DMRB Stage 2 Route Options - Sifting Assessment
The route options were subject to a sifting assessment. The first part of this involved assessing the cross-sections under consideration, Dual Carriageway (end-to-end), WS2+1 Carriageway (end-to-end) and Single Carriageway (with overtaking opportunities).
This Cross-section Assessment found that the WS2+1 Carriageway (end-to-end) route options offered no significant benefits over the Single Carriageway (with overtaking opportunities) route options and would have higher associated costs. It was therefore concluded that the WS2+1 Carriageway (end-to-end) route options should not be taken forward for further assessment.
The second part of the sifting assessment involved a Comparative Assessment of the remaining route options to determine the relative performance of each when assessed against the following criteria:
- Scheme objectives
- Environment (including potential impacts, likely mitigation and key issues)
- Engineering (including safety, engineering characteristics, constraints and complexity)
- Traffic and Economics (the effect of scheme options on operational performance indicators including accidents, journey times, and economic performance informed through traffic modelling and forecasting)
The outcome of the Comparative Assessment is summarised below:
Route Option 2A – Dual (end-to-end) – Taken Forward
Scheme Objectives – Three Checkmarks
Environment – One Checkmark
Engineering – Three Checkmarks
Economics – Two Checkmarks
Route Option 2C – Single (with overtaking opportunities) – Taken Forward
Scheme Objectives – Three Checkmarks
Environment – One Checkmark
Engineering – Three Checkmarks
Economics – One Checkmark
Route Option 4A – Dual (end-to-end) – Taken Forward
Scheme Objectives – Three Checkmarks
Environment – Three Checkmarks
Engineering – Three Checkmarks
Economics – Three Checkmarks
Route Option 4C – Single (with overtaking opportunities) – Taken Forward
Scheme Objectives – Three Checkmarks
Environment – Three Checkmarks
Engineering – Three Checkmarks
Economics – Three Checkmarks
Route Option 5A – Dual (end-to-end) – Sifted Out
Scheme Objectives – Three Checkmarks
Environment – One Checkmark
Engineering – One Checkmark
Economics – Three Checkmarks
Route Option 5C – Single (with overtaking opportunities) – Sifted Out
Scheme Objectives – Three Checkmarks
Environment – One Checkmark
Engineering – One Checkmark
Economics – Two Checkmarks
Route Option 45A – Dual (end-to-end) – Sifted Out
Scheme Objectives – Three Checkmarks
Environment – One Checkmark
Engineering – One Checkmark
Economics – Three Checkmarks
Route Option 45C – Single (with overtaking opportunities) – Sifted Out
Scheme Objectives – Three Checkmarks
Environment – One Checkmark
Engineering – One Checkmark
Economics – Two Checkmarks
Route Option 54A – Dual (end-to-end) – Taken Forward
Scheme Objectives – Three Checkmarks
Environment – Three Checkmarks
Engineering – Three Checkmarks
Economics – Two Checkmarks
Route Option 54C – Single (with overtaking opportunities) – Taken Forward
Scheme Objectives – Three Checkmarks
Environment – Three Checkmarks
Engineering – Three Checkmarks
Economics – Two Checkmarks
Route options 5A and 45A were found to be the least advantageous Dual Carriageway (end-to-end) route options. Route options 5C and 45C were found to be the least advantageous Single Carriageway (with overtaking opportunities) route options. It was therefore concluded that those route options should not be taken forward for further assessment.
Specific reasons for sifting these route options include encroachment on the Milton Loch Site of Special Scientific Interest (SSSI) and increased construction complexity at the northern tie-in to the existing A75.
Route options 2A, 2C, 4A, 4C, 54A and 54C have been taken forward for further consideration at DMRB Stage 2.