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 an off-line alternating wide single 2+1 carriageway (WS2+1) over 2.5 kilometres between Caynyen Glen and the village of Mennock, to provide a dedicated overtaking opportunity for vehicles travelling in both directions, with 0.5 kilometres of on-line improvements to the southern end of the project.
The new road consists of a dedicated 1.2 kilometre northbound overtaking section with a 0.8 kilometre southbound overtaking section.
The general location of the project is shown in Figure A.10a.
The A76(T) Glenairlie project was officially opened to traffic on 3rd March 2009.
Project Objectives
The objectives of the A76(T) Glenairlie project were set as follows:
- to improve and increase the number of overtaking opportunities to reduce the conflicts between long distance users, local and agricultural traffic;
- to improve the operational performance and level of service on the A76(T) by reducing the effect of driver stress and journey times by constructing guaranteed overtaking sections designed to break up convoys/platoons;
- to incorporate measures for non-motorised users, wherever practicable. In particular, cycling proposals shall be designed in accordance with the "Trunk Road Cycling Initiative";
- to maintain the asset value of the A76(T) route;
- to mitigate the environmental impact of the new works where possible; and
- to achieve good value for money for both taxpayers and road users.
Figure A.10a A76(T) Glenairlie
Evaluation Methodology
The A76(T) Glenairlie project has been evaluated against the above objectives and the following criteria:
- Environment;
- Safety;
- Economy;
- Accessibility & Social Inclusion;
- Costs to Government; and
- Value for Money.
As the evaluation focuses on impacts relating to the project objectives, a specific evaluation against the Integration criterion has 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.10.2 Network Traffic Indicators
Traffic Volumes
The location of the Automatic Traffic Counter (ATC) within the study area is shown in Figure A.10a.
Comparison Between Pre and Post Opening Traffic Flows
The Annual Average Daily Traffic (AADT) flows pre and post project opening on the A76(T) within the study area are presented in Table A.10.1.
Table A.10.1: A76(T) Glenairlie - ATC Data
| ATC Reference | AADT by Year | |||||
|---|---|---|---|---|---|---|
| 2006 | 2007 | 2008 | 2009 | 2010 | 2011 | |
| A76(T) East of Sanquhar | ||||||
| ATC09056 | 3,369 | 3,416 | 3,415 | Year of Opening | 3,397 | 3,118 |
A comparison between pre and post opening traffic volumes on the A76(T) mainline east of Sanquhar indicates that traffic flows in 2010 were comparable with pre‑opening levels. Traffic flows between 2010 and 2011 have reduced by approximately 300 vehicles per day (vpd), approximately 8%.
Given the nature of the A76(T) Glenairlie project, changes in traffic levels are not likely to be as a consequence of changes to the carriageway standard.
Comparison Between Predicted and Actual Traffic Flows
The opening year flow comparisons for the A76(T) Glenairlie project is based on AADT flows from 2010 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 2010 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.10.2.
Table A.10.2: A76(T) Glenairlie - Traffic Analysis Summary
|
ATC Ref |
Actual AADT* | Predicted AADT |
% Difference (Predicted - Actual) / Actual |
||||
|---|---|---|---|---|---|---|---|
| Low | 60/40 | High | Low | 60/40 | High | ||
| A76(T) East of Sanquhar | |||||||
| ATC09056 | 3,397 | 3,368 | 3,438 | 3,545 | -0.9% | 1.2% | 4.4% |
* 2010 flows (first full year of ATC data available)
The comparison between predicted and actual AADT flows in Table A.10.2 indicates that the predicted 2010 flow (derived by interpolating between the modelled assessment year traffic flows) was consistent with the observed 2010 flow.
Carriageway Standard Assessment
In order to satisfy the project objectives, a wide single 2+1 carriageway was constructed on the A76(T) at Glenairie, providing dedicated overtaking opportunities to help reduce platooning, 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.10.3 based on the observed 2009 traffic flow.
Table A.10.3: A76(T) Glenairlie - Assessment of Carriageway Standard (TA 46/97)
| Opening Year AADT* | TA 46/97 Standard | Constructed Standard |
|---|---|---|
| 3,397 | Single 2-Lane |
Wide Single 2+1 |
* 2010 flows (first full year of ATC data available)
The carriageway assessment indicates that the observed 2010 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 wide single 2+1 given in TA 46/97 and, given the project objectives, the constructed carriageway standard is considered appropriate.
