Description of Proