Transport Scotland Scottish Trunk Road Infrastructure Project Evaluation Evaluation Report for Trunk Road Projects Opened between April 07 and March 09
A APPENDIX A: EVALUATIONS FOR PROJECTS THAT OPENED BETWEEN APRIL 07 AND MARCH 09
A.1 A75(T) BARFIL TO BETTYKNOWES
A.1.1 Introduction
Project Overview
The project involved the upgrading of 1.4 kilometres of single carriageway to wide single 2+1 carriageway on the A75(T) between Barfil and Bettyknowes, providing a dedicated westbound overtaking opportunity over approximately 0.9 kilometres, and the improvement of the route's horizontal and vertical alignment.
The general location of the project is shown in Figure A.1a.
The A75(T) Barfil to Bettyknowes project was officially opened to traffic on 7th April 2008.
The project was implemented as part of a wider Route Action Plan including the A75(T) Newton Stewart and A75(T) Planting End to Drumflower projects for which evaluations are included in section A.2 and A.3 respectively.
Project Objectives
The objectives of the A75(T) Barfil to Bettyknowes project were set as follows:
- to reduce vehicle 'platoons' developing behind commercial vehicles;
- to reduce driver frustration by providing a guaranteed overtaking opportunity thus providing greater safety on the network;
- to reduce delays and improve travel time for drivers using the trunk road; and
- to be implemented as part of a wider Route Action Plan to improve operational performance and level of service.
Evaluation Methodology
The A75(T) Barfil to Bettyknowes project has been evaluated against the above objectives and the following criteria:
- Environment;
- Safety;
- Economy;
- Costs to Government; and
- Value for Money.
Figure A.1a A75(T) Barfil to Bettyknowes
As the evaluation focuses on impacts relating to the project objectives, specific evaluations against the Integration and Accessibility & Social Inclusion criteria have not been undertaken.
The evaluation is supported by the consideration of network traffic indicators, including traffic volumes, overtaking opportunities and travel times presented in the following section.
A.1.2 Network Traffic Indicators
Traffic Volumes
The location of the Automatic Traffic Counter (ATC) within the study area is shown in Figure A.1a.
Comparison Between Pre and Post Opening Traffic Flows
The Annual Average Daily Traffic (AADT) flows pre and post project opening on the key routes within the study area are presented in Table A.1.1.
Table A.1.1: A75(T) Barfil to Bettyknowes - ATC Data
| ATC Reference | AADT by Year | ||||
|---|---|---|---|---|---|
| 2007 | 2008 | 2009 | 2010 | 2011 | |
| A75(T) at Crocketford | |||||
| JTC00375 | 9,072 | Year of Opening | 9,034 | 8,681 | 8,650 |
A comparison between pre and post project opening traffic volumes on the A75(T) mainline at Crocketford indicates that traffic flows in 2009 were comparable with 2007 flow levels, whilst flows in 2010 reflected a marginal reduction of around 300 vehicles per day (vpd) (approximately 5%). Traffic flows in 2011 were broadly consistent with 2010 traffic flow levels.
Given the nature of the A75(T) Barfil to Bettyknowes project, changes in traffic are not likely to be as a consequence of changes to the carriageway standard and may be as a result of reductions in traffic volumes across the wider trunk road network due to the economic downturn experienced during the evaluation period.
Comparison Between Predicted and Actual Traffic Flows
The opening year flow comparisons for the A75(T) Barfil to Bettyknowes project are based on AADT flows from 2009 as this was the first full year of reliable traffic data available from Transport Scotland's traffic counter within the study area.
As part of the project's appraisal, National Road Traffic Forecasts (NRTF) low and high growth factors were applied to the observed 2003 base year traffic flows to derive opening and future modelled assessment year traffic flows.
Predicted traffic flows for 2009 were derived by interpolating between the modelled assessment year, design network flows.
A summary of the actual and predicted traffic data is shown in Table A.1.2 below.
