Transport Scotland Scottish Trunk Road Infrastructure Project Evaluation - 1YA Evaluation Report for A77(T) Park End to Bennane
A Methodology and Data Sources
A.1 OVERVIEW
The project presented in this report has been evaluated against its objectives and the following criteria, to support the evaluation:
- Environment;
- Safety;
- Economy;
- Costs to Government; and
- Value for Money.
As the evaluation focuses on impacts relating to the project’s objectives, evaluations against all of the criteria set out within STRIPE may not be undertaken for all projects. In this evaluation of the A77(T) Park End to Bennane, no assessment has been carried out against the criteria of Integration, Accessibility and Social Inclusion, as the scheme did not have any transport planning objectives related to these criteria.
The evaluation is supported by the consideration of network traffic indicators, including traffic volumes, overtaking opportunities and travel speeds (as a proxy for travel times), as presented in the following section.
A.2 NETWORK TRAFFIC INDICATORS
Traffic Volumes
Comparison Between Pre and Post Opening Traffic Flows
A comparison of traffic flows pre and post opening has been undertaken for the project to provide an indication of the impact that the project has had on traffic volumes. The amount of traffic data presented is dependent upon the complexity of the project. The comparison can also serve as a proxy for the effect that the project has had on noise and air quality.
Comparison Between Predicted and Actual Traffic Flows
A comparison of predicted and actual opening year traffic flows has been undertaken for the project to confirm the accuracy of predictions during the project’s preparation. The comparison can also serve as a proxy for whether the predicted benefits of the project are likely to be realised.
Depending on the nature of the traffic modelling undertaken to assess the project, the predicted traffic flow is either derived by:
- factoring the base year or the predicted opening year, design network flows to the actual opening year using National Road Traffic Forecast (NRTF) growth factors; or
- extrapolating from, or interpolating between, the modelled assessment year, design network flows.
The difference between the actual traffic flow and the predictions has been calculated and expressed as a percentage of the actual flow. A threshold of +/-20% is generally accepted by Transport Scotland as being a reasonable range for future year forecast traffic flow comparisons.
The amount of traffic data presented is dependent upon the complexity of the project. The comparison can also serve as a proxy for the likely impact of the project on noise and air quality.
| Predicted Traffic Flows | Obtained/derived from the traffic/economic modelling undertaken to support the pre-tender economic assessment. |
| Actual Traffic Flows | Obtained from automatic traffic counters in the vicinity of the project/study area. |
Overtaking Opportunities
Pre and Post Opening Overtaking Opportunities
Both pre and post-opening overtaking surveys were carried out on this scheme. The pre-opening surveys informed the scheme assessment, whilst the postopening surveys were commissioned by Transport Scotland to inform postopening evaluation and an overall assessment of the performance of WS2+1 schemes in Scotland.
Temporary roadworks were present on site to the north of Ballantrae on the day of the pre opening survey which comprised a section of temporary shuttleworking controlled by traffic signals and it is considered that the results of the pre opening survey for the Park End to Bennane scheme are not representative of typical operating conditions.
As such, it is difficult to draw any firm conclusions from the comparison of the level of overtaking manoeuvres carried out during the pre and post opening surveys.
Pre and Post Opening Platooning levels
For this scheme, data on pre and post opening platooning levels was available, and has been reported in this evaluation.
Temporary roadworks were present on site to the north of Ballantrae on the day of the pre opening survey which comprised a section of temporary shuttleworking controlled by traffic signals and it is considered that the results of the pre opening survey for the Park End to Bennane scheme are not representative of typical operating conditions.
As such, it is difficult to draw any firm conclusions from the comparison of the number of platoons occurring during the pre and post opening surveys.
Anecdotal, qualitative evidence from stakeholders has also been gathered, where available.
| Pre and Post Opening Overtaking Conditions and Platooning levels | Judged from pre and post opening survey information for this scheme. |
| Stakeholder Feedback | Obtained from South Ayrshire Council and Stena Line. |
Travel Times
Change in Travel Times
Based on the evaluation of other projects with a comparable standard of carriageway for which pre and post opening journey time data is available, supported by anecdotal evidence where available.
Comparison Between Pre and Post Opening Travel Times
A comparison between pre and post opening travel times has been not been carried out for this scheme as data was not available. However, pre and postopening speed data has been used as a proxy for this analysis, the assumption being higher speeds may result in shorter journey times.
Comparison Between Predicted and Actual Travel Times
A comparison between predicted and actual travel times has not been carried out for this scheme as predicted and post opening travel time information was not readily available.
| Pre and Post Opening Travel Times | Proxy indicator of traffic speed confirmed through pre and post opening survey information collected to support the project’s economic assessment. |
| Stakeholder Feedback | Obtained from Stena Line Ltd and South Ayrshire Council. |
A.3 ENVIRONMENTAL
Mitigation Measures
A review of the environmental mitigation measures implemented during construction has been undertaken for the project to establish whether or not the measures proposed during the project’s preparation have been introduced and to provide comment on their success. The mitigation measures implemented were confirmed through site visits.
| Proposed Mitigation Measures | Presented in the Environmental Statement produced during the project’s preparation. |
| Implemented Mitigation Measures | Confirmed through site visit. |
Noise and Air Quality
A review of noise and air quality has not been undertaken for the project as no significant impacts on noise and air quality were expected.
