Y14116 Slane Traffic Management Review Rev C

Transcription

Comhairle Chontae na Mi
Meath County Council
PROJECT:
Slane Traffic Management Review
DATE:
July 2015
Comhairle Chontae na Mi
Document title: Slane Traffic Management Review
Document Number: Y14116 DOC-002
Contents amendment record
This document has been issued and amended as follows:
Issue
Revision
Description
Issue Date
Originator
Checked By
Approved By
1
A
Issued
27/02/14
JK
GT
LP
2
B
General Revision
15/06/15
GT
HH
LP
3
C
Final
28/07/15
GT
HH
LP
Document Number: Doc 002 Rev: C
Date: July 2015
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Contents
1
Introduction
1.1 Introduction
1.2 Background
1.3 Existing Conditions
1.4 Objectives
1.5 General Approach
1.6 Scope of Work
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2
Review Existing Published Papers
2.1 Existing Documentation
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3
Review Existing Work
3.1 Visum Transport Model
3.2 Goods Vehicle Travel Movements
3.3 Tolling Scenario Study (Aug 2012)
3.4 Slane Traffic Management Study (Oct 2012)
3.5 N2 Speed Restriction Study (June 2013)
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4
Review Results from Toll Free Holiday
4.1 Background to Toll Scheme Trial
4.2 Observed impact of Toll Free Period on N2 Flows
4.3 Comparative Assessment of Observed and Modelled Flows
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5
Gap Analysis Options Development
5.1 Scheme Design
5.2 Gap Analysis
5.3 Existing HGV traffic patterns
5.4 Traffic Management Gap Analysis Outline Design
5.5 Traffic Management Gap Analysis Preliminary Design Review
5.6 Traffic Management Gap Analysis Detailed Design
5.7 Proposed Junction Improvements
5.8 Junction Design Traffic Flows
5.9 LINSIG Modelling
5.10 Results
5.11 Traffic Control System Options
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6
Identification of Options Using Visum
6.1 Methodology
6.2 Base Scenario
6.3 Phase 1 Modelling
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6.4
6.5
6.6
6.7
6.8
6.9
6.10
6.11
6.12
6.13
6.14
7
Phase 1 Option Result
Phase 1: Highway Network Performances
Phase 1: Review of Options
Phase 2: Combination Option Development
Phase 2: Combination Option Results
Accident Analysis
Highway network performances – Combined options
Appraisal Summary Table
Early Assessment and Sifting Tool
Key Link Analysis
Analysis
Summary and Conclusions
7.1 Summary
7.2 Assessment of Options
7.3 Conclusions
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Appendix A
Linsig Analysis
Appendix B
Gap Analysis Flow Difference Plots
Appendix C
Management/ Implementation Plan
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Acronyms and Abbreviations
AADT
Annual Average Daily Traffic
ABP
An Bord Pleanala
COBA
Cost Benefit Analysis
HGV
Heavy Goods Vehicle
HV
Heavy Vehicles
MCC
Manual Classified Count
MCC
MOVA
Microprocessor Optimised Vehicle Actuation
NRA
National Roads Authority
NMT
Non- Motorised Transport
OGV
Other Goods Vehicles
PAG
Project Appraisal Guidelines
PPP
Public Private Partnership
SCOOT
Split Cycle Offset Optimisation Technique
SDI
Social and Distributional Impact
VFM
Value for Money
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1
1.1
Introduction
Introduction
This report describes the results from a detailed Gap Analysis study of traffic management options
relating to the N2 National Route crossing at Slane Bridge. The study considered and analysed
a series of new traffic management options as well as combinations of existing and new measures.
A consolidated summary of the earlier studies is presented within the report
The studies were undertaken following the N2 Slane Bypass Road Scheme Oral Hearing and the
subsequent An Bórd Pleanála decision. The current analysis has primarily considered the
possibility of traffic management schemes to address severe traffic concerns in the village of Slane
that align with the principles of proper planning and sustainable development.
1.2
Background
The basis for the proposed N2 Slane Bypass arose out of the high volume of goods vehicle traffic
which travels through the town on the N2 and the resulting road safety problems through Slane
Village. The problems in the village centre are broadly acknowledged noise and air quality issues
resulting from goods vehicle activity, and exacerbated by the steep gradient leading out to
the north and the south of the town. The safety issue was particularly notable, with a number
of incidents occurring in the town centre in recent years.
In 2001, a Traffic Management Scheme was implemented in Slane to address the significant road
safety issues that existed. The scheme complemented the existing shuttle system across Slane
Bridge and included the implementation of advanced traffic signals which provided priority to
light vehicles, and associated signage. This scheme did lead to a safety improvement, but at
significant journey time cost to non-goods vehicles.
The proposed N2 Slane Bypass was intended to act as a long term solution to the existing issues
in addition to the existing traffic management measures. By removing a large volume of goods
vehicle traffic from the town centre, the scheme would provide significant safety and
environmental improvements to residents of the town, in addition to journey time savings for
road users. Following the preparation of the proposed N2 Slane Bypass Scheme and its
submission for planning approval, the scheme was refused planning consent by An Bórd Pleánala
in March 2012.
In its report, An Bórd Pleanála suggested that the need for a bypass of the town had not been
demonstrated, and that lower cost 'management' measures which would achieve the desired
outcomes had not been fully explored. The findings are summarised below;
•
Due to the location of the bypass in the view shed of Bru na Boinne, An Bórd Pleanála
considered that the proposed bypass would be acceptable only where it has been
demonstrated that no appropriate alternative is available. Following on from the
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submissions received and the oral evidence given during the Oral Hearing, An Bórd
Pleanála was not satisfied that alternatives to a bypass have been adequately explored. In
this context, they considered that:
“The proposed development would have a detrimental impact on the setting of the Bru na Boinne
archaeological complex which would be contrary to the heritage protection provisions of the County
Development Plan" and that "The bypass would be contrary to proper planning and sustainable
development, as it would tend to undermine the investments that had been made improving the M1 and
M3 corridors, and would have negative implications for the quality of the environment and road safety
along the N2 route."
•
Whilst it was accepted that the Slane Bypass would assist in alleviating the high traffic
levels in the village in a north-south direction it would not impact upon the east-west
traffic. An Bard also reported that the scheme was:
"likely to attract additional traffic, including a substantial proportion of additional heavy commercial
vehicles onto the single carriageway N2 along its length, and through the settlements of Collon and
Ardee"
•
An Bórd Pleanála also reported its conclusion that the proposed Slane Bypass would
undermine public investment given the current configuration of the overall national road
network in the region, and that alternatives to a bypass had not been fully explored.
An Bórd Pleanála went on to state that although it has no role in developing regional transport
policy or the implementation of a traffic management system they suggested that traffic
management in the form of a HGV ban merited more investigation. An Bórd Pleanála stated that
potential negative impacts for local business would need to be considered as would potential
improvements on alternative routes to alleviate safety concerns. An Bórd Pleanála concluded that
traffic management alternatives might align well with the principles of proper planning and
sustainable development, and ought to be given further consideration.
1.3
Existing Conditions
The N2 National Primary Route is a strategic corridor connecting Dublin with Northern Ireland
and the border counties. The National Spatial Strategy identifies Monaghan as a ‘Hub’ which is
defined as:
“An important local node in transportation and communication terms: (a) on the national road and rail or
bus networks, (b) with access to a national or regional airport (c) having adequate, reliable, cost effective and
efficient access to port facilities (d) with effective and competitive broadband access”
In this regard, the N2 is obviously seen as key to supporting the intended function of Monaghan
as a designated Hub.
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Nevertheless, the M1 runs almost parallel to the N2 between Dublin and Ardee. Furthermore,
the M1 is connected to the N2 by a number of east-west routes of varying quality, most notably
the N51 (Slane – Drogheda), the R169 (Collon – Dunleer), the N33 (Ardee – Dunleer), and the
N52 (Ardee – Dundalk). This connectivity between both corridors leads to a notable degree of
traffic mixing between corridors on trips between the Greater Dublin Area and areas to the north.
The M1 toll applies on the section between junction 7 (Julianstown) and junction 10 (Drogheda
North) and currently charges a toll of between €1.90 for cars to €6.00 for above 4-axle goods
vehicles. Understandably, this toll reduces the attraction of the M1 for trips, particularly for those
who might be otherwise drawn from the parallel N2 corridor.
Surveys undertaken in May 2012 showed that Slane Village currently caters for traffic flows of
over 13,000 vehicles per day. The surveys found that over 9% of the vehicles travelling through
the village are Heavy Goods Vehicles (HGV) and a further 11% are Light Goods Vehicles (LGV).
Slane Bridge itself experiences a traffic flow in the region of 7,000 vehicles per day of which 12%
are Heavy Goods Vehicles.
The existing N2 route passes through Slane village in a north-south direction as it descends from
high ground adjoining Slane Hill to cross the River Boyne Valley at a much lower level. The route
descends some 80m over a short distance of 1km, which leads to an average gradient of 8%, which
exceeds the maximum permissible gradient of 6% for a single carriageway road. The steep road
gradient is a significant contributory factor to the traffic safety problems in Slane.
Further major safety problems arise at Slane Bridge over the River Boyne, where the road
alignment involves very sharp corners at the bottom of steep hills at both ends of the bridge. This
bridge is too narrow for two-way traffic, and a shuttle traffic signal system manages the flow in
alternate directions. Inherent traffic hazards arise from the seriously deficient road layout at the
bridge, and this has led to frequent accidents due to loss of control, mainly by trucks. Following
the most recent fatal accident at this location in 2001, a major road safety scheme was constructed
in 2002, which involves separate signal control of light traffic and trucks with a holding point in
a safer location further up the hill where there is enough width for a virtual escape lane for runaway
trucks. In 2009 non-skid surfaces were reapplied on various road sections around Slane however
residual safety issues still remain due to the layout and topography of the area as evident by the
occurrence of a multi vehicle accidents in 2009 and 2014.
1.4
Objectives
To ensure that sufficient consideration was given to the analysis and understanding of the
problems (perceived and actual) and the opportunities associated with addressing the flow of
traffic through Slane, prior to commencing the Gap Analysis and option development, the studies
previously undertaken by AECOM were reviewed.
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The primary objective of the study is the identification of a traffic management solution selected
through an alternatives analysis to identify the optimum solution to the perceived traffic problems
through Slane and the N2 environs using the existing infrastructure. Much of the fundamental
analysis for this has already been undertaken by AECOM on behalf of MCC and the NRA.
The objectives are shaped by the An Bórd Pleanála decision and their Inspector’s comments on
the need for alternative traffic management alternatives to be identified and considered in isolation
and together.
It has been noted in the ABP Decision that they took the view that, in the particular circumstances,
adequate consideration was not given to exploring alternatives to a bypass. The specific tasks
reviewed looked to identify and close any gap in the current alternative traffic management
options to support robust consideration of and response to the ABP decision. The objectives are
as follows:
1.5
•
Safety: Improve overall safety
•
Environment: Improve air quality in Slane Village and other populated areas; and
Reduce transport emissions
•
Economy: Maximise the efficiency of the transport network
•
Accessibility: Improve the accessibility of rural areas to designated Gateways,
including the Greater Dublin Area
•
Integration: Support government plans and policies in relation to transport and
spatial development in the study area.
General Approach
The approach proposed was to undertake gap analysis to identify any gap in the current work to
date, and develop and evaluate a number of traffic management options to address the traffic
concerns in the village of Slane. The Options were assessed against the key criteria:
•
•
•
•
•
Overall traffic safety
Air quality
Transport Emissions
Accessibility
Network efficiency
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Consideration was given to the following issues within the modelling:
•
Robustness of models.
•
Appropriateness of the scale and scope of the models – strategic, local, detailed
(sufficient level of detail and disaggregation to simulate realistic responses to
proposed transport measures).
•
Whether the objectives of the study can be assessed (traffic flows, environmental,
pedestrian, emissions, air quality, economic evaluation, etc.) and whether the relative
benefits be assessed on a common basis.
•
Timescales. Do the models capture all the benefits on a consistent basis – peak hour,
off peak, week day, week end, annual, forecast year, economic (60 years).
•
Policy. Are planning guidance, land use, local development plans and national plans
be taken into consideration within the model
Solutions to provide a bypass solution consistent with proper planning and sustainable
development for the area and to remedy bypass environmental impacts were not explored further
in the study.
1.6
Scope of Work
The report is structured as follows:
•
Chapter 2: Review of the current published papers on the N2 Slane Bypass and Traffic
Management options and basic objectives.
•
Chapter 3: Review existing work.
•
Chapter 4: Review results from the November 2013 toll holiday and identify any
significant differences from forecast travel patterns.
•
Chapter 5: Undertake gap analysis and identify new options or combinations of
options not previously considered, utilising traffic model as required.
•
Chapter 6: Identify of options using Visum.
•
Chapter 7: Summary and Conclusions
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2
Review Existing Published Papers
2.1
Existing Documentation
Meath County Council (MCC) lodged a Planning Application inclusive of EIS with An Bórd
Pleanála (ABP) in December 2009. An Oral Hearing was held to consider the application in
February 2011 and a refusal to the road development was confirmed by ABP in March 2012.
Following the refusal there have been a number of meetings, development papers and technical
notes drafted to consider the way forward.
The currently available documents are as follows:
•
Slane Road Tolling Study, NRA – AECOM, August 2012.
•
Slane Traffic Management Study- Stage 1: Report, MCC – AECOM, October 2012
•
Slane Traffic Management Study- Stage 2 : Draft Project Appraisal of HGV Restriction
in Slane, MCC – AECOM, May 2013
•
Technical Note No 2 –Slane Traffic management – Impact of Reduced Speed Limits,
MCC – AECOM, June 2013
•
NRA Transport Policy and Evaluation. Technical Note Assessment of Toll Diversion
Rates During Toll-Free November, NRA – AECOM, March 2014
These studies and report(s) are currently in draft form with the NRA. Copies of the above
documents together with the traffic model were provided by Meath County Council and examined
during the course of the study.
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3
Review Existing Work
3.1
Visum Transport Model
For the purpose of the review and analysis of traffic patterns and design options, a traffic model
was developed by AECOM on behalf of the NRA. The Slane model encompasses the M1, N2,
and M3 corridors and was validated in accordance with the NRA Project Appraisal Guidelines to
a 2012 Base Year utilising link flows and extensive HGV traffic vehicle number plate survey data
collected in May 2012. The revised models allow detailed assessments of the impact of potential
measures on HGV movements in the area to be undertaken. The extent of the Visum model is
presented in Figure 1 overleaf.
