3 Initial 1YA Evaluation - A75(T) Cairntop To Barlae
3 Initial 1YA Evaluation - A75(T) Cairntop To Barlae
The A75(T) is approximately 159km in length, and is located in Dumfries and Galloway. It is an important transportation corridor in the south-west of Scotland, linking the A74(M) with the port at Loch Ryan.
The project involved the construction of approximately 2.4 kilometres of off-line dual carriageway, extending from west of Derskelpin Farm to west of the Barlae Burn, approximately 5km to the east of Glenluce and 14km to the west of Newton Stewart.
The project utilised the existing A75(T) as the westbound carriageway and a new eastbound carriageway was constructed to the north of the existing A75(T), utilising a disused railway line corridor. The distance between the eastbound and westbound carriageways varies between 20 and 60 metres.
Due to the risks of soft ground conditions associated with improvements to the existing A75(T) carriageway, an initially preferred option of on-line widening was not carried out. The final scheme included a section of off-line widening.
The general location of the project is shown in Figure 3.1.
The A75(T) Cairntop to Barlae project was officially opened to traffic in October 2010, some two months ahead of schedule. However, the preparation of the scheme was initially delayed by early changes to the economic analysis methodology, which involved additional traffic modelling to better reflect traffic movements on the route.
The final scheme involved a departure from Design Standards for dual carriageway schemes, which was approved by the Transport Scotland Standards Branch.
Rationale and mandate for the scheme
The project was implemented as part of a wider Route Action Plan for the A75(T) including a number of other overtaking projects on the A75(T) which have been reported within previous evaluation reports.
In combination with other overtaking projects on the A75(T), the A75(T) Cairntop to Barlae scheme was targeted principally to break up platoons of vehicles which form when ferries unload at the ports associated with the Irish Sea Ferry operations.
Approval to proceed with the scheme was made by Transport Scotland in June 2004.
The objectives of the A75(T) Cairntop to Barlae project were set as follows:
- to improve operational performance and level of service and safety on the A75 by reducing the effects of driver stress and journey times by constructing guaranteed overtaking sections to break up convoys;
- to improve and increase the number of overtaking opportunities to eradicate the conflicts between long distance users and local / agricultural traffic;
- the construction of medium term on-line overtaking sections; carriageway widening; rationalisation of side road junctions and alignment improvements to bends;
- the incorporation of the needs of pedestrians and cyclists;
- to maintain the asset value of the A75; and
- to achieve good value for money for both tax payers and transport users.
3.2 Evaluation Methodology
As set out in Section 1.1, this One Year After report presents the results of a One Year Evaluation of the A75(T) Cairntop to Barlae project, focusing on:
- The operation of the scheme: how the scheme is operating (in terms of traffic and safety in particular); and
- Objectives: whether the scheme is on-track to achieving its objectives.
This evaluation was supported by a site visit carried out on Thursday 30th January 2013. Internal to Transport Scotland, stakeholder views were sought from the Construction Project Manager. External stakeholder views were invited from Dumfries and Galloway Council, the Road Haulage Association, and Stena Line. Where received, these are presented throughout the report.
The evaluation is supported by the consideration of pre and post opening comparison of operational indicators, which focuses on network traffic indicators including traffic volumes and travel times, presented in the following section.
The locations of the Automatic Traffic Counters (ATC) within the study area are shown in Figure 3.2.
Comparison Between Pre and Post Opening Traffic Flows
The Annual Average Daily Traffic (AADT) flows pre and post project opening on the A75(T) route within the vicinity of the project are presented in Table 3.1.
A comparison between pre and post opening traffic volumes on the A75(T) to both the east and west of the scheme indicates that traffic flows have been reducing on this route for several years. Traffic flows in 2012 were broadly consistent with 2011 traffic flow levels.
Given the nature of the A75(T) Cairntop to Barlae 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. Moreover, a review of changes in traffic levels at other points on the A75 suggests a general decline in traffic volumes on this route since 2007, which is consistent with national trends.
Comparison Between Predicted and Actual Traffic Flows
The opening year flow comparisons for the A75(T) Cairntop to Barlae project are based on AADT flows from 2011 as this was the first full year of reliable traffic data available from Transport Scotland’s traffic counters within the vicinity of the project.
As part of the project’s appraisal, National Road Traffic Forecasts (NRTF) low and high traffic growth factors were applied to the 2003 base year traffic flows to derive opening and future modelled assessment year traffic flows.
Predicted traffic flows for 2011 have been derived by interpolating between the modelled assessment year design network flows.
A summary of the actual and predicted traffic data is shown in Table 3.2 below.
* 2011 flows (first full year of ATC data available)
The comparison between predicted and actual AADT flows in Table 3.2 indicates that the predicted 2011 flow (derived by interpolating between the modelled assessment year traffic flows) was 24% and 31% greater than the observed 2011 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 2.2% between 2003 and 2011 may also have contributed to observed flows being lower than forecast.
