate produced. Eleven inch and 13"
double-shouldered plates are also available in readily available quantities. Some railways
believe that CWR should not be used with second-hand plates, although it is a
common practice on other railways.
Specialty plates (Figure 3-15) used for
elastic type hold-down fasteners, are
also produced in large quantities.
Various types of specialty plates are
used at insulated joint locations where
the rail ends are supported
immediately underneath by a tie. A
non-conductive plate must be used to
prevent the shorting out of the two
insulated rail ends.
Figure 3-15 Pandrol Plate & Fastener on a Concrete Tie
Past practices sometimes constructed
trackage without tie plates. However, under today's wheel loading conditions, tie life
will be severely shortened if the rail is spiked directly to the tie without using a plate to
distribute the applied load.
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3.1.6 Rail Anchors
Rail anchors are used to control the longitudinal running or creeping of the rail caused
by changing temperature, grades, traffic patterns and braking action of trains.7
Anchors are applied directly to the rail base and lodge up against the tie. The tie is
embedded in the ballast and the completed system together provides resistance against
longitudinal and lateral movement. Anchors are made for a specific rail weight and
base width.
Anchors manufactured today can be classified into two major groups: (See Figure 316)
•
Drive-On
•
Spring-Type
Figure 3-16 Tru-Temper Channeloc Drive On Anchor; Adjacent Photo: Woodings-Verona Spring Anchor, Unit Spring Anchor,
Portec Improved Fair Drive-On Anchor – Photos by J. E. Riley
3.1.7 Fasteners
There are many different types of fasteners commonly used.8 Fasteners can be
grouped by use as either connecting rail or track components together or to fasten rails
to ties. Fastenings and hold-down devices, with modern tie plate design, are aimed
primarily at reducing movement between the tie plate and the tie, both vertically and
laterally. As the track deflects under a wheel load, a reverse curve with upward bending
is formed immediately in front of and behind the wheel. Lateral restraint is necessary
to prevent wide gauge and plate cutting. Vertical restraint also reduces plate cutting.
The rail should be restrained within the tie plate shoulders. Its own weight is usually
sufficient without unduly restricting the wave action in the rail. The plate must be held
firmly to the tie by plate holding spikes to prevent any differential movement between
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8
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plate and tie. The AREMA Manual for Railway Engineering gives a recommended
spiking procedure. However, the Engineer should check to make sure that the railway
has adopted the AREMA spiking standard.
SPIKES
Track Spikes
The purpose of the track spike is to first maintain gage between the running rails and
to secondly secure the rail to the tie. The underside of spike head is sloped to fit the
top surface of the rail base (Figure 3-17).
Spikes come in different lengths to ensure an adequate length of spike penetrates into
the tie. The most common track spikes used are the 5/8" x 6" and the 9/16" x 5-1/2"
for smaller rail sections. Spikes can be commonly secured in either 200 lb. kegs or 50
lb. kegs (Figure 3-18).
Figure 3-17 Cut Track Spike (5/8” x 6”)
Figure 3-18 200# Kegs of Spikes - Photos Taken By J. E. Riley
Ship Spikes
Ship spikes, also commonly called line spikes, are used to secure timber crossing planks
and to secure shims used in frost heaved track. Ship spikes come in a variety of sizes.
Lag Screws
Lag screws are used to fasten elastic fastener plates as well as other specialty track
componentry to wood ties. The tie must be bored before installing the lag screw.
Drive Spikes
Drive spikes with quadruple threads are used to fasten crossing timbers or rubber/cast
crossing sections to the tie. They may be used in other locations where significant pullout resistance is required.
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BOLTS
Track bolts
The track bolt (Figure 3-19) is used to
connect rail ends together at a joint. Track
bolt sizes are determined by the section of
rail in use. Check the applicable railway
standard to determine the proper bolt
diameter and length. Track bolts are
normally supplied as oval neck to prevent
the bolt from turning when torqued. Track
bolts are heat-treated and will stretch a little,
thus they must be tightened after initial
application. Track bolts are used with
square nuts and spring washers. Overtorquing track bolts creates frozen joints,
which in most cases, is undesirable.
Figure 3-19 1” x 6” Oval Necked Track Bolts – Photo
by J. E. Riley
Frog/Guard Rail Bolts
Frog bolts are square headed and come in a variety of lengths and diameters depending
on the rail section in use and the location of the bolt in the frog.
Rod and Clip Bolts
Rod bolts are typically square headed and
drilled for a cotter pin to prevent the nut from
falling off. They secure the switch rods in a
turnout to the jaw clips mounted on the
switch points. The clip bolts secure the clip or
side jaw to the switch point and are also
square headed with often a milled head that
will permit the switch point to fit up tight
against the stock rail. (See Figure 3-20)
Figure 3-20 Rod & Clip Bolts – Photo by J. E. Riley
3.1.8 Specialized Components
There are a number of specialty track items with which the engineer must be familiar.9
These components include:
•
9
Derails
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•
Wheel stops or bumping posts
•
Gauge rods
•
Sliding joints
•
Miter rails
•
Bridge/tunnel guard rails
Derails
The purpose of the derail is to keep tracks free of unsecured rolling stock. When
properly placed and in the derailing position, the derail will guide the wheels off the
track. This prevents unintentional movement of rolling stock from fouling the main
line.
The derail should be left in the derailing position
whether or not there are cars occupying the
track. Derails are designated as right hand or left
hand for derailing in the desired direction. The
engineer must select the appropriate model of
derail on the basis of the rail section to be
utilized. An under-sized derail will not properly
cover the rail head and may not derail the car as
intended. An over-sized derail may be damaged
because of inadequate support.
Figure 3-21 Sliding Derail
There are several different types of derails. These include:
•
Hinged derails, which are manually applied. The derail is rotated in a vertical
semicircle to move the derail on or off the rail.
•
Sliding derails (Figure 3-21) are mounted on two switch ties and are operated by a
switch stand.
•
Switch point derails are used at special locations such as steep gradients or where
the possibility of high-speed movement, for example at movable bridges, could
knock a hinged or sliding derail off the rail, rather than derailing the movement.
Wheel Stops and Bumping Posts
The purpose of the wheel stop is to prevent rail cars from rolling off the ends of stub
tracks and to safeguard against damage to structures. Wheel stops can be classified as
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either rigid, which bind securely to the rail or cast which are one-piece half moons that
are easy to install.
Bumping posts are used for heavier service. Some models actually engage the coupler.
Gauge Rods
The purpose of a gauge rod is to maintain track gauge. They are often used to
supplement the tie in preventing lateral movement of the rail in sharp curvature
locations. They can also be used as a temporary means of maintaining traffic in
defective tie conditions. They are not a permanent alternative to replacing a defective
tie. Most gauge rods are adjustable with a nut on one end.
Gauge rods are provided as either insulated for signaled territory or non-insulated,
where track circuits are not used.
Sliding (Conley) Joints
The purpose of a sliding joint (Figure 322) is to accommodate the longitudinal
expansion and contraction of the rail on
long open decked bridges. Rail anchors
are not typically used on open decked
bridges because of the damage done to the
softwood bridge ties. The sliding joint
accommodates the thermal expansion
produced by enabling the beveled rail ends
to move but yet still maintain the
continuity of the running rail.
Figure 3-22 Conley Joint to Permit Expansion on Bridge
Deck
Mitre Rail
Whenever track is to be opened and
closed at frequent intervals, it will be costly
and cumbersome to use regular joint bars.
Mitre rails (Figure 3-23) allow easy
opening of track at drawbridges and swing
spans. Each rail of a track is cut through
on a long angle and planed to make a neat
overlapping fit of the mitred ends. The
rail fits in a special shoe and is locked in
place. The rail on each side of the mitred
cut must be well enclosed to maintain a
very small gap between the mitred rail
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Figure 3-23 Mitre Rails
ends to allow proper opening and closing of the joint structure.
Bridge/tunnel/overpass Guard Rails
The purpose of installing bridge guard rails
(Figure 3-24) is to keep derailed equipment
from falling off an overpass or deck of a
bridge, or striking the sides of a structure or
piling up in a tunnel. Typically, the inner
guard rail will be a T-rail section, which does
not extend to the height of the running rail.
The outside guard rails are usually timber
members.
3.2 Turnouts
Figure 3-24 Inner Bridge Guard Rails - Photo by J. E.
Riley
A turnout is a combination of a switch, a frog, the rails necessary to connect the switch
and the frog, two guard rails, unless the frog is self-guarded, and a switch stand or
switch machine for operating the switch.10 A turnout begins with the switch and ends
with the frog. The purpose of a turnout is to permit engines and cars to pass from one
track to another.
3.2.1 Types of Turnouts
Turnouts can be categorized into three
groupings:
•
Lateral turnouts
•
Equilateral turnouts
•
Lap turnouts
Lateral turnouts (Figure 3-25) are defined
Figure 3-25 Lateral Right Hand Turnout
as right hand when the diverging track
runs to the right and left hand when the diverging track runs to the left when facing the
turnout.
10
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Equilateral turnouts (Figure 3-26) are
common at the ends of double track
territory (where two tracks go to one
and vice versa). Both routes curve or
diverge as opposed to only one route
diverging in the lateral turnout. They are
used for higher operating speeds or in
congested areas. Half of the curvature is
on the main track side and the other half
is on the turnout side.
Figure 3-26 Equilateral Turnout - Photo by J. E. Riley
Lap turnouts (Figure 3-27) are used when
maximum track lengths and minimum
clearance points are required, for example
in hump yards. They contain two sets of
switch points and three different frogs.
The turnout's direction is determined by
which way the first set of points diverge.
Figure 3-27 Lap Turnout
Basic Turnout Terminology
•
Straight side called the main track or straight (normal) route.
•
Curved side termed the turnout or diverging route.
•
Facing point move is from points toward frog, either route.
•
Trailing point move is from frog toward points, either route.
•
Point of switch (PS) is the location where the diverging or straight route is
determined.
•
Heel of switch (HS) is the location at which the switch point pivots about.
•
Switch is the area from Point of Switch to Heel of Switch.
•
Toe of frog (TF) is the joint location ahead of the frog point connected to the
closure rails.
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©2003 AREMA®
•
One-half inch point of frog (PF) is the location behind theoretical point of frog,
where the gauge spread is ½”.
•
Heel of frog (HF) is the joint location behind the point of frog.
The true definition of a turnout is the portion of the track assembly from PS to HF.
But we commonly refer to all of the track structure resting on switch ties as the
turnout.
Each turnout is identified as a number
(e.g. # 10). The number of the turnout is
determined by the angle of the frog
(discussed later).
Every turnout consists of the following
components:
Figure 3-28 Switch Section of a Turnout – Photo by J. E.
Riley
3.2.2 Switch
A switch is a device to deflect, at will, the wheels of a train from the track upon which
they are running.11 A switch refers to portion of turnout from Point of Switch (PS) to
Heel of Switch (HS).
The split switch (Figure 3-28) is the most common switch used, although the tongue
switch may be used on transit properties operating within pavement. The split switch
consists of two switch or point rails connected by switch rods and operated as a unit.
The switch rails are of full section at one end, and are tapered to a 1/4-in. or 1/8-in.
point at the other end. The tapered end is called the point of switch and the other end
is called the heel of switch. The switch rails rest upon metal plates fastened to the ties.
The heel of each switch rail is connected to its lead rail by means of special joint bars,
or in some cases is continuous, and the switch as a unit pivots about these connections.
The point of switch moves through a distance of about 5 inches, which is called the
throw. The movement of the switch rails is controlled by a switch stand placed outside
the track on the head block ties. The distance between the gage lines of the main track
and of the turnout at the heel of the switch rails is called the heel spread and varies
from 5-1/2 to 6-1/4 in. The angle between the gage lines of the switch rail and of the
main track rail is called the switch angle, s, and is computed from the equation found
in Figure 3-29:
11
Route Surveying Chapter 7 “Turnouts,” Pickels & Wiley, 1947, John Wiley & Sons
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Figure 3-29 Switch Angle
Switch rails vary in length from 11 to 39 ft. and even longer for high turnout numbers,
depending on the weight of the rail and the curvature of the turnout.
3.2.3 Switching Mechanism
There are two means of moving the switch points12:
•
Hand operated (switch stand).
•
Power operated (machine).
Hand operated switching mechanisms can be rigid (See Figure 3-30) or spring switch
type. A spring switch has special components enabling points to close automatically
after being trailed through from the diverging side. There are also dual-control power
switches (See Figure 3-31) that can be operated either by hand (using the hand throw
lever) or power operated remotely by the dispatcher.
Figure 3-30 Hand Throw Switch Stand
12
Figure 3-31 Dual Control Switch Machine – Photo by J. E. Riley
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3.2.4 Turnout Rails
Turnouts are made up of a combination of rails. Some have special names and
purposes, for example.
Stock rails are the outside rails in a switch that the points bear against.
Closure rails are the connection rails between the heel of the switch points and the toe
of the frog.
Knuckle rails (Figure 3-32) are the rails
that the movable point in a movable
point frog or the rail that the center
point in a double slip switch bears
against.
Figure 3-32 Knuckle Rails in a Double Slip Switch
- Photo by J. E. Riley
3.2.5 Frog
A frog is a device at the intersection of two running rails to permit the flange of a
wheel moving along one rail to cross the other rail.13 Turnout frogs may be classified
as rigid frogs or spring-rail frogs. Both types of frogs are made with straight gage lines,
except those used on street railways. The point is finished with a blunt point about 1/2
in. wide. The distance “P” between the actual frog point and the theoretical point
(intersection of gage lines) equals the width of the blunt point multiplied by the frog
number (i.e., 1/2 N).
Rail Bound Manganese (RBM)
This is a heavy-duty frog used on mainlines
because of its durability.14 The insert is
made of a one-piece manganese casting.