In order to obtain suitable detail within the N2 Slane Local Area Model (LAM) a more detailed
zoning system than that used in the NMT was developed. The village of Slane and its environs,
which is represented as one zone in the NTM, was disaggregated into four sub-zones. At the
majority of junctions, detailed junction coding was not included within the model due to the
strategic nature of the NTM model from which it was cordoned out. Junction delays associated
with traffic movements such as Slane Bridge crossing are simulated through the use of speed/flow
curves.
The following time periods are modelled in the N2 Slane model:
•
Average hour in the morning peak from 07:00 – 09:00 (AM peak period)
•
Average hour in the inter peak period from 12:00 – 14:00 Inter Peak period)
The development of the traffic model is summarised in Slane Road Tolling Study Report, August
2012, AECOM. The model was calibrated against a series of link calibration criteria to ensure that
the model assignments reflect observations. The model validation comprises the comparison of
calibrated flows against an independent data set which was not used as part of the calibration
process. The validation checks included matrix validation, turning count validation and journey
time validation. AECOM report that the comparison of the model outputs against the model
calibration and validation criteria showed that the models exceeded the PAG model calibration
and validation criteria.
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Figure 1 –Visum model study area
The model simulates the average AM peak and Inter Peak average hourly flows (referred to as
the AM and IP respectively) from which the annual average daily traffic (AADT) can be calculated
using regression analysis based on daily traffic flows, and the AM and Inter Peak hour flows. For
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the purpose of consistency, the same factors are applied to cars, LGV and HGV. The regression
suggested the following relationship to convert flows to AADT:
AADT = (5.330077 * X + (10.9989 * Y)
Where:
X = AM peak period average hourly flow; and
Y = Inter Peak period average hourly flow
During the course of the model development, the model was not audited and a Base Year model
development report was not prepared.
To undertake the Gap Analysis and design option appraisal a copy of the Reference Case/Do
Minimum model was provided to Halcrow Barry as follows:
•
MCC AM Peak DM 1 – Rev1 (AM Model)
•
MCC Inter Peak DM1 – Rev1 (IP Model)
The Reference Case models were developed from the Base Year model by AECOM over a
number of years and updated as more data became available through various studies. The version
of Visum was also updated in the interim. AECOM have confirmed that during the interim period
there have been increases in traffic, changes in patterns and road infrastructure upgrades which
may result in differences between the model and observed traffic flows
An appraisal was undertaken by Halcrow Barry to validate the Reference Case model using
available survey data consisting of recent traffic counts, which showed that almost 75% of the
48 traffic counts locations were within acceptable limits.
3.2
Goods Vehicle Travel Movements
A comprehensive goods vehicle origin and destination surveys was undertaken by AECOM in
2012 to enable travel patterns (Figure 2) and vehicle classifications (Table 1) within the Visum
model to be updated. Detailed analysis of the survey indicated that on an average weekday a total
of 2,318 goods vehicles pass through Slane, of which 1,546 cross Slane Bridge (Table 2) and 772
use other routes through Slane. Of the 1,546 trips which cross Slane Bridge, 345 have local a local
origin or destination (of which 44 have both an origin and destination within Slane) and a further
411 have a wider area local origin or destination located along the N2 corridor between Ashbourne
and Ardee, excluding the towns (Table 3)). In total there are 790 goods vehicle movements
crossing the bridge (51%) which do not have a local origin or destination and are through trips.
Of the 790 goods vehicles through movements, the vast majority (654 vehicles) travel between
Dublin and either Ardee or R169. On average the flow across Slane Bridge consists of 55%
HGV2 (5+ axles) but for through movements this increases to 70%
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The level of detail coded within the model allows local trips or longer distance through-trips to
be more robustly modelled than trips in the wider local area (zone 4 and 13). Trips with origins
or destinations in the wider local area (345 trips) have a number of route choices available and are
coded within the model as either through trips or local trips.
Figure 2 - HGV survey zone plan
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Table 1 Vehicle classification by HGV
Table 2 HGV flows crossing Slane Bridge
Table 3 HGV flows with local origin/destination crossing Slane Bridge
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3.3
Tolling Scenario Study (Aug 2012)
In 2012 a study was undertaken by AECOM on behalf of the NRA to develop a number of
scenarios (Table 4) for comparative analysis in order to identify the most effective fiscal solution
for managing traffic demand through Slane. Following an initial screening process, the alternatives
outlined below were defined. In order to provide a robust assessment the initial options were
considered with an increasing HGV toll in order to ascertain the price at which the maximum
impact of the toll were reached. All toll locations were proposed as barrier free flow tolling points.
Table 4 - Tolling test options
3.4
Slane Traffic Management Study (Oct 2012)
In October 2012 the Slane Traffic Management Study: Stage 1 was prepared by AECOM on
behalf of Meath County Council. The study assessed the impact of seven possible scenarios
(Figure 3) for goods vehicle restrictions through Slane Village, ranging from restrictions on 3 axle
vehicles up to 5+ axle vehicles. Note that the terminology for vehicle restrictions was based on
axle numbers, with 5+ referring to vehicles with 5 axles or greater.
The data analysis highlighted that approximately 20% of goods vehicle traffic across Slane Bridge
could be considered traffic that was using the N2 to avoid the M1. A further 25% was legitimate
N2 traffic travelling between Ardee/Monaghan and either Ashbourne or onwards to the Greater
Dublin Area.
Traffic Management Scenarios considered are outlined in Table 5 below. Note that the
terminology for vehicle restrictions is based on axle numbers, with 5+ referring to vehicles with
5 axles or greater.
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Table 5: Slane traffic management study options
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Figure 3: Traffic Management Scenarios
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3.4.1
Scenario Testing
The impact of the different scenario options was assessed against the Reference Case AM and IP
traffic model developed by AECOM from the original Base Year 2012 model. The models were
run by applying restrictions on relevant links in the model for the specific user classes. The model
then reassigned traffic from within those restricted user classes onto alternative routes as
appropriate. The following information was extracted from the traffic model results:
•
The pattern of traffic reassignment, showing alternative routes travelled and the extent of
traffic flow increase on those alternative routes;
•
Goods Vehicle traffic flows on key links across the Study Area Road Network, including on
the roads through Slane;
•
Total vehicle km travelled by all vehicles in the study area – this provides a proxy of fuel
consumption and resulting vehicular emissions; and
•
Total travel time travelled by all vehicles in the study area – providing a measure of network
efficiency.
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3.4.2
Scenario 1: 5+ Axle Ban on Slane Bridge
This option leads to a reduction of 66% in HGV (3axles or greater) across Slane Bridge and an
increase of HGV traffic on the M1 toll of 21%. There is an increase in goods vehicle flows along
a number of routes as it introduces a number of evident diversion routes, including the N33, N51
and R152 and reductions in R169.
3.4.3
Scenario 2: 5+ Axle Ban on Slane Bridge, and on N2 between Slane and Collon
The inclusion of such a restriction to the north of Slane Village leads to a more pronounced
reduction in goods vehicles, particularly north of Slane, than in Option 1. The impact on Slane
Bridge, and on the M1 Toll is relatively similar to Scenario 1.
3.4.4
Scenario 2a: 4+ Axle Ban on Slane Bridge, and on N2 between Slane and Collon
Scenario 2a is an enhancement on Scenario 2, in that the restrictions will additionally apply to 4
axle vehicles. As such, the pattern of impacts of Scenario 2a is similar to Scenario 2. The impact
on Slane Bridge is a reduction of 74%
3.4.5
Scenario 3: 3+ Axle Ban on Slane Bridge, and on N2 between Slane and Collon
The measures in Scenario 3 remove all goods vehicle traffic of 3 axles or greater from the N2 to
the north and south of Slane. The restrictions lead to traffic impacts that are similar in pattern to
Scenario 2 and 2a,
3.4.6
Scenario 4: 3+ Axle Ban on Slane Bridge, on N2 between Slane and Collon, and on N51
Scenario 4 restricts all heavy goods vehicles (3 axles or greater) from all roads approaching Slane.
The traffic modelling demonstrates that such measures will have quite substantial impacts on
roads through the study area as a larger number of vehicles seek alternative routes due to road
restrictions at Slane. In essence, the R152 and R153 would operate as informal bypass routes of
Slane to the south, with traffic travelling via Drogheda/Navan and returning to the N2 further
north. The impact on Slane Bridge is a reduction of 100% and an increase at the M1 toll of 37%.
3.4.7
Scenario 5: 3+ Axle Ban on Slane Bridge, and N2 between Slane and Collon but in Southbound direction only
Scenario 5 seeks to remove the southbound movement of all heavy goods vehicles through Slane
Village in order to address the safety concerns associated with southbound traffic through Slane
Village. Scenario 5 delivers a reasonable reduction in HGVs over Slane Bridge with HGV flows
decreasing by approximately 50% and flows at the M1 toll increasing by 19%.
3.4.8
Scenario 6: 3+ Axle Ban on Slane Bridge, but in southbound direction only
The analysis of a southbound 3+ axle restriction on Slane Bridge shows a broad rerouting of
goods vehicle traffic from the N2 onto the N1 corridor. The results of the analysis show a range
of reassignment impacts for southbound traffic, with the alternative routes being the
N52/R162/R153 and the N33/R168/M1. Scenario 6 delivers a reasonable reduction in HGVs
over Slane Bridge with HGV flows decreasing by approximately 50% and increasing at the M1
toll by 19%.
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3.4.9
Summary of Traffic Analysis
In order to support a comparative assessment of the alternatives, a summary of the findings are
presented below in Table 6.
Table 6 – Summary Traffic Management Findings
The study concluded that a high proportion of HGV could be encouraged to transfer to the M1
under the right conditions. Following the detailed analysis of alternatives, it was concluded that,
of the options considered, the implementation of 5 axle restrictions on Slane Bridge represented
the most manageable approach for implementing vehicle size restrictions through Slane village.
The draft Project Appraisal of HGV restriction in Slane (May 2013) prepared by AECOM
indicated that the scheme benefit-cost ratio was 0.4. Nevertheless, the proposal brought with it a
number of notable adverse impacts:
•
An increase in goods vehicle traffic using the R152, R168 and R153 as an alternative to the
N2 via Slane;
•
A reduction in network efficiency as drivers seek longer routes to avoid the restricted area and;
•
A reduction in strategic accessibility for 5 axle heavy vehicles between Ashbourne and the
M1/Monaghan which is currently available via the N2 corridor.
The draft report of the study was presented to the Elected Representatives of Meath Council on
the 5th November 2012. Subsequently, AECOM was requested by Meath County Council to
undertake a project appraisal on the preferred option of a 5+ axle restriction on Slane Bridge.
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3.5
N2 Speed Restriction Study (June 2013)
A study was undertaken to assess the potential outcomes associated with revising the speed limits
on the N2 between Ardee and Ashbourne. The reduction in speed limit from 100 km/h would
increase the journey time as follows:
•
Changing the current speed limit on the N2 to 60km/h (additional 16 minutes)
•
Changing the current speed limit on the N2 to 80km/h (additional 6 minutes)
The impact on the reduction in speed limit would be two fold, with some traffic staying on the
M1 instead of travelling across to the untolled N2 and the remainder of the impacts represented
by traffic diverting off the N2 and onto the M2 at Ardee. The option for reduction to 60kh/h
results in a decrease in all traffic through Slane of 16% and a 31% decrease in HGV crossing Slane
Bridge. The option for reduction to 80kh/h results in a decrease in all traffic through Slane of 6%
and a 14% decrease in HGV crossing Slane Bridge.
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4
4.1
Review Results from Toll Free Holiday
Background to Toll Scheme Trial
A review was undertaken of the assessment on observed toll diversion rates in Slane during the
period of the toll-free period trial undertaken by the NRA in November 2013. Following a
direction from the Minister of Transport, Tourism and Sport the National Roads Authority
engaged with its various Public-Private Partnership (PPP’s) contract counterparties to arrange to
allow goods vehicles with a design gross vehicle weight exceeding 3,500 kilograms and having two
or more axles toll free passage on selected PPP’s from the 1st to the 30th of November 2013
inclusive. The road schemes included within the scope of this exercise are as follows:
4.2
•
M1 Dundalk Western Bypass which impacts upon both the M1 and N2
corridors;
•
M3 Clonee Kells;
•
M6 Galway to East Ballinasloe; and
•
N18 Limerick Tunnel.
Observed impact of Toll Free Period on N2 Flows
To monitor the impacts of the toll-free period on these corridors and to capture the levels of
diverted traffic on alternative routes, automatic traffic counters (ATC) were commissioned on a
number of non-national roads adjacent to the PPP roads outlined above. The traffic surveys
commenced in mid October to establish baseline traffic flows and patterns prior to the toll fee
holiday and were undertaken continuously through to mid December to provide a full set of
information on traffic conditions before, during and after the HV toll free holiday.
Flows reported in the study included all heavy vehicles (HV) including OGV1, OGV2 and Bus as
data without buses included was not available for all sites. Bus flows were assumed to be constant
throughout as they were unaffected by the HGV Toll Free Holiday. Flows are presented as
average weekday flows. Flows from November and December were adjusted for seasonality based
on season patterns derived from 2011 NRA traffic counter data from the relevant corridors to
ensure a like with like comparison with data from October.
The study suggests that users are aware of the route options available to them i.e. those who
transferred from the N2 to the M1 during the toll holiday are aware of higher level of service
provided by the higher standard M1 (because they decided to transfer during Nov) but choose to
revert to the N2 (or other route) when the toll was reinstated. This may also suggest that whilst
users are aware of toll costs they may not account for the full cost of travel such as fuel, vehicle
depreciation and travel time savings when making their route choice decision. The extent of this
occurrence will be further explored as part of the analysis of the Origin-Destination data.
Date: July 2015
21
The table below outlines the average daily volume of HV’s recorded at the N2 counters sites. It
shows a decrease in HV’s across all sites during the toll free month of November. It also shows
that during the month of December the levels of HV increase back to similar levels recorded
during October.
Figure 4 overleaf shows the percentage change in the number of HV’s recorded at each counter
during November and December compared to flows from October 2013. The figure suggests
there was a significant decrease in HV’s on the route during the month of November, with an
average daily decrease in HV’s of 6% at the junction between the M50 and N2 (J2), and a 38%
reduction at Slane Bridge.
