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
Project Overview
The project involved the construction of a Differential Acceleration Lane to the west of the A75(T)/A714 Roundabout, south of Newton Stewart, providing a dedicated westbound overtaking opportunity over a length of 375 metres. The project included the stopping up of the A75(T)/Station Road Junction.
The general location of the project is shown in Figure A.2a.
The A75(T) Newton Stewart 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) Barfil to Bettyknowes and A75(T) Planting End to Drumflower projects for which evaluations are included in section A.1 and A.3 respectively.
Project Objectives
The objectives of the A75(T) Newton Stewart 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) Newton Stewart project has been evaluated against the above objectives and the following criteria:
- Environment;
- Safety;
- Economy;
- Costs to Government; and
- Value for Money.
Figure A.2a A75(T) Newton Stewart
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.2.2 Network Traffic Indicators
Traffic Volumes
The location of the Automatic Traffic Counter (ATC) within the study area is shown in Figure A.2a.
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.2.1.
Table A.2.1: A75(T) Newton Stewart - ATC Data
| ATC Reference | AADT by Year | ||||
|---|---|---|---|---|---|
| 2007 | 2008 | 2009 | 2010 | 2011 | |
| A75(T) West of Newton Stewart | |||||
| JTC00377 | 4,536 | Year of Opening | 4,438 | 4,363 | 4,307 |
A comparison between pre and post opening traffic volumes on the A75(T) mainline west of Newton Stewart indicates that traffic flows in 2009 were around 100 vehicles per day (vpd) (approximately 2%) lower than 2007 flow levels with a similar annual reductions in flows between 2009 and 2011.
Given the nature of the A75(T) Newton Stewart 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) Newton Stewart 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.2.2 below.
Table A.2.2: A75(T) Newton Stewart - Traffic Analysis Summary
|
ATC Ref |
Actual AADT* | Predicted AADT |
% Difference (Predicted - Actual) / Actual |
||||
|---|---|---|---|---|---|---|---|
| Low | 60/40 | High | Low | 60/40 | High | ||
| A75(T) West of Newton Stewart | |||||||
| JTC00377 | 4,438 | 5,418 | 5,538 | 5,718 | 22.1% | 24.8% | 28.8% |
* 2009 flows (first full year of ATC data available)
The comparison between predicted and actual AADT flows in Table A.2.2 indicates that the predicted 2009 flow (derived by interpolating between the modelled assessment year traffic flows) was 22% and 29% 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 differential acceleration lane was constructed on the A75(T) at Newton Stewart 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.2.3 based on the observed 2009 traffic flow.
Table A.2.3: A75(T) Newton Stewart - Assessment of Carriageway Standard (TA 46/97)
| Opening Year AADT* | TA 46/97 Standard | Constructed Standard |
| 4,438 | Single 2-Lane | Differential Acceleration Lane |
* 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 single 2-lane standard of carriageway. There are no specific flow ranges for the justification of a differential acceleration lane given in TA 46/97 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
Based on the evaluation of other projects within the same geographic region for which overtaking surveys have been carried out, the provision of the Differential Acceleration Lane in the westbound direction of travel is judged to have a positive impact on the number of overtaking manoeuvres in this direction. The impact in the eastbound direction, over which overtaking is restricted, is unlikely to be significant given that vehicles are likely to be slowing on approach to the A75(T)/A714 roundabout at the eastern extent of the project.
As a consequence of providing overtaking opportunities, the project is also likely to help reduce platooning.
Travel Times
Change in Travel Times
Based on the evaluation of other projects within the same geographic region for which journey time data is available, the provision of the Differential Acceleration Lane in the westbound direction of travel is judged to reduce journey times in this direction. In the restricted eastbound direction of travel, given vehicles are approaching the roundabout at the eastern extent of the project, impacts on journey times will not be significant.
Review of Environmental Mitigation Measures
The environmental mitigation measures originally proposed for the A75(T) Newton Stewart 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) Newton Stewart 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) Newton Stewart 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) Newton Stewart project 3 years before and 1 year after project completion are shown in Figures A.2b and A.2c.
A summary of the personal injury accident data is shown in Table A.2.4.
Table A.2.4: A75(T) Newton Stewart - Personal Injury Accident Data Summary
| Period | Fatal | Serious | Slight | Total Accidents |
|---|---|---|---|---|
| 3 Years Before | ||||
| A75(T) | 0 | 1 | 1 | 2 |
| 1 Year After | ||||
| A75(T) | 0 | 0 | 0 | 0 |
Figure A.2b A75(T) Newton Stewart
Figure A.2c A75(T) Newton Stewart
As can be seen from Table A.2.4, no personal injury accidents occurred in the 1 year period following the opening of the project in comparison to two personal injury accidents (one serious and one 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 confirmed that no personal injury accidents occurred in the 1 year period after project opening.
The RSA report also noted four non-injury accidents which occurred within the vicinity of the project during the period 1 year after opening. It was concluded that these accidents were related to traffic approaching the Wigtown Roundabout and, as such, were not attributable to the design or 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) Newton Stewart 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.2.5. This confirms that the out-turn cost of the three A75(T) projects was approximately £1.0m (15%) greater than the predicted cost.
Table A.2.5: 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.2.5 and A.2.6, 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.2.8 Achievement of Objectives
As specific indicators to measure the performance of the A75(T) Newton Stewart 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) Newton Stewart project is progressing towards achieving its objectives, is presented in Table A.2.6.
Table A.2.6: A75(T) Newton Stewart - Progress Towards Achieving Objectives
| Objective | Commentary | Progress | |||
|---|---|---|---|---|---|
| To reduce vehicle 'platoons' developing behind commercial vehicles |
The provision of the Differential Acceleration Lane can be expected to help disperse platoons in the westbound direction of travel as a consequence of the positive impact the A75(T) Newton Stewart project is likely to have on overtaking manoeuvres in this direction. In the eastbound direction, despite the restricted overtaking section, it is judged that there is unlikley to have been any significant impact on platooning given the proximity of the project to the Wigtown Roundabout at its eastern extent. |
+ve for westbound vehicles | |||
| To reduce driver frustration by providing a guaranteed overtaking opportunity thus providing greater safety on the network |
The provision of the Differential Acceleration Lane in the westbound direction of travel is likely to have a positive impact on the number of overtaking manoeuvres. 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) Newton Stewart project is operating safely. |
+ve for westbound vehicles | |||
| To reduce delays and improve travel times for drivers using the trunk road |
The provision of overtaking opportunities in the westbound direction of travel is likley to reduce journey times in this direction. In the eastbound direction, despite the restricted overtaking section, it is judged that there is unlikley to have been any significant impact on journey times given the proximity of the project to the Wigtown Roundabout at its eastern extent. |
+ve for westbound vehicles | |||
| Implemented as part of a wider Route Action Plan to improve operational performance and level of service | The A75(T) Newton Stewart project has been constructed as part of a wider set of improvements along the A75(T) route that have contributed to an improvement in 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