Lengths of machined rail (binder rails) are
bolted to the insert. (See Figure 3-33)
Figure 3-33 RBM Frog – Courtesy of the Union Pacific
Railroad
13
14
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Spring Frog
The spring frog (Figure 3-34) provides
continuous support for the wheel as it
transits through the frog flangeway. This
frog has a moveable wing rail. The wing rail
is held closed by a spring assembly. It also
has an anchor block, thimble and a bent
joint bar at the toe end to allow the wing rail
to pivot. The guardrail pulls the wheels
over, forcing the wing to open on the
diverging side. The wing rail springs closed
again after the wheels are through. Spring Figure 3-34 Spring Frog - Courtesy of the Union Pacific
frogs are supplied as either right or left hand. Railroad
To determine the hand of a spring frog,
stand at the rigid wing end, facing the frog. The side the moveable wing is on indicates
left or right.
The spring frog is used for trackage with predominate main line traffic, especially high
speed movements, because there is less pounding and a smoother ride. The
disadvantage is that it requires more maintenance than conventional frogs. Recent
advancements in spring frog design have eliminated some of the rigorous maintenance
needed to keep a spring frog functional.
Solid Manganese Self-guarded Frog
The solid manganese self-guarded frog, also
called SMSG (Figure 3-35) has a built-in guard
rail to prevent wheels from mis-routing. Thus,
conventional guard rails are not required.
SMSG frogs are supplied either with plates as
part of the casting or utilize hook plates to
secure the frog to the switch ties. SMSG frogs
are normally limited to yard use primarily
because of the resultant impact that the
guarding face would suffer at higher speeds.
AREMA does not recommend their use in
main line trackage with speeds over 30 mph.
Figure 3-35 Solid Manganese Self-Guarded Frog
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Bolted Rigid Frogs
Bolted rigid frogs (Figure 3-36) are made of
machined rail bolted together. They are cheap
to make and are used primarily in yards and
secondary lines. They are designated as right
or left hand. The straight route side of the
bolted rigid frog point is continuous, whereas
the diverging side of the frog point is milled to
intersect the straight side frog point rail, hence
the need to differentiate the hand of the
frog.
Figure 3-36 Bolted Rigid Frog - Photo by J. E. Riley
Movable Point Frogs
Movable point frogs (Figure 3-37) are used
in locations where the crossing angle
between two sets of tracks is less than 14°15’.
The excessively long throat created by using
conventional crossing diamond frogs would
be impractical to maintain and to guard. A
movable point frog consists of two movable
center point rails. The free points face each
other a few inches apart where each pair
Figure 3-37 Movable Point Frog
may be alternately operated against two
knuckle rails kinked to a point between the free ends of the movable points. The
closed movable point, thereby maintains the flangeway. High-speed, high-number
turnouts may also utilize a variation of the movable point frog described above in order
to gain the benefits of the continuous flangeway too.
Determining Frog Number
The frog used in a turnout determines the number of the turnout, e.g.:
•
# 10 turnout uses a number 10 frog.
•
# 12 uses a number 12 frog.
The point of the frog is machined off from the true (theoretical) point to where the
spread is 1/2". This is referred to as the actual point of frog. To find the number of
the frog:
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©2003 AREMA®
•
Utilizing a tape measure, find the location behind the point of frog where the
spread between the gauge lines equals an even increment of inches.
•
Starting at that point, measure along the gauge line to the location where the spread
between gauge lines equals one inch more than that previously measured.
•
The distance in inches between the two locations where the gauge spread differed
by one-inch equals the frog number.
3.2.6 Switch Ties
AREMA as well as many railways have
standardized plans for the switch tie layout
for the turnouts utilized on their property.
The two switch ties under the switch
mechanism are called head block ties
(Figure 3-38). The ties under the heel
block assembly are called heel block ties
and those under the frog are called frog
ties.
Figure 3-38 Head Block Ties
3.2.7 Stock Rails
The stock rails (Figure 3-39) are made of rail of the same weight and section as the
switch point. The stock rail on the diverging side is bent (Figure 3-40) so that a proper
fit is maintained between the switch point and the stock rail and to protect the point
from wheel impact. In the case of an equilateral turnout, both stock rails are bent.
Stock rails are either Samson (called "undercut" when ordered) or standard. The
beveled samson stock rail allows the samson point to tuck underneath the stock rail,
thus protecting the point from impact.
Figure 3-39 Point and Stock Rail - Photo
by Craig Kerner
Figure 3-40 Stock Rails with Bend - Photo by J. E. Riley
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3.2.8 Switch Points
The switch points (Figure 3-41) are
the movable rails that permit a
change of route direction in the
turnout.15 There are different types
of switch points, each with some
unique characteristics.
But the
following parts of switch point are
common to all:
•
Tip
•
Heel
•
Planed (or "machined") portion
•
Reinforcing bar
•
Switch clips
•
Stop blocks
Figure 3-41 Switch Points - Photo by J. E. Riley
The switch points are machined from rails, so that the middle of
the rail becomes the middle of the actual point, to give it
structural support. The switch points are planed at an angle for
about 1/2 of their length down to approximately 1/8 in. wide at
the tip. This permits a snug fit against the stock rail. (See Figure
3-42) As the point begins to move away from the planed
supporting portion, it loses its horizontal support against flexing.
A stop block is mounted on the switch point between the planed
portion and the heel block. The block bears against the stock rail
when the point is in the closed portion, thereby providing
support as the lateral forces from the wheel pushes outward.
The turnout number or the angle of the frog normally
determines the length of the point required, as well as
whether the switch is a curved switch or straight. All
switch points are either standard or Samson. (Figure 3-43)
The smaller rail section turnouts (under 100 lb.) typically
utilize standard points and are straight switches. Larger,
newer rail sections and turnouts located in main line use
are typically Samson points and frequently curved switches.
15
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Figure 3-42 Switch Point Fit
Figure 3-43 Samson Vs. Standard Switch
Point and Stock Rail
Samson points must be used with a Samson (undercut) stock rail.
Identifying Left or Right Hand Points
The hand of a switch point (Figure 3-44) can be determined by standing at the tip end
of the point and looking along its length:
•
If switch clips are on the right side of the point, the point is a left hand switch
point (and vice versa).
Another method when not installed:
•
If it looks like an "L" when viewed from the point end, then it is left hand:
3.2.9 Specialty Components
Figure 3-44 Switch Specialty Components – Courtesy of Bernie Forcier
Switch Clips
The switch clips connect the switch rods to the
points. There are different styles such as the
horizontal transit type vs. the vertical MJ type.
(See Figure 3-45)
Figure 3-45 Side Jaw Clip - Courtesy of the
Union Pacific Railroad
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©2003 AREMA®
Switch Rods
The switch rods hold the switch points together at a fixed distance.16 They restrict the
up and down movement of the points. The number of rods used depends on the
length and type of switch point. The longer the point, the more rods are required
(from 1 to 7). The rods are spaced from the tip of the point to 1/2 or 2/3 the point
length (depending on the type of point). Switch point rods may be supplied as either
insulated or non-insulated type.
The first rod is called the front or head rod. The last rod is called the back rod and the
others are called intermediate rods.
Types of Switch Rods
There are a variety of available switch rods including:
Horizontal, non-adjustable switch rods (Figure 346) typically are used in conjunction with multiplehole switch clips to provide adjustment. The rod
bolts can be used in various holes when adjusting,
but they must be in corresponding holes in the
clips, i.e. the same on each side. The rod must be
able to move inside the clips as the points are lined
back and forth. The rod bolts must be installed
with the nut up and cotter pin installed.
Figure 3-46 Horizontal Non-Adjustable Switch
Rod - Photo by J. E. Riley
Horizontal, adjustable switch rods secure its length
adjustment by interlocking the serrated edges of
the rod to various positions and then bolting the
rod back together. One must ensure that the teeth
properly interlock when installing or adjusting.
Vertical switch rods are used in conjunction with
MJ and MJS type switch clips. (Figure 3-47)
Figure 3-47 SMJ Rod - Photo by J. E. Riley
16
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Connecting Rod
Connecting rods are also called the operating or
throw rod. The connecting rod connects the
front switch rod to the switch stand. It may be
attached by an adjustable connection (called a
clevis) to the crank eye bolt in the switch stand
and (by a rigid connection) to the front switch
rod. There are different types of connecting
rods. Some are adjustable, some are not. They
come in a variety of lengths depending on their
use and the type of switch stand being used. Figure 3-48 Connecting Rods - Photo by J. E. Riley
(Figure 3-48) On a power switch, the throw
(operating) rod is attached to a barrel shaped basket (Figure 3-47), which is connected
to the No. 1 switch rod. Adjustment of the lock nuts to either side of the basket
enables adjustment of the switch throw.
3.2.10 Special Turnout Plates
Each type of turnout has a specific set of plates.17 The plates differ in type and
quantities for each turnout. These plates include the gauge, switch, heel, hook and frog
turnout plates.
Gauge Plates
Gauge plates are placed under the tip end
and on the first tie ahead of the point of
switch to hold the rails in proper gauge.
Additional gauge plates are used on spring
and power switches to provide rigidity.
Gauge plates are machined to enable the
stock rails to sit in the plate and points to
sit on the plate. A rail brace assembly is
then used to fasten the stock rails to the
plate. (Figure 3-49) Gauge plates are
either right or left hand. They may be
supplied as insulated or non-insulated. A
gauge plate is angle cut on the turnout side
to accommodate the angle of the bent stock rail.
17
Figure 3-49 Gauge Plates - Photo by J. E. Riley
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Switch Plates
At the point of switch, the point is beveled back such that it is below the top of the
stock rail. (See Figure 3-44) However, the base of the point is elevated above the base
of the stock rail. Switch or slide plates are used under the switch points. (Figure 3-50)
Depending on the turnout, they are either of the graduated riser style or the uniform
style. Slide plates maintain the required elevation of the switch points above the top of
the stock rail as one moves back to the heel of switch and presents a smooth surface,
upon which the points may move right or left. (Figure 3-51) The graduated riser plate
has a riser that decreases in thickness, such that at the heel, the elevation of the stock
rail and point are the same. The uniform riser plate is the same thickness all the way
back to the heel, such that the switch point is above the stock rail at the heel. Specialty
turnout plates then lower the raised rail behind the heel back down to the elevation of
the closure rail. In both slide plate types, the riser provides a shoulder to prevent
inward lateral movement of the stock rail. The stock rail is secured against outward
movement by spiking to the ties and by rail braces. One cannot mix the type of switch
plates being used.
Figure 3-50 Graduated Riser Plates - Photo by
J. E. Riley
Figure 3-51 Switch Point Raised Above Stock Rail - Photo by
J. E. Riley
Rail Braces
A rail brace is used to resist the lateral
thrust on the point and stock rails. Rail
braces bear against the outside of the stock
rails. They are secured to the gauge and
switch plates. There are two general types
in use with many variations of each.
•
Adjustable (fastened with bolts).
•
Rigid (older type, fastened with track
spikes). (Figure 3-52)
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©2003 AREMA®
Figure 3-52 Rigid Type Rail Braces
Heel Block Assembly
The heel block assembly maintains the correct distance between the gauge side of the
stock rail and the gauge side of the points. It adds strength and rigidity. The block will
be different for each switch and rail section. The conventional bolted heel block,
assembly, (Figure 3-54) permits movement of the point rails at the heel block. In the
floating heel block (Figure 3-53) the point flexes over its length. The floating heel
block merely acts as a bearing point between point and stock rail to limit movement.
Special plates are used under the heel block assembly.
Figure 3-53 Floating Heel Block
Figure 3-54 4-Hole Heel Block
Turnout Plates
Turnout plates are used immediately beyond
the heel block assembly. These plates raise the
switch end of the closure rail to the level of the
heel of the switch point, where uniform riser
plates were used under the switch. (Figure 355)
Figure 3-55 Turnout Plates Through the Closure
Rails - Courtesy of Union Pacific Railroad
Hook Twin Tie Plates
Hook twin tie plates may be used through the
closure rails or in locations where there is no
room for standard tie plates, e.g.:
•
Beyond the heel block.
•
Before and after the frog.
Figure 3-56 Hook Twin Tie Plates - Courtesy of
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©2003 AREMA®
•
Under guard rails.
The hook on the plate always goes on the field side of the rail. There are a variety of
hook twin tie plates. They are typically numbered to correspond on the turnout
drawing with the location that they are to be used (Figure 3-56).
Frog Plates
Hook twin tie plates are often used at
the frog. (Figure 3-57) Spring frogs use
special slide plates to allow the wing rail
to move on it. Some RBM frogs use toe
plates to support wheel loads in this
area. Newer style turnouts will often use
full-length base plates under the frog.
Figure 3-57 Hook Twin Plates Under a Frog - Courtesy of the
3.2.11 Guard Rails
Guard rails are used to prevent misrouting and derailing at the frog point
and to prevent wheels from striking the
frog point.18 (Figure 3-58) They may be
of either the adjustable or non-adjustable
type. The guard rail captures the back of
the flange on the wheel opposite the
frog and guides the other wheel through
the throat opening of the frog. Thus,
the mid-point of the guard rail must be
positioned ahead of the frog point to
ensure that the wheel is properly
tracking when it reaches the throat of
the frog.
Figure 3-58 Guard Rail
The non-adjustable guard rail is secured directly to the running rail with fixed castings.
On the adjustable guard rail, end castings are located at each end of the guard rail,
which are designated as right or left hand (by standing between the rails and facing the
18
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guard rail). An adjustable separator block along with the end castings are used to space
the flangeway opening initially at 1-7/8 inches. As the outside flange of the wheel
abrades away the gage face of the guard rail, this dimension will increase. The FRA
sets limits defined by the guard face and guard check dimensions to ensure that the
wheel is properly contained through the frog flangeway.
Guard rails are supplied in different lengths as specified by the railway’s standard plan.
They use a variety of plates, which must be spiked on each end, plus spiked between
running rail and guard rail.
3.2.12 Switch Stands
There are a variety of switch stands in
use.19 Typically, high stand switch stands
are used in main line applications; whereas
the ground throw stands (Figure 3-59) are
used in industry or yard applications.
