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 approximately 1.0 kilometre of off-line wide single carriageway (WS2) in addition to approximately 250 metres of on-line improvement.
The general location of the project is shown in Figure A.9a.
The A77(T) Glen App project was officially opened to traffic on 22nd December 2008.
Project Objectives
The objectives of the A77(T) Glen App project were set as follows:
- to improve and increase the number of overtaking opportunities to eradicate the conflicts between long distance users and local / agricultural traffic;
- to improve the operational performance and level of services and safety on the A77(T) by reducing the effects of driver stress and journey times by constructing dedicated overtaking sections designed to break up the effects of convoys / platoons;
- to maintain the asset value of the A77(T) route;
- to mitigate the environmental impact of the new works where possible; and
- to achieve good value for money for both taxpayers and transport users.
Evaluation Methodology
The A77(T) Glen App project has been evaluated against the above objectives and the following criteria:
- Environment;
- Safety;
- Economy;
- Costs to Government; and
- Value for Money.
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.9.2 Network Traffic Indicators
Traffic Volumes
The location of the Automatic Traffic Counter (ATC) within the study area is shown in Figure A.9a.
Comparison Between Pre and Post Opening Traffic Flows
The Annual Average Daily Traffic (AADT) flows pre and post project opening on the A77(T) within the study area are presented in Table A.9.1.
Table A.9.1: A77(T) Glen App - ATC Data
| ATC Reference | AADT by Year | ||||||
|---|---|---|---|---|---|---|---|
| 2005 | 2006 | 2007 | 2008 | 2009 | 2010 | 2011 | |
| A77(T) at Auchencrosh | |||||||
| ATC08527 | 3,196 | 3,205 | 3,164 | Year of Opening | 3,079 | 3,113 | 3,066 |
A comparison between pre and post opening traffic volumes on the A77(T) at Auchencrosh indicates that traffic flows in 2009 were around 100 vehicles per day (vpd) (4%) lower than 2005 flow levels. Traffic volumes between 2009 and 2011 were broadly consistent.
Given the nature of the A77(T) Glen App project, changes in traffic levels 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 A77(T) Glen App project is 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 2004 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.9.2 below.
Table A.9.2: A77(T) Glen App - Traffic Analysis Summary
|
ATC Ref |
Actual AADT* | Predicted AADT |
% Difference (Predicted - Actual) / Actual |
||||
|---|---|---|---|---|---|---|---|
| Low | 60/40 | High | Low | 60/40 | High | ||
| A77(T) at Auchencrosh | |||||||
| ATC08527 | 3,079 | 3,481 | 3,523 | 3,586 | 13.0% | 14.4% | 16.5% |
* 2009 flows (first full year of ATC data available)
The comparison between predicted and actual AADT flows in Table A.9.2 indicates that the predicted 2009 flow (derived by interpolating between the modelled assessment year traffic flows) was 13% and 17% greater than the observed 2009 flows under low and high traffic forecast scenarios respectively.
Whilst this comparison indicates that traffic growth on the A77(T) has fallen short of the assumed NRTF forecasts, the difference is within accepted limits. 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 2004 coupled with an overall reduction in the total number of cars using the ferry services of approximately 11.5% between 2004 and 2009 (Ref. Scottish Transport Statistics No 29: 2010 Edition), which may also have resulted in a redistribution of traffic and also have contributed to observed flows being lower than forecast.
Carriageway Standard Assessment
In order to satisfy the project objectives, a wide single 2-lane carriageway was constructed on the A77(T) at Glen App as part of a series of improvements along the route, providing increased 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.9.3 based on the observed 2009 traffic flow.
Table A.9.3: A77(T) Glen App - Assessment of Carriageway Standard (TA 46/97)
| Opening Year AADT* | TA 46/97 Standard | Constructed Standard |
|---|---|---|
| 3,079 | Single 2-Lane |
Wide Single 2-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. Given the project objectives and the nature of traffic on the route, the constructed carriageway standard is considered appropriate.
Overtaking Opportunities
Comparison Between Pre and Post Opening Overtaking Opportunities
A post opening overtaking survey was undertaken on the A77(T) in November 2011 to provide an indication of conditions at Glen App.
The results from the post opening survey were compared against the results from a pre opening survey undertaken in March 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.9.4 below.
Table A.9.4: A77(T) Glen App - Level of Overtaking
| AM Survey Period | PM Survey Period | |||
|---|---|---|---|---|
| Northbound | Southbound | Northbound | Southbound | |
| Pre Opening | 20% | 14% | 20% | 19% |
| Post Opening | 26% | 20% | 17% | 21% |
The percentage of northbound vehicles that carried out an overtaking manoeuvre during both the pre opening AM and PM survey periods was 20%, which can be compared to 26% and 17% respectively during the post opening survey. The comparison indicates that the level of northbound overtaking has reduced during the PM period. This could be as a result of the higher opposing traffic flows on the route during the post opening PM survey period when compared with the pre opening survey, which may present fewer opportunities for northbound vehicles to carry out an overtaking manoeuvre.
In the southbound direction, 14% and 19% 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 20% and 21% respectively during the post opening survey. This suggests that the A77(T) Glen App 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.9.5.