Date: July 2015
22
Figure 4 Toll holiday observed changes in HGV flows
4.3
Comparative Assessment of Observed and Modelled Flows
The removal of the M1 tolls was modelled by AECOM during the course of the Slane Road
Tolling Study (Aug 2012) and the forecast level of reduction in HGV at Slane Bridge was 58%
compared with the observed reduction of 38%. The differences between modelled and survey
diversion due to M1 toll removal is likely to be different for a number of factors as follows:
•
Difference between the vehicle types included in both studies
•
the time period over which the flows are measured, as the observed flows are compared
with model flows derived from factoring the AM peak hour and interpeak hour to
average daily flows.
•
The strategic Visum model represents trip patterns on the basis of average movements
between a limited number of origins and destination. In reality the observed level of
change may indicate that local travel patterns have more significant influence than
represented within the model.
•
The model assumes that drivers have perfect knowledge about the cost of using
alternative routes which may not be the case in practice and during the period of the
trial toll-free period, travel patterns may not have settled down.
It is not possible to comprehensively understand all the reasons for the forecast differences
compared with the observed flows. It is apparent from the HGV origin and destination survey
that was undertaken that not all travel movements could be fully modelled within the Visum
model due to the limited number of origin and destination locations available in the model within
the vicinity of Slane. It is likely that some local trips would have been represented as through trips
Date: July 2015
23
which the model would then have forecast diverting to the M1 when the tolls were removed. The
model validation was compared against existing survey data, which consisted of traffic counts at
48 locations, and this indicated that the model is reasonably well calibrated at many of these
locations.
It can be concluded that the model provides a strong analytic base on which to assess the
comparative performance of a wide range of options in the analysis and appraisal of Slane Bridge
crossing traffic management proposals.
Date: July 2015
24
5
Gap Analysis Options Development
5.1
Scheme Design
Gap Analysis was undertaken for the N2 Slane corridor, taking into consideration AECOM’s
previous studies to identify a measure or combination of measures which would be capable of
modifying the route choice of Heavy Goods Vehicles (HGV’s) currently travelling on the N2
across Slane Bridge. This would provide a range of alternative options to the proposed Slane
bypass.
The analysis focused on the identification of gaps within the work undertaken to date and options
which had not previously been considered. The potential benefits and disbenefits of each of the
existing and proposed traffic management measures have been identified on the basis of the
following criteria:
•
Overall traffic safety
•
The percentage of HGV’s removed from Slane Bridge
•
Total distance travelled
•
Accessibility and social inclusion
•
Integration
The previous studies indicated that an additional delay for longer distance trips of around 15
minute or an additional travel cost of around €5 would be sufficient to give rise to the required
level of HGV re-routing.
The majority of measures considered to date are designed to achieve the objectives set out above
by encouraging users to make use of the National Primary and Secondary Road network, which
has recently received significant levels of investment as part of the National Development Plan
and Transport 21.
Following the introduction of temporary traffic management measures in Slane in 2001 to reduce
the accident risk on the southbound approach to Slane Bridge, the occurrence of accidents has
fallen, although the underlying hazards remain (substandard vertical and horizontal road
geometry) and the potential consequences of an accident are severe. Proposed schemes are only
likely to achieve a positive Benefit Cost Ratio (BCR) where they encourage the use of lower risk
category roads, introduce road safety improvements and/or give rise to reductions in travel
times and distances. For many options it is likely that benefits will be lower than the direct
economic costs to users due to an increase in travel times, travel distances and charges (tolls).
Date: July 2015
25
5.2
Gap Analysis
Following detailed consideration of the local scheme objectives and reported results from earlier
studies, the Gap Analysis was undertaken in two stages as follows:
5.3
•
Stage one: identification of traffic management measures not previously considered
(chapter 5) and
•
Stage two: identification of optimum combinations of options (chapter 6).
Existing HGV traffic patterns
Previous surveys have indicated that the main HGV weekday daily traffic flows within the study
area are:
•
729 vehicles using N33 as link road between N2 North and M1
•
373 vehicles between N2 (North of Ardee) and Dublin/ Ashbourne area
•
272 vehicles between Ashbourne and R169 (adjacent to M1), this traffic is using longer
route of the N2 to avoid the M1
It is clear that there is a potentially large number of HGV’s which have the alternative M1 route,
but choose to travel through Slane to avoid the toll costs between junctions 7 and 10.
5.4
Traffic Management Gap Analysis Outline Design
During the course of the first stage of the gap analysis carried out by Halcrow Barry, the following
new options at the junctions shown in Figure 6 were identified for more detailed consideration.
i. Re-allocation of Toll points on M1 to between J6 and J8
A toll is currently applied to vehicles on the M1 between junction 7 (Julianstown) and junction 10
(Drogheda North) and consists of a charge between €1.90 (cars) and €6.00 (5 axle HGV’s).
Given the choice, many HGV drivers prefer to travel (assuming northbound travel here) on the
N2 through Ashbourne, then cut across to the M1 at Junction 10 via the R152/ R132/ N51 and
then either cut back across to the N2 at Monaghan or carry on the M1 to Dundalk.
If the tolls on the M1 were positioned further south to between Junction 6 and Junction 8, then
the R152 route would attract more HGV trips.
ii. Electronic Tolling system for HGV’s
An electronic tolling system could be employed using ANPR (Automatic Number Plate
Recognition Cameras), this would apply only to HGV’s using the N2 through Slane (or any other
specified section of the N2).
Date: July 2015
26
This system would allow the HGV’s to be segregated (only HGV’s would be charged) from other
vehicles and also the system would not incur any vehicle delays (as would be experienced at
manual toll booths).
This system would have the additional benefits of being able to be expanded or re-positioned and
for tolls to be applied flexibly during different periods of the day without significant additional
cost.
iii. Disprioritise for HGV’s at traffic signalled junctions
Currently, HGV priority can be provided at signalised junctions. This system could be
innovatively adapted (although it is untested) to apply a negative priority to HGV’s approaching
signalised intersections along defined corridors.
The system would detect approaching HGV’s (or more likely proportion of approaching HGV
traffic) and call other traffic signal stages at the junction with the purpose of causing additional
delays to HGV’s.
The system would be semi-discriminatory, as delays would also be incurred to normal vehicles,
and therefore it would be recommended that this system only be turned on during off-peak
periods (this coincides with HGV peak) to minimise delays to other traffic.
Existing signal controlled junctions where this system could be employed to deter trips through
Slane are as follows:
•
N2/ N51 (Slane Village)
•
N2/ R155 (Phibblestown Wood)
The following junctions on the N2 could be signalised so that HGV flows may be negatively
affected:
•
N2/ R169
•
N2/ R168 (Collon Village)
•
N2/ R150 (Flemington Cross)
•
N2/ R152 (Kilmoon Cross)
iv. Optimise traffic signals at N2 Slane Bridge
The traffic signals timings at N2 Slane Bridge could be altered such that an increase in delays is
experienced by HGV’s only on the southbound approach. This is made possible by the presence
of a separate HGV lane on the southbound approach.
Date: July 2015
27
One of the disadvantages with this option is an increase in noise and air pollution in Slane village.
There are also limitations on how much delay can be applied to HGV’s due to the length of the
segregated HGV lane at the junction and the high proportion of HGV’s within the traffic flow.
v. Improve Access northbound from R152 to M1
This option seeks to improve the access for HGV’s on this alternative route. The options for
improving access onto the M1 could include construction of a new northbound on-slip onto the
M1 or junction upgrades to the network in this vicinity, including signalisation of existing priority
junctions (and installation of MOVA control).
Access to the alternative R152 and N33 route could be promoted by improving/ providing the
following junctions:
•
Creation of northbound on-slip from R152 to M1 at junction 8
•
Improved/ signalised dumbells (grade separated roundabouts) arrangement at
junction 8
•
Improved/ signalised dumbells (grade separated roundabouts) arrangement at
junction 9
•
Signalisation of M1/ R168 at junction 10
•
Signalisation of M1/ N33 at junction 14
vi. New Signal controlled Junction at N2/ R152
This option would signalise this junction, improving safety and capacity and hence making the
R152 a more attractive alternative route for HGV’s. The right turn northbound would be
improved (improving safety), as would the left turn southbound (improving capacity and safety).
Road Safety Authority records show that a number of accidents, including 2 fatalities, have
occurred in the vicinity of the junctions in recent years. Any accident savings attributed to
signalisation would have a positive effect on the Benefit Cost Ratio (BCR) of the scheme.
vii. Creating new segregated Car/ HGV signalised intersection at M2/ N2/ R135
This option would create an additional LV/ HGV segregated intersection in an attempt to increase
delays to HGV’s on the route. This would be similar to the existing segregated intersection at N2
Slane Bridge, but again would increase delays to HGV’s and increase fuel consumption and
emissions.
A major junction could be created at M2/ N2/ R135 to serve this purpose. A ‘hamburger’ type
layout may be adopted allowing LV to traverse through the roundabout whilst delaying HGV’s
Date: July 2015
28
on both northbound and southbound approaches. A simple sketch of this layout can be seen
below in Figure 5.
Figure 5 – Sketch of proposed M2/ N2 HGV segregated layout
viii. Installation of SCOOT/ MOVA system at signal controlled junctions
The installation of dynamic signal control is an option that would not deter any traffic from
travelling through Slane, however it would make alternative routes more attractive for HGV’s.
Two traffic control systems are available as follows:
•
Signalisation with MOVA is particularly attractive for HGV’s, as certain approaches (with
high percentages of HGV’s) can be allocated stop penalties within MOVA. This means
that where, previously HGV’s experienced delays and had to stop-start at priority
intersections they now have reduced delays and are more likely to pass the junction first
time.
•
SCOOT can be installed on a corridor of closely spaced signal junctions to improve traffic
flow, travel times, decrease fuel consumption and improve air quality.
Both SCOOT and MOVA are techniques to optimise the performance of signalised junctions.
Whilst MOVA is designed for isolated junctions, SCOOT enables optimisation of signalised
junctions over a larger area, typically in urban areas or corridors.
Date: July 2015
29
Studies have found that SCOOT/MOVA could generate significant benefits. Hunt et al (1982)
found that SCOOT could reduce average delays by up to 12% when compared to fixed time signal
plans. In the Eddington Transport Study (2006) it was hypothesised that a 5% reduction in travel
time for all business travel on the roads (in the UK) could generate £2.5 billion of cost savings.
The Department for Transport UK (DfT) in 1997 estimated that if the MOVA system of control
was applied to all isolated traffic signal junctions in the UK, the savings would be in excess of
£220 million.
Signalisation and adoption of intelligent traffic control systems would reduce travel times and
could have a positive effect on the BCR of any scheme (assuming congestion is currently
experienced).
ix. HGV ban through Slane
This option was considered in the Slane Traffic Management Study- Stage 1: Report by AECOM,
however disadvantages exist for example with the local economy (at least some HGV access
would be required to serve Slane) and also HGV may find alternative local routes to bypass Slane
on similarly unsuitable roads.
x. Speed Limit reduction on N2
This option was considered under the previous study ‘AECOM Technical Note 2 – Impact of
reduced speed limits’ and better fuel efficiency could result from such an option, however this
system is non-discriminatory with respect to LV’s and the speed reduction would disbenefit all
traffic.
xi. Combined Options
A number of the above options would impose additional operational costs or restrictions on all
users and not just on through movements, including local trips that currently make appropriate
use of the Secondary Road network. In some instances, the cost and restrictions imposed would
not be sufficient to deter long distance HGV’s travelling through Slane. Combinations of the
above options would modify HGV route choice without significantly adversely effecting local trip
routing or cost, ensuring that local economies are not disadvantaged.
5.5
Traffic Management Gap Analysis Preliminary Design Review
The potential advantages and disadvantages of the options identified in Stage 1 are summarised
in Table 7. A review of the Stage 1 Gap Analysis options was undertaken in consultation with
MCC on 1st July 2014 to identify which options were to be taken forward to simulate the impact
using the N2 Slane transport model.
Date: July 2015
30
It was agreed that due to the identified disadvantages, high costs and current legislative limitations
the following proposals would not be advanced at this stage:
•
Option 1 (reallocation of toll points);
•
Option 2 (electronic tolling); and
•
Option 5 (Improve access northbound from R152 to M1 through the creation of
northbound on-slip from R152 to M1 at junction 8).
To robustly test Option 8 would require the development of a micro simulation model and
specialised control software. The option was provisionally tested on the basis of an assessment
of likely impact based on experience.
Options 9 (HGV ban) and 10 (speed restrictions on N2) were not taken forward as both were
subjected to detailed review during the earlier studies. These two options were retained for further
consideration in combination with other measures during Stage 2 of the Gap Analysis.
Date: July 2015
31
Figure 6 – Locations of junction traffic management options
Date: July 2015
32
Option
i
Advantages
Disadvantages
OPTION NOT BEING PROGRESSED
Re-allocation of toll points to M1 J6 - M1 J8
ii
Installation of electronic tolling system for HGV's
through Slane via ANPR
iii
Dis-priority for HGV's at traffic signals
(existing or proposed traffic signals apply)
A measure of discrimination of HGV's, but not total
relatively low cost - only operates off peak
Not total discrimination of HGV's
poorer air quality off peak
iv
Re-optimise (dis) traffic signals at River view
Increase in generalised cost for HGV traffic
able to segregate HGV's, low cost
Air quality reduction, noise, incraese in fuel consumption
v
Improve access to M1-R152 route by
signalisation of alternative
route (including new signals at J9)
install new signals on M1/ J33 and R152/ N2
Positive measures increase attractiveness of
alternative route (especially for HGV drivers, signals
with MOVA are popular with HGV drivers, safety
vi
New junction N2/ R152 + MOVA
takes care of existing accident/ congestion problem?
relatively low cost, safet improved with MOVA
vii Creation of additional LV/ HGV segregated intersection discrimination of vehicle types
High cost, increased delays for HGV's, reduction in air quality
viii Installation of SCOOT/ MOVA system (or optimise FT)
Makes route more attractive for HGV's
Better all round traffic flow through Slane
improved air quality, noise, fuel consumption
ix
HGV Ban (Local) through Slane
x
Speed limit reduction on N2
(backed up by average speed camera ANPR)
Table 7 – Option Analysis Summary
Date: July 2015
33
5.6
Traffic Management Gap Analysis Detailed Design
The following designs were taken forward to Stage 2 for detailed modelling:
5.6.1
•
Option 3 – Install number of new traffic signal junctions to disbenefit northbound and
southbound traffic on N2 between Ardee and Ashbourne
•
Option 4 – Optimise traffic signals at N2 Slane Bridge such that southbound HGV trips
receive a larger disbenefit than currently experienced
•
Option 5 – Improve journey times/ ease of use for HGV’s on preferred routes
•
Option 6 – Install signal controlled junction at N2/ R152 to disbenefit northbound and
southbound traffic on N2 but favour the left turn out of R152 and right turn in to R152
•
Option 7 – New segregated Car/ HGV signalised intersection at M2/ N2/ R135
•
Option 8 – MOVA signal optimisation
•
Option 9 – Combination of options 3, 4, 5 and 7 (option 6 is included in option 3 and
detailed modelling would be required to determine the small additional benefits of
Option 8 compared with option 5)
Junction Design Methodology
The design methodology was to deter HGV traffic from using the N2 Slane as an alternative route
and hence reduce HGV trips across Slane Bridge. This was achieved by introducing additional
delays on northbound and southbound movements on the N2. This additional delay was incurred
via the introduction of traffic signal junctions at salient points on the N2 route. Signal timings
were altered so as to disbenefit northbound and southbound movements on the N2, this can be
further refined in practice by providing a negative signal priority for HGV’s.
