Transport Scotland Trunk Road Project Evaluation - Report for Trunk Road Projects Opened between April 05 and March 07
4 Evaluation Summary
The Evaluation Report for Trunk Road Projects Opened between April 05 and March 07 is the first evaluation report issued by Transport Scotland for projects that the agency took responsibility for following its creation in January 2006.
The following is a summary of the evaluations undertaken.
Traffic Analysis
For those projects where it was possible to carry out a comparison of the forecast opening year flows against the observed opening year flows (or nearest year to opening), the majority of comparisons are reasonably close and nearly all are within the National Audit Office's threshold of +/-20%. This would suggest that the traffic modelling techniques, and the use of NRTF growth forecasts to predict opening year flows for these projects, were generally appropriate.
The one notable exception to this, however, is the A80 Auchenkilns Junction Improvement project.
From Table 3.2a it can be seen that the predicted flows for the A80 Auchenkilns Junction Improvement project are between 25% and 26% higher than the observed opening year flows.
Whilst there can be a number of possible explanations for variations between observed and forecast flows, the reason(s) for the difference is not clear.
Carriageway Standards
Although the implied carriageway standards generally match the standards constructed, the exception within this report is the A96 Coachford project.
For the A96 Coachford project, the carriageway assessment, using TA 46/97, suggests that both the observed and forecast flows warrant either an Single 2-Lane or a Wide Single 2-Lane standard of carriageway.
Although there are no specific flow ranges for the justification of a Climbing Lane given in TA 46/97, the Climbing Lane at Coachford forms part of a series of improvements along the A96 corridor that provide overtaking opportunities to help reduce platooning and to improve journey times and reliability.
Project Costs
Of the three cost comparisons presented in this report, the A90 Glendoick and Kinfauns Interchange projects have a combined actual out-turn cost significantly higher than the estimated cost.
For the A90 Glendoick & Kinfauns Interchange projects, the combined out-turn cost is +21% higher than the estimated cost, which represents an actual overspend of £2,041,825 (expressed in mid 1998 prices and values discounted to 1998 at 3.5%).
Whilst an increase of this magnitude impacts upon the overall economic appraisal of the projects, a review of the pre-tender estimate suggests that the combined projects would continue to represent value for money.
Accidents
For the majority of the projects examined in this report, the accidents recorded in the 3 years after opening are lower than those recorded during the 3 years before opening.
Whilst there has been a general reduction in accident numbers, there appears to have been a slight increase in the severity of accidents on the A80 Auchenkilns Junction Improvement and A90 Glendoick Interchange projects.
A review of the accident data for the A80 Auchenkilns Junction Improvement and A90 Glendoick Interchange projects suggest that the serious accidents that occurred in the 3 year period after opening were not attributable to the design or layout of the projects.
Stage 4 and 5 RSA reports are not currently available for the projects examined in this report. Transport Scotland is currently reviewing the RSA management process to ensure that Stage 4 and 5 reports are available for future projects.
Environmental Mitigation Measures
The environmental mitigation measures contained in the environmental reports produced at the time the M77 Fenwick to Malletsheugh project was originally assessed were examined and compared against the actual measures put in place.
The review of mitigation measures associated with the M77 Fenwick to Malletsheugh project confirmed that the majority of the proposed mitigation measures presented within the Environmental Statement were delivered and that variations had not resulted in a material detrimental impact on the general integration of the project into its surroundings.
There were some mitigation measures that were not evident on site and Transport Scotland is considering how the environmental review process can be improved to provide a better record of the mitigation measures that have been implemented, including details of any agreed variations.
- Overall, the evaluations undertaken for trunk road projects that opened between April 05 and March 07 indicate that the projects are operating as expected.
- Whilst there appears to be a bias towards the under prediction of traffic flows for projects that opened between April 05 and March 07, forecast flows are (with one exception) within acceptable limits, which suggests that the forecasting techniques used for appraising projects are generally suitable.
- The standards of carriageway constructed are appropriate.
- Although there is some variability between the estimated and out-turn costs for projects, which can be expected, there does not appear to be a bias towards the over or under prediction of project costs.
- There has been a general reduction in accident numbers, although RSA reports for projects that opened between April 05 and March 07 are not currently available.
- A review of the proposed mitigation measures presented within the Environmental Statement for the M77 Fenwick to Malletsheugh project indicates that mitigation measures are generally being delivered.