Automatic switch stands are used to
enable the stand to line when points are
trailed through from either route. Main
line switch stands are equipped with a
target that is colored green when the
Figure 3-59 Ground Style Switch Stand
switch is lined for the normal route and
red if the switch is reversed. Yard switches equipped with targets are usually green for
the normal route and yellow for the reverse route.
Spring Switch
This is a hand throw switch equipped with a spring mechanism instead of a rigid
connecting rod. It is often called a mechanical switchman because the points return to
normal position after the passage of each wheel. It is designed to allow trailing point
movements from the diverging route without having to stop and reset the switch. The
spring switch stands must be bolted to the ties and be of the rigid type. The spring
switch is typically provided with a target marked “SS” or other designation.
Power Switch
A power switch is an electrically powered machine that lines the switch. Some power
switches are known as dual control switches. Dual control power switches (Figure 360) can be operated either by hand using the hand throw lever, or remotely by the
dispatcher.
19
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As with the rest of the track, but even more
so, quality turnout and crossing maintenance
demand initially a strong, stable base and
excellent drainage. This may require special
subgrade preparation including asphaltic or
concrete pads, especially under crossings
with high traffic densities. The use of catch
basins and subsurface drainage systems are
recommended where moisture conditions
and traffic are both severe.
The proper location of a crossing or turnout
Figure 3-60 Dual Control Power Switch - Photo by J. E.
is important. It should be placed off of Riley
curves. Sharp curvatures or reversals should
be avoided at the back of the frog to avoid excessive lurching and lateral thrust in the
frog area.
All parts of a turnout or crossing subject to excessive wear and thrust should be of
high-wear resistant materials. Heat-treated or manganese switch points, frogs and
guard rails, and heat-treated stock rails are recommended for heavy tonnage locations.
3.3 Railway Crossings &
Crossovers
Crossovers (Figure 3-61) can be
considered as two turnouts, with
minor limitations.
The track
between the two frogs follows the
frog angle. Thus the timber layout
for half of the crossover is different
from that of a turnout.
A crossing is a device used at the
intersection of two tracks.20 It
consists of four frogs and the
necessary connecting rails. Any one
Figure 3-61 Crossover
of the frogs is a crossing frog. The
crossing angle is the angle between the centerline of the tracks at their point of
intersection.
20
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©2003 AREMA®
Crossings are designated as single
curve, double curve or straight,
according to one, both or neither of
the tracks being curved. Crossings are
usually made of rolled rails or
manganese castings fitted together.
When the crossing angle is greater
than about 25°, the various pieces are
cut to fit against each other and are
united by filling blocks and heavy
straps well bolted. This is frequently
termed solid construction. For angles
Figure 3-62 Crossing Frog (Diamond)
under about 25°, regular frog point
construction is used, and such crossings are termed frog crossings versus a crossing
frog.
The end frogs of a frog crossing are similar to a standard rigid frog in that there is a
single point on which the wheels run. The middle frogs, however, have two running
points and are therefore frequently termed "double-pointed frogs.”
When "slip switches" are used, the
crossing is made to a standard frog
number, and if located at an
interlocking plant, the middle frogs
are frequently made with movable
points. That is, with movable points
joined in pairs and moving together,
similar to a split switch, in such a
way that the wheels have a solid
bearing and no flangeway to jump.
A "slip switch" or "combination
crossing" (Figure 3-63) is a
Figure 3-63 Double Slip Switches - Photo by J. E. Riley
combination of a small angle
crossing with a pair of connecting tracks placed entirely within the limits of the
crossing. They are used in large yards and terminals and are usually made to some
standard frog number.
Very few railways construct their own crossings, but have them built by manufacturers
who make a specialty of such work. The field engineer is rarely called on to compute
the dimensions of a crossing, and to do so is a waste of time if the crossing is ordered
from a manufacturer. It is far more important that the manufacturer has all the data,
and the field engineer is frequently required to furnish the data. The information
required is:
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-
The crossing angle.
-
The gage of each track.
-
The curvature - degree of curve, radii, or the equivalent.
-
The direction of curvature.
-
The length along each gage line from one gage line intersection (theoretical P.F.) to
the nearest rail joint.
-
Length overall along each gage line.
-
The height, weight and style of rail of which the crossing is to be made.
-
The height, weight, and style of rail in the intersecting track if offset or
compromise joints are to be furnished.
-
The spacing and size of holes for joint bars.
-
The type of crossing, etc., unless covered by general specifications.
This information can best be given by means of a small sketch. Field dimensions
should he taken to the nearest 1/8 in. (0.01 ft.). Occasionally, the field engineer is
called on to compute the dimensions of a crossing. The values required are the frog
angles F1, F2, F3, F4, the length of sides along the gage lines, and the two diagonals.
The computations should be made with sufficient accuracy to give results correct to
the nearest 1/16 in., which is the working limit of the manufacturers.
3.4 Highway Crossings
The renewal of road crossings represents one of the largest budgetary
expenditures faced by the Maintenance of Way and Signals Departments.
Typically, railways will look for governmental partnership and participation when
contemplating crossing renewal projects on all but farm and private crossings.
Chapter 5, Part 8 of the AREMA Manual for Railway Engineering gives specific
guidelines for the design, construction and maintenance of road crossings. The
Commerce Commission of each state in the United States regulates the design,
construction and installation of public road crossings within their respective state.
This information is contained within bulletins accessible through their respective
web pages.
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Road Crossings are where roads, streets or highways intersect the track at grade.21
Road crossings, or grade crossings as they are sometimes called, result in increased
maintenance requirements of the track and the road itself. In addition to the
maintenance requirements, public safety is obviously of serious concern at road
crossings.
There are many different types of road crossing materials that are commonly
found throughout North America. These include: unsurfaced, timber, asphalt,
asphalt with timber headers, concrete (both cast in place and precast) and
pre-manufactured rubber. Some transit and light rail systems utilize specialty rail
chairs to support an inner rail, thereby creating a proper flangeway in highway
crossings. The type of crossing material used is determined primarily by the
amount of vehicular traffic that uses the crossing.
Unsurfaced crossings are typically used at temporary crossing locations such as
shoe-flys or where construction traffic is required to cross the railway. These
crossings may consist of ballast backfilled to the top of rail. Where unsurfaced
crossings are used, care must be taken to maintain a sufficient flangeway for the
train wheels.
Timber crossings may be constructed
of either treated wooden planks (often
used in farm or private crossings)
(Figure 3-64) or full gumwood
crossings,
which
have
been
successfully used for many years. This
type of crossing can be used for all
types of traffic levels from light to
heavy. Figure 3-65 presents a typical
cross section for a full-depth timber
crossing.
Figure 3-64 Plank Crossing - Photo by J. E. Riley
Figure 3-65 Gumwood Timber Crossing – Courtesy of Bernie Forcier
21
US Army Track Maintenance Standards – Bernard Forcier
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Asphalt or Bituminous crossings
(Figure 3-66) are used for crossings
with all levels of traffic from light to
heavy. These crossings are
constructed by filling in the area
between the rails with compacted
base material covered by several
inches of asphalt as surfacing
material. In some cases, full-depth
asphalt may be used between the
rails. Depending on the level of train
and highway traffic, the flangeways
may either be formed in the asphalt
itself or formed by the use of timber
flangeway headers.
Figure 3-66 Asphalt & Timber Flangeway Crossing - Photo by
Robert Schuster
Concrete road crossings (Figure 367) may be either cast-in-place or
constructed from pre-cast panels.
Concrete crossings are typically used
at locations with medium to heavy
vehicular traffic. Precast concrete
crossing panels are available from
several different suppliers.
For road crossings with heavy
volumes of vehicular traffic, premanufactured rubber road crossings
are often used. (Figure 3-68) This
type of crossing may be either a
full-depth rubber material or a
system of wood shims that are
placed on the ties with the rubber
crossing material placed on top of
the shims.
Figure 3-67 Precast Concrete Crossing - Photo by J. E. Riley
3.4.1 Crossing
Construction and
Reconstruction
The following comments are Figure 3-68 Rubber Crossing - Photo by Robert Schuster
independent of the type of
crossing surface that is used. When crossings are built or rebuilt, it is
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recommended that all of the ties in the crossing itself, and for 20 feet beyond each
end of the crossing, should be replaced with new high-quality, properly treated, 7”
X 9” hardwood ties. Each tie should be tie plated and double spiked with 4 railholding spikes per plate. Box anchor all ties through the crossing. For crossings
having heavy volumes of rail and highway traffic, it may be desirable to install tie
pads beneath the tie plates in the crossing area. The presence of bolted rail joints
in a road crossing compounds the maintenance problems normally associated with
joints. All of the joints in the crossing area and for 20 feet to either side of the
crossing should be welded to prevent these problems.
When a crossing is constructed, care must be taken to insure that the track
structure is sound and durable prior to placing the crossing cover. The rail, tie
plates, spikes and ties should be new. Once the crossing cover is on, track
material replacement become difficult and costly. The track geometry (gage,
surface and alignment) should be near perfection prior to placing the crossing
cover. The ballast in and around all of the ties should be well compacted. It is
important that fouled ballast materials be removed during crossing reconstruction
for a distance of at least 20 feet off the ends of the crossing. However, it is equally
important that excavation not penetrate the hardpan found below the ballast/subballast section. Whenever possible, full closure of a highway crossing from
vehicular traffic is desirable for the longest period possible. This ensures that the
entire crossing can be raised to an elevation that permits surface water drainage
away from the crossing and that provides the greatest amount of train traffic over
the crossing prior to sealing it up. This helps to prevent settlement and other
movement of the crossing that would be difficult to adjust later. Close
communication with local and state/province authorities, arranged well in
advance, can do much towards mitigating problems associated with temporary
crossing closures.
In multiple track territory, it is desirable that the top of the rails for all tracks be in
the same plane (See Figure 3-69). The highway surface should match the plane of
the tracks for at least 24” to either side of the outside rails of the crossing.
Connect this plane to the grade line of the highway each way by vertical curves
sufficiently long enough to provide adequate sight distance and a smooth riding
condition for approaching highway traffic (See Figure 3-70).
AREMA
recommends that the highway elevation at 30 feet from the nearest rail be not
more than 3” higher or 6” lower than the top of rail unless track superelevation
dictates otherwise. Tractor trailer rigs can get hung up on a humped crossing.
The engineer should verify that the vertical curve gradients utilized are within local
ordinance or Commerce Commission statutes. Some states require that the
railway assume the responsibility of repaving the approaches if the resultant
crossing reconstruction will raise the approach grade by more than 1%.
Proper drainage away from the road crossing of surface water is essential to the
satisfactory long-term performance of the track and the highway. Inadequate
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drainage leads to water ponding in the crossing area. Water should not be allowed
to pond anywhere on or near the track. Drainage facilities such as ditches, gutters,
catch basins, subdrains and culverts should be in-place, free of debris and working
properly. The use of geotextile fabrics and/or perforated CMP between the
subgrade and the sub-ballast/ballast section is highly recommended to carry away
water trapped within the crossing proper.
Figure 3-69 Maintenance of the Plane Across All Superelevated
Tracks - Photo by J. E. Riley
Figure 3-70 Highway Approach Grade – Photo by J. E. Riley
3.4.2 Crossing Warning Devices
The safety of a grade crossing to both the motor vehicles and trains should be a
priority item for both the engineer and the railway. Past experience has shown
that drivers familiar with a crossing may be very cautious when they know that
train traffic is either very heavy or irregular. Conversely, a driver may give little
thought to the grade crossing if experience has shown that trains rarely operate
over it. Therefore warning signs, signals and pavement markings are important
and must be visible and legible to the motor vehicle operators approaching the
crossing. The state/providential Commerce Commission regulates the type of
signage, pavement markings and appliances required. In most cases, they refer to
“The Manual on Uniform Traffic Control for Streets and Highways.”
The U.S. Department of Transportation, Federal Highway Administration Manual
on Uniform Traffic Control Devices provides guidance on marking and signage of
railway grade crossings. The amount of marking and signing required is a function
of the amount of vehicular traffic using the road, the amount of rail traffic, the
type of train operations (e.g., speed, direction, switching operations, etc.) and the
geometrics of the crossing. The minimum requirement is for a crossbuck and
advance warning sign (if applicable). Additional warning signs, signals and
pavement markings may be used as necessary.
In some cases, the crossing may be marked with automatic warning devices
commonly termed flashers. These devices are activated by the approaching train to
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warn vehicles of the train. Gates are sometimes used in conjunction with this type
of signal. Automatic warning devices must be inspected and tested monthly to
insure that they are in proper working order. All inspections and tests conducted
on these automatic signals must be documented and kept on file per FRA
requirement. This provides valuable information in the event of an accident or
other sources of litigation. (See Chapter 7 of the Practical Guide To Railway
Engineering for a complete explanation of how highway crossing warning devices
are activated by the track circuits.)
3.5 Utility Crossings
Because tracks usually traverse great distances, railways will encounter many utility
crossings such as pipes, wires, cables and other conduits.22 These can be longitudinal
along the right-of-way, perpendicular or crossing diagonally. They can also be either
overhead or underground. Most railways and many regulatory agencies have standards
and rules for such installations.
The following are general standards for utility crossings. Check first with the railway to
verify acceptance therewith.
1. Overhead crossings must have adequate support at or above the prescribed
clearances above the top of the high rail.
2. Underground crossings must be in carrier pipes or casings at or below the
prescribed distances below the lowest base of cross tie or other baseline
measurement.
3. Underground crossings must be in carrier pipes or casings of sufficient strength
to withstand dynamic railway loading in addition to the weight of soil
overburden at the crossings.
4. Underground pipes carrying volatile substances often require vented casing
under the railway rights-of-way.
5. Underground pipes, wires and cables should have warning signs at ground
surface identifying the utility type, as well as contact names and telephone
numbers.
6. Some underground installations have color-coded plastic tapes buried just above
them, so that excavators will first encounter the tapes before damaging the utilities.