Conversely HGV traffic was encouraged to use alternative routes to access the M1, including the
N33, R152 and R168. This was achieved by the introduction of traffic signals with timing settings
such that benefitted the alternative routes to the M1. In practice, this can be further refined by
providing signal priority for HGV’s.
It is anticipated that traffic signals would firstly be introduced at junctions with higher rates of
accidents, this would also assist the Benefit Cost Ratio (BCR) of the scheme. The type of accidents
that traffic signals may reduce are:
•
Collision involving emergence from give way side road onto N2
•
Collision involving traffic turning right in gaps on N2
A further strategy for determining the locations of additional potential signalised junctions would
be to investigate where pedestrian, cycle or equestrian routes cross the N2 and provide signal
controlled crossings which also add benefit to the local community, promoting accessibility and
social inclusion.
Date: July 2015
34
Detailed local traffic signal junction models were developed using Linsig traffic modelling
software to determine the optimum additional delay timings. The traffic flows used in the Linsig
modelling were obtained from the existing Visum model. The timings obtained were then fed
back into the Visum model to gauge the level of HGV re-assignment.
Linsig and Visum are both specialised traffic modelling software applications. Linsig is a tool to
design/assess signalised junction(s) and their performance whilst Visum is used for strategic
modelling that looks at wider area impacts of any transport intervention.
Two assessment periods were tested, AM and Inter-peak models.
5.7
Proposed Junction Improvements
The following junctions (Figure 7) were modelled with appropriate alterations based on desired
HGV traffic movements:
Date: July 2015
35
Figure 7 – Junction Locations for Traffic Modelling
1.
M1 junction 14
M1 junction 14 is located at the intersection of the M1 and N33 to the East of Ardee. The N33
would carry a significant volume of re-routed HGV traffic. The proposed junction improvement
Date: July 2015
36
(Figure 8) consists of signalisation on all approaches to the interchange, with priority provided for
HGV’s travelling from the N33 to M1 South and vice versa.
Figure 8 – Design sketch for M1 junction 14 proposed signalisation
2.
N2/ R169
The N2/ R169 junction is located approximately 2km North of Collon and is currently a priority
controlled T-junction .The proposed design includes signalisation and alterations of signal timings
to disbenefit the N2 northbound and southbound movements. Negative priority would also be
applied to approaching HGV’s on the N2 North and N2 South approaches.
3.
N2/ R168
The N2/ R168 junction is located at Collon and is currently a priority controlled crossroads. The
proposed design signalises the junction and specifies timings such that the N2 northbound and
N2 southbound movements are additionally delayed, but the R168 and left turn into the R168 is
applied a minimal delay. This is to encourage the alternative route of the R168 for HGV drivers.
4.
M1 junction 10
M1 junction 10 is located at the intersection of the R168, N51 and M1 and is currently a priority
controlled interchange. The proposed design signalises all approaches to the interchange and
provides HGV priority from R168 to M1 South and vice versa (preferred route).
5.
M1 Junction 9
M1 Junction 9 is located at the intersection of the M1, L1601 and Platin Terrace. Signalisation is
provided on approaches which aid the movement of HGV’s through the interchange from M1
North to Platin Terrace and vice versa.
Date: July 2015
37
6.
M1 Junction 8
M1 Junction 8 consists of a dumbells arrangement where the R152 intersects the M1 and Platin
Terrace. All approaches on the West roundabout are proposed to be signalised, with eastbound
and southbound movements at the East roundabout signalised with the intention of providing
HGV priority on the R152 to M1 route and vice versa.
7.
N2/ N51
The N2/ N51 junction is situated in Slane village centre and is currently signalised. The proposed
alteration consists of the alteration of signal timings intended to increase delay on both N2
approaches. This would be supplemented with negative priority for HGV’s.
8.
N2 Slane Bridge
The N2 Slane Bridge is located just to the South of Slane and consists of a signalised shuttle
working arrangement. On the southbound direction, cars and HGVs are separated. In the
proposed scenario, signal timings were altered to provide additional delay to the southbound
HGV lane.
9.
N2/ R150
The N2/ R150 junction is located approximately 10km South of Slane and consists of a priority
controlled staggered crossroads. The proposed design signalises all movements at the junction
with the aim of introducing additional delays to northbound and southbound traffic on the N2.
10. N2/ R152
The N2/ R152 junction is currently a priority controlled T-junction approximately 6km North of
Ashbourne. The proposed design signalises the junction and provides priority for traffic travelling
from N2 South to the R152 and vice versa (preferred HGV route) and seeks to disbenefit HGV’s
travelling northbound and southbound on the N2.
11.
N2/ R135
The N2/ R135 roundabout is located to the North of Ashbourne, and the proposed design
consists of separate northbound and southbound Car and HGV lanes. The proposed signal
timings are altered such that the HGV lanes experience significant additional delay whilst
minimising delays to cars.
5.8
Junction Design Traffic Flows
Traffic flows (Figure 9) were available from the existing Visum model for AM and Inter-peak
periods and these were supplemented with local traffic count and ATC data to check accuracy.
Traffic data was available from the existing Vissum model in 3 vehicle classes; Car, HGV1 and
HGV2. These vehicle classes were converted to Passenger Car Units (PCU) using factors of 2.3
(for both HGV classes) and 1.0 (Cars).
Date: July 2015
38
PCU
382
3
10
120
359
137
Figure 9 – Traffic flow at N2/ R152 during Inter-peak period (PCU)
Automatic Traffic Count data (ATC) was available for some of the intersections proposed to be
within the model. The data was classified by vehicle type, so a check was also able to be made on
the percentage mix of HGV’s predicted by the Visum Reference Case model. A summary of this
comparison can be found in the Appendix A.
At some junction locations (N2/ R150 for example), no traffic flows were available for some
approaches (the R150 West in this case) as these routes were not included within the existing
Visum model. In these cases, traffic flows were estimated based on likely cross movement traffic
flows.
5.9
LINSIG Modelling
The above junctions were modelled using LINSIG, a software originally developed for analysis
of isolated junctions (Figure 10).
Date: July 2015
39
Figure 10 – Screenshot of LINSIG model
At existing signalised junctions (N2/ N51 and N2 Slane Bridge), the optimised timings formed
the Reference Case model. Signal timings were altered in the proposed model such that additional
delays were applied to the N2 northbound and southbound approaches.
At existing priority controlled junctions the Reference Case model consisted of a give way priority
controlled LINSIG model. The proposed models signalised the junctions and additional delays
were applied to the N2 routes in the models. Geometric measurements were input into ARCADY
and PICADY models to obtain relevant maximum flow and slope parameters. This promoted
accuracy and quality within the LINSIG models.
Saturation flows used were calculated within the model using geometrical measurements taken
from OS scalable map tiles. The width of the approach lanes and turning radii are the
measurements which affect signalised lane saturation flow.
Intergreen timings were calculated from scalable plans (Figure 11) for input to the LINSIG
models.
Date: July 2015
40
Figure 11 – Intergreen calculations for N2/ R150
At some locations (Slane Bridge for example), the altered signal timings were constrained by
physical factors, such as the length of the HGV lane. It was ensured that the HGV lane did not
queue back the full length of the HGV lane within the LINSIG model. This is illustrated by Figure
A1 in Appendix A which shows the mean maximum queue on this HGV lane to be a maximum
of 5 PCU during the Inter-peak period, this equates to a length of 30m, where the available storage
length for HGV’s is approximately 120m.
5.10
Results
The LINSIG modelling was used to calculate the additional delay that could be created by
signalising junctions on the N2 route. The additional delay was included within the Visum model
to gauge the likely trip re-assignment due to the proposed measures.
Table 8 and Figure 12 shows an example of the output from the LINSIG modelling and shows
the estimated average additional delay in seconds per PCU (compared to the Reference Case
model) incurred on each movement by the introduction of traffic signals.
Table A1 in Appendix A tabulates the results from both the LINSIG base and proposed models
during Inter-peak and AM periods, indicating predicted Degree of Saturation (DoS), Mean
Maximum Queue (MMQ) and Delay for each approach.
Date: July 2015
41
Junction
Approach/
Movement
Additional Delays (s/ PCU)
AM
IP
N2/ R169
N2 southbound
N2 northbound Ahead
N2 northbound RT
46
10
22
27
3
9
N2/ R168
N2 southbound
N2 northbound
N2 southbound LT
51
25
5
29
48
5
N2/ N51
N2 southbound
N2 northbound
25
14
12
20
N2 Slane Bridge
N2 southbound
N2 northbound
64
-8
84
6
N2/ R150
N2 southbound
N2 northbound
72
23
34
34
N2/ R152
N2 southbound
N2 northbound Ahead
N2 northbound RT
50
17
27
41
32
12
N2/ R135
N2 southbound
N2 northbound
40
40
29
30
Table 8 – Additional Delay predicted by LINSIG for HGV’s on N2 corridor
Date: July 2015
42
Figure 12 – Additional Delay predicted by LINSIG for each Gap Analysis Option
5.11
Traffic Control System Options
There are a range of traffic signal control systems available which offer varying levels of vehicle
detection, discrimination and optimisation, enabling delays and prioritisation to be controlled by
vehicle type.
5.11.1
Fixed Time
The modelled options could be introduced by implementing a fixed time cycle at each signalised
junction. This would have the facility to vary timings by time of day, thus causing less delay offpeak but enabling the junction to cope with higher traffic levels during peak hours.
With this type of signal control, no information about the arrival of HGV’s is known and hence
none is relayed to the traffic signal controller. The delay experienced by traffic is therefore shared
out equally between all classifications of traffic, cars would experience the same delay as 5-axle
heavy goods vehicles.
Because no advanced detection is used for fixed time control, the controller is also unaware of
the position of approaching vehicles and may therefore present an approaching vehicle with a red
Date: July 2015
43
signal on the immediate approach (the dilemma zone) to the stop-line. This causes un-predicable
driving behaviour which has more potential to cause accidents.
Fixed time signal is less costly to implement as the vehicle detection costs and other Intelligent
Transport Systems (ITS) data is not required. However the control is non-discriminatory and all
vehicles are subjected to the same average delay
5.11.2
MOVA – Adaptive Signal Control
The MOVA system of control is better suited to high speed roads such as the N2. This is because
the system detects and tracks vehicles on all approaches and is able to vary the green time such
that approaching vehicles pass through the junction without stopping.
MOVA is proven to yield accident benefits compared to fixed time systems and is often employed
where traffic signals are installed to assist with particular types of accidents.
5.11.3
HGV Priority
Technology can be provided which detects HGV’s on each approach and provide priority through
the signalised junction. Specialist detector cards can be installed within the traffic controller which
recognise HGV’s by detecting their inductance profile through inductive loops on the approach.
It is envisaged that HGV priority would be provided on preferred routes, such as the N33 – M1
route at M1 Junction 14 interchange. If this system was well publicised with HGV drivers and
their associated businesses, this may assist in achieving the required re-routing.
5.11.4
HGV – Negative Priority
This is an innovative proposal which would require careful on site validation and testing to ensure
a safe system of operation.
The HGV detection system would detect approaching HGV’s and ensure that the vehicles
received a red signal (at an appropriate stopping distance) for an extended duration.
This would have the effect of allowing minimal delays for light traffic, but imposing larger delays
on HGV class vehicles.
The initial cost of installation of this type of system would be higher than the previously described
systems, as detection of HGV’s would have to be provided farther back on the N2 to enable the
safe stopping of these vehicles.
5.12
HGV Detection Options
Signal priority for HGV’s may be implemented by detection of HGV’s via:
•
Date: July 2015
On-board computer
44
•
Vehicle classification
The European pilot project ‘Freilot’ examined the possible use of on-board computers to provide
HGV’s with priority through signalised junctions. A message is sent from the HGV’s on-board
computer to the local traffic signal controller where the signal is processed and the relevant action
can be applied.
Trials have also taken place using specialist inductive loop detector cards within the controller
which utilise existing inductive loops to identify approaching HGV’s. Again, the signal is passed
to the traffic signal controller and processed to provide the required action (this may be priority
on preferred routes, negative priority on N2).
Date: July 2015
45
6
6.1
Identification of Options Using Visum
Methodology
The Stage 1 Gap Analysis described in the previous chapter identified the traffic management
measures and options that are capable of modifying the route choice for Heavy Goods Vehicles
(HGV’s) travelling through Slane. This chapter describes Stage 2, the identification of the
optimum combination of options, which was undertaken in two phases as follows:
6.2
•
Phase 1 - Option Sifting. The impact of the proposed traffic management measures on
HGV delays and route choice was modelled for 7 option tests and the change in
flows compared with the existing flows across Slane Bridge and along key links.
•
Phase 2 - Combined Options Tests. A review was undertaken of the traffic management
option results in conjunction with the findings from the preceding studies. The
optimum features of the earlier option tests (speed restrictions, vehicle restrictions
and HGV tolls) were considered in conjunction the traffic management measures to
define four additional tests.
Base Scenario
Each of the options were assessed by forecasting the change in HGV flows at key locations using
the traffic model developed on behalf of the NRA by AECOM. For this purpose an AM peak
hour and Inter Peak period hour models forwarded to Halcrow Barry:
The models supplied represented the ‘Reference Case scenario/Do Minimum’ network against
which each of the option tests were compared. In line with best practice, a review was undertaken
of the model to ensure that the model outputs provided were largely consistent with available
survey information and output from the model in earlier studies. Following discussion with
AECOM, revised AM model was provided against which it was possible to replicate previous
results.