Table A.1.2: A75(T) Barfil to Bettyknowes - Traffic Analysis Summary
|
ATC Ref |
Actual AADT* |
Predicted AADT |
% Difference (Predicted - Actual) / Actual |
||||
|---|---|---|---|---|---|---|---|
| Low | 60/40 | High | Low | 60/40 | High | ||
| A75(T) at Crocketford | |||||||
| JTC00375 | 9,034 | 10,518 | 10,747 | 11,091 | 16.4% | 19.0% | 22.8% |
* 2009 flows (first full year of ATC data available)
The comparison between predicted and actual AADT flows in Table A.1.2 indicates that the predicted 2009 flow (derived by interpolating between the modelled assessment year traffic flows) was 16% and 23% greater than the observed 2009 flow under low and high traffic forecast scenarios respectively.
Whilst this comparison indicates that traffic growth on the A75(T) has fallen significantly short of the assumed NRTF forecasts, it is recognised that there has been a general fall in traffic volumes across the wider trunk road network in recent years due to the economic downturn that may in part account for the difference.
Changes in Irish Sea Ferry operations since the original assessment in 2003 coupled with an overall reduction in the total number of cars using the ferry services of approximately 6.5% between 2003 and 2009 (Ref. Scottish Transport Statistics No 29: 2010 Edition), which may also have contributed to observed flows being lower than forecast.
Carriageway Standard Assessment
In order to satisfy the project objectives, a wide single 2+1 carriageway was constructed on the A75(T) between Barfil and Bettyknowes as part of a series of improvements along the route, providing dedicated overtaking opportunities to help reduce platooning (seen as a particular issue on this route due to the nature of ferry traffic) as well as to reduce journey times and improve journey time reliability.
An assessment of the carriageway standard according to TA 46/97 - Economic Assessment and Recommended Flow Ranges for New Rural Road Links, which applied at the time of the project design, is shown in Table A.1.3 based on the observed 2009 traffic flow.
Table A.1.3: A75(T) Barfil to Bettyknowes - Assessment of Carriageway Standard (TA 46/97)
| Opening Year AADT* | TA 46/97 Standard | Constructed Standard |
|---|---|---|
| 9,034 |
Wide Single 2-Lane |
Wide Single 2+1 |
* 2009 flows (first full year of ATC data available)
The carriageway assessment indicates that the observed 2009 flow lies within the flow range appropriate for a wide single 2-lane standard of carriageway. There are no specific flow ranges for the justification of a wide single 2+1 carriageway given in TA 46/97 (or TD 70/80 - Design of Wide Single 2+1 Roads) and, given the project objectives and the nature of traffic on the route, the constructed carriageway standard is considered appropriate.
Overtaking Opportunities
Post Opening Overtaking Opportunities
A post opening overtaking survey was undertaken on the A75(T) in October 2011 to provide an indication of conditions between Barfil and Bettyknowes.
Analysis of the results from the post opening survey indicates that approximately 37% of vehicles that travelled through the survey site in the 2‑lane westbound direction during the AM and PM survey periods carried out an overtaking manoeuvre. Overtaking in the 1-lane eastbound direction was limited due to the restriction on overtaking in this direction of travel.
The results suggest that westbound vehicles in platoon were dispersed over the extents of the survey site as a consequence of vehicles carrying out overtaking manoeuvres. In the eastbound direction of travel, the length of platoons increased over the extents of the survey site as a consequence of the restriction on overtaking in this direction.
Travel Times
Change in Travel Times
The provision of a dedicated overtaking opportunity in the westbound direction of travel is likely to have improved journey times between Barfil and Bettyknowes in this direction.
Whilst journey times may have increased in the eastbound direction, as a consequence of the restriction on overtaking in this direction and an increase in the number of vehicles travelling in platoon, any increase is likely to be alleviated, to some extent, by the provision of overtaking opportunities on the dual carriageway section to the east of the A75(T) Barfil to Bettyknowes project.
Review of Environmental Mitigation Measures
The environmental mitigation measures originally proposed for the A75(T) Barfil to Bettyknowes project were obtained from the project's Environmental Statement.
A review of the environmental mitigation measures was carried out in April 2010, which confirmed that the majority of measures committed within the Environmental Statement were in place and were providing appropriate levels of mitigation.