22
Railroad Track Design Manual, Prepared for the Parsons Transportation Group by James Strong, PE
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7. Prior to beginning any excavations on a railway right-of-way, the entity undertaking
the work should have arranged for the location and surface marking of all
underground pipes, wires and cables (including those owned by the railway). Do
this by checking existing records and through field investigations.
8. Avoid underground crossings very near the ground surface, or those traversing the
track ballast or existing drainage structures. These present tripping hazards to train
crews and expose the utilities to breakage, possibly causing dangerous situations,
contamination and/or erosion.
3.6 Track Geometry
Having now acquired a basic knowledge of the components making up the track
structure, the engineer needs to understand what drives the need for maintenance,
component replacement or track structure rehabilitation and how decisions are made
to prioritize their replacement. For most railways, the decision for component
replacement and the basis of funding justification is driven by:
Maintenance of Safe Operation at Track Speeds - Ensuring the train stays on the track at time
table speeds and that cars, equipment and lading or passengers are not unduly damaged
or injured.
On-Time Performance & Service Reliability - Minimizing speed restrictions by performing
interim maintenance consisting of small-scale replacement of components, touch-up
work (smoothing) and other functions that ensure that the track structure remains
serviceable until it is no longer cost effective to maintain for given speeds or that
customer service commitments are endangered.
Ride Quality - Maintaining the geometry of the track structure, such that it complies not
only with minimum safety standards demanded by the FRA, but also minimizes damage
to lading, as well as ensuring a comfortable ride for the riding public for passenger/transit
railways.
Secure Expected Component Life of the Entire Track Structure - Premature failure of one
component will produce a reduced life span for the remaining track components because
of the interdependent relationships.
Cycle Based Renewals - E.g., tie replacement of 20% of ties every 6-7 years in a given mile to
prevent wholesale failure 30 years down the line. This distributes capital replacement
costs evenly to prevent one time staggering expenditures.
This last criteria has for the most part been attained by the Class 1’s, commuter roads and
bigger regionals through heavy capital investment. Many of the short lines are still
suffering from the effects of years of former deferred maintenance and are unable to earn
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the cost of capital required to achieve a cycle based program. It is not desirable to replace
1200 to 1400 ties per mile (out of the normal 3,200 ties found per mile) just so that one
meets the minimum safety standards required to operate at the speeds desired.
Now let's look at how each of the criteria mentioned are utilized. Safe operation at track
speeds and On-Time Performance (reliability) are for the most part speed related. The
FRA (Federal Railroad Administration) Track Safety Standards defines minimum
requirements to which the track structure must be maintained for a given range of speeds.
The following table defines the permissible speed ranges for the Class of Track for freight
trains running up to 80 mph and passenger trains running up to 90 mph.
Over track that meets all of
the requirements prescribed
in this part for
Excepted
1
2
3
4
5
The maximum
allowable speed for
freight trains is
10
10
25
40
60
80
The maximum
allowable speed for
passenger trains is
N/A
15
30
60
80
90
An additional table for passenger trains defines the class of track for speeds between 91
mph and 200 mph (FRA Class 6 – 9). It must be understood that the FRA Track Safety
Standards set the minimum requirements for safe operation of trains. Maintenance
standards must be much more rigorous in order to continue to operate at a given speed.
Design and new construction standards require significantly tighter tolerances than that
employed by maintenance standards i.e., it may not be cost effective to maintain the
railway at the same level of design/new construction standards if safety and service
reliability are not compromised.
In general, track is dynamic. Other than timber ties, it does not degrade under the absence
of train operations. It, however, degrades exponentially as train speeds are increased.
Thus, as speeds go up, the variance or acceptable tolerances from desired parameters
must become tighter. These parameters are broken down into:
-
Roadbed
-
Geometry
-
Track Structure
-
Track Appliances
-
Inspection Requirements
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Specific minimum parameters dependent on the class of track operated (speed
operated) are defined. Railways, not meeting the minimum requirements for the class
of track being operated, are left with several immediate options to remedy the problem.
They may immediately make repairs such that the track is now in compliance. They
may reduce the speed to a class of track that would be in compliance. They may
classify the track as Sub-Class 1 and operate at Class 1 speeds for a period not to
exceed 30 days prior to repairing the track (assuming the track is safe to operate), or
they may remove the track from service.
On trackage where occupied revenue passenger trains do not operate, and
simultaneous movement at track speeds in excess of 10 mph does not occur within 30
feet of the centerline of track on any adjacent track, and trains do not contain more
than 5 placarded Haz-Mat cars (with several other restrictions), track may be declared
as Excepted Track. Such track may be operated at Class 1 speeds and is exempt from
the 213 Track Safety Standard’s requirements except for a maximum gage limit and the
requirement to perform track inspection at Class 1 frequencies.
Service reliability demands that immediate repairs are made. The other avenues for
remediation are unacceptable, except for very short duration. As noted before, day-today deviations are taken care of under the normal operating budget. When, however,
undue labor or materials are required to remain in compliance for the speed to be
operated, railways must seek capital funding for component replacement or
rehabilitation. Rail relays are classic cases of the above. Elimination of jointed rail and
replacement with Continuous Welded Rail (CWR) lowers significantly maintenance
costs. Rail wear occurs not only on the top of the head of the rail (tread) and at the
gauge corner (wheel flange contacts the rail), but also where the joint bar comes into
contact with the rail. As this contact area becomes worn (bar and rail), it becomes
impossible to keep the joint bolts tight. This accelerates tie deterioration, as well as
promoting secondary batter of the rail end, chipped joints, dangerous rail defects, mud
pumping and a host of other problems related to poor track.
The maintenance of good track geometry is essential to securing good ride quality.
When the parameters defined by geometry begin to deteriorate, one very quickly
moves from poor ride quality to component deterioration and outright failure.
3.6.1 Gage
Consider the parameters making up geometry. The first parameter is gage, which is the
right angle distance between rails measured 5/8" down from the top of the rail on the
gage (inside) corner (Figure 3-71).
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Standard gage is 4' 8-1/2" (56-1/2").
Railways are concerned about not only
wide gage, which comes from rail head
abrasion in curves, worn spike killed ties
which allow the rail to move outward,
worn rail base eaten away by salt in
crossings and numerous other factors, but
also by tight rail that may cause the wheel
to climb up onto the ball of the rail and
then drop in. Dependent on location, type
and wear of wheel and a host of other
Figure 3-71 Measuring Gage – Photo by Larry Slater
factors, the wheel may fall in when the
gage exceeds 58-1/2" (2" wide gage). Under the 49 CFR 213 FRA Track Safety
Standards, one is not allowed to operate trains at any speed if the gage exceeds 1-3/4"
wide. In comparison, to operate at Class 4 (80 mph passenger/60 mph freight),
trackage may not exceed more than 1" wide gage under load.
Maintenance of gage is a priority not only because of the need to not have trains falling
through between the rails, but also because it permits the flange of the train wheel to
hunt from rail to rail, thus knocking the track out of alignment . Replacement of curve
worn rail in curves or the transposition of rail (making the low rail the high and vice
versa) and replacement of deteriorated ties (the primary cause of wide gage) are the
chief weapons in combating wide gage problems.
3.6.2 Alignment
Another parameter of geometry already
mentioned is alignment. Alignment is
the position of the track or rail in the
horizontal plane. It is expressed as being
tangent or curved. (See Figure 3-72)
Alignment is measured in straight track
by stretching a 62' string between two
points along the gage corner of the rail.
The offset measurement between the
string and the gage corner of the rail is
Figure 3-72 Curved Alignment - Photo by Bill Ross
taken at the midordinate (center of the
string (31')). If the track is perfectly
straight, the offset should be zero (i.e., the string touches the gage corner of the rail
along the entire 62' chord). Again, the FRA has set maximum permissible amounts of
alignment deviation (difference between 0” offset and the measured offset in inches),
which become more restrictive as speeds increase. In a curve, alignment is also
measured by the use of a 62' chord and for classes 3 – 5 track, a 31' chord as well. To
understand how alignment is measured in a curve, one needs to first examine the
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components of a curve. There are three specific elements of a curve that must be
considered:
-
Full Body of the Curve
-
Transition Spiral Entering and Leaving the Curve
-
Superelevation in the Curve
Full Body of the Curve
In a perfectly circular curve, the radius
of the curve at any point along the curve
is the same length. (Figure 3-73) It just
so happens, that when one stretches a
62' chord (string) with either end of the
string at the gage corner of the rail (5/8
inches below the top of rail), at any
point throughout the curve, the
measured offset (between the string and
the gage corner of the rail) at the midordinate (center of the string) in inches
is also the degree of curvature of the Figure 3-73 Full Body of Curve - Photo by Larry Slater
curve at that point. (See Figure 3-74)
(See the Appendix for diagrams and literature detailing the relationship between midordinate measured
and degree of curve.)
The degree of curvature should be the same at every point checked around the full
length of the full body of the curve. But curves are hard to keep in line, especially
where gage and surface related problems are present. By taking successive
measurements around the curve and then averaging these measurements, one can
determine an average existing midordinate or degree of curvature. Dependent on the
class of track operated, the FRA in the Track Safety Standards defines the procedure
utilized for determining the average midordinate for the curve.
The difference, then, from the measured
mid-ordinate (degree of curvature) at a
point of concern, and the average
midordinate determined for the curve as
it presently lies, is the deviation in
alignment. Again the higher the speed,
the more restrictive the allowable
deviation from desired alignment.
Alignment allowed to deteriorate initially
will cause a poor ride and very quickly
Figure 3-74 Measuring the Mid-ordinate - Photo by Larry Slater
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will lead to surface related problems.
Transition Spiral of the Curve
A train progressing at speed down tangent
track would undergo a significant lateral
acceleration if it instantaneously went from
tangent track to full degree of curvature
where the tangent track ended and the curve
began. To combat this problem, a transition
curve called a spiral is introduced at the
beginning of the curve and at the end before
the curve returns to tangent. (See Figure 375) The degree of curvature of a spiral
(cubic parabola) starts at zero and ends up at Figure 3-75 Transition Spiral Curve - Photo by Larry
the full curvature over its length at roughly Slater
an even rate. (See Chapter 6 Railway Track Design for a complete discussion of the spiral curve. A
sample calculation illustrating the calculation of deflection angles and other required curve components
can be found in the Appendix.)
Curve Elevation
The other element of a curve that must be considered is the effect of centrifugal force as
the car moves around the curve. The sharper the curve (the shorter the curve radius)
and the higher the speed, the greater the centrifugal force. This force tends to cause the
wheels to move towards the outside rail as much as one may have experienced on an
amusement park ride. To counter this force, railways elevate the outside rail of the
curve, or in railway parlance add superelevation, to counter the effects of centrifugal
force. Through the full body of the curve (the circular segment of the curve), the
elevation required to offset the effects of centrifugal force is constant for a given speed.
The amount of superelevation required is determined by the speed of the fastest train
and the degree of curvature present. Excessive elevation for the speeds operated will
mash the low rail or even cause low rail turnover. Too little elevation for the speed
operated may cause the wheel to climb the high side and derail. Not all trains operate at
the same speed through a curve. Railways are permitted to operate with a maximum of
three inches of unbalance for conventional equipment and with approval of the FRA, at
higher levels of unbalance for specialty equipment per Subpart B. This enables the
balancing of elevation for both the highest and slowest speed trains operating through
the same curve without compromising the safety of the train or causing premature
deterioration of the track structure. Railways will specify the amount of unbalance
utilized up to a maximum of three inches.
One cannot go instantaneously from zero elevation in the tangent section to full
superelevation when the full body of the curve is reached either. The spiral curve is
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used to also transition in the increase in elevation until at the end of the spiral when full
elevation is reached. At the end of the full body of the curve, a spiral is used to
transition the full elevation back to zero when the tangent section is again reached. (See
Chapter 6 Railway Track Design for a complete discussion on the use of the spiral curve to transition in
full superelevation.) Thus, both lateral and vertical increase in acceleration of the car body
occurs at a constant rate without feeling an abrupt change. The weight of the train,
deviation in gage and alignment, as well as resultant surface track problems, make it
difficult to maintain these elements in the desired state. Deterioration of other track
components further exacerbates the maintenance of curves and tangent track. The
correction of alignment, surface and how these two relate to curves is called surfacing.
It is a key component in the renewal or rehabilitation of the track structure.
3.6.3 Surface
The next primary element of geometry is surface. Surface describes the vertical
relationship of the track structure and is comprised of run-off, profile, crosslevel,
reverse elevation in curves and warp or twist (difference in crosslevel).
Each category of surface affects the train's response to the track and must be
considered in performing all track construction and repair tasks. Speed-sensitive
maximum tolerances have been established
for all of the elements of surface.
The top of rail elevation of newly worked
track must be blended into the elevation of
the existing track during surfacing
operations, where the track is raised, when
renewing the deck of a bridge or performing
work on other track structure elements
changing the top of rail elevation. If not
careful in blending the new elevation of the Figure 3-76 Run-off Between Bridge Segments - Photo
track, a car traversing over the blended track by James Bertrand
section will get a severe bounce, which in
some cases may uncouple the train. We call this abrupt change in elevation run-off.
(See Figure 3-76) The greater the speed, the greater the bounce, if the run-off is too
abrupt. Run-off allowable limits are determined by stretching a string along the top of
the rail and by measuring the change in elevation of either rail in 31'.
The profile of each rail is the mid-offset in inches measured from the midordinate of a
62' string stretched along the top of the rail. Profile problems look like sags or humps in
the track. (Figure 3-77)
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Figure 3-77 Measuring Profile
Figure 3-78 Measuring Crosslevel
Surface also includes crosslevel (Figure 3-78), which is the difference in elevation
between two rails at any given point. In tangent track, the crosslevel should be zero.
Both rails should be at the same elevation.
In curved track in the full body of the
curve, the crosslevel should be at
whatever
is
the
designated
superelevation.