6.3
Phase 1 Modelling
To identify the level of HGV diversion achieved by each of the options (Stage 1 and stage 2),
Visum 12.52 (version used by AECOM) was used. For each option a separate scenario was
developed accompanied with appropriate delays in AM and IP model. These scenarios were
subsequently compared with the Reference Case model to identify the level of diversion.
For Phase 1, the following options were tested:
•
Option 3: Disprioritise HGV’s at traffic signalled junctions;
•
Option 4: Optimise traffic signals at N2/ Mill Hill (Slane bridge);
•
Option 5: Improve alternative routes to N2 for HGV’s (fixed time signals);
•
Option 6: New signal controlled junction at N2/ R152;
Date: July 2015
46
•
Option 7: Delays on M2/N2/R135;
•
Option 8: Option 5 with MOVA/SCOOT signal optimisation; and
•
Option 9: Combination of Option 3 to Option 7 (option 6 is included in
Option 3).
Options 3 to 9 focus on introducing delays at various junctions along the N2 corridor as well as
those feeding into N2. For more information regarding the development and details of the traffic
management options, reference should be made to the preceding chapter.
The location of the junctions where delays were introduced and the combinations of junctions
for each option are shown in Figure 13 and Table 10
Date: July 2015
47
Figure 13 – Location of Proposed Traffic Management measures
Date: July 2015
48
Table 9 below shows the final set of additional delays applied for each option for the routes
within Visum.
Table 9: Delays (seconds) introduced by options
Junction
N2/ R152
M1/ R152 (Jcn 8)
M1 Junction 9
M1 Junction 10
M1 Junction 14
N2/ N51
N2/ River View
N2/ R135
N2/ R169
N2/ R168
N2/ R150
SCOOT_M1/ R152 (Jcn 8)
SCOOT_M1 Junction 9
SCOOT_M1 Junction 10
SCOOT_M1 Junction 14
Options
Option 3 Option 4 Option 5 Option 6 Option 7 Option 8 Option 9
√
√
√
√
√
√
√
√
√
√
√
√
√
√
√
√
√
√
√
√
√
√
√
√
√
√
√
Table 10: Junction combinations for options
To identify the level of HGV diversion achieved by each of the options, Visum 12.52 (version
used by AECOM) was used. For each option a separate scenario was developed accompanied
with appropriate delays in AM and IP model. These scenarios were subsequently compared with
the Reference Case model to identify the level of diversion.
6.4
Phase 1 Option Result
All options were compared against the Reference Case to identify the level of HGVs diversion
through Slane village. In the model there are two different types of HGVs:
•
HGV1 – less than 5 axles
•
HGV2 – greater than 5 axles
Date: July 2015
49
Following the comparisons of options with the reference case, Option 3 and Option 9 were
identified as the potential options offering higher levels of HGV’s diversion compared to other
options.
Table 11 and Table 12 Table below show HGV1 and HGV2 flows on Slane Bridge for each
options including the Reference Case. It also shows the level of diversion (%) resulted by each
option compared to Reference Case scenario for AM and IP hour and AADT.
The tables show that Option 9, which is a combination of all other options, offers maximum
diversion rates of 29% in AM and 20% in IP. Option 3 results in diversion rates of 11% in AM
and 7% in IP. Others option offer very low or nil diversion. Option 5 (introducing delays at
junctions on M1) and Option 8 (installing SCOOT systems) attract more HGVs to N2.
Slane Bridge
(number of
vehicles)
NB
SB
Slane Bridge
(number of
vehicles)
NB
SB
Slane Bridge
(number of
vehicles)
NB
SB
Level of Diversion
Reference
20
16
Option 3
19
13
AM
Option 4
20
16
Option 5
21
16
Option 6
20
16
Option 7
20
16
Option 8
21
16
Option 9
18
10
HGV2
Reference
23
24
Option 3
23
19
Option 4
24
23
Option 5
25
23
Option 6
23
24
Option 7
23
24
Option 8
24
24
Option 9
21
10
HGVs
Reference
43
40
Option 3
42
32
Option 4
44
39
Option 5
46
39
Option 6
43
40
Option 7
43
40
Option 8
45
40
Option 9
39
20
83
74
-11%
83
0%
85
2%
83
0%
83
0%
85
2%
59
-29%
11
5
HGV1
Reference
9
11
Option 3
8
11
IP
Option 4
9
10
Option 5
9
11
Option 6
9
11
Option 7
9
11
Option 8
9
11
Option 9
8
9
HGV2
Reference
26
24
Option 3
23
23
Option 4
26
21
Option 5
26
24
Option 6
25
24
Option 7
25
24
Option 8
26
24
Option 9
23
16
HGVs
Reference
35
35
Option 3
31
34
Option 4
35
31
Option 5
35
35
Option 6
34
35
Option 7
34
35
Option 8
35
35
Option 9
31
25
70
65
-7%
66
-6%
70
0%
69
-1%
69
-1%
70
0%
56
-20%
No. of HGVs
Percentages
Slane Bridge
(number of
vehicles)
NB
SB
Slane Bridge
(number of
vehicles)
NB
SB
Slane Bridge
(number of
vehicles)
NB
SB
Level of Diversion
HGV1
No. of HGVs
Percentages
Table 11: Diversion in percentage (%) and absolute by different options – AM and Inter Peak hour
Date: July 2015
50
Slane Bridge
(number of
vehicles)
NB
SB
Slane Bridge
(number of
vehicles)
NB
SB
Slane Bridge
(number of
vehicles)
NB
SB
Level of Diversion
HGV1
Reference
206
176
Option 3
189
143
AADT
Option 4
206
176
Option 5
211
176
Option 6
206
176
Option 7
206
176
Option 8
211
176
Option 9
184
110
HGV2
Reference
409
392
Option 3
376
354
Option 4
414
354
Option 5
419
387
Option 6
398
392
Option 7
398
392
Option 8
414
392
Option 9
365
229
HGVs
Reference
614
568
Option 3
565
497
Option 4
619
530
Option 5
630
563
Option 6
603
568
Option 7
603
568
Option 8
625
568
Option 9
549
339
1182
1062
-10%
1149
-3%
1193
1%
1171
-1%
1171
-1%
1193
1%
888
-25%
No. of HGVs
Percentages
Table 12: Diversion in percentage (%) and absolute by different options – AADT
Table 9 shows the delays in seconds introduced by different options in both AM and IP to achieve
the level of diversion. These demonstrate that there are appreciable HGV diversion rates when
more than 5 minutes of delay are introduced.
The following sections discuss in detail the level of diversion achieved by Option 3 and Option 9
for HGV1 and HGV2 in AM and IP hour and AADT, as the remaining options do not result in
appreciable diversion rates of HGVs.
6.4.1
AM Model
Figure 14 and Figure 15 below show the difference in flow of HGV1 and HGV2 both as absolute
changes percentage changes for AM Model under Option 3. For both HGV1 and HGV2 this
option indicates diversion from N2 in both directions. Comparisons have been made at two
locations along the N2, to the north of Slane at the junction with R150 and at Slane Bridge. The
results are presented graphically, with numerical annotation as well as bandwidths, where the
width is proportional to the level of change in flow, with increases in flows shown in green and
decreases in red.
The level of diversion in the southbound direction is generally greater than that northbound as
the level of delay imposed by the proposed traffic management measures in the southbound
direction is significantly greater than northbound.
For HGV1, on N2, northbound shows 5% and southbound 28% diversion whilst on Slane Bridge
northbound shows 4% diversion and southbound shows 20% diversion.
For HGV2, diversion rates on the N2 are 3% in northbound direction and 23% in southbound
direction. On Slane Bridge the diversion is 2% northbound and 19% southbound.
Date: July 2015
51
Figure 14: Option 3 AM compared with Reference – HGV 1
Figure 15: Option 3 AM compared with Reference - HGV 2
Date: July 2015
52
Date: July 2015
53
Figure 16 and figure 17 illustrate the level of diversion for HGV1 and HGV2 under Option 9
compared to the Reference Case. For HGV1, diversion rates on N2 in the northbound direction
are 17% and 51% in southbound direction. On Slane Bridge, the diversion rates are 14% in
northbound and 40% in southbound directions.
For HGV2, the diversion rates are 13% northbound and 67% in the southbound direction along
N2. On Slane Bridge the diversion rates are 11% northbound and 59% in the southbound
direction.
6.4.2
Inter Peak (IP) model
The level of diversion relative to the Reference Case under Option 3 in the IP for both HGV1
and HGV2 in absolute and percentages are shown in Figure 18 and figure 19 below.
HGV1 diversion rates are 14% in northbound direction and 1% in southbound direction along
N2. On Slane Bridge the diversion rates in northbound are 14% but there is no diversion in
southbound.
Figure 18: Option 3 IP compared with Reference – HGV 1
Date: July 2015
54
For HGV2 the diversion rates on the N2 and Slane Bridge are the same, with 12% diversion in
the northbound and 4% in the southbound direction.
The level of diversion relative to the Reference Case under option 9 in the IP for both HGV1
and HGV2 in absolute and percentages are shown in Figure 20 and figure 21 below.
For HGV1 along N2 the diversion rates are 11% in the northbound and 13% in the southbound
direction. On Slane Bridge the diversion rates are 11% in the northbound and 17% in the
southbound direction.
For HGV2 along N2 the diversion rates are 12% in the northbound and 31% in the southbound
direction. On Slane Bridge the diversion rates are 13% in the northbound direction and 34% in
southbound direction.
Date: July 2015
55
Figure 20: Option 9 IP compared with Reference– HGV 1
Date: July 2015
56
6.5
Phase 1: Highway Network Performances
Table 13 and 14 show vehicle kilometres and vehicle hours travelled for HGV1, HGV2 and
LGV/Car for AADT average day, and AM and IP average hour. The tables show the absolute
values and the changes (in percentages) the options offer in comparison with Reference Case.
There is no significant change in both total vehicle km and vehicle hours for AM and IP time
periods. The change in both vehicle kilometres and vehicle-hours are less than 1%
In AM Option 9 offers maximum reduction for vehicle-km but most increase in vehicle hours for
both HGV1 and HGV2, due primarily to the delays introduced at various junctions. It also
increases the vehicle hour for car trips.
The patterns are very similar in the IP period with Option 9 showing most reduction in vehiclekm and most increase in vehicle-hours.
AADT
Vehicle - km - HGV1
Reference
454,515
Option 3
454,216
Option 4
454,449
Highway Statistics (value)
Option 5
Option 6
454,433
454,363
Option 7
454,382
Option 8
454,498
Option 9
453,836
Vehicle - km - HGV2
577,290
576,853
577,141
577,087
577,230
577,108
577,196
576,230
Total veh km HGV
1,031,806
1,031,068
1,031,591
1,031,520
1,031,592
1,031,490
1,031,695
1,030,066
Vehicle - km- Car
Vehicle - hrs - HGV1
10,748,370
6,015
7,507
10,747,503
6,027
7,530
10,748,760
6,019
7,515
10,746,848
6,020
7,511
10,747,112
6,020
7,515
10,748,303
6,022
7,517
10,747,343
6,018
7,509
10,745,873
6,036
7,537
Total veh hrs HGV
13,521
13,557
13,534
13,530
13,535
13,540
13,527
13,573
Vehicle - hrs - Car (hrs)
148,131
148,407
148,128
148,268
148,229
148,149
148,248
148,566
Highway Statistics (% changes compared with Do-Min)
Vehicle - km - HGV1
Vehicle - km - HGV2
-0.07%
-0.08%
-0.01%
-0.03%
-0.02%
-0.04%
-0.03%
-0.01%
-0.03%
-0.03%
0.00%
-0.02%
-0.15%
-0.18%
Total veh km HGV
-0.07%
-0.02%
-0.03%
-0.02%
-0.03%
-0.01%
-0.17%
Vehicle - km- Car
-0.01%
0.20%
0.31%
0.00%
0.07%
0.11%
-0.01%
0.08%
0.06%
-0.01%
0.09%
0.11%
0.00%
0.12%
0.15%
-0.01%
0.05%
0.04%
-0.02%
0.35%
0.40%
Total veh hrs HGV
0.26%
0.09%
0.07%
0.10%
0.14%
0.04%
0.38%
0.19%
0.00%
0.09%
0.07%
0.01%
0.08%
0.29%
Table 13: Network Summary Statistics – AADT
Date: July 2015
57
AM Model
vehicle - km - HGV1
vehicle - km - HGV2
vehicle - km- Car
vehicle - hrs - HGV1(hrs)
vehicle - hrs - HGV2 (hrs)
vehicle - hrs - Car (hrs)
Reference
Option 3
Option 4
Option 5
Option 6
Option 7
Option 8
Option 9
27812
31744
809217
377
422
11,621
27797
31728
809044
378
423
11,648
27812
31747
809158
378
423
11,620
27,813
31741
808983
378
423
11,633
27806
31743
809080
378
423
11,629
27,789
31716
809227
378
423
11,623
27817
31745
809080
378
423
11,632
27767
31704
808,833
378
423
11,664
0.02%
0.00%
-0.02%
0.05%
0.04%
0.09%
-0.16%
-0.13%
-0.05%
0.24%
0.04%
0.37%
Highway Statistics (% changes with Reference Case)
vehicle - km - HGV1
vehicle - km - HGV2
vehicle - km- Car
vehicle - hrs - HGV1
vehicle - hrs - Car
-0.05%
-0.05%
-0.02%
0.15%
0.21%
0.23%
0.00%
0.01%
-0.01%
0.06%
0.06%
-0.01%
0.00%
-0.01%
-0.03%
0.13%
0.11%
0.11%
-0.02%
0.00%
-0.02%
0.09%
0.10%
0.07%
-0.08%
-0.09%
0.00%
0.20%
0.23%
0.02%
IP Model
Reference
vehicle - km - HGV1
vehicle - km - HGV2
vehicle - km- Car
27846
37103
585075
364
478
7,836
Option 3 Option 4 Option 5 Option 6 Option 7 Option 8
27826
37071
585080
365
479
7,848
27840
37088
585139
364
478
7,836
27838
37086
585050
364
478
7,843
27835
37098
585027
364
478
7,841
27845
37100
585064
364
478
7,837
27842
37094
585048
364
478
7,842
Option 9
27806
37026
585034
365
480
7,855
vehicle - km - HGV1
vehicle - km - HGV2
vehicle - km- Car
vehicle - hrs - Car
-0.07%
-0.09%
0.00%
0.23%
0.35%
0.15%
-0.02%
-0.04%
0.01%
0.08%
0.13%
0.00%
-0.03%
-0.05%
0.00%
0.06%
0.04%
0.08%
-0.04%
-0.01%
-0.01%
0.09%
0.11%
0.06%
0.00%
-0.01%
0.00%
0.08%
0.11%
0.01%
-0.01%
-0.02%
0.00%
0.05%
0.03%
0.07%
-0.14%
-0.21%
-0.01%
0.41%
0.56%
0.23%
Table 14: Network Summary Statistics – AM and Inter Peak hour
6.6
Phase 1: Review of Options
Following discussions with MCC seven options were considered where delays were introduced at
11 junctions in both northbound and southbound directions, and reduced delays along alternative
routes.