Noise and Air Quality
Given the rural nature of the A75(T) Barfil to Bettyknowes project, no significant impact on noise and air quality is expected. It is therefore not appropriate to evaluate the project's impact on noise and air quality.
Environment: Key Findings
The review of mitigation measures implemented for the A75(T) Barfil to Bettyknowes project confirmed that the majority of measures committed within the Environmental Statement were in place. Whilst some variations from the proposed mitigation measures had been identified, these were not considered to have had a material detrimental impact on the general integration of the project into its surrounding.
Accidents
Comparison Between Pre and Post Opening Personal Injury Accident Numbers
The locations and severities of personal injury accidents occurring within the vicinity of the A75(T) Barfil to Bettyknowes project 3 years before and 1 year after project completion are shown in Figures A.1b and A.1c.
A summary of the personal injury accident data is shown in Table A.1.4.
Table A.1.4: A75(T) Barfil to Bettyknowes - Personal Injury Accident Data Summary
| Period | Fatal | Serious | Slight | Total Accidents |
|---|---|---|---|---|
| 3 Years Before | ||||
| A75(T) | 0 | 0 | 1 | 1 |
| 1 Year After | ||||
| A75(T) | 0 | 0 | 0 | 0 |
As can be seen from Table A.1.4, no personal injury accidents occurred in the 1 year period following the opening of the project in comparison to one personal injury accident (slight) in the 3 years before opening, suggesting a potential improvement in road safety.
Road Safety Audits
The Stage 4 Road Safety Audit (RSA) was carried out in July and August 2009. The RSA report notes that one personal injury accident (slight) occurred during the construction of the project (i.e. during the period 3 years before opening) and involved the collision of five vehicles during a period when a temporary traffic management scheme was active.
Figure A.1b A75(T) Barfil to Bettyknowes
Figure A.1c A75(T) Barfil to Bettyknowes
The RSA report also notes that the collision was caused by a vehicle braking suddenly due to an oncoming Heavy Goods Vehicle (HGV), in wet conditions. The report suggests that the main factors were reduced lane widths through the works and possible reckless driving by the driver of the HGV.
The RSA report concluded that as the collision occurred during construction of the overtaking section, it could not be considered to be connected to the layout of the project.
The RSA report also noted two non-injury accidents which occurred within the vicinity of the project during the period 1 year after opening. It was concluded, however, that both of these accidents were attributable to poor driving rather than the layout of the project.
Safety: Key Findings
An assessment of the 1 year post opening personal injury accidents and a review of the Stage 4 RSA report, suggests that the A75(T) Barfil to Bettyknowes project is operating safely.
Transport Economic Efficiency
Comparison Between Predicted and Actual Traffic Flows
The A75(T) Barfil to Bettyknowes, A75(T) Newton Stewart and A75(T) Planting End to Drumflower projects were constructed under a single contract with a single outturn cost. Accordingly the evaluation under the economy and cost to government criteria considers the collective performance of the projects.
The comparisons between predicted and actual traffic flows, presented in sections A.1.2, A.2.2 and A.3.2 can be considered a proxy for whether the predicted economic benefits of the combined projects are likely to be realised.
The comparison indicates that the predicted 2009 flows were up to 23% greater than the observed 2009 flows on the A75(T) within the vicinity of Barfil and Bettyknowes, up to 29% greater within the vicinity of Newton Stewart and up to 15% greater within the vicinity of Planting End to Drumflower. This overestimation is likely due to the combination of changes in Irish Sea Ferry operations and general economic downturn.
Economy: Key Findings
A difference between predicted and actual AADT flows of this magnitude suggests that the economic benefits of the combined projects will have been overestimated due to external factors that could not have readily been foreseen at the time of assessment.
Investment Costs
Comparison Between Predicted and Out-turn Costs
The A75(T) Barfil to Bettyknowes, A75(T) Newton Stewart and A75(T) Planting End to Drumflower projects were constructed under a single contract with a single out-turn cost. The predicted project costs used in the economic assessment of each project have been combined to allow the comparison between predicted and out-turn costs to be undertaken.
The combined out-turn and predicted project costs for the three A75(T) projects are shown in Table A.1.5. This confirms that the combined out-turn cost of the three A75(T) projects was approximately £1.0m (15%) greater than the predicted cost.
