Safety
Overview
The evaluation seeks to generate evidence on which key theme areas were the most effective at achieving the objectives and the progress of outcomes. The outcomes in safety, such as collision numbers, collision rates, collision severity and the number of killed or seriously injured casualties were compared to previous years’ collisions rates and the severity of these cases.
The safety objective for this project was to improve current safety standards.
Has the project achieved its safety objectives?
The evaluation has demonstrated that the project is on track to meet its safety objective.
What impact did the project have on collisions?
In the five years before the project opened, 118 personal injury collisions were recorded, an average of around 24 per year. This reduced to an average of nine per year five-years after the project opened. The figure below shows changes in the number of personal injury collisions before the project, during construction and after opening.
Number of personal injury collisions before the project, during construction, and after the project opened
What impact did the scheme have on collision rates?
The average collision rate was 8.4 personal injury collisions (PICs) per hundred million vehicle miles (hmvm) before the project opening. The five-years after evaluation has shown that the average collision rate had decreased to 3.1 PICs per hmvm.
Do we believe the project has contributed to this change?
As part of the safety evaluation, we look to assess what changes in collisions might have occurred due to factors external to the project over this timeframe. We estimate that if the new configuration of the A1 had not occurred, the trend in the number of PICs and collision rates would likely have reduced, similar to the extent to what has been observed.
What impact did the project have on the severity of collisions?
The project has resulted in a severity reduction across all three categories (fatal, serious, slight).
Number of personal injury collisions by severity
| Severity | Before | After | Observed change |
|---|---|---|---|
| Fatal (total) | 7 | 0 | -7 |
| Serious (per year) | 4.41 | 2.38 | -2.03 |
| Slight (per year) | 17.79 | 6.62 | 11.17 |
What impact did the project have on killed or seriously injured casualties?
The impact on casualty severity is measured using the number of killed or seriously injured casualties (KSI) and fatal weighted injuries (FWI).
The number of KSI casualties reduced from an average of 7.3 before the project opened to 2.5 after opening. The KSI rate also reduced from an average of 2.6 per hundred million vehicle miles (hmvm) to 0.9 per hmvm.
Similarly, FWI reduced from an average of 2.3 before opening to 0.4 after opening. The FWI rate also reduced from an average of 0.8 per hmvm to 0.1 per hmvm.
Overall, these findings suggest the project is having a positive impact on the severity of casualties within the project extent.
Change in casualties
| Metric | Before | After | Observed change |
|---|---|---|---|
| Killed or seriously injured | 7.3 | 2.5 | -4.8 |
| killed or seriously injured rate (hmvm) | 2.6 | 0.9 | -1.7 |
| Fatal weighted injury (hmvm) | 2.3 | 0.4 | -1.9 |
| fatal weighted injury rate (hmvm) | 0.8 | 0.1 | -0.7 |
What impact has the project on the wider safety area?
We observed a reduction in PICs across the wider safety area, with the number of collisions falling from 39 to 19. The collision rate also reduced from 17.9 to 8.7 PICs per hmvm. Reductions were observed across all collision severities, KSI and FWI casualties. We also compared the results with what would have been expected without the project. This suggests the reduction in collision rates is higher than would be expected from wider road safety trends alone, indicating the project is helping to improve safety on surrounding roads.