In both the AM and IP models the maximum delays was introduced at all locations in Option 9
closely followed by Option 3. By introducing high level of delays appreciable levels of HGV
diversion were achieved under Option 9 closely followed by Option 3. In AM model hour, Option
9 offered 29% diversion whereas Option 3 shows 11% (both HGVs). Similarly in IP, Option 9
offered 20% diversion and Option 3 showed 7% diversion. Other options showed significantly
lower levels of diversion.
Date: July 2015
58
Comparing all options it is evident that Option 9 offers maximum diversion in both AM and IP
model with maximum delays to HGV’s. More delays introduced to the southbound direction of
travel reflects a higher proportion diverting off N2 whilst travelling south and this is consistent
with the safety objectives associated with the scheme.
These results demonstrate there are potential additional options to those previously considered
(i.e. HGV ban, tolling options, speed limit restrictions) to address the issue of high HGV traffic
along N2 travelling across Slane Bridge.
The combination of the traffic management options considered within the current study along
with an element of other measures, such as those previously considered within earlier studies,
would give rise to a still greater level of diversion.
A review was undertaken to determine whether the forecast level of delay and diversion to HGVs
associated with each traffic management option considered to date was cost effective. The review
indicated that the benefits of the proposed Option 5 junction improvements along the M1
(junctions 8, 9, 10 and 14), which were designed to make alternative routes to the N2 more
attractive by reducing the level of delays to HGV were found to be limited and only reduced
delays by up to 12 seconds (Table 9).
The option 5 traffic management measures were included in all Option 9 tests within the study
and contributed to the forecast level of diversion of 29% because traffic will reassign to alternative
routes as soon as a given threshold level of delay is reached. Within the Phase 2 combined option
development traffic management option testing, the small benefit of the Option 5 junction delays
along the M1 relative to the overall benefits of the combined measures is unlikely to be a factor
in determining whether the route choice delay threshold is reached and therefore the Option 5
measures are unlikely to be cost effective or have any significant impact on the level of HGV
diversion along N2 at Slane. For consistency Option 5 has been included in Option 9 throughout
all stages of the study but it is suggested that the inclusion of the Option 5 within the final scheme
option should be excluded as the impacts on the M1 Motorway are disproportionate to the
potential minimal benefits.
The forecast maximum level of HGV diversion associated with option 9 (all traffic management
combined together) was considered to be insufficient to meet the objectives of the study and
further measures would be required
6.7
Phase 2: Combination Option Development
The Phase 1 analysis shows that alternative traffic management options which address the issue
of high levels of HGV traffic travelling across Slane Bridge exist, albeit at rates less than 30% of
HGVs. Following the identification of Option 9 as the preferred traffic management option,
additional options that combined more than one measure to encourage further HGV trips to reroute were developed by HB in consultation with MCC on 3rd October.
Date: July 2015
59
•
Option 13: Combination of Option 9 and speed limit reduction along N2 from 100kph
to 80kph between N2/M2 Ashbourne and Ardee (see Figure 22);
•
Option 14: Combination of Option 9 and restricting 50% of HGVs with 5+ axles across
Slane Bridge (exemption to trips with local origin or destination);
•
Option 15: Combination of Option 9 and HGV tolls (both HGV1 and HGV2) on Slane
Bridge, with local trips being exempt from tolls (the toll levy was assumed to be €5.30),
and;
•
Option 16: Combination of Option 9 and HGV tolls (both HGV1 and HGV2) on M1
toll removed at Drogheda (both from main carriageway and slip roads).
Local trips are defined as any trip with either an origin or destination in the area adjacent to Slane
Bridge. Figure 23 shows the boundary of the area considered as being local to Slane. The area is
represented within the model by four zones and all HGV trips travelling to or from these zones
were considered local for Options 14 and 15. HGV trips travelling from and to a zone within
this area were also exempt, although very few trips made such movements.
Each of the combined options (Options 13 to 16) were modelled using the Visum model and the
impact on HGV flows across Slane Bridge and along key links of options. Analysis of the results
is presented below.
Date: July 2015
60
Figure 22 – Location of N2 speed restriction
Date: July 2015
61
Figure 23 - Local Zones (origin or destination for local trips)
6.8
Phase 2: Combination Option Results
The Stage 2 option results were all compared against the Reference Case to identify the level of
HGVs diversion on Slane Bridge.
Option 15 was identified as the potential option offering higher levels of HGV’s diversion
compared to other combined options.
Table 15 and Table 16 below show HGV1 and HGV2 flows on Slane bridge for the Reference
Case and each combination option, with their level of diversion in percentages for AM and IP
average hour and AADT. They show:
•
Option 13 providing HGV diversion of 41% in AM and 59% in IP.
•
Option 14 providing HGV diversion on Slane Bridge as 43% in AM and 47% in IP.
•
Option 15 offering maximum HGV diversion on Slane Bridge with 77% in AM and 94%
in IP.
•
Option 16 providing HGV diversion on Slane Bridge of 55% in AM and 87% in IP.
Date: July 2015
62
Slane Bridge
(number of
vehicles)
HGV1
NB
SB
Slane Bridge
(number of
vehicles)
NB
SB
Slane Bridge
(number of
vehicles)
NB
SB
Level of Diversion
NB
SB
Slane Bridge
(number of
vehicles)
NB
SB
Slane Bridge
(number of
vehicles)
Level of Diversion
HGV2
Reference Option 13 Option 14 Option 15 Option 16
23
17
13
6
12
24
9
6
3
7
HGVs
43
30
31
13
23
40
19
16
6
14
No. of HGVs
Percentages
Slane Bridge
(number of
vehicles)
AM
20
13
18
7
11
16
10
10
3
7
HGV1
83
49
-41%
47
-43%
19
-77%
37
-55%
IP
9
6
8
0
1
11
6
9
1
2
HGV2
26
8
11
0
2
24
9
9
3
4
HGVs
35
14
19
0
3
35
15
18
4
6
NB
SB
No. of HGVs
Percentages
70
29
-59%
37
-47%
4
-94%
9
-87%
Table 15: Diversion in percentage (%) and absolute by different combined options – AM and IP
Date: July 2015
63
Slane Bridge
(number of
vehicles)
Slane Bridge
(number of
vehicles)
Slane Bridge
(number of
vehicles)
Level of Diversion
HGV1
NB
SB
AADT
206
135
184
37
70
176
110
110
33
77
HGV2
409
179
190
32
86
392
147
131
49
81
HGVs
614
314
374
69
156
568
257
241
82
158
NB
SB
NB
SB
No. of HGVs
Percentages
1182
571
-52%
615
-48%
151
-87%
314
-73%
Table 16: Diversion in percentage (%) and absolute by different combined options – AADT
The following section discusses in detail the level of diversion achieved by Option 15 for HGV1
and HGV2 both for AM and IP as this option offers the maximum level of diversion compared
to all other combined options. Flow diagrams for the other options for HGV1 and HGV2 are
included in Appendix B.
Figures 24 to 27 shows the difference in HGV1 and HGV2 flows both as absolute changes and
percentage changes for AM and IP model under Option 15. For both HGV1 and HGV2 this
option indicates diversion from N2 in both directions. Comparisons have been made on the N2
between its junction with Mill Hill and R150. The results are presented numerically as well as
bandwidths (the width is proportional to the level of flow, with increases in flows shown in green
and decreases in red). The plots show that with the introduction of tolls on Slane Bridge along
with Option 9, most of the HGV trips divert off N2 on to other routes, primarily along M1 and
M3.
Figures 24-26 show the forecast theoretical maximum level of reduction in HGV flows as a result
of the proposed tolls. In practice, some local HGV trips will be given exemptions and the
reduction in HGV flows will not be as high as that shown in the Figures 24-26. If local trips
(those with an origin and/or destination local to Slane) were given exemption from the tolls,
Tables 15 and 16 show that the forecast level of reduction in HGV flows will not be quite as high
as that shown in the figures.
For HGV1, in the AM, on N2 the diversion rates are up to 81% in the northbound direction and
up to 83% in southbound direction. On Slane Bridge, the diversion rates are 85% in the
northbound and 87% in the southbound direction.
Date: July 2015
64
For HGV2, in the AM, on N2 the diversion rates are up to 84% in the northbound direction and
Date: July 2015
65
Figure 24: Option 15 compared with Reference Case - HGV1 –AM
Figure 25: Option 15 compared with Reference Case - HGV2 –AM
Date: July 2015
66
For HGV1, in the IP, on N2 the diversion rates are up to 94% in the northbound direction and
For HGV2, in the IP, on N2 the diversion rates are up to 99% in the northbound direction and
Figure 26: Option 15 compared with Reference Case - HGV1 –IP
Date: July 2015
67
Figure 27: Option 15 compared with Reference Case - HGV2 –IP
6.9
Accident Analysis
Accident analysis was undertaken using the methodology specified in COBA that lists accident
rates for various link types. The various links in the model were assigned a COBA link type. The
following relationship as specified in COBA was used to forecast accident rates.
AN = A0 x βN
Where: AN = the accident rate or number of casualties per accident N years after base year;
A0 = the accident rate or number of casualties per accident in the base year;
βN = change coefficient raised to the power N (the number of years after the base
year).
The values for the accident rate change coefficient β incorporated in the COBA program for the
different link accident types were taken from Table 4/1 of COBA manual. For forecast years
between 2011 and 2020, and 2021 and 2030 the accident rate change is assumed to be one half
and one quarter respectively of the 1995 to 2010 reduction. For example, if the coefficient β is 0.9
Date: July 2015
68
for 1995 to 2010 then it is 0.95 for 2011 to 2020 (or [1 + β]/2 ). Zero change is assumed post
2030.
Accident rates were derived for the various link types for 2012 that corresponds to the reference
case scenario and applied on the total modelled vehicle kilometres. The forecast change in
Personal Injury Accidents (PIA) per annum are given in Table 17 for the reference case and the
various combined options assessed under Stage 2.
The table shows that decrease marginally under all options offering slight benefits overall in terms
of safety.
Road Safety
PIA*/annum
Do-Min
Option
9
Option
13
Option
14
Option
15
Option
16
721.10
720.16
719.11
719.90
719.90
718.38
-0.13%
-0.28%
-0.17%
-0.17%
-0.38%
Percentage changes
*Personal Injury Accidents
Table 17: Accident rate calculation
6.10
Highway network performances – Combined options
The impact of the various combined options on the overall highway network statistics were
compared against the Reference Case and the results are shown in Table 18 and Table 19 for the
average AADT, AM and IP periods.
The tables show that the total HGV vehicle-kms under Options 13, 14 and 15 reduce marginally
in both AM and IP periods whilst they increase under Option 16 (due to the removal of tolls on
M1). This is reflected by a corresponding slight increase in vehicle-hours for Options 13 to 15
and a decrease in Option 16.
Date: July 2015
69
AADT
Reference
Vehicle - km - HGV1
Vehicle - km - HGV2
454,515
577,290
Option 9
453,836
576,230
Option 13
454,044
575,800
Option 14
453,847
573,471
Option 15
454,357
575,918
Option 16
454,792
578,308
Total veh km HGV
1,031,806
1,030,066
1,029,844
1,027,318
1,030,275
1,033,100
Vehicle - km- Car
10,748,370
6,015
7,507
10,745,873
6,036
7,537
10,748,192
6,044
7,550
10,745,512
6,035
7,475
10,745,657
6,040
7,539
10,744,858
5,982
7,446
Total veh hrs HGV
13,521
13,573
13,595
13,510
13,578
13,428
148,131
148,566
148,915
148,554
148,556
148,559
Highway Statistics (% changes compared with Do-Min)
Vehicle - km - HGV1
Vehicle - km - HGV2
-0.15%
-0.18%
-0.10%
-0.26%
-0.15%
-0.66%
-0.03%
-0.24%
Total veh km HGV
-0.17%
-0.19%
-0.43%
-0.15%
0.13%
Vehicle - km- Car
-0.02%
0.35%
0.40%
0.00%
0.49%
0.58%
-0.03%
0.34%
-0.42%
-0.03%
0.42%
0.43%
-0.03%
-0.54%
-0.81%
Total veh hrs HGV
0.38%
0.54%
-0.08%
0.42%
-0.69%
0.29%
0.53%
0.29%
0.29%
0.29%
0.06%
0.18%
Table 18: Network summary statistics for combined options – Average AADT
Date: July 2015
70
AM Model
Vehicle - km - HGV1
Vehicle - km - HGV2
Vehicle - km- Car
Vehicle - hrs - HGV1(hrs)
Vehicle - hrs - HGV2 (hrs)
Reference
Option 9
Option 13
Option 14
Option 15
Option 16
27812
31744
809217
377
422
11,621
27767
31704
808,833
378
423
11,664
27771
31710
808,581
379
424
11,693
27767
31,640
808817
378
425
11,663
27,795
31,716
808840
380
424
11,664
27835
31774
808818
374
419
11,661
Vehicle - km - HGV1
Vehicle - km - HGV2
Vehicle - km- Car
Vehicle - hrs - Car
-0.16%
-0.13%
-0.05%
0.24%
0.04%
0.37%
-0.15%
-0.11%
-0.08%
0.44%
0.36%
0.62%
-0.16%
-0.33%
-0.05%
0.22%
0.51%
0.36%
-0.06%
-0.09%
-0.05%
0.70%
0.41%
0.37%
0.08%
0.09%
-0.05%
-0.76%
-0.91%
0.35%
IP Model
Reference
vehicle - km - HGV1
vehicle - km - HGV2
vehicle - km- Car
27846
37103
585075
364
478
7,836
Option 9 Option 13 Option 14 Option 15 Option 16
27806
37026
585034
365
480
7,855
27823
36984
585367
366
481
7,873
27807
36,806
585009
365
474
7,854
27,840
36,992
585011
365
480
7,854
27860
37181
584949
362
474
7,856
vehicle - km - HGV1
-0.14%
-0.08%
-0.14%
-0.02%
vehicle - km - HGV2
-0.21%
-0.32%
-0.80%
-0.30%
vehicle - km- Car
-0.01%
0.05%
-0.01%
-0.01%
0.41%
0.52%
0.40%
0.28%
0.56%
0.68%
-0.82%
0.44%
vehicle - hrs - Car
0.23%
0.46%
0.23%
0.22%
Table 19: Network summary statistics for combined options – AM and IP
6.11
0.05%
0.21%
-0.02%
-0.43%
-0.76%
0.25%
Appraisal Summary Table
The aim of this study is to identify the opportunities and understand the case for future investment
solutions in the N2 Slane corridor that are deliverable, affordable and offer value for money.
