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.3 A75(T) PLANTING END TO DRUMFLOWER
Project Overview
The project involved the construction of a wide single 2+1 (WS2+1) carriageway on the A75(T) between Planting End and Drumflower, providing a dedicated eastbound overtaking opportunity over a length of 1 kilometre with the horizontal and vertical alignment of the route being improved to current design standards.
The general location of the project is shown in Figure A.3a.
The A75(T) Planting End to Drumflower 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) Newton Stewart projects for which evaluations are included in section A.1 and A.2 respectively.
Project Objectives
The objectives of the A75(T) Planting End to Drumflower 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) Planting End to Drumflower project has been evaluated against the above objectives and the following criteria:
- Environment;
- Safety;
- Economy;
- Costs to Government; and
- Value for Money.
Figure A.3a A75(T) Planting to Drumflower
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.3.2 Network Traffic Indicators
Traffic Volumes
The location of the Automatic Traffic Counter (ATC) within the study area is shown in Figure A.3a.
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.3.1.
Table A.3.1: A75(T) Planting End to Drumflower - ATC Data
| ATC Reference | AADT by Year | |||||
|---|---|---|---|---|---|---|
| 2006 | 2007 | 2008 | 2009 | 2010 | 2011 | |
| A75(T) West of Castle Kennedy | ||||||
| JTC00118 | 6,609 | 6,904 | Year of Opening | 6,708 | 6,837 | 6,826 |
A comparison between pre and post opening traffic volumes on the A75(T) mainline west of Castle Kennedy indicates that traffic flows in 2009 were around 200 vehicles per day (vpd) (approximately 3%) lower than 2007 flow levels, whilst flows in 2010 reflected a marginal increase of around 100 vpd compared with 2009. Traffic flows in 2011 were broadly consistent with 2010 traffic flow levels.
Given the nature of the A75(T) Planting End to Drumflower 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) Planting End to Drumflower 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 the predicted traffic data is shown in Table A.3.2 below.
Table A.3.2: A75(T) Planting End to Drumflower - 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 Castle Kennedy | |||||||
| JTC00118 | 6,708 | 7,350 | 7,490 | 7,700 | 9.6% | 11.7% | 14.8% |
* 2009 flows (first full year of ATC data available)
The comparison between predicted and actual AADT flows in Table A.3.2 indicates that the predicted 2009 flow (derived by interpolating between the modelled assessment year traffic flows) was 10% and 15% greater than the observed 2009 flow 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 Planting End and Drumflower 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.3.3 based on the observed 2009 traffic flow.
Table A.3.3: A75(T) Planting End to Drumflower - Assessment of Carriageway Standard (TA 46/97)
| Opening Year AADT* | TA 46/97 Standard | Constructed Standard |
|---|---|---|
| 6,708 |
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 wide single 2+1 carriageways 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 Planting End and Drumflower.
Analysis of the results from the post opening survey indicates that approximately 30% of vehicles that travelled through the survey site in the 2‑lane eastbound direction during the AM and PM survey periods carried out an overtaking manoeuvre. Overtaking in the 1-lane westbound direction was limited due to the restriction on overtaking in this direction of travel.
The results suggest that eastbound vehicles in platoon were dispersed over the extents of the survey site as a consequence of vehicles carrying out overtaking manoeuvres. In the westbound 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
As a result of the provision of a dedicated overtaking opportunity in the eastbound direction of travel, journey times between Planting End and Drumflower in this direction are likely to have reduced.
Journey times may have increased in the westbound direction, as a consequence of the restriction on overtaking in this direction and an increase in the number of vehicles travelling in platoon.
Review of Environmental Mitigation Measures
The environmental mitigation measures originally proposed for the A75(T) Planting End to Drumflower 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) Planting End to Drumflower 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 for the A75(T) Planting End to Drumflower 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) Planting End to Drumflower project 3 years before and 1 year after project completion are shown in Figures A.3b and A.3c.
A summary of the personal injury accident data is shown in Table A.3.4.
Table A.3.4: A75(T) Planting End to Drumflower - Personal Injury Accident Data Summary
| Period | Fatal | Serious | Slight | Total Accidents |
|---|---|---|---|---|
| 3 Years Before | ||||
| A75(T) | 0 | 0 | 2 | 2 |
| 1 Year After | ||||
| A75(T) | 0 | 0 | 0 | 0 |
As can be seen in Table A.3.4, no personal injury accidents occurred in the 1 year period following the opening of the project in comparison to two personal injury accidents (two 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 referred to one personal injury accident (serious) that occurred in the 1 year period following the opening of the project. The accident (involving a single vehicle which lost control and collided with a tree on the verge) occurred outwith the extents of the project and, as such, does not appear in the analysis of 1 year after opening personal injury accidents presented in Table A.3.4 above.
The RSA report also notes that the driver lost control at a bend before coming to rest further along the road and that the alignment of the road had not changed due to the overtaking section, however, the wider cross-section may be encouraging higher vehicle speeds. It is stated that it is unclear from the data provided what the main contributing factors to the accident were, however, it is noted that Dumfries and Galloway Police have indicated concerns from the public regarding this tie-in and increased vehicle speeds.
Figure A.3b A75(T) Planting End to Drumflower
Figure A.3c A75(T) Planting End to Drumflower
The report recommended that a 'junction on bend' warning sign and a 'slow' carriageway marking be provided in place of the existing side road ahead sign to provide sufficient warning of both the junction and the change in horizontal alignment. A site visit carried out in October 2011, however, confirmed that neither the warning sign nor the 'slow' carriageway marking had been provided.
The RSA report also confirmed one non-injury accident which occurred within the vicinity of the project during the period 1 year after opening. It was concluded, however, that the accident was attributable to the Temporary Traffic Management Scheme associated with the completion of the project rather than the layout of the project.
Safety: Key Findings
From an assessment of the 1 year post opening personal injury accidents and a review of the Stage 4 RSA report, there is no evidence to suggest that the A75(T) Planting End to Drumflower project is not operating safely, however, concerns have been raised surrounding vehicle speeds.
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 Actual Project 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 is shown in Table A.3.5. 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.3.5: 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.3.5 and A.3.6, 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.3.8 Achievement of Objectives
As specific indicators to measure the performance of the A75(T) Planting End to Drumflower 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) Planting End to Drumflower project is progressing towards achieving its objectives, is presented in Table A.3.6.
Table A.3.6: A75(T) Planting End to Drumflower - 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 eastbound vehicles carrying out overtaking manoeuvres. In the westbound direction of travel with the restriction on overtaking, the survey data indicates that the number of platoons increased. |
+ve for eastbound 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 30% of eastbound vehicles carried out an overtaking manoeuvre which suggests that the project facilitates overtaking. Whilst the level of overtaking in the 1-lane westbound direction was significantly lower due to the restriction on overtaking in this direction of travel, the Planting End to Drumflower 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. While there is no evidence to suggest that the A75(T) Planting End to Drumflower project is not operating safely from the 1 year post opening personal injury accident data, concerns have been raised surrounding vehicle speeds. |
+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 eastbound direction of travel, the journey times between Planting End and Drumflower in this direction are likely to have reduced. In the westbound direction of travel, over which overtaking is restricted, the project may have increased journey times as a result of an increase in the number of vehicles travelling in platoon. |
+ve for eastbound vehicles | |||
| Implemented as part of a wider Route Action Plan to improve operational performance and level of service | The A75(T) Planting End to Drumflower 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