Table A.9.5: A77(T) Glen App - Assessment of Mean Vehicle Speeds (mph)
| AM Survey Period | PM Survey Period | |||
|---|---|---|---|---|
| Northbound | Southbound | Northbound | Southbound | |
| Pre Opening | 56 | 53 | 58 | 51 |
| Post Opening | 56 | 50 | 56 | 50 |
The comparison between mean vehicle speeds over the extents of the survey site indicate that speeds in both directions of travel have not been significantly affected by the A77(T) Glen App project.
Review of Environmental Mitigation Measures
The environmental mitigation measures originally proposed for the A77(T) Glen App 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 A77(T) Glen App project and its limited effect on mean vehicle speeds, 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 A77(T) Glen App 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 A77(T) Glen App project 3 years before and 1 year after project completion are shown in Figures A.9b and A.9c.
A summary of the personal injury accident data is shown in Table A.9.6.
Table A.9.6: A77(T) Glen App - Personal Injury Accident Data Summary
| Period | Fatal | Serious | Slight | Total Accidents |
|---|---|---|---|---|
| 3 Years Before | ||||
| A77(T) | 0 | 0 | 0 | 0 |
| 1 Year After | ||||
| A77(T) | 0 | 0 | 1 | 1 |
As can be seen from Table A.9.6, one personal injury accident (slight) occurred in the 1 year period following the opening of the project in comparison to no personal injury accidents in the 3 years before opening.
Road Safety Audits
The Stage 4 Road Safety Audit (RSA) was carried out in October 2010. The RSA report confirmed that only one personal injury accident (slight) occurred in the 1 year period following the opening of the project and involved a collision between three vehicles.
The RSA report noted that the driver of the first vehicle lost control and swerved across both lanes of the carriageway then struck the rear of the second vehicle. The first vehicle then crossed the centre line markings and collided with the third vehicle.
The RSA report concluded that the action of overtaking does not appear to have contributed to the cause of the slight accident, and that no firm conclusions can be drawn from the accident information provided which would suggest road safety deficiencies in 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 A77(T) Glen App project is operating safely.
Transport Economic Efficiency
Comparison Between Predicted and Actual Traffic Flows
The A77(T) Haggstone and A77(T) Glen App 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 comparison between predicted and actual traffic flows, presented in sections A.8.2 and A.9.2, 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 flow was up to 17% greater than the observed 2009 flow on the A77(T). 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 A77(T) Haggstone and Glen App 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 both A77(T) projects are shown in Table A.9.7. This confirms that the out-turn cost of the two A77(T) projects was approximately £3.2m (22%) lower than the predicted cost.
Table A.9.7: A77(T) Haggstone & Glen App - Project Cost Summary
| Out-turn Cost | Predicted Cost | Difference (Out-turn - Pred) | |||
|---|---|---|---|---|---|
| @ April 10 |
Mid-98 Prices in 1998 at 3.5% Discount |
June 07 Prices |
Mid-98 Prices in 1998 at 3.5% Discount |
Mid-98 Prices in 1998 at 3.5% Discount |
|
| Total | £20,758,541 | £11,486,943 | £26,129,190 | £14,736,160 |
-£3,249,257
(22%) |
Cost to Government: Key Findings
The combined out-turn cost of the two A77(T) projects is approximately £3.2m (22%) lower than predicted.
Initial Indications
The economic appraisal results predicted a combined Net Present Value (NPV) of -£9.69m and Benefit to Cost Ratio (BCR) of 0.54 under the 60/40 traffic forecast scenario.
Based on the comparisons presented in sections A.9.5 and A.9.6, which suggest that the benefits will have been overestimated and indicate that the cost is lower than predicted, the NPV and BCR of the combined projects are unlikely to be greater than predicted.
Value for Money: Key Findings
The NPV and BCR of the combined A77(T) projects are unlikely to be significantly greater than predicted at the time of assessment, although it is judged that the projects will continue to provide a benefit to road users and will help encourage economic development within south west Scotland and beyond.
A.9.8 Achievement of Objectives
As specific indicators to measure the performance of the A77(T) Glen App 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 A77(T) Glen App project is progressing towards achieving its objectives, is presented in Table A.9.8.
Table A.9.8: A77(T) Glen App - Progress Towards Achieving Objectives
| Objective | Commentary | Progress | |||
|---|---|---|---|---|---|
| Improve and increase the number of overtaking opportunities to eradicate the conflicts between long distance users and local / agricultural traffic. | A comparison between the results of the pre and post overtaking surveys indicate that the provision of the improved carriageway standard has, generally, increased overtaking in both directions of travel. | +ve | |||
| Improve the operational performance and level of services and safety on the A77(T) by reducing the effects of driver stress and journey times by constructing dedicated overtaking sections designed to break up the effects of convoys / platoons. |
Although mean vehicle speeds in both directions of travel have not been significantly affected by the A77(T) Glen App project,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. An assessment of the 1 year post opening personal injury accidents and a review of the Stage 4 RSA report, suggests that the A77(T) Glen App project is operating safely. |
+ve | |||
| Maintain the asset value of the A77(T) route. | Given the nature of the A77(T) Glen App project, which involved replacing 1.5 kilometres of existing single carriageway with 1.0 kilometre of off-line wide single carriageway and 250m of on-line improvements, the asset value of the A77(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 transport users. | Although the NPV and BCR are unlikely to be greater than predicted at the time of assessment, the Haggstone and Glen App projects form part of a series of improvements along the A77(T) corridor that can be expected to provide benefits to transport users and help encourage economic development within south west Scotland and beyond. | = | |||
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