Table A.1.5: A75(T) Barfil to Bettyknowes, Newton Stewart & Planting End to Drumflower - Project Cost Summary
| Out-turn Cost | Predicted Cost | Difference (Out-turn - Pred) | |||
|---|---|---|---|---|---|
| @ April 10 | Mid 98 Prices in 1998 at 3.5% Discount | Apr 06 Prices | Mid 98 Prices in 1998 at 3.5% Discount | Mid 98 Prices in 1998 at 3.5% Discount | |
| Total | £13,551,294 | £7,889,543 | £11,472,500 | £6,889,094 |
£1,010,449 (15%) |
Cost to Government: Key Findings
The combined out-turn cost of the three A75(T) projects is approximately £1.0m (15%) greater than was predicted at the time of assessment.
Initial Indications
The economic appraisal results predicted a combined Net Present Value (NPV) of £2.42m and Benefit to Cost Ratio (BCR) of 1.34 under the 60/40 traffic forecast scenario.
Based on the comparisons presented in sections A.1.5 and A.1.6, which suggest that the benefits will have been overestimated and indicate that the cost is greater than predicted, the NPV and BCR of the combined projects are unlikely to be as great as predicted.
Value for Money: Key Findings
Although the NPV and BCR of the combined projects are unlikely to be as great as predicted at the time of assessment, it is judged that the projects will continue to provide a benefit to road users.
A.1.8 Achievement of Objectives
As specific indicators to measure the performance of the A75(T) Barfil to Bettyknowes project against its objectives have not been developed, an initial indication of how the project is progressing towards achieving its objectives is based on the pre opening data available, supplemented by post opening data collected as part of the evaluation.
Initial Indications
A summary of the evaluation, providing an indication of how the A75(T) Barfil to Bettyknowes project is progressing towards achieving its objectives, is presented in Table A.1.6.
Table A.1.6: A75(T) Barfil to Bettyknowes - Progress Towards Achieving Objectives
| Objective | Commentary | Progress | |||
| To reduce vehicle 'platoons' developing behind commercial vehicles |
The results of the post opening overtaking survey suggest that platoons disperse over the wide single 2+1 section of carriageway as a consequence of westbound vehicles carrying out overtaking manoeuvres. In the eastbound direction of travel with the restriction on overtaking, the survey data indicates that platoons are merging to give longer but fewer platoons exiting the project. |
+ve for westbound vehicles | |||
| To reduce driver frustration by providing a guaranteed overtaking opportunity thus providing greater safety on the network |
The results of the post opening overtaking survey indicate that approximately 37% of westbound vehicles carried out an overtaking manoeuvre, which suggests that the project facilitates overtaking. Whilst the level of overtaking in the 1-lane eastbound direction was significantly lower due to the restriction on overtaking in this direction of travel, the Barfil to Bettyknowes project forms part of a series of improvements along the A75(T) corridor that provide vehicles travelling both east and west with dedicated overtaking opportunities. An assessment of the 1 year post opening personal injury accidents and a review of the Stage 4 RSA report, suggests that the A75(T) Barfil to Bettyknowes project is operating safely. |
+ve | |||
| To reduce delays and improve travel times for drivers using the trunk road |
As a result of the provision of a dedicated overtaking opportunity in the westbound direction of travel, the journey times between Barfil and Bettyknowes in this direction are likely to have reduced. Whilst journey times may have increased in the eastbound direction, as a consequence of the restriction on overtaking in this direction, any increase is likely to be alleviated, to some extent, by the provision of overtaking opportunities on the dual carriageway section to the east of the A75(T) Barfil to Bettyknowes project. |
+ve for westbound vehicles | |||
| Implemented as part of a wider Route Action Plan to improve operational performance and level of service | The A75(T) Barfil to Bettyknowes project forms part of a series of improvements along the A75(T) corridor that have positively contributed to the operational performance and level of service of the route. | +ve | |||
Key:
+ve Initial indication(s) that objective may be achieved
= Progress towards achievement of objective cannot be confirmed
O Initial indication(s) that objective may not be achieved