In the spiral, the
crosslevel should be whatever the
incremental amount of elevation is
between zero and full elevation for that
point in the transition curve. The
difference between what the crosslevel is
and what it should be at that point is
known as the deviation in crosslevel.
Specific limits are also set on the amount Figure 3-79 Difference in Crosslevel (Warp) Within 62'
of reverse elevation permissible in curves (i.e., the outside rail in a curve is lower than
the inside rail at a given spot).
Difference in crosslevel or warp (Figure 3-79), the fourth category of surface, can cause
the front of the car to lean in one direction and the rear of the car to lean in the other
simultaneously. The resultant wracking action on the car may cause a wheel to lift.
Warp is also the cause of the famous rock-n-roll phenomena, whereby successive low
joints at critical speeds will cause certain types of cars to go into resonance (reach their
natural frequency). They will literally rock themselves off of the track from the wheel
lift produced.
Warp is defined as the change in crosslevel between any two points less than 62 feet
apart. The change between the highest and lowest crosslevel reading in any 62'
determines the speed that can be operated. Warp in a spiral curve can often be
dangerous. Because of the lateral and vertical changes the car is undergoing in the spiral,
a low spot or even reverse elevation in the spiral may require a speed reduction perhaps to 10 mph until the problem can be corrected. Allowable warp in a spiral for
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Class 4 is 1", but just a 2" difference in crosslevel requires one to reduce speeds down to
Class 1 track.
Surface problems are often directly related to tie condition. If a significant number of
ties are no longer capable of providing support (i.e., they're split, broken, plate cut or just
abraded away from the bottom) surface problems will result. Out-of-face tie renewal, at
that point, is the only permanent option to correct the resultant surface problems.
If the free draining characteristics of the ballast are disrupted, i.e., it becomes plugged
with mud or fines, surface will be impossible to maintain. Because the mud does not
have the bearing support of clean rock, the track structure will compress under each
passing wheel. A siphoning effect much like a toliet plunger will only bring more water
and fines up into the ballast section. Undercutting, shoulder cleaning or in some cases a
full out-of-face ballast raise (2" to 3"), are about the only options available to alleviate
this condition. If rail condition has deteriorated to the point that secondary batter or
bent ends cause the wheel to pound every time it goes over a joint - surface will be
impossible to maintain. Inadequate drainage because of fouled ballast or other related
factor may be considered an FRA non-class specific defect under certain situations.
3.7 Safety
The importance of safety on the ROW was highlighted in Chapter 2, Industry
Overview. Indeed, the first rule in virtually every railway safety rule book is “Safety is
the most important element in the discharge of duties.” The cardinal rule of
railroading is “Expect a train on any track, at any time and in any direction. Never step
in the foul without looking both ways.” These rules are key to staying out of harm’s
way any time one is out on the ROW.
Within the United States, the Federal Railroad Administration has set very strict
requirements regarding the protection required for roadway workers (individuals
inspecting, constructing, maintaining or repairing track, bridges, signal and
communication systems, roadway, roadway related facilities, electric traction systems or
anyone operating roadway equipment in the foul of the track or with the potential of
fouling the track). These regulations are known as the On-Track Safety or Roadway
Worker regulations. Each railway has developed an On-Track Safety Policy that
defines how protection will be provided to roadway workers from trains or roadway
maintenance equipment any time they are in the foul of the track. Contractors,
consultants, manufacturer equipment personnel and railway employees meeting the
criteria of a roadway worker are bound to comply with these requirements by federal
law, and there are severe corporate and personal financial penalties for failure to
observe these requirements. Per the FRA, one is in the foul any time one occupies the
track or is within four feet of the near running rail or is within the envelope where
he/she could be struck by a projection from a piece of on-track roadway maintenance
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machinery. Railways may have more stringent requirements than that posed by the
FRA.
Each railway On-Track Safety policy will mandate but is not limited to the following:
•
Every roadway worker must have a daily job briefing that defines the qualified
employee-in-charge of his on-track safety and the type of on-track safety that will
be provided him on the track from which he is fouling and/or on adjacent tracks
as well. The physical and time limits of the protection must be provided if
appropriate.
•
No roadway worker may foul the track unless an appropriate form of on-track
safety is provided him at all times.
•
A qualified employee-in-charge, who is providing or arranging for the protection,
must be present at all times when the track is fouled by roadway worker(s).
•
A designated form of warning and a designated place of safety will be identified in
the job briefing that the roadway worker must immediately move to with the
approach of a train or piece of roadway maintenance machinery on the track from
which he is fouling as well as on any adjacent tracks. (An adjacent track is defined
as any track with a track center distance of less than 25 feet from the track which
protection is being provided.)
•
A roadway worker may challenge the on-track safety protection provided him if he,
in good faith, believes that the on-track safety protection provided is inadequate or
is in violation of the railway’s On-Track Safety policy or the FRA regulation,
without fear of retribution.
Roadway workers can provide protection for themselves utilizing several different
methods of protection. However, they must be a qualified employee-in-charge in
order to do so. To be qualified, one must:
•
Successfully pass an annual railway operating rules exam.
•
Successfully pass an annual railway On-Track Safety Exam.
•
Be familiar with the physical characteristics of the railway segment where
protection will be provided.
In all but the most rare cases, railways typically do not qualify other than employees to
be employees-in-charge. This means that anyone coming onto the property in a
consultant/contractor mode must be accompanied by a qualified employee-in-charge
any time he/she is within the envelope defined as foul – FRA or railway, no matter
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how short the period. Some railways further restrict this to any time one comes onto
railway property.
Roadway workers must receive annual roadway worker training prior to fouling the
track. Some railways utilize the job briefing in order to satisfy the training requirements
for infrequent contractors/consultants. However, a number of railways require
contractors or consultants to be roadway worker trained prior to receiving permission
to come onto the property. There are a number of qualified entities that can provide
this training, including AREMA.
The On-Track Safety regulation is complex and there are a number of other very
significant requirements. The engineer must have a clear understanding of it. One can
download the regulation and explanation from WWW.FRA.DOT.GOV.
The FRA requires the use of fall protection when working on a railway bridge:
•
Outside the running rails of any bridge structure not equipped with a handrail on
the side from which one is working,
•
With a height greater than 12 feet or more from the working surface to the surface
below, and
•
With an overall span length greater than 12 feet.
Similar requirements exist in Canada under Labour Canada law.
The FRA Blue Flag requirements govern the protection provided personnel working
on, under or between railway cars and locomotives. Equipment blue flagged cannot be
moved, coupled into, or equipment cannot be moved onto a track where the view of
the blue flag will be restricted by the equipment unless personnel placing the blue flag
have removed it and are in the clear.
The FRA has adopted other governmental regulatory requirements where specific
FRA regulations have not been adopted, including OSHA regulations. Although the
FRA cannot enforce other governmental regulations, it can notify other governmental
entities when it believes violations exist or employee/public life or safety may be
endangered.
3.8 Maintenance Activities
At this point, the interrelation between the various elements of the track structure and
how deterioration of one component very shortly affects the other components is
evident. To insure that the component life guaranteed is secured, railways have to look
at their capital rehabilitation programs from a systems approach. It is a waste of funding
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to relay rail in a track segment plagued with defective ties incapable of supporting the
wheel loads unless the tie problem first is corrected. A full out-of-face tie renewal,
bringing the track structure up to Class 4 or Class 5 tie condition, will quickly deteriorate
if the ballast section consists of mudcaps, poor alignment and surface problems.
Alleviation or attention provided one aspect of the track structure will not correct other
problems, both from the integrity of the track structure, but also from a regulatory
perspective as well.
On the other hand, a well-planned rehabilitation program, that minimizes disturbance of
the track structure, but that also includes coordination and consideration of all phases of
track maintenance, will often yield life cycles that will go well beyond the life expectancy
guaranteed.
Coupled with on-going cycle based rehabilitation programs, is the need for consistent
operating dollar-based maintenance programs. Spot replacement of ties, correction of
gage deficiencies, smoothing, elimination of joints, adjustment of CWR, turnout
maintenance, repair of battered or chipped rail ends, grinding of rail to maintain
optimum rail profile, are all essential to keeping the track structure in equilibrium until
capital component replacement occurs. The industry must never let deferred
maintenance become a way of life again. As older, more experienced workforce retire,
as new regulations add restrictions to the way maintenance activities are performed with
resultant loss of efficiencies, and as train traffic increases and work windows decrease,
railways are going to need more sophisticated and productive equipment for their
maintenance forces to counter these problems.
The reader is encouraged to turn to the Appendix for a synopsis by the Canadian
National Railway of procedural steps used in performing various maintenance activities
including:
•
Ballast Unloading
•
Gauging on Wood and Concrete Ties
•
Mechanical Surfacing of Track
•
Switch Tie, Yard and Siding Ties & Programmed Maintenance Tie Renewal
•
Rail Train Rail Pickup
•
CWR Rail Relay on Wood or Concrete Ties
•
Mechanized Tie Renewal
•
Track Abandonment
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•
Track Sledding
•
Installation of Panelized Turnouts
•
Unloading Continuous Welded Rail
Note: These practices are provided only as a guideline and may be in significant variance with the
procedures and practices of other railways.
Maintenance has always been performed, more or less, on a cyclic basis.23 Cyclic
maintenance, in its modern connotation, must therefore mean more than mere
repetitive programming. Quality does not wait until the entire service life of a tie has
been consumed before renewing that tie. An almost worn-out tie is not giving full and
uniform support to the track. Neither does quality maintenance wait until alignment
and surface have deteriorated before performing the necessary lining and surfacing
operations. These work activities must be established on a cycle that does not permit
significant deterioration to set in. Additional cost may seem to be involved. This may
well be since one often has to pay more for a product of higher quality. The actual
over-all-cost effects may not be as adverse as one might anticipate, because it is easier
to keep up than to catch up.
Cyclic maintenance is a desirable feature of standardization of methods. Tie renewals
and surfacing are related operations. Surfacing should follow tie renewals to insure a
final quality surface after the track has been disturbed by the tie renewals. Because the
two operations frequently move at different speeds (depending on the number of tie
renewals per mile), the one operation should not be permitted to hold back the other.
3.8.1 Track Disturbance
Many of the major production and maintenance activities constitutes significant
disturbance of the track structure, especially in welded rail. Railways work hard to keep
the track structure in equilibrium. The thermal expansion of a single piece of rail 1440
feet long for a 60 degree F rail temperature rise, not uncommon on a clear, hot day,
would allow that rail to grow 7 inches if it were not restrained. But the rail ends are
restrained. They are welded together. The forces produced are significant (106,780 lbsF for 136# rail for a 40°F rise in temperature) as each rail tries to expand against the
other. Using Euler's buckling theory, a compressive force of sufficient magnitude
applied at either end of long narrow member (rail or rails fastened to the ties), will result
in the buckling of the member before the ultimate compressive strength is exceeded.
By increasing the moment of inertia of the member or by shortening its effective length,
the force required to achieve buckling is increased. So it is with the rail. The moment
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of inertia or resistance to buckling of the track structure is increased by adding solid fully
spiked ties, providing a full ballast section between the ties and on the shoulder, and by
applying anchors.
But thermal forces are not the only forces that are applied to the track structure. Train
braking and acceleration, locomotive nosing back and forth, truck hunting, line kinks,
centrifugal force on curves, etc., all add additional forces to promote buckling. There's a
limit to how much the track structure can resist. In most cases, the only force that can
be controlled is thermal expansion. North American railways lay the rail at an elevated
temperature (80°F - 120°F depending on the expected temperature range), and then
lock the rail in place by applying enough anchors. Theoretically, the rail is not thermally
stressed (no compressive or tensile forces imposed) anytime the rail temperature is at
the temperature the rail was laid. We call this “as laid temperature,” the neutral
temperature. Unfortunately, over time, the neutral temperature tends to drop
significantly from the inadvertent adding of rail when changing out rail or making welds,
lining curves in during cold weather and natural microscopic creeping of the rail through
the anchors.
Where does this all lead? Although excessive rail can be cut out and stretched with big
hydraulic jacks to raise the neutral temperature, this is not a realistic approach every time
maintenance functions are performed and the track is disturbed.
3.8.2 Track Disturbance Activities
Disturbance constitutes any procedure that reduces track moment of inertia or stability,
such that it cannot resist the compressive forces imposed under normal ambient
temperatures, either under or without train loadings. When the track is raised out of its
naturally consolidated bed and the bonds are broken that have developed through the
natural interlocking of the individual stones making up the ballast section, or the ballast
is removed between the ties and on the shoulders, we have disturbed the track and
promoted the possibility of track buckling or a sun-kink.
Engineering out the potential for a sun-kink ahead or under a train in CWR is achieved
through the adherence to specified procedures utilizing a combination of limiting speed
restrictions applied for a given amount of tonnage and/or number of trains over a given
time period until consolidation is achieved. The specifics to these procedures will vary
according to the type of traffic, train consist, ambient temperature, physical
characteristics of the railway and speeds operated. Each railway will have developed
CWR policies and procedures pertinent to their operation. Procedures applicable to
commuter/transit operations may not be applicable to unit train operations. However,
it is essential that individual railway procedures be followed any time track disturbance
occurs. Today, railways can quickly regain about 80% of the original track stability
through the use of a dynamic track stabilizer.
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Thus the goal when performing track work of any kind is to minimize disturbance.
But when disturbance does occur, appropriate measures must be instituted until
the track is again stable while still safely keeping train delays to the minimum
possible.
3.8.3 Rail Lubrication
Lubrication of the rail in curves, if appropriate, is an essential task in the battle to
maximize rail life. Even with properly superelevated curves, the flange of the wheel
tends to crowd the high or outer rail (desirable for a good ride). The resultant abrasion
of rail and wheel can be significant, thereby leading to wide gage and unfavorable wheel
loading stresses that aggravate the formation of dangerous rail and track defects. The
proper application of lubricants will significantly reduce the amount of rail and wheel
wear imposed and thus increase the life expectancy of both rail and wheels. The
resulting reduction in wheel hunting action from proper lubrication will slow down the
formation of alignment and gage related problems.