The specific objectives of the study are to:
Date: July 2015
71
•
Identify and assess investments on the N2 corridor that address existing problems on the
Slane Bridge;
•
Understand the balance of benefits and impacts from potential individual investment
proposals and any additional benefits or impacts from investment on a corridor basis; and
•
Evidence where possible, the wider economic benefits from the transport investment in
the corridor.
Using the information gathered from the earlier studies already completed on behalf of MCC and
NRA, new modelling based on the Visum transport model previously developed by AECOM and
using our engineering judgement, a series of a combination of traffic management options were
generated for the N2 route (Slane) considered in this stage of the report.
Options have been generated in order to satisfy the objectives, both strategic and operational. A
range of schemes have been generated, some are of a small scale within the highway boundary,
whilst others are wider area strategic potentially involving new structures.
The analysis presented above demonstrates that the various scenarios can lead to substantial
reductions in goods vehicle traffic through Slane. Nevertheless, although this meets one element
of the project objectives, it is noted that the scenarios can lead to adverse impacts through other
populated areas, most notably Kentstown and Duleek. In addition, excessive restrictions can lead
to reductions in network efficiency as vehicles are required to route over longer distances to access
specific destinations. A two level assessment has been carried out, the first consists of a broader
assessment of the alternatives on the basis of project objectives and the second is consistent with
the Department for Transport’s (DfT) Early Assessment and Sifting Tool (EAST) to
comparatively examine the options generated.
The broader assessment is based on the following metrics within the Appraisal Summary Table:
•
Traffic Safety The potential impact upon safety was accounted for by utilising accident
rates for each road type and vehicle kilometres on each road type extracted from the
various models.
•
Air Quality Reductions in goods vehicle movements through Slane.
•
Transport Emissions Total kilometres travelled by all vehicles are extracted from the
traffic models.
•
Network Efficiency Total hours travelled by all vehicles are extracted from the traffic
models.
Date: July 2015
72
•
Accessibility The impact on accessibility in terms of vehicle hours, the impact of traffic
management measures on HGV flows and journey times, local exemptions and
accessibility between Dublin and Monaghan, and to/from Slane is qualitatively assessed.
An Appraisal Summary Table is presented in Table 20 overleaf which summarises the key impacts
discussed above, and includes the network performance indicators as extracted from the traffic
model. Positive impacts are highlighted in green, with negative impacts in red.
Date: July 2015
73
Options
9
13
14
15
16
Traffic Safety
Air Quality*
Slight reduction in HGV traffic
Slight increase in traffic safety
through Slane village. Overall
due to diversion of larger
moderate reduction in HGV
vehicles to M1.
vehicle km.
Moderate reduction in HGV
traffic through Slane village.
Overall moderate reduction in
vehicles to M1.
HGV vehicle km.
Transport Emissions
Network Efficiency
Accessibility
Slight reduction in total Slight reduction in network
Slight improvement. No significant impact to
vehicle km due to
efficiency as total travel hours
Slane for local traffic.
reassignment.
increases.
Slight improvement. No significant impact to
vehicle km due to
efficiency as total travel hours Slane for local traffic as the speed change took
reassignment.
increases.
place outside of the local area.
Moderate improvement. No significant impact
to Slane for local traffic as permit system
traffic through Slane village.
vehicle km due to
efficiency as total travel hours exclude local traffic. Appreciable level of
Overall moderate reduction in
vehicles to M1.
reassignment.
increases.
reduction of HGVs will increase perceived
HGV vehicle km.
accessibility.
Strong reduction in HGV
Moderate improvement. No significant impact
Slight increase in traffic safety traffic through Slane village.
to Slane for local traffic as permit system
Overall slight reduction in HGV vehicle km due to
efficiency as total travel hours exclude local traffic. Appreciable level of
vehicles to M1.
vehicle km due to
reassignment.
increases.
reduction of HGVs will increase perceived
reassignment.
accessibility.
Slight increase in traffic safety traffic through Slane village.
Slight improvement. As the toll will be
Overall slight increase in HGV vehicle km due to
efficiency as total travel hours
removed on M1.
vehicles to M1.
vehicle km due to
reassignment.
increases.
reassignment.
* Assessment based on Slane Village only
Table 20 – Appraisal Summary Table
6.12
Early Assessment and Sifting Tool
Each option was assessed against a broader range of measures than the scheme objectives utilising
the Department for Transport’s (DfT) Early Assessment and Sifting Tool (EAST).
EAST is a decision support tool that has been developed to quickly summarise and present
evidence on options in a clear and consistent format using a spreadsheet. Detailed evidence often
required to support funding applications is not needed; EAST allows a view to be taken on the
best evidence available whilst remaining consistent with Transport Business Case principles.
Where possible, we have used available information gathered during earlier stages of this study as
well as undertaking detailed design and modelling of new options as well as combinations of
options, although for some criteria, data is not yet available and as such we have utilised our
engineering judgement to derive a score. Other criteria have required assumptions to be made; as
it has not been possible to apply previous experience.
The results from the EAST assessment are presented in a tabular format for each option. EAST
does not provide a means for obtaining an overall score for an intervention and therefore doesn’t
provide a means of directly ranking them.
A key to the categorisation is depicted in Table 21 below:
Date: July 2015
74
Capital Costs
(£m)
Revenue Cost
(£m)
Cost Risk
Flexibility of
Option
2
2:
High
2-4
2: 1-6
mths
2
2: 5-10
2: 0-5
2
2
3
3:
Med
1.5-2
3: 612
mths
3
3: 1025
3: 510
3
3
4
4:
Low
1-1.5
4: 1-2
yrs
4
4: 2550
4: 1025
4
4
5: High
5:
Poor
<1
5: 2-5
yrs
5: High
5: 50100
5: 2550
5:
Low
Risk
5: Dynamic
Economic
Growth
Quality of
Evidence
1: Static
Practical
Feasibility
1:
High
Risk
Public
Acceptability
1:
None
Well Being
1: 0-5
Local Env
1: Low
SDI & The
Regions
1: 0-1
mths
Carbon
Emissions
1: V
High
>4
6: 510 yrs
6: 100250
7: 10+
yrs
7: 250
-500
Table 21: EAST Scoring Categorisation
Date: July 2015
Commercial
Implementati
on Timetable
Financial
Expected
VfM Category
Managerial
1: Low
Degree of
Consensus
Fit with other
objectives
Fit with wider
objectives
Scale of
Impact
Economic
Categorisation
Criteria
Strategic
75
The broader assessment is based on the following metrics within the EAST Table:
STRATEGIC
•
Scale of Impact. Assessment to determine whether the scheme is closely aligned to
deliver benefits locally and nationally (in accordance with local, regional and national policy)
•
Fit with wider objectives. An assessment against national policies including N2 national
road hierarchy, accessibility (a lorry ban would reduce commercial accessibility to
Ashbourne and Monaghan), network efficiency (decrease in vehicle kms/increase in vehicle
hours), integration, air quality and emissions (overall decrease in total vehicle kms by
avoiding Slane and other populated areas but increase in vehicle hours by HGV), safety
(generally slight reduction in accidents), economic growth (commercial HGV constraints)
and environment (emissions, noise, air quality). For example, both tolls and vehicle type
bans do not comply with the role of the N2 as a National Route and there is a national
commitment to maintain alternative non-tolled roads to M1 and M3 tolled roads.
•
Fit with other objectives. An assessment against local scheme objectives, economic
regeneration, environment, safety, etc.
•
Degree of consensus. The N2 is a national route that impacts on the local community,
business community, MCC, NRA, etc. For example Meath County Council brought
forward the current traffic management measures between the N2/N51 junction and the
bridge as a temporary accident remedial measure pending delivery of a bypass. These were
accepted by the local community on that basis.
ECONOMIC
•
Economic Growth. The N2 is an integral part of the road hierarchy, which provides the
essential link between local communities, economic hubs, Dublin and the strategic road
network. Evaluation as to whether the proposed scheme provides commercially efficient
hierarchical road network.
•
Carbon Emissions. There is a national commitment to reduce carbon emissions, through
a reduction in network inefficiencies.
•
SDI & the Regions
•
Local Environment. Evaluation as to whether proposed scheme will lead to rerouting of
HGV flows through other centres of population but otherwise have a positive
environmental impact as flows no longer pass through Slane and other local centres of
population and local communities.
•
Well Being. Reduction in number of accidents as HGV transfer to safer road types
•
Expected VfM category. Evaluation of value for money within a market affected by
tolling of strategic road network. All benefits cost ratios are expected to be less than 1.
MANAGERIAL
•
Implementation Timetable. The timeframe in which an option can be implemented
varies depending on the level of infrastructure to be built, whether legislative change is
required and whether innovative techniques are proposed.
Date: July 2015
76
•
Public Acceptability. Reflects the local community’s acceptance of the proposed scheme
as well as commercial perspective.
•
Practical feasibility. Reflects the technical feasibility of the scheme, legislative powers,
users compliance and enforceability
•
Quality of Evidence. The robustness and reliability of the evaluation techniques,
including the Visum modelling, supporting evidence locally and elsewhere, and current best
practice
FINANCIAL
•
Capital costs. Anticipated capital costs of scheme.
•
Revenue costs. Anticipated revenue impact, particularly PPP M1 motorway tolls. Are
the majority of the monetary benefits to the exchequer balanced by the costs to the
consumer
COMMERCIAL
•
Flexibility of Options. The ability to refine and extend an option is advantageous where
there is uncertainty within the assessment and in forecast future growth.
Date: July 2015
77
Table 22: EAST Option Appraisal Table
Date: July 2015
78
6.13
Key Link Analysis
The change in HGV and all vehicle flows for 17 key links are shown in Table 23 (see Figure 28
for locations) for the following options:
•
Reference Case
•
Option 9 Traffic management along N2 to selectively delay HGV’s
•
Option 13 – option 9 plus speed restriction 80 kph along N2
•
Option 14 – option 9 plus HGV restrictions on Slane Bridge (with local exemptions)
•
Option 15 – option 9 plus tolls on Slane Bridge (with local exemptions)
•
Option 16 – option 9 plus M1 tolls removal for HGV
As a consequence of the additional delays and travel costs/vehicle restrictions imposed by the
proposed N2 traffic management measures, the northbound and southbound HGV flows along
N2 at Slane Bridge decrease for each option, reducing by 23% for Option 9, around 40% for
Options 13 and 14, by 88% for Option 15 and 76% for Option 16. To the south of Slane, HGV
flows along the N2 to the north of Ashbourne progressively reduce in Options 9 to 16 by between
19% and 53%. To the north of Slane HGV flows along N2 reduce by between 20% and 66%.
For Option 9 (proposed Traffic Management measures along N2) HGV through trips strategically
reassign from N2 to M1 along the N33 east of Ardee, with increasingly higher levels of flows
reassigning in Options 9 to 16 ranging from between 11% and 40%. Correspondingly, the HGV
flows along the main routes previously taken to avoid the Drogheda M1 tolls via N2 along R169,
fall by between 11% and 59%, and along R150 fall by 10% and 47%. The pattern of change in
HGV flows between Options along R152 to the east of N2 is more variable, decreasing for
Options 9, 14 and 16 (N2 traffic management measures, Slane vehicle restrictions and M1 HGV
toll exemption respectively) and increasing for Option 13 and 15 (N2 speed restriction 80 kph
and HGV tolls respectively). The change in HGV flows along the M1 reflect to a large extent the
change in flows along the R152, R150, R168 and R169, with the greatest increase in HGV flows
at Drogheda as expected.
Date: July 2015
79
Figure 28 – Key Link Locations
Date: July 2015
80
HGV Flow AADT
Ref.
Location
Scenario
Base
Option 9
Option 13
Option 14
Option 15
Option 16
930
-23%
1088
-20%
282
0%
645
-8%
1460
13%
4073
4%
1538
-19%
328
-14%
589
-13%
520
1%
98
-51%
902
-1%
151
0%
1051
11%
539
-19%
1460
13%
3465
7%
580
-52%
487
-64%
523
85%
624
-11%
1597
24%
4199
7%
1341
-30%
311
-19%
736
8%
525
2%
76
-62%
902
-1%
151
0%
1128
20%
139
-79%
1597
24%
3985
23%
657
-46%
864
-36%
277
-2%
656
-6%
1663
29%
4161
6%
1335
-30%
344
-10%
605
-11%
547
6%
98
-51%
902
-1%
151
0%
1144
21%
457
-31%
1663
29%
3646
12%
145
-88%
464
-66%
271
-4%
575
-18%
1689
31%
4325
10%
1239
-35%
305
-20%
824
21%
650
27%
131
-35%
902
-1%
173
14%
1292
37%
282
-57%
1689
31%
3963
22%
296
-76%
530
-61%
364
29%
684
-2%
2720
111%
4352
11%
892
-53%
201
-47%
474
-30%
465
-9%
71
-65%
880
-3%
184
22%
1319
40%
272
-59%
3266
154%
4012
24%
1
Flow Slane Bridge
1212
2
Flow North of Slane Bridge
1359
3
Flow East of Slane N51
282
4
Flow West of Slane N51
700
5
Flow M1 Droghedra Toll
1288
6
Flow M1 Dunleer
3932
7
Flow North of Ashbourbne Bypass
1904
8
Flow East of N2 - R150
382
9
680
10
Flow West of N2 - R153
513
11
Flow between N2 and M1 - R125
201
12
Flow between Kell and Navan - R147
908
13
Flow South of Collon - R168
151
14
Flow East of Ardee - N33
943
15
663
16
Flow Drogheda South M1
1288
17
Flow Dunleer South M1
3244
Date: July 2015
81
All Vehicle Flow AADT
Ref.