A.4 SAFETY
Accidents
Comparison Between Pre and Post Opening Personal Injury Accident Numbers
A comparison of the personal injury accident numbers pre and post opening has been undertaken for the project to provide an early indication of whether the project is operating safely.
The number of personal injury accidents for the 3 years within the vicinity of the project prior to opening has been compared with the observed number of personal injury accidents for the project in its first year of operation. The comparison shall be updated to include the observed number of accidents in the three year period after opening when the accident data is available.
It is important to realise that road infrastructure projects normally take a minimum of 5 to 7 years to plan prior to the commencement of construction. Many proposed road projects are derived from safety concerns such as fatal and serious accidents and often, these are treated in terms of Accident Investigation and Prevention work prior to planning the permanent solution. The comparison between 3 year pre and post opening accidents, therefore, only demonstrate the minimum road safety improvement derived from the project.
Where the influence of a trunk road improvement project has a significant impact on the local road network, it may be appropriate to extend the scope of the accident analysis.
Road Safety Audits
Road Safety Audit (RSA) reports have been reviewed for the project, where available, to confirm whether there is any evidence that the project is not operating safely and where recommendations have been made for ameliorative measures, if appropriate.
| Personal Injury Accident Numbers | Obtained from the STATS19 data collection system. |
| Safety Issues | Detailed within RSA reports produced following audits carried out 1 year after project opening. |
A.5 ECONOMY
Transport Economic Efficiency
A comparison between predicted and actual traffic flows and/or travel times has been undertaken for the project as a proxy for whether the predicted benefits of the project are likely to be realised.
A comparison which returns a positive traffic flow difference in an uncongested situation indicates that the economic benefits of the project may have been over predicted as fewer vehicles will actually accrue journey time savings than predicted. Similarly, the economic benefits of a project may also be over predicted where actual travel times are greater (i.e. speeds lower) than predicted.
Conversely, where the comparison returns a negative traffic flow difference or actual travel times are less (i.e. speeds higher) than predicted, the economic benefits of the project may have been under predicted.
Commentary on the impact of the project on local economic development has been provided where anecdotal feedback is available.
| Stakeholder Feedback | Obtained from Stena Line. |
A.6 INTEGRATION
Commentary on Transport Integration and Policy Integration is provided for projects that have specific objectives relating to the Integration criterion. In this instance, no scheme objectives related to integration and this criteria has therefore not been assessed.
A.7 ACCESSIBILITY & SOCIAL INCLUSION
Commentary on Community Accessibility is provided for projects that have specific objectives relating to the Accessibility & Social Inclusion criterion. However, in this instance, no scheme objectives related to Accessibility and Social Inclusion, and this criteria has therefore not been assessed.
A.8 COSTS TO GOVERNMENT
Investment Costs
Comparison Between Predicted and Out-turn Costs
A comparison between predicted and out-turn costs has been undertaken for the project to confirm the accuracy of predictions during the pre-tender stage and support the evaluation of value for money.
The project cost predicted during the pre-tender stage has been used in the evaluation as it is at this stage that the decision is taken on whether or not to proceed with the project.
One of the features of the progressive analysis of projects is that the economic assessment is undertaken at each stage based on the return on future investment. This means that project costs incurred prior to the pre-tender economic assessment, which are already spent and cannot be recovered (whether or not the project goes ahead) are excluded from the overall project costs input to the economic assessment. As such, only out-turn costs incurred after the pre-tender economic assessment have been included in the comparison.
Adjustments for Retail Price Indices and discount rates to both the predicted and out-turn costs have been made, taking expenditure by year into account, to convert the figures to a common ‘present value year’ for prices and values – either 1998 or 2002 depending on the ‘present value year’ used in the pre-tender economic assessment.
| Predicted Project Costs | Obtained from the pre-tender economic assessment undertaken during the project’s preparation. |
| Out-turn Costs | Obtained from out-turn cost records. |
A.9 VALUE FOR MONEY
Initial Indications
Based on the evaluation of economic benefits and project costs outlined in Sections 3.6 and 3.7 respectively, a judgement in terms of the potential impact on the projects’ value for money has been made.
The value for money of a project is considered to be greater than predicted where the economic benefits have been under predicted and/or the project costs over predicted. Conversely, the value for money of a project is considered to be lower than predicted where the economic benefits have been over predicted and/or the project costs under predicted.
Where both the economic benefits and project cost have been under predicted or over predicted, a judgement has been made with regards to the likely overall impact on value for money.
| Predicted NPV and BCR | Obtained from the pre-tender economic assessment undertaken during the project’s preparation. |
A.10 ACHIEVEMENT OF OBJECTIVES
Initial Indications
The evaluation includes an indication of how the project is progressing towards achieving its objectives. Where specific indicators to measure the project’s performance against its objectives have not been developed, an 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.
| Objectives | Confirmed from reported Environmental Statements or Route Action Plan, where applicable. |