Pre-opening overtaking surveys were not carried out for this scheme, therefore, post-opening overtaking surveys have not been carried out in the absence of a comparable baseline.
However, it is reasonable to assume that, due to the nature of the improvement, (a single 2-lane carriageway upgraded to a dual 2-lane carriageway), the number of unambiguous overtaking opportunities will have increased in both directions of travel as a direct result of the project.
Comparison Between Pre and Post Opening Journey Times
Pre-opening journey time surveys were carried out for the A75(T) Cairntop to Barlae project in 2003 to validate the traffic model used in the assessment of the project. Post opening journey time surveys were carried out in March 2013 to provide an indication of the changes in average journey times along the A75(T) between Cairntop and Barlae.
The average pre and post opening journey times along with the savings in travel time are shown in Table 3.3 below.
The extents of the journey time survey route are shown in Figure 3.3.
Examination of the pre and post opening journey times, presented in Table 3.3, indicates that the directional journey times recorded within each peak period are broadly comparable (within 6 seconds pre opening and 14 seconds post opening) suggesting that there are no issues relating to congestion within the extents of the survey site.
Comparison Between Predicted and Actual Travel Times
The available predicted 2023 journey times have been compared with the post opening journey times collected in March 2013. While there is a significant period (ten years) between the available predicted and actual journey times, the predicted flow in 2023 is well below the capacity of the A75(T) at this location, which suggests that predicted journey times are unlikely to vary significantly between the 2010 opening year and 2023.
A comparison between the available predicted and actual journey times indicates a saving of 12 seconds in 2023 in both directions of travel following the opening of the scheme. This is in comparison to actual savings of between 43 and 46 seconds in the eastbound direction of travel and between 34 and 54 seconds in the westbound direction of travel derived from the observed journey times.
The following section provides a summary of the assessment of environmental mitigation measures proposed for the A75(T) Cairntop to Barlae scheme. A fuller report is provided in Appendix B.
Review of Environmental Mitigation Measures
The environmental mitigation measures originally proposed for the A75 Cairntop to Barlae were obtained from the project’s Environmental Statement (ES). A review of the environmental mitigation measures was carried out in January 2013, as well as a review of the as-built scheme plans. Following this review a site visit was undertaken to establish whether or not the proposed mitigation measures as set out in the Schedule of Committed Mitigation within the ES had been implemented.
The ES for the scheme proposed mitigation measures to address impacts under the following criteria:
- Water Quality, Drainage and Flood Defence
- Biodiversity and Habitats
- Visual Amenity
- Agriculture and Soils
- Physical Fitness
The proposed scheme was not considered to generate any additional traffic, and therefore no issues were identified in relation to noise and vibration, global and local air quality.
Much of the mitigation which was included within the ES has been implemented on site; however, the site inspection did highlight some issues related to the drainage of the area, which has associated impacts upon the movement of protected species. This issue is creating a barrier to the movement of mammals across the road corridor.
The A75 Cairntop to Barlae scheme fits well within the existing landscape and the effective grading the central peat bunding and the wider embankment slopes integrates the scheme into the topography of the area. The planting of native species to supplement the existing woodland planting in the area further strengthens the integration of the scheme in to the wider landscape setting.
Environment: Key Findings
Much of the mitigation which was included within the ES has been implemented on site.
The site inspection highlighted some issues related to the drainage of the area, which has associated impacts upon the movement of protected species. This issue is creating a barrier to the movement of mammals across the road corridor, and needs to be addressed.
This issue has been brought to the attention of the Contractor for the scheme by the Engineer.
Comparison Between Pre and Post Opening Personal Injury Accident Numbers
A summary of the personal injury accident data is shown in Table 3.4.
|3 Years Before|
|1 Year After|
As can be seen from Table 3.4, 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.
Road Safety Audits
The RSA process has been followed, with Stage 1, 2, 3 and 4 Audits carried out. The Stage 4 Audit, undertaken in June 2013, confirmed that no accidents had occurred within the vicinity of the scheme in the 1 year period following the opening of the project and indicated that no conclusions can be drawn that would suggest road safety deficiencies in the scheme. A number of issues were raised as part of the Stage 3 Audit, dated October 2010, with recommendations for implementation. The outstanding issues raised as part of the Stage 3 Audit were addressed within the Stage 4 Audit.
Safety: Key Findings
An assessment of the 1 year post opening personal injury accidents and the findings from the Stage 4 RSA suggests that the A75(T) Cairntop to Barlae project is operating safely.
The Stage 4 RSA recommends that the performance and operation of the scheme should continue to be monitored.