Overtaking Opportunities
Comparison Between Pre and Post Opening Overtaking Opportunities
A post opening overtaking surveys was undertaken on the A76(T) in October 2011 to provide an indication of conditions at Glenairlie.
The results from the post opening survey were compared against the results from a pre opening survey undertaken in April 2004. This provides an indication of the effect that the project has had on overtaking conditions.
The level of overtaking pre and post opening is shown in Table A.10.4 below.
Table A.10.4: A76(T) Glenairlie - Level of Overtaking
| AM Survey Period | PM Survey Period | |||
|---|---|---|---|---|
| Northbound | Southbound | Northbound | Southbound | |
| Pre Opening | 8% | 10% | 14% | 22% |
| Post Opening | 28% | 31% | 33% | 28% |
The percentage of northbound vehicles that carried out an overtaking manoeuvre during the pre opening AM and PM survey periods was 8% and 14% respectively, which can be compared to 28% and 33% respectively during the post opening survey. This indicates that the A76(T) Glenairlie project has increased overtaking in the northbound direction of travel.
In the southbound direction, 10% and 22% of all southbound vehicles that travelled through the survey site during the pre opening AM and PM survey periods respectively carried out an overtaking manoeuvre, which can be compared against 31% and 28% respectively during the post opening survey. This suggests that the A76(T) Glenairlie project has increased overtaking in the southbound direction of travel.
As a consequence of the increased overtaking in both directions of travel, a greater number of platoons were dispersed over the survey site post opening compared to the level of platoons dispersed during the pre opening survey.
Travel Times
Comparison Between Pre and Post Opening Travel Times
Mean vehicle speeds during the AM and PM survey periods, estimated from the information collected as part of the pre and post opening overtaking surveys, have been used as a proxy for changes in travel times.
A comparison between the mean vehicle speeds observed during the pre and post opening overtaking surveys is shown in Table A.10.5.
Table A.10.5: A76(T) Glenairlie - Assessment of Mean Vehicle Speeds (mph)
| AM Survey Period | PM Survey Period | |||
|---|---|---|---|---|
| Northbound | Southbound | Northbound | Southbound | |
| Pre Opening | 44 | 48 | 48 | 51 |
| Post Opening | 63 | 59 | 64 | 60 |
A comparison between mean vehicle speeds over the extents of the survey site indicate that speeds in both directions of travel have increased following the opening of the A76(T) Glenairlie project and it can therefore be expected that journey times are likely to have reduced and become more reliable as a result of the provision of the dedicated overtaking opportunities.
Review of Environmental Mitigation Measures
The environmental mitigation measures originally proposed for the A76(T) Glenairlie 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 A76(T) Glenairlie 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 A76(T) Glenairlie 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 A76(T) Glenairlie project 3 years before and 1 year after project completion are shown in Figures A.10b and A.10c.
A summary of the personal injury accident data is shown in Table A.10.6.
Table A.10.6: A76(T) Glenairlie - Personal Injury Accident Data Summary
| Period | Fatal | Serious | Slight | Total Accidents |
|---|---|---|---|---|
| 3 Years Before | ||||
| A76(T) | 1 | 1 | 2 | 4 |
| 1 Year After | ||||
| A76(T) | 0 | 0 | 1 | 1 |
As can be seen in Table A.10.6, one personal injury accident (slight) occurred in the 1 year period following the opening of the project in comparison to four personal injury accidents (one fatal, one serious and two slight) in the 3 years before opening, suggesting a potential improvement in road safety.
Road Safety Audits
Transport Scotland has not yet received a copy of the Stage 4 RSA report for this project.
Safety: Key Findings
An assessment of the 1 year post opening personal injury accidents suggests that the A76(T) Glenairlie project is operating safely.
Figure A.10b A76(T) Glenairlie
Figure A.10c A76(T) Glenairlie
Transport Economic Efficiency
Comparison Between Predicted and Actual Traffic Flows
The comparison between predicted and actual traffic flows, presented in section A.10.2, can be considered a proxy for whether the predicted economic benefits of the project are likely to be realised.
The comparison indicates that the predicted 2010 flow was within 4% of the observed 2010 flow on the A76(T).
Economy: Key Findings
A difference between predicted and actual AADT flows of this magnitude suggests that the economic benefits of the project may be realised.
A.10.6 Accessibility & Social Inclusion
Community Accessibility
Cycle Audits
In accordance with 'Cycling By Design' (1999), a Stage 2 Cycle Audit for the A76(T) Glenairlie project was carried out over the months of September to November in 2005.