Lubricant is applied to the rail through the use of locomotive on-board lubricators,
wayside lubricators (Figure 3-80) and hi-rail equipped lubricant pump/nozzle systems
or by hand application. Regardless of the method of application, it is important that
the lubricant only be applied on the gage corner of the rail and not upon the tread of
the rail where it could seriously impact locomotive traction or braking. This is
particularly important in commuter rail and transit properties, which are operating a
limited number of cars per train set. Loss of friction at the rail/wheel interface can
cause sliding under the severe braking applications often required for short distance
intervals between station stops. It is also important that wayside lubricators be
properly located to ensure that the lubricant is carried throughout the curve.
The low rail should also be lubricated to
ensure that the truck assembly steers
itself around the curve rather than
slewing around the curve. Failure to do
this, in double-stack/container territory,
or in terminals where stiffer high-speed
engines operate, can result in lateral
forces that will roll the low rail over,
even in the best of track conditions.
Figure 3-80 Wiper Bars of a Rail Lubricator – Conrail
Lubrication on transit properties is also
utilized to reduce noise levels as equipment traverses around the curve. There are a
variety of petroleum, synthetic and even soybean based greases available that are
environmentally friendly, but also maintain their viscosity over a wide range of ambient
temperatures.
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Recent developments in the application of friction modifiers (not a lubricant) to the
tread of the rail optimize the coefficient of friction on the running surface of the rail.
This promotes better steering with significant reduction in propulsive energy costs,
reduced noise and longer rail service life. The use of head hardened (heat treated) rail,
in addition to lubrication, can be used to promote rail life in severe curvature.
3.8.4 Rail Grinding
Rail grinding is another maintenance
activity that promotes increased rail life.
Both the rail and the wheel have a radii
at the contact point. By modifying the
radii of the rail head, the rail/wheel
interface (contact point) can be shifted
to a situation more favorable for the
imposition of induced stresses for a
given rail section. The applied lateral
and vertical forces create a resultant Figure 3-81 Switch Grinder - Courtesy of Canadian Pacific
vector described by the L/V ratio. Rail
Shifting the contact point similarly shifts
the application point of the resultant vector. Keeping the L/V ratio below 0.6 is
important, although low rail turnover has occurred with L/V ratios as low as 0.4 with
hollow worn wheel treads. The optimum rail profile then is a function of the wheels
utilized and the car characteristics to the extent that they can be controlled.
Rail grinding is achieved through the use of specialized grinding machines or trains
equipped with adjustable grinding wheels (See Figure 3-81), that can remove small
amounts of metal at a very controlled rate in a series of passes. Depending on the
amount of material to be removed and the number of stones utilized, grinding is
typically performed at speeds ranging from 1 – 7 mph. Grinding is also used to
remove surface imperfections in the rail such as gage corner shells, spalls on the low
rail and corrugations on the rail head. Corrugations in transit properties produce the
infamous roaring rail sound. In freight and commuter territory, it can eventually lead
to detail rail fractures.
Localized grinding is also performed on manganese components such as RBM frogs
and crossing diamonds. It requires the imposition of tonnage to work harden
manganese. Until manganese is work hardened, it flows very easily. It is important to
remove this overflow (grinding) before it breaks out, which requires extensive welding
to make repairs. The longer welding can be postponed, the longer the service life of
the manganese component. Thus intermittent touch-up grinding is essential.
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3.8.5 Rail Defect Testing
Rail defects can be classified as
external or internal. Although most
internal defects give some external
indication of their presence, it may not
be recognized prior to a train finding
it, with a resultant derailment. Internal
defects are found through the use of
an ultra-sonic or ultra-sonic/electroinductive vehicle (Figure 3-82)
designed to look at the reflective wave Figure 3-82 Ultra-sonic Electro Induction Rail Defect Testing
imposed on the rail at several angles.
Some form of discontinuity or aberration in the rail will be visible on a CRT screen as
the vehicle traverses over the rail. The FRA has established required rail inspection
frequencies dependent on the speed operated, tonnage levels the prior year and
whether or not passenger trains are operated. The FRA 213.113 section of the Track
Safety Standards provides the minimum required remedial action for a found defect,
which is dependent on the type of defect and its cross-sectional area or length.
The Sperry Rail Service provides an excellent pictorial manual of the various types of
rail defects and the more common visible indicators of their presence. Good
knowledgeable track inspection will often find the indicators of the presence of rail
defects prior to their breakout.
3.8.6 Geometry Cars
Many of the larger railways utilize a
geometry car (self-propelled or pulled by a
train) to periodically check basic track
geometry and gage compliance for
FRA/Transport Canada or their own more
restrictive requirements.
These heavy
vehicles can test at speeds up to 70 mph.
The newer vehicles use Optical Rail Figure 3-83 FRA T-2000 Geometry Car - Courtesy of
Plasser American
Scanning to measure gage and geometry
parameters in real-time mode. The resultant print-out flags non-compliant locations or
close to non-compliant locations. A visible paint mark is left on the track structure to
assist repair crews in locating the deficiency. Older cars utilized a gage feeler system
and required significantly slower testing speeds. The FRA operates its own Geometry
Car (Figure 3-83) in order to verify railway compliance with the standards on a more
wide based range than that which can be done by having an inspector making localized
inspections.
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3.8.7 Gauge Restraint Measuring System (GRMS)
A new tool in finding the presence
of wide gage under loading
conditions is the Gauge Restraint
Measuring System or GRMS
(Figure 3-84). These vehicles,
through the use of a sliding axle,
impose vertical and lateral loads
and measure the resultant lateral Figure 3-84 GRMS Vehicle - Courtesy of Plasser American
movement of the rail. Specific
requirements for the imposed load's L/V ratio are stipulated in the FRA Track Safety
Standards. Based on the amount of movement and the imposed load, a resultant gage
widening under load measurement is extrapolated for actual train imposed loadings.
The FRA permits the use of these data in determining gage compliance in lieu of the
required number of non-defective ties for a given class of track per 39-foot segment as
stipulated in 213.109. Thus, available capital replacement dollars can be utilized where
they are most effective and needed, not just to maintain compliance with the Track
Safety Standards. GRMS testing must be done at the required frequency in order to
have relief from the 213.109 requirements. Many railways are utilizing this tool to plan
capital tie replacement programs or to find weak spots in their track structure.
3.8.8 Vegetation Control
The control of unwanted vegetation is
another essential maintenance activity.
Some ROW vegetation is desirable, for
example, the root structure of selected
grasses used to prevent erosion or
sliding of fill sections, the use of trees to
serve as wind breaks for minimizing
snow drifting or sand blowing, or
shrubbery to act as a sound damper or
sight break in residential areas.
Unwanted vegetation (See Figure 3-85)
serves to block drainage, reduce sight
visibility for approaching motorists at Figure 3-85 Overgrown Vegetation - Photo by J. E. Riley
highway crossings, reduce signal or
whistle post visibility for locomotive engineers, create fire hazards around bridges and
other railway structures, increase the risk of injury to employees performing their job
functions, hamper track inspection and may ground out track circuits in pole line
which possibly could give a false clear indication to an approaching train. Unwanted
vegetation may also provide a habitat for rodents and other unwanted vermin, spread
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noxious weed seeds and provide unfavorable publicity and exposure to the railway
from surrounding communities.
Vegetation is controlled through the use of either herbicide application or mechanical
cutting. There are a number of successful formulations developed by the chemical
industry for the control of vegetation. The specific weed or tree species, climatic
conditions and the neighboring environment will dictate which formulations or
combination of formulations are recommended. The Environmental Protection
Agency in the United States regulates the application of herbicides. Herbicide
application rates and type of usage are very clearly spelled out. Failure to comply can
bring severe penalties. Licensing of applicators and operators is done by the states and
is required of anyone applying herbicides to railway property.
Herbicide formulations can be broken down into two categories:
•
Pre-emergent
•
Post-emergent
Pre-emergent herbicides are applied before germination of the seeds or very early in
the plants juvenile stage of life. They typically possess residual characteristics that carry
on some time after their application and prevent seed germination. Timing of
application is obviously critical as is the need for moisture some time after application
to move the herbicide into the soil. Post-emergent herbicides are applied after the
plant has sprouted. They typically have no or little residual characteristics. They are
applied to the foliage and translocate to the root structure to kill the plant. Some postemergent herbicides are classified as contact herbicides. They cause the plant to drop
or damage the foliage on which the herbicide came into contact. This results in the
disruption of the plant's ability to utilize photosynthesis and may stunt or kill the weed
or tree.
Herbicides are applied through the use of backpack sprayers, hi-rail truck-equipped
booms or hoses, or through the use of spray trains. Some states and providences have
very strict notification regulations prior to the application of herbicides. Check before
initiating a program.
Mechanical cutting of vegetation can be broken down into localized mowing or chain
saw removal of brush and tree species, a very labor intensive and expensive endeavor,
or the use of on-track based production cutting machines. Many of these machines are
not suitable for use in urban areas because of the debris thrown and the splintered
remains of the tree that is left behind. However, in more remote locations they are an
effective means of clearing the ROW. Other on-track based equipment may not have
the production rates, but are more urban environment friendly and enable the judicious
employment of tree trimming. Chipping or removal of the cut material is almost
always a requirement in urban areas.
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3.8.9 ROW Stabilization and Drainage
Railways are faced with a number of soil
and ROW stabilization problems. These
can result from saturation of soils due to
lack of or blocked drainage, overloading of
placed or natural fill materials from years
of ballast raises and heavy train traffic,
poor initial soil selection in the
construction of the ROW or inability of
retaining walls to hold back the ballast
because of ballast raises that do not permit
an acceptable angle of repose within the
Figure 3-86 Slope Failure - Photo by Bill Ross
height of the wall. Many of the commonly
applied highway stabilization methods used are also applicable to railways.
Reducing water content below saturation through the installation of lateral drains,
outlet drains and the cleaning out of ditches will often alleviate locations requiring
frequent surfacing to stay within required parameters. (See Figure 3-86) Often ballast
pockets will form deep in the subgrade, which act as a natural wick for water. These
pockets form as the ballast is pushed down into the underlying soft-saturated subgrade.
The addition of more ballast simply exacerbates the problem. These pockets must be
located and drains installed to alleviate the situation. Similar problems will often occur
when using a ballast regulator to bring ballast from outside the toe of slope back into
the ballast section. Often dirt and other fines are also dragged up creating a small
berm. This "bathtub" type curb, if located at or below the bottom of the ballast
section, will often trap water with its attendant surface related problems.
Unfavorable soils can sometimes be alleviated through the use of lime injection or
cement grouting dependent on the soil type. Other mechanical means include driving
second-hand ties vertically and spaced at intervals outside the edge of ties if the
problem is localized over a short length. The placement of rip-rap at the toe of slope
will sometimes alleviate the problem. Reducing the angle of repose by dumping and
spreading ballast is another means often used, so long as the fill section is not failing
because it is already overloaded. In the case of some varved clays and other very
unfavorable soils, the only permanent solution may be the removal of the track and the
excavation of the poor soils with replacement of a more favorable soil.
Tie-back walls and techniques such as soil nailing are now also coming into vogue.
Temporary relief from ballast sliding problems at bridge ends and culvert headwalls can
often be rectified through the use of timber ballast stops as well.
Localized ditching can be done through the use of backhoes and crawler excavators.
The major excavator manufacturers have designed and built crawler equipment that
can move from air-dump car to air-dump car, loading the cars as it progresses through
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each car. More conventional equipment includes the use of Jordan ditchers, which
have powerful cylinder, equipped wings that will blade the ditch through the toughest
of terrain. It is important that any ditch created be trapezoidal in shape to minimize
future plugging with debris. Avoid V-shaped ditches.
3.8.10 Welding
The most common track welding functions are electric arc, thermite and flash butt.
Standard arc welding processes such as SMAW, GMAW and FCAW are used to weld
manganese and carbon steel track components. However, thermite and flash butt are
used for joining continuous welded rail. The flash butt method is used in the plant to
create quarter-mile ribbon rails, which are then transported by a rail train to the
location where they will be installed. Both flash butt (portable In-Track welding)
(Figure 3-88) and thermite (sometimes known as alumino-thermic) are then used in the
field, to join the longer lengths of rail together into continuous welded rail. They are
also used in maintenance welding for replacing defective rail and for light construction.
Thermite welding (See Figure 3-87) is a process
that joins rail ends by melting them with
superheated liquid metal from a chemical reaction
between finely divided aluminum and iron oxide.
Filler metal is obtained from a combination of the
liquid metal produced by the reaction and
pre-alloyed shot in the mixture.
Flash butt welding (Figure 3-88) is a resistance
welding process that produces a weld at the
closely-fit surfaces of a butt joint by a flashing
action, followed by the application of pressure
after heating is substantially completed. Very high
current densities at small contact points between
the rail ends cause the
flashing action, which
forcibly expels the material
from the joint as the rail
ends are moved together
slowly. A rapid upsetting of
the two work pieces
completes the weld.
Figure 3-87 Thermite Welding a Joint Courtesy of Canadian Pacific Railway
Figure 3-88 On-Track Flash Butt Welder - Courtesy of Plasser American
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Electric Welding refers to the standard arc welding processes used elsewhere,
particularly shielded metal arc welding (SMAW) or "stick welding,” gas metal arc
welding (GMAW) and flux-cored arc welding (FCAW), with or without additional gas
shielding. These processes are used on frogs and crossing diamonds (both manganese
and carbon steel), for carbon steel rail ends, switch points and wheel burns, and for
joining carbon steel rails.
Oxy-Acetylene Welding is now primarily limited to the build-up of rail ends that will
later be thermit welded.
3.9 Production Gangs
Major restoration or renewal of the track structure is typically accomplished through
the use of organized production gangs dedicated solely to performing a single function.