Location
Scenario
Base
Option 9
Option 13
Option 14
Option 15
Option 16
6543
-7%
7510
-6%
4996
0%
7856
-1%
29619
4%
36396
0%
17067
-3%
4065
-4%
5950
1%
7437
1%
6863
1%
5910
0%
5670
1%
9046
2%
3410
-6%
28824
2%
33115
1%
5889
-16%
6753
-16%
5022
0%
7856
-1%
30018
5%
36584
0%
16391
-7%
4016
-5%
5973
1%
7394
0%
6837
0%
5897
-1%
5677
1%
9166
4%
3005
-17%
28919
3%
33599
2%
6478
-8%
7467
-7%
4995
0%
7853
-1%
29643
4%
36410
0%
17046
-3%
4067
-4%
5977
1%
7450
1%
6863
1%
5910
0%
5678
1%
9063
3%
3395
-6%
28852
2%
33146
1%
6343
-10%
7413
-8%
4994
0%
7831
-1%
29689
4%
36426
0%
16960
-3%
4075
-3%
5963
1%
7498
1%
6859
1%
5910
0%
5678
1%
9077
3%
3372
-7%
28892
3%
33185
1%
6434
-8%
7409
-8%
5017
0%
7848
-1%
29943
5%
36433
0%
16946
-3%
4050
-4%
5928
0%
7424
0%
6850
1%
5910
0%
5678
1%
9083
3%
3349
-7%
29287
4%
33214
1%
1
Flow Slane Bridge
7017
2
Flow North of Slane Bridge
8021
3
Flow East of Slane N51
5008
4
Flow West of Slane N51
7912
5
Flow M1 Droghedra Toll
28599
6
Flow M1 Dunleer
36420
7
Flow North of Ashbourbne Bypass
17533
8
4220
9
5911
10
Flow West of N2 - R153
7396
11
Flow between N2 and M1 - R125
6814
12
Flow between Kell and Navan - R147
5928
13
Flow South of Collon - R168
5636
14
Flow East of Ardee - N33
8828
15
3613
16
Flow Drogheda South M1
28155
17
Flow Dunleer South M1
32800
Table 23. Key link flows
Date: July 2015
82
6.14
Analysis
During the preliminary design stage (Stage 1), a series of traffic management options were
discussed with MCC from which nine options were taken forward for detailed appraisal, where
designs were developed to calculate delays at 11 junctions in both northbound and southbound
directions. Junctions along M1 (J8, J9, J10 and J14) were also considered with fixed time signal in
Option 5 and SCOOT/MOVA signal controlled method in Option 8.
In both AM and IP model a combination of all options were modelled to simulate the impact of
the maximum level of delay on HGV, with less delay imposed, where possible, on other vehicles.
By introducing high level of delays appreciable levels of HGV diversion were achieved under
Option 9 followed by Option 3. In AM model hour, Option 9 offered 29% diversion whereas
Option 3 shows 11% (both HGVs). Similarly in IP, Option 9 offered 20% diversion and Option
3 showed 7% diversion. Other options showed very low level of diversion. The forecast level of
HGV diversion associated with the Option 9 traffic management measures do not completely
satisfy the objectives of the study.
To achieve greater levels of diversion, it is necessary to increase the level of delay (or cost) along
N2 until it exceeds that along alternative routes including M1. As part of Stage 2, further options
were developed in combination with Option 9 that included toll options, speed restrictions and
banning specified HGV user classes. The options assessed showed that Option 15 that combined
Option 9 and a toll on HGVs for through traffic achieve the maximum levels of diversion of 77%
in the AM and in 94% in the IP periods. Traffic restrictions on HGV 5+ axles with exemptions
for local trips achieved a level of reduction of between 43% and 47% by time of day. Option 16
which removed tolls to HGV along the M1 resulted in level of diversion of 55-87%. Speed
restrictions of 80km/hr along N2 gives rise a reduction in flow of HGVs by 41-59%. To minimise
the impact of local vehicle bans or vehicle restrictions on local businesses, exemptions would be
provided for HGV trips that have either a local origins or destinations.
An appraisal against the other scheme objectives in the Appraisal Summary Table indicated that
the relative difference in benefits is small. A weighted scoring has not been applied in this instance
to maintain transparency of the appraisal process.
The study has based the assessment of options on HGV 5+ axle restrictions (with exemptions to
50% local trips) and tolls to all HGV. It is likely that the toll level of Euro 5.30 can be significantly
reduced as a consequence of the delays proposed through traffic management measures along the
N2.
Based on the various options considered, Option 15 achieves the maximum level of HGV
diversion away from Slane Bridge. The highest level of diversion of HGVs is achieved by tolling
within Option 15. Within an earlier study, it was found that a similar level of diversion can largely
be achieved without adding in Option 9, although it is likely that the level of the toll to achieve
the same level of diversion could be significantly reduced. The installation of tolls along the N2
Date: July 2015
82
at Slane would discourage HGV traffic from using the primary N2 route network as no new
infrastructure with improved journey times is provided and no real alternative toll-free route is
available for road users. This is unlike other toll schemes taken forward within Ireland that
attracted private investment to provide public infrastructure which would otherwise not have been
built as quickly if they had been funded in the traditional way. It is also noted that Tolling was
previously discounted by Minister Varadkar in 2013 and successful implementation of this
measure would require ministerial support.
Option 16 proposes the removal of tolls along the parallel M1 corridor, which is forecast to give
rise to a significant level of diversion away from Slane to the primary M1 road network. By
combining Option 9 traffic management measures with the removal of M1 tolls, the diversion of
traffic is constrained to a small number of appropriate routes. The successful implementation of
this option his would require negotiations’ to be undertaken to ‘buy-out’ the M1 CRG contract
and the timescale, costs and likelihood of success associated with this process is uncertain.
Options 13 and 14 are associated with the application of more conventional traffic management
techniques (speed restriction and HGV bans respectively) which could be introduced within a
shorter timescale and higher level of certainty. They represent genuine and credible options in
terms of HGV diversion rates, but as evidenced from Table 22, these (and the other options
considered) have wider impacts that must be factored into any decision to implement a traffic
management alternative if there is to be no bypass. However the forecast level of diversion of
HGV’s away from Slane would be lower and Option 14 is forecast to give rise to a diversion of
48% of HGVs from Slane Bridge. The combination of a HGV ban in Slane with Option 9 is
forecast to result in less diversion from the N2 to lower class roads particularly the R152.
However, no alternative untolled route to the N2 exists if HGV’s are banned at Slane.
Option 13 combines a speed restriction along the N2 of 80kph with the Option 9 traffic
management measures, giving rise to a 52 % diversion. However the speed limit would apply to
all vehicles not just the goods vehicles which are the focus of the study.
Date: July 2015
83
7
7.1
Summary and Conclusions
Summary
The development of the road infrastructure and network north of Dublin has been the result of
a significant level of investment, providing good connectivity and integration between local,
regional, national and strategic traffic movements. The M1 forms part of the core TransEuropean Transport Network and together with the M3, provide major strategic road corridors
north of Dublin. The N2 is located between these two corridors and provides connectivity
between the regional and strategic network, functioning as a national route for longer distance
traffic and commercial traffic movements between Dublin, Ashbourne, Ardee and northwards to
Monaghan.
As the consequence of the combination of good network connectivity at a number of locations
along the N2 and M1, as well as the presences of tolls on the M1 at Drogheda, significant levels
of strategic HGV traffic movements choose to travel along N2 rather than the M1, compromising
to some extent both the ability of the N2 to function as a regional/national strategic traffic
corridor and the benefit of the significant levels of investment in the strategic motorway network.
The traffic capacity along the N2 is constrained at Slane village by Slane Bridge and gives rise to
delays as the result of the single lane crossing. The case for the N2 Slane Bypass was refused
permission by An Bord Pleanala’s decision in March 2012 and resulted in further traffic
management alternatives to a Slane Bypass being investigated.
A series of detailed studies were undertaken to explore options to deter HGV through
movements, including an HGV ban and tolling, as well as speed restrictions along N2. Tolling
was apparently ruled out by the Minister following a report by the NRA on the effects of tolling,
and the implementation of vehicle restrictions through Slane would result in the N2 having a more
limited function as a strategic corridor for commercial traffic. A further study was commissioned
to consider alternative traffic management options, including consideration of the context of a
strategic plan for the N2, M1 and M3 corridors, as well as traffic management options in
combination rather than in isolation to integrate all strands of the studies that have been carried
out by both NRA and Meath County Council into a single consolidated report.
A comprehensive Gap Analysis review was undertaken by Halcrow Barry of the previous studies
and a series of new traffic management options along the N2 and M1 designed to encourage HGV
to reroute to the M1 by increasing HGV travel times along N2 through Slane and reducing travel
times along the M1 and alternative routes. The transport modelling forecast that the level of HGV
rerouting for any single measure would not be significant but for all the measures combined
together, the travel time for HGVs along N2 increased substantially, thereby providing route
choice between N2 and M1, and increasing the level of re-routing to from N2 to M1 by 29%.
The increase in the level of delay to other vehicles types would be lower through the design of
Date: July 2015
84
discriminatory measures where possible and application of HGV vehicle detection and traffic
management measures.
To achieve greater levels of HGV rerouting, the level of delay along N2 through Slane must
exceed that along alternative routes. At the point at which the travel time along the N2 is greater
than that along alternative routes, HGV’s will switch routes. There is no benefit of imposing
delays greater than the point at which traffic reroutes. As the result of the proposed traffic
management measures (Option 9) along the N2 increasing delays, the incremental additional delay
required to encourage the remaining HGV’s to reassign from N2 to another route is significantly
lower than that predicted within earlier studies.
A review of the earlier studies identified a combination of options that would encourage further
HGV to reassign from N2 to M1 corridor, and provide exemption to local trips.
The proposed traffic management measures along N2 were combined with the following
measures in four tests:
•
Speed restrictions along N2 between Ardee and Ashbourne
•
HGV 5+ axle vehicle restrictions on Slane Bridge with 50% exemptions to
local traffic
•
HGV toll on Slane Bridge (€5.30)
•
M1 tolls removed for HGVs at Drogheda
An appraisal was undertaken against the project objectives in the form of an Appraisal Summary
Table and the Department of Transport’s decision support tool Early Assessment and Sifting
Tool, EAST. All options were modelled in detail using the Visum traffic model developed by
AECOM for the study and analysis undertaken of the change in flow across the network and
flows including 17 key links. Detailed analysis indicated that road accident levels were forecast to
fall slightly in all options.
7.2
Assessment of Options
The review found that there were slightly negative impacts against the majority of assessment
criteria identified at the outset of the design study. A number of the local benefits are mirrored
by disbenefits within the wider network. For the majority of options there are some safety benefits
as HGVs transfer to safer routes. Overall there is a reduction in vehicle kilometres, with benefits
to car users outweighing the increase for HGVs. There is an increase in total travel times increase
however.
The option which gives rise to the highest level of HGV diversion at Slane along the N2 combined
traffic management measures along N2 to increase delays to HGVs with tolls for HGV 5+axle
vehicles along the N2 immediately south of Slane (Option 15). The toll level was set at €5.30
Date: July 2015
85
although it is expected that further tests would show that this level could be much lower as the
delays arising from the traffic management measures along the N2 increase delays along the route.
The forecast level of diversion is between 77% and 94% in the morning and interpeak period
respectively. This scheme does not comply with the role of the N2 as a National Route as it
would result in the implementation of tolls along all national and strategic routes to the north of
Dublin (M1, M3 and N2), which would result in no reasonable non tolled route being available .
The next best performing scheme comprised the proposed traffic management measures along
N2 with the removal of HGV tolls on the M1 at Drogheda (Option 16). The level of diversion of
HGVs at Slane would be 73%. The option for the removal of tolls from the M1 would have
significant revenue implications for the PPP tolling operator and it would be necessary for the
NRA to negotiate a revised revenue contract with the M1 PPP operator.
Option 14 combines the proposed traffic management measures along N2 with traffic restrictions
across Slane Bridge to HGV 5+ axle vehicles achieving a level of diversion of 48%. However
once again, there could be an anomaly in relation to current policy as no alternative untolled route
would exist for HGV 5+axles vehicles within the wider Slane area.
The proposed discriminatory traffic management measures along the N2 to increase delays and
overall travel costs to HGVs (Option 9) would result in up to 29% of HGVs re-routeing to
alternative roads, such as M1. The level of diversion does not meet the objectives of the study
and additional measures would be required.
The final design option combines the proposed traffic management measures along N2 with the
introduction of speed restrictions of 80kph (Option 13) enforced by Automatic Number Plate
Recognition (APNR) cameras to monitor average speed along N2 between Ardee and Ashbourne.
The level of diversion of HGVs at Slane would be 52%. This option 13 is depicted in Drawing
100-001 in Appendix C. The lower speed limits would be non-discriminatory and apply to all
traffic including HGVs, reducing speed limits along a National route from 100kph to 80kph. The
overall network efficiency would decline due to the increase in travel times.
7.3
Conclusions
The traffic modelling undertaken as part of this study has proposed traffic management options
to achieve the stated primary objective of diverting HGV movements away from Slane using
existing infrastructure. However, it is clear that there are significant challenges in delivering these
options as they impact upon the ability of all modes of transport to move efficiently within this
section of the National Primary Road Network which continues to provide strategic accessibility
between Ashbourne and M1/Monaghan. Furthermore, these solutions while reducing goods
vehicles in Slane could lead to adverse impacts in areas such as Kentstown and Duleek due to
HGVs diverting onto other parts of the road network. It is noted that for some of the options
proposed, they would require a change in government policy or commercial tolling contracts as a
consequence.
Date: July 2015
86
As shown in Table 22, the assessment of each option against a range of discreet metrics shows
the myriad of considerations which are relevant in choosing between options of this nature. As
noted in Section 7.2, local benefits have corresponding disbenefits across the wider network. In
addition, Table 22 indicates that all the measures are likely to have poor returns in terms of value
for money and that public acceptance for most proposals is likely to be low.
The work undertaken for this report in relation to the predicted accident savings as shown in
Table 17 also illustrates that these are relatively modest for all options. These indicators in
particular suggest that the overall return of the options would not be enough to secure the required
capital funding to implement them using current project appraisal measures. This will be a major
consideration in the decision to proceed with any of the options presented in this report
Date: July 2015
87

Y14116 Slane Traffic Management Review Rev C

Transcription

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