Transport Economic Efficiency
The comparisons between predicted and actual traffic flows and travel times, presented in section 3.3, can be considered a proxy for whether the predicted economic benefits of the project are likely to be realised.
Comparison Between Predicted and Actual Traffic Flows
The comparison indicates that the predicted 2011 flows were up to 31% greater than the observed 2011 flows on the A75(T) within the vicinity of Cairntop to Barlae. This overestimation is likely due to the combination of changes in Irish Sea Ferry operations and general economic downturn.
Comparison Between Predicted and Actual Travel Times
The comparison of predicted and actual travel times indicates that the predicted journey time savings are approximately 20 to 40 seconds less than the observed journey time savings.
Stena Line offered feedback on the scheme for the purposes of this Evaluation report. Stena stated that the A75(T) Cairntop to Barlae scheme was designed with the prospect of increased traffic flows serving the new port at Loch Ryan in mind. In their view, the scheme has indeed benefitted traffic leaving the ports, as it allows passing opportunities for car traffic in particular which are discharged from ferries behind freight vehicles.
Specifically, Stena Line have also stated “Without this scheme there could be substantial delay in journey times from the ports as there are very few alternative, safe opportunities further along the route and, of course, there is a 40mph limit for freight vehicles on the route. The idea is to reduce driver frustration and make the A75 safer.”
Economy: Key Findings
While actual journey time savings are likely to be greater than predicted, a difference between predicted and actual AADT flows of this magnitude suggests that, should current trends in traffic volumes continue, the economic benefits of the project may have been overestimated in the short-term. However, this is likely due to external factors that could not have readily been foreseen at the time of assessment (the economic downturn and resulting decline in traffic flows).
3.7 Accessibility & Social Inclusion
A 1.5m shared cycleway and footway was designed into the A75(T) Cairntop to Barlae scheme, on the basis of low traffic and cyclist flows (average of 6 cyclists per 12 hour day from traffic count data) and adjacent grass verges. This dedicated track was provided along the length of the improvement with crossing points provided at specific locations.
A Stage 2 Cycling Audit was carried out for this scheme in March 2010, reporting on the facilities proposed for pedestrians and cyclists. The Cycling Audit records that “Dumfries & Galloway Council, the Cyclists Touring Club, Sustrans, and the Chief Constable were all consulted. Local disabled and blind groups were not consulted as given the remote and rural nature of the site they were not considered to be ‘interested user groups’”. A DDA Audit was not undertaken for these reasons.
The Audit also highlighted the lack of adjacent communities to the scheme, and concluded that commuter cyclists were unlikely to use the pathway given its rural and remote location.
During the environmental mitigation measures review (one day site visit), it was observed that no cyclists and / or pedestrians were present on site and that the shared footway and cycleway and associated crossing points were not used. No evidence has been identified to confirm whether there has been a change in the levels of use of this route by active travel users.
Accessibility & Social Inclusion: Key Findings
A new shared cycleway and footway and associated crossing points have been implemented as part of the project. This is in line with Transport Scotland commitments to improve facilities on the trunk road network for active travel users.
A review of policy was carried out for the Environmental Assessment of the scheme, as reported in the Environmental Statement (2006). It identified one policy conflict with the Dumfries and Galloway General Local Plan Policy 63: Safeguarding Former Rail Transport Routes. The scheme uses a section of a former, now dismantled, railway line, and therefore renders this route unavailable for potential future redevelopment.
Integration: Key Findings
An assessment of policy integration was carried out in the planning and preparation for the scheme. One policy conflict was identified, in that the scheme would prevent any future redevelopment of an existing (un-used) railway line. However, this was taken into account in the decision-making process.
3.9 Cost to Government
Comparison Between Predicted and Out-turn Costs
The out-turn and predicted project costs are shown in Table 3.5.
Cost to Government: Key Findings
The out-turn cost of the A75(T) Cairntop to Barlae project is approximately £0.9m (16%) lower than was predicted at the time of assessment.
3.10 Value for Money
The economic appraisal results for the A75(T) Cairntop to Barlae project predicted a Net Present Value (NPV) of £0.03m and Benefit to Cost Ratio (BCR) of 1.00 under the 60/40 traffic forecast scenario.
The comparisons presented in sections 3.3 and 3.6 suggest that the traffic flows have been overestimated, whilst journey time benefits may have been underestimated. Furthermore, the out-turn cost is less than predicted. Therefore, NPV and BCR of the project may be greater than predicted.
Value for Money: Key Findings
It is judged that the project will continue to provide a benefit to road users and the NPV and BCR may be greater than predicted at the time of assessment.
3.11 Working towards achievement of objectives
As specific indicators to measure the performance of the A75(T) Cairntop to Barlae 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.
A summary of the evaluation, providing an indication of how the A75(T) Cairntop to Barlae project is progressing towards achieving its objectives, is presented in Table 3.6.