Turn Lane Warrants: Concepts, Standards, Application in Review

Turn Lane Warrants:
Concepts, Standards,
Application in Review
David J. DeBaie P.E., P.T.O.E.
2004 ITE District 1 Annual Meeting
Burlington,Vermont
Turn Lane Warrants Review
Included
•
•
•
•
Left and Right
2 & 4 Lanes
Unsignalized
Hourly Volume
Turn Lane Warrants Review
Not Included
•Accidents
•V/C Ratio
•Delay
•LOS
STANDARDS
Turn Lane Warrants
ASSHTO Guidance
Left
Right
Signal
ASSHTO
(HCM)
ASSHTO
(HCM)
UnSignalized
AASHTO
(HRR 211)
None
States’ Unsignalized Turn Lane
Guidance Sources
Left
Right
•AASHTO
•HRR 211
•TRR 855
•HRR 211
Harmelink
•Cottrell
•Harmelink
CONCEPTS
Right Turn Lane
Warrants and Guidelines
Right Turn Lane
Warrants and Guidelines
• Cottrell, B.H. JR., Guidelines for Treatment of
Right-Turn Movements on Rural Roads, in TRR
855, 1982.
• Virginia HTRC, The Development of Criteria For
the Treatment of Right Turn Movements on Rural
Roads, 1981 (in NCHRP 279, 1985).
• Willey,L.B.,Traffic Volume Warrants for Right
Turn Auxiliary Lanes at Unsignalized
Intersections, 1989 ( in VTrans Guidelines, 1994)
Cottrell’s and VHTRC
Right Turn Lane Guidelines
States’
Right Turn Lane Guideline
Vtrans’ Right Turn Lane Warrants
CONCEPTS
Left Turn Lane
Warrants and Guidelines
Left Turn Lane Warrants
Harmelink, M.D., Volume Warrants
for Left-Turn Storage Lanes at Unsignalized
Grade Intersections, in HRR 211, 1967.
Harmelink Left Turn Lane
Warrant
Probability of an
advancing through
vehicle in a queue
behind a left-turn
vehicle waiting for
gap in opposing flow.
Harmelink Warrant Forms
Harmelink’s Warranting
Probabilities
Probability of Thru Vehicle
Arriving in Queue
Speed
(mph) 2-Lane
4-Lane
Undivided
Divided
40
0.020
0.030
0.005
50
0.015
0.030
0.005
60
0.010
0.030
0.005
Harmelink's ModelQueue Theory Utilization:
Arrival Rate
Service Rate
Harmelink’s ModelArrival Rate:
[(Percent lefts)(1-Percent lefts)(Advancing Volume)]
X
[(average Time to Wait) + (Time to Clear adv.lane)]
[0.667 (mean Headway of Adv.Volume)]
Harmelink’s ModelService Rate:
Unblocked Time in Opposing Flow
Time to Turn Left
Harmelink ModelTime Assumptions (seconds)
2-Lane
4-Lane
Critical Gap
5.0
6.0
Left Turn
3.0
4.0
Clear Adv. Lane
1.9
NA
Left Turn Warrant Application
NCHRP 279
Graph
AASHTO Table
Two-Lane
Volumes
Opposing Advancing
1000
800
600
400
200
1000
800
400
400
200
FourLane
Left
Turn
40 mph
50 mph
60 mph
10
15
15
20
40
Off
Off
N
N
N
Off
Y
?
?
N
Off
Y
Y
Y
N
Y
Y
?
?
N
Harmelink Concept Applied
• AASHTO “ Green Book”
• NCHRP 279 “ Intersection Channelization
Design Guide”
• NCHRP Synthesis 225 “ Left Turn
Treatments at Intersections”
• NCHRP 348 “ Access Management
Guidelines for Activity Centers”
NCHRP 279 Consistency
NCHRP 348
Figure 9-14 (Four-Lanes Only )
NCHRP 225
Warrant
Type
Source
Concept
ASSHTO
(Harmelink)
Unsignalized
Left Turn
Application
2-Lane Table
ITE 4A-22
(Harmelink)
Expanded
Graphs 2 and 4
Lanes
Idaho
Transportation
Department
Graph
Altered Axes
DHV>100/lane
12 lefts Warrant
Harmelink’s Warrant
Conditions Expanded
1990 ITE Committee 4A-22
“ Guidelines for Left- Turn Lanes”
Harmelink overestimate suggested.
Harmelink’s Warrant’s
Accuracy Evaluated
Kikukchi and Chakroborty, Analysis of LeftTurn Lane Warrants at Unsignalized TIntersections on Two –Lane Roadways, in
TRR 1327, 1991
• Two problems with Harmelink were noted .
• Harmelink underestimate suggested.
Kikuchi and Chakroborty
Problems with Harmelink
•
•
Inconsistent definitions for arrival and
service rates.
Incorrect left turn possibilities in the
service rate.
Kukuchi and Chakroborty Issue
with Harmelink Definitions
• Arrival Rate relates to through vehicles
arriving in a left turn vehicle queue.
• Service Rate relates to left turning vehicles.
• If one through vehicle-OK.
• If multiple throughs in queue then arrival
rate is overstated and warrant is too low.
Kukuchi and Chakroborty Issue
with Harmelink Left Turns
• Harmelink left turn capacity calculation:
(1) count gaps greater than the required time to turn;
(2) these gaps reduced by one half the critical gap;
and time to turn subtracted; gap remainders
aggregated; and divided again by the time to
turn.
•
Overestimated left turn capacity is suggested.