These gangs will vary in size, make-up and equipment consists according to the
railways established procedures. They are designed to secure maximum production
within the limited track time window that is made available. Often, these gangs will
have system-wide seniority, which permits them to be utilized as geographic and
climatic conditions permit. Their acquired experience and expertise lend real efficiency
in the performance of their work. Many production gangs possess impressive safety
records in comparison to other railway work units. Albeit production work often
poses significantly more hazards.
Many of the regional, short line or commuter/transit properties will contract
production work to railway contractors, as they do not possess the required workforce
or equipment to effectively perform these tasks. Class I railways and the larger regional
and commuter railways typically perform this work themselves because of negotiated
labor agreements, although there is a growing trend to contract new track construction.
The specific production gangs to be covered in this chapter include:
•
Rail Gangs
•
Tie Gangs
•
Undercutting Gangs
•
Surfacing Gangs
•
Road Crossing Renewal Gangs
•
Turnout Gangs
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•
New Track Construction Gangs/Cutovers
3.9.1 Production Rail Gang
The first production gang to be considered is the rail gang. Rail renewal is determined
chiefly by the condition of the existing rail. Rail with significant secondary batter,
chipped ends, bent joints, corrugations too deep to grind out or with excessive curve
wear, becomes impossible to maintain surface and speed restrictions have to be
imposed. Rail segments that have had a history of recent failures, whether discovered
ultrasonically or as outright broken rail, are placed for special priority. Older jointed
rail, within acceptable wear limits and that has been work-hardened by tonnage prior to
the inception of 100-ton cars, is rail that can often be utilized for relay purposes. By
cutting off 18" or more from each end, the bolt holes are eliminated and the rail can be
welded into lengths of up to 1440 or 1600 foot long strings. This cascading effect
generates a significant amount of the rail laid in North America, particularly on
medium tonnage and secondary lines.
Rail gangs will typically range from 30 to 60 men in size. As such, they are the most
labor-intensive work function utilized. Expansion of the rail and installation at gage are
the primary performance criteria that must be considered when laying jointed or
continuous welded rail (CWR). Jointed rail must have shims installed between rail ends
in order to permit thermal expansion. The thickness of the shim utilized is a function
of the rail's present temperature. CWR is laid at a Preferred Rail Laying Temperature
(PRLT), which will be the rail's neutral temperature after anchoring, and is designated
per geographic location by the railway. The neutral temperature favors the higher
range of expected rail temperatures, as a sun kink is typically more dangerous than a
pull-apart. If necessary, the rail is artificially heated or cooled or adjusted hydraulically
to a corresponding length in order that it is within an acceptable neutral temperature
range. The rail is then anchored per railway standard in order to lock in the neutral
temperature.
The rail laying operation begins with the distribution of the material. CWR strings are
carefully unloaded at their point of installation off of specialized roller rack cars
carrying up to 40 strings of rail (Figure 3-89). These cars are permanently connected to
each other as the strings span the cars. Tie downs are located for each string near the
middle of the train. This permits the ends of the string to be free and accommodate
going around curves and moving through turnouts. Each rail train is equipped with a
winch car and a set of adjustable threader guideways (Figure 3-90) that guide the rail to
the ground.
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Figure 3-89 Partially Loaded Rail Train
Figure 3-90 Rail Train Threader Car - Photos by J. E. Riley
The end of the string is then secured once it is on the ground. The rail is either pulled
or pushed out from under the train as the train progresses down the track. As the
trailing end of the string approaches the beginning end of the remainder of the strings,
it is temporarily connected to the next string and the process begins anew. Rail can be
unloaded simultaneously on both sides of the train. Unloading of CWR or picking up
of CWR that has been relayed is a potentially dangerous operation and great care must
be exercised so that workers are not pinned by a string of rail that for any reason does
not successfully line up with its corresponding roller rack. At crossings, a trench is
either excavated through the crossing into which the rail can be inserted, or the rail is
torch cut and the crossing is jumped. Should rail be required to renew the crossing, it
may also be unloaded at the crossing ends. Jointed rail will also be unloaded by rail
cranes onto the shoulder of the track ready for installation. See the article entitled
Unloading Continuous Welded Rail in the Appendix for further information on this
topic.
Tie plates are distributed ahead as well. In some cases, the existing plates will be used
for the rail to be relayed (curve patching or relays utilizing the same rail section). Other
material, depending on railway procedures, such as tie plugs, spikes or anchors, are
distributed just ahead of the gang to discourage theft. Depending on the equipment
consist, these materials may be carried with the machines. CWR is threaded by the use
of a specialized crane ball (head) up into the center of the track so that it is in position
to be threaded into the tie plate. (See Figures 3-91 and 3-92)
Figure 3-92 CPR Rail Gang - Photo by Bill Ross
Figure 3-91 UP Rail Gang - Photo by C. C. Rupel
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Although rail gangs vary significantly in their make-up and sequence of operation, in
general, they follow the activities listed in the Appendix article entitled CWR Rail Relay
on Wood or Concrete Ties.
When laying CWR, frequent rail temperature and gage measurements must be taken.
Gage measurements are performed between base to base rather than the customary
ball to ball measurements. The base to base measurements will vary according to the
rail's base width. This ensures that the rail will be at the proper gage once the first train
is operated over it and the rail has had a chance to set in the tie plate. Match marking
of the strings of rail and tie plates are performed at the string quarter points to ensure
that adequate expansion is secured when the rail is heated artificially.
As with all maintenance activities, compliance with FRA 214 Roadway Worker
provisions is mandatory. It is particularly important with a rail gang, that all activities
cease and that personnel get in the clear prior to clearing trains by the gang on an
adjacent track because of the spread out nature of a rail gang and the noise and sight
obstructions that are present.
Although virtually every rail gang operation has become mechanized, frequent machine
breakdowns necessitate that personnel are present and equipped to perform the task
manually. Rail gang productivity can range from a partial string per day on transit
properties up to 9 to 10 strings per day on large highly mechanized gangs. An
acceptable average is three strings per day with an 8-hour track window.
3.9.2 Production Tie Gang
Tie renewal is typically scheduled ahead of rail relays to meet minimum FRA standards
or to fit within cycle based programs. For medium and light tonnage lines, a tie life of
approximately 25 to 30 years is realistic except under joints or crossings. On heavyhaul, high tonnage lines, a tie life of 15 to 20 years is more realistic. Tie gangs will range
from mini-gangs of 12 – 15 personnel to 30 to 35 men for high production units.
Production may range from 500 ties per day installed for a mini-gang to an average of
1500 ties per day for a typical tie gang. High production gangs can install upwards of
3000 ties per day with a full 8-hour window.
Of particular concern is the disposal of the removed tie. Ties cannot be hauled to a
landfill because of their creosote content. Nor can they be left to slide down the slope
where they will impede drainage. Ties left in such locations are classified as an
unregistered hazardous material storage site by the EPA and can bring severe financial
penalties to the railway if prosecuted. Formerly, ties were either sheared or sawn into
thirds as part of the extraction process. Today, most railways prefer to remove the tie
in one piece, as it is more desirable for use by landscapers. Some railways have
contracted with small power plant operations to provide fuel to generate energy.
However, in most cases, the shipping costs associated with such operations make it
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prohibitive to do so. The problem of what to do with scrap ties will only get worse as
acceptable disposal sites become fewer in number.
Production renewal of ties begins with a tie inspector marking the ties. Selection of ties
to be renewed is done by examining the joint area to ensure adequate support and then
to the location of weak ties in relation to solid ties. Weak ties include:
•
Spike killed
•
Plate cut
•
Decayed
•
Burnt
•
End broke
•
Center bound partial split
•
Center split
•
Derailment damaged
The presence of such ties does not automatically lead to replacement, particularly if
there are a number of solid bearing, non-spike killed ties around it. On the other hand,
one might skip a few of these ties and select several marginal ties in a nest of marginal
but still serviceable ties. The inspector has to make his decision on not only what is the
tie condition today, but what will it be over the ensuing years, until another tie gang is
in this segment. Finally, the FRA Track Safety Standards dictates the minimum number
of non-defective ties permissible in a 39 ft segment. This requirement can be waived if
the railway operates a GRMS (Gauge Restraint Measuring System) car at stipulated
frequencies. Through the use of a sliding axle, the car applies both a designated lateral
and vertical load and measures the resultant movement. However, good ride quality
mandates a significantly greater number of non-defective ties than that required by the
FRA.
Ties are distributed to the ROW by a number of methods including the use of selfpropelled rail cranes to peddle ties with a tie grapple bucket from loaded gondolas, to
the use of a specialized backhoe equipped with clamps and projecting travel beams that
permit the grabbing of the top sill of cars and the cantilevering of the backhoe from car
to car, thereby unloading the ties as it proceeds through the work train. As with the rail
gang, tie gang consists and procedures vary widely from railway to railway, but in
general follow the procedures noted in the Appendix article, Mechanized Tie Renewal.
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Figure 3-93 Tie Gang Inserter - Photo by J. E. Riley
Figure 3-94 Mechanized Tie Gang Consist - Photo by J.
E. Riley
Tie gangs have also become highly mechanized (See Figures 3-93 and 3-94), but as with
rail gangs, the machines are subject to frequent breakdowns. Thus, every operation can
be performed manually.
3.9.3 Production Undercutting
Undercutting, shoulder cleaning, sledding, plowing or track removal with open cut
excavations is performed whenever the ballast section becomes so fouled with mud
that line and surface can no longer be maintained, or overhead clearances are so tight
that track raising is unacceptable. Undercutting production is generally limited to
availability of ballast and the amount of hard packed mud present in the track.
Typically, this will require 40 - 50 cars of ballast per mile of track assuming that 6” to 8"
of ballast is removed from the bottom of the tie. The amount of ballast re-claimed will
vary depending on the type of ballast in place and its condition. The dirt removed
from the track is either wasted off on the ROW or loaded by conveyors into air dump
cars. It is important that spoils wasted are bladed off so that a berm trapping water is
not created. A tie gang should be operated through the track segment prior to
undercutting so that downed ties will be a minimum.
Undercutting operations also vary widely in set-up. However, the key component is
the undercutter (Figure 3-95). This machine has a large chain with cutting teeth that is
pivoted under the ties at the required depth to be undercut until the chain is
perpendicular to the rail (Figure 3-96). As the chain rotates, the machine is moved
forward. A large vertical rotating wheel equipped with buckets is mounted on the side
of the machine. The buckets first create space at the end of the tie from which the
chain can operate. The chain brings the material to the rotating buckets, whereby the
ballast is carried upward and dumped onto vibrating screens. The dirt and smaller
ballast fines drop through and are deposited onto a conveyor that wastes the material
onto the ROW or into an air dump car. The larger ballast is returned to the track.
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Figure 3-95 Undercutting Roadbed - Photo by J. E. Riley
Figure 3-96 Undercutter Chain & Digging Wheel - Photo by
J. E. Riley
Smaller, less productive undercutters are used for switch undercutting and even smaller
units, called gophers, waste all material and are ideal for spot undercutting through
bridges, platforms, etc.
Shoulder cleaning performs the same operation with a large digging wheel, but only in
the shoulder area. It is ideal for locations where the track is mildly fouled. Removal of
fouled materials from the shoulder creates a natural siphoning action that will draw the
fouled soil particles out of the center of the track to the shoulder, thus opening up the
drainage required. Obviously, ballast requirements are not as heavy with shoulder
cleaning, but the results are not as effective either.
In plowing, a plow is inserted under the track structure and pulled ahead by either a
crawler cat or a locomotive. The ballast material is then plowed out to the shoulders,
leaving the track structure setting at whatever the depth the plow was set out. Ballast is
dumped to restore cribs and shoulders and the track is lined and surfaced. Sledding is
similar to plowing, except that the track structure is left atop the ballast section.
(See an article entitled Track Sledding in the Appendix.)
3.9.4 Production Surfacing Gangs
Surfacing refers to the operation, whereby the alignment and surface of the track are
restored to within acceptable maintenance limits and the ballast is tamped underneath
the ties. It can be classified as "spot" which is the localized repair to isolated locations
often done through the use of jacks and ballast forks or shovels, or through the
mechanized use of tampers, which is often referred to as smoothing. Production
surfacing includes skin lifts, whereby low spots are corrected and the entire track
structure is given a skin lift of under an inch to full out-of-face surfacing, whereby the
track is raised 2" to 3" in a single pass, as would occur under undercutting operations
or at road crossing renewals.
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Today's modern production tamper,
not only can tamp the ballast under
the tie with vibrating tools that are
inserted to either side of the tie and
drop below the tie, where they
perform a squeezing operation that
compacts the ballast underneath, but
are also equipped with jacks that can
lift the rail vertically at the point of
tamping. They also can move the
rail horizontally for lining the track.
Both vertical and horizontal jacking Figure 3-97 Surfacing with MK III Production Tamper - Photo by J.
are controlled by projecting an ultra- E. Riley
violet light from a buggy set ahead
of the machine (Figure 3-97), which sends a light beam back to sensors located at the
rear of the machine. Shadow boards are mounted on the machine between the light
transmitters on the buggy and the receivers located at the back of the machine. Using
the principles of triangulation, both vertical and horizontal jacks continue to jack until
their respective shadow boards cut-off the light beam. Since the buggy is setting out at
some elevation and at some horizontal location and the shadow board is much closer
to the receiver than the buggy, the light beams will both be cut-off at some distance
proportionately smaller because of the similar triangles that are created. Hence an
averaging operation occurs as the machine moves down the track.
A pendulum mounted in the rear of the machine senses crosslevel, and further controls
the vertical jacks over each rail to correct crosslevel deviations. By manually dialing in
adjustments, the operator can feather out line swings, add superelevation or create runoffs that feather track raises into existing elevations. Many of these machines are
equipped with autograph liners, that once the beginning of the spiral is located, the
machine is run through the curve without tamping and mid-ordinates are automatically
plotted out through the other end of the curve. Depending on the machine's
sophistication, corrective mid-ordinates are created through either the use of a
magnetic tape overlaid over the plotted mid-ordinates or it is performed automatically.
When the machine is returned to the starting point, the required corrections will be
made.
Today's production tampers (Figure 3-98) are equipped with automatic indexing
features that automatically move the machine to the next tie to be tamped, thereby
greatly increasing the productivity of the machine. Further improvements include
machines that permit the work head to move ahead and tamp faster than the machine
can travel forward. These super tampers can surface as much as 3 - 4 miles of track in
a day. As an option, laser equipped buggys, that do not move as the machine
progresses forward, can be set as much as one-half mile ahead of the machine. This
permits excellent averaging of alignment into fixed locations such as a bridge, where
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the track cannot be thrown, thereby reducing the danger of creating a line swing into
the bridge. Other improvements include keyboard entry of data (Figure 3-99) with
sophisticated software that presents menu options to the operator, thereby greatly
increasing his/her efficiency and the quality of work performed.
Other machines included within the surfacing gang may include a tamper not equipped
with jacks, that tamps every other tie behind the production tamper, thereby increasing
hourly production rates. One or more ballast regulators are used to transfer or recover
ballast where needed for tamping or filling the cribs and shoulders. The regulator is
equipped with a power broom that sweeps excess ballast off the top of the tie and
provides that “completed” look. The surfacing gang may include a dynamic stabilizer.
This machine imparts vibrations of a given frequency into the rail to secure
consolidation of the ballast structure. This restores lateral stability after the track
disturbance created by surfacing and minimizes the placement of necessary slow
orders.
Figure 3-98 Surfacing Gang Consist - Photo by J. E. Riley
Figure 3-99 Menu Driven Operations in MK IV Production Tamper
- Photo by J. E. Riley
Production surfacing typically will entail the operations noted in the Appendix article
entitled “Mechanical Surfacing of the Track.”
It is interesting to note that in an article from the 1934 Roadmasters Maintenance of
Way Association Annual Proceedings, William Shea, General Roadmaster of the
Milwaukee, St. Paul & Pacific Railroad, bragged about his high speed surfacing and
lining gang that could surface a mile per day. It consisted of 300 men tamping and
raising the track, 100 men lining the track and 100 men following up two weeks later as
a touch-up gang. Today with a foreman, 4 – 5 machine operators and possibly 1
laborer, 2-1/2 or more miles can be surfaced with a far greater degree of quality in the
work performed. Indeed today, there are machines that combine all of the operations
noted above in the typical surfacing gang into one machine, which can travel out to the
work site at near train speeds.
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3.9.5 Road Crossing Renewal Gangs
In all but the smallest crossings, the
crossing track structure is often prepaneled out adjacent to the crossing
(Figure 3-100) or at some other
convenient location. The completed
panels are then either off-loaded by
crane or slid into place once
excavation of the crossing is
performed. Where adjacent ROW is
available, completed panels several
hundred feet in length can be installed
if sufficient equipment is available.
Figure 3-100 Crossing Panels - Photo by J. E. Riley
Prior to removal of the crossing
surface material, the appropriate crossing permits must be secured from the local
authorities, highway traffic detours arranged, a work window obtained from the
railway’s Transportation Department and the appropriate detour signage and
barricades placed.
Pneumatic or hydraulic impact tools are required to remove threaded lags in timber,
rubber or concrete cast panel crossing materials. In some cases, it may be more
expeditious to torch cut off the lag screw heads and use a loader or crane to pop the
crossing surface materials out. The existing track is then cut into convenient panel
lengths, typically 39’, and lifted out by a crane, if tie condition is adequate to hold rail in
place while the panel is lifted. With the trackbed exposed, excavation can begin. It is
important that the graded surface be level and no more than 10” be removed below
bottom of tie. At all costs, avoid excavating beyond the hardpan that has formed from
years of consolidation from train traffic. The use of small tilt-blade dozers or
comparable equipment is effective in holding a level grade. Other suitable pieces of
equipment for removing and loading spoil from the immediate crossing site are also
required. The crossing panels are either slid in or placed by a crane, depending on the
length and adjacent available ROW.
Once the panel ends are connected to the existing track, ballast is dumped either
by ballast cars or via loaders. The track panels are then raised by the use of jacks
to permit machine tamping and raising of the crossing to grade. Additional ballast
is dumped and final surfacing and regulating is performed. Additional surfacing
will often be required after train operation until all settlement is complete. The
appropriate surface material is then applied.
In CWR territory, it is extremely important that reference marks be placed at either end
of the crossing outside of where the cuts for the panels will be made before cutting the
rail to remove the existing crossing. The distance between the reference marks must
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be determined. After the crossing panels are installed and prior to welding the end of
the panel to the existing track, the distance between reference marks must again be
measured. The rail must be shortened by any dimensional quantity greater than that
previously recorded. The rail is closed either hydraulically or through the use of
applied artificial heat, and after shortening the rail an additional 1” for each weld made,
the rail is welded.
3.9.6 Turnout Renewal
Turnouts are renewed in one of three ways. Either a small work crew replaces the
components in piece mill fashion or the panel is pre-built on-site off to the side, or it is
brought to the site on specially built cars designed to handle the panel sections.
Replacing the components piece mill is not cost effective and is a very time consuming
operation unless not all of the components need replacement, i.e., perhaps the timber
is sound. On the other hand, panelization minimizes train delay during installation, but
requires cranes and other special equipment to handle the panels.
In the same manner as the rehabilitation of a road crossing, the existing turnout is cut
up into panel size segments and removed from the roadbed. The roadbed is then
graded out to remove fouled ballast and to prepare a smooth bed for the laid panels.
Many railways will install geo-textile fabric under the turnout to provide for capillary
action drainage of water trapped in the subgrade. Care must be taken to ensure that
the fabric is placed deep enough that the tamper tools do not punch holes in the fabric.
If sufficient equipment and
on-site ROW is available,
the pre-built panels may be
welded together and the
completed turnout (Figure
3-101), as large as a #24,
can be slid into place within
a minimal period of time.
Other alternatives (Figure 3102) call for the use of
mobile
panel/complete
turnout carrying rigs. These
units bring the turnout or
turnout segments to the
Figure 3-101 Moving a one-piece turnout into place
switch via rail bound
wheels. Special jacking arrangements lift the completed turnout up off the car and
walk the unit in-place via crawler treads once the car is moved out underneath.
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The
most
common
installation method calls for
the use of either rail bound
or mobile cranes to handle
individual turnout panel
sections loaded on special
cars (Figure 3-103), which
are set in place and
connected to the existing
trackage.
Figure 3-102 Switch Panel Laying Rig - Courtesy of Plasser American
The panels are pre-loaded so
that either the frog or point
section is the first unit to be
unloaded,
depending
on
whether the first panel to be laid
is the frog or point section.
From this point on, the
procedures
replicate
the
rebuilding of a road crossing.
Figure 3-103 Panel Car - Courtesy of Plasser American
Installation of the switch stand
or switch machine occurs after the turnout is installed. In signal territory, close
coordination with the signal department is required, particularly with the placement of
insulated joints, hook-up of switch machine if so equipped, connection of switch
circuit controller and conduction of switch obstruction test, all of which must be
performed prior to placing the switch back into service.
The Canadian National Railway provides a step-by-step procedure, provided in the
Appendix entitled “Installation of Panelized Turnouts.”
3.9.7 New Track Construction/Cutovers
Several manufacturers for the construction of new track have developed specialized
equipment. One machine is pulled by a crawler cat (Figure 3-104) over the graded
subgrade. The CWR strings have been unloaded and dragged adjacent and to either
side of the location of the new track. Special cars containing the new ties to be placed
are coupled to the machine. The machine contains a conveyor system that brings the
ties forward, where they are automatically spaced. Simultaneous with this operation,
the rail is threaded from the front end of the machine onto the placed plates. A
following work station places the fastener (See Figure 3-105). In this manner, over a
mile of track can be built in one day. Other machines are capable of replacing all of the
ties and rail on existing track in one operation. These very large machines are typically
leased directly from the manufacturer. As such, they are cost effective only for large
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jobs. More typical for siding construction is the placement of pre-plated ties by hand
and the threading of rail onto the ties. Spikes are set and driven home by pneumatic
spike drivers. Pre-built panels may also be used. However, this requires the staggering
of joints after the panels are laid.
Figure 3-104 Track Laying Machine - Courtesy of Charley Chambers
Figure 3-105 TLM Clip car – Courtesy of Charley Chambers
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Railway cutovers, unlike their highway counterpart, are accomplished very quickly with
the completed connection often being made in several hours. In the case of track
shifts, the roadbed, where the new alignment is to lay and the shift is to occur, is
graded. A ballast regulator will blade out the shoulder on the side of the existing track
where the shift is to be made. A tamper equipped with rail jacks is operated through
the segment and the track is placed on top of the ballast section, or the ballast will be
cribbed by hand between the ties. Utilizing cranes, Speed Swings, dozers, rubber-tired
endloaders or crawler loaders, the track section is lined over so that it is in the new
alignment location. After placing ties and rail required to make the physical
connection, the connection is made, ballast dumped and the track surfaced and lined.
Of greater concern is the signal work to be performed in signalized territory. In cutovers to new connections, extensive shunt tests must be made. In interlockings,
extensive route and traffic locking tests must be made duplicating every possible
movement that could occur. Additional tests have to be made on all searchlight and
color light signals. These tests are very time consuming and must be figured in when
planning a cut-over involving an interlocking.
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References:
1. “AREMA Manual for Railway Engineering.”
2. “Railway Engineering”, W. W. Hay, John Wiley & Sons.
3. AREMA “Roadmasters & Maintenance of Way Association Proceedings 1930 –
1997” (CD-ROM).
4. "Modern Railway Track," Coenraad Esveld, MRT Productions, 2nd Edition, P.O.
Box 331, NL-5300, AH Zaltbommel, The Netherlands, Tel: +31 418 516369,
[email protected].
5. “Talbot’s Railway Transition Spirals,” Edward H. Roth, J. P. Bell, Inc.
6. “Railroad Curves & Earthwork,” C. Frank Allen, McGraw-Hill Book Company.
7. “Route Surveying and Design,” Carl F. Meyer, International Textbook Company.
8. “Route Surveying,” Pickels & Wiley, John Wiley & Sons.
9. “Introduction to Transportation Engineering,” W. W. Hay, John Wiley & Sons.
10. “Railroad Technical Manual,” C. R. Kaelin, Atcheson Topeka & Santa Fe Railway
(BNSF).
11. “Federal Railroad Administration, CFR 213 Track Safety Standards, A-E.”
12. “Federal Railroad Administration, CFR 213 Track Safety Standards, G.”
13. “Track Design Handbook for Light Rail Transit,” TCRP Report 57,
Transportation Research Board, National Research Council, Sponsored by The
Federal Transit Administration.
14. “Dictionary of Railway Track Terms,” Christopher Schulte, Simmons-Boardman
Books, Omaha, NE.
15. “The Railroad/What It Is, What It Does,” John Armstrong, Simmons-Boardman
Books, Omaha, NE.
16. “US Department of Transportation Manual on Uniform Traffic Control Devices
for Streets and Highways,” USDOT, Washington, DC.
17. “The Economic Theory of Railway Location,” Arthur M. Wellington, 1887, John
Wiley & Sons, New York, NY.
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Ballast and Sub-Ballast24
The following table should be used as a guide when AREMA ballast gradations are not available. For quality recommendations of
ballast refer to Chapter 1, Section 2.4 of the AREMA Manual for Railway Engineering.
Ballast/Sub-Ballast Gradation Chart for Coarse Aggregate Suppliers in the United States
Use
Mainline
Mainline
Mainline
Mainline
Mainline
Mainline
Mainline
Mainline
Yard/Side Track
Yard/Side Track
Yard/Side Track
Yard/Side Track
Yard/Side Track
Standard
AREMA
AASHTO
AREMA
AREMA
AASHTO and ASTM
AREMA
AREMA
AASHTO and ASTM
AASHTO and ASTM
AREMA
AASHTO and ASTM
AREMA
AASHTO and ASTM
Gradation #
24
24
25
3
3
4A
4
4
5
5
56
57
57
Sub-Ballast
Generic
DGA/ABC
Nominal Size Square Openings
2 1/2"
to
3/4"
2 1/2"
to
3/4"
2 1/2"
to
3/8"
2"
to
1"
2"
to
1"
2"
to
3/4"
1 1/2"
to
3/4"
1 1/2"
to
3/4"
1"
to
1/2"
1"
to
3/8"
1"
to
3/8"
1"
to
#4
1"
to
#4
1"
to
3"
2 1/2"
100
100
100
90-100
90-100
80-100
100
100
100
2"
60-85
95-100
90-100
90-100
100
100
Sieve Size
Size of Opening
Number of Openings/sq. in.
1 1/2"
1"
3/4"
1/2"
3/8"
#4
#8
#30
# 200
Percent Passing Through Sieve Size (min.-max.)
25-60
0-10
0-5
25-60
0-10
0-5
50-70
25-50
5-20
0-10
0-3
35-70
0-15
0-5
35-70
0-15
0-5
60-90
10-35
0-10
0-3
90-100 20-55
0-15
0-5
90-100 20-55
0-15
0-5
100
90-100 20-55
0-10
0-5
100
90-100 40-75
15-35
0-15
0-5
100
90-100 40-75
15-35
0-15
0-5
100
95-100
25-60
0-10
0-5
100
95-100
25-60
0-10
0-5
#200
100
AREMA - American Railway Engineering and Maintenance-of-Way Association
AASHTO - American Association of State Highway and Transportation Officials
ASTM - American Society for Testing and Materials
DGA - Dense Graded Aggregate
ABC - Aggregate Base Course
24
Developed by Michael Garcia, Illinois DOT & AREMA Committee 18
3- 82
©2003 AREMA®
90-100
60-90
30-60
10-40
4-13

Basic Track

Transcription

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