An update to the Stage 2 Cycle Audit was carried out in August 2009 due to alignment changes to the cycleway route along the B797 at the northern end of the project.
The Stage 2 audit report notes, but does not confirm, implementation of the following cycling provisions in the A76(T) Glenairlie project:
- Cycle tracks in both verges and utilisation of sections of old road where possible.
Accessibility & Social Inclusion: Key Findings
On site observations have confirmed that a shared cycle and pedestrian facility has been provided that utilises the redundant section of the bypassed A76.
Investment Costs
Comparison Between Predicted and Out-turn Costs
The out-turn and predicted project costs are shown in Table A.10.7.
Table A.10.7: A76(T) Glenairlie - Project Cost Summary
| Out-turn Cost | Predicted Cost | Difference (Out-turn - Pred) | |||
|---|---|---|---|---|---|
| @ April 10 |
Mid-98 Prices in 1998 at 3.5% Discount |
Aug 05 prices |
Mid-98 Prices in 1998 at 3.5% Discount |
Mid-98 Prices in 1998 at 3.5% Discount |
|
| Total | £5,730,530 | £3,125,035 | £4,500,000 | £2,812,183 |
£312,851
(11%) |
Cost to Government: Key Findings
The out-turn cost of the A76(T) Glenairlie project is approximately £0.3m (11%) greater than was predicted at the time of assessment.
Initial Indications
The appraisal results for the A76(T) Glenairlie project predicted a Net Present Value (NPV) of £0.09m and Benefit to Cost Ratio (BCR) of 1.02 under the 60/40 traffic forecast scenario.
Based on the comparisons presented in sections A.10.5 and A.10.7, which suggest that the benefits may realised and indicate that the cost is marginally greater than predicted, the NPV and BCR of the project are unlikely to be as great as predicted.
Value for Money: Key Findings
The NPV and BCR are unlikely to be as great as predicted at the time of assessment, although it is judged that the project will continue to provide a benefit to road users.
A.10.9 Achievement of Objectives
As specific indicators to measure the performance of the A76(T) Glanairlie 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 A76(T) Glenairlie project is progressing towards achieving its objectives, is presented in Table A.10.8.
Table A.10.8: A76(T) Glenairlie - Progress Towards Achieving Objectives
| Objective | Commentary | Progress | |||
|---|---|---|---|---|---|
| Improve and increase the number of overtaking opportunities to reduce the conflicts between long distance users, local and agricultural traffic. | A comparison between the results of the pre and post overtaking surveys indicate that the provision of a dedicated overtaking opportunity has increased overtaking in both directions of travel. | +ve | |||
| Improve the operational performance and level of service on the A76(T) by reducing the effect of driver stress and journey times by constructing guaranteed overtaking sections designed to break up convoys / platoons. |
A comparison between the results of the pre and post overtaking surveys indicate that as a consequence of the increased overtaking in both directions of travel, a greater number of platoons are dispersed. Mean vehicle speeds in both directions of travel have increased following the opening of the A76(T) Glenairlie project and it can be expected that any overall impact on journey times is likely to be positive. |
+ve | |||
| Wherever practicable incorporate measures for non-motorised users. In particular, cycling proposals shall be designed in accordance with the "Trunk Road Cycling Initiative". |
A Cycle Audit was carried out for the project, which noted. cycling provisions. A shared cycle and pedestrian facility, as identified in the Environmental Statement, was provided which utilised the redundant section of the bypassed A76. |
+ve | |||
| Maintain the asset value of the A76(T) route. | Given the nature of the A76(T) Glenairlie project, which involved replacing 2.9 kilometres of existing single carriageway with 2.5 kilometres of off-line wide single 2+1 carriageway and 500m of on-line improvements, the asset value of the A76(T) between the project tie-in points is likely to have increased thus maintaining the value of the route. | +ve | |||
| Mitigate the environmental impact of the new works where possible. | The majority of measures committed within the Environmental Statement are in place. Whilst some variations from the proposed mitigation measures have been identified, these are not considered to have had a material detrimental impact on the general integration of the project into its surrounding. | +ve | |||
| Achieve good value for money for both taxpayers and road users. | Although the NPV and BCR are unlikely to be as great as predicted at the time of assessment, it is judged that the Glenairlie project will continue to provide a benefit to road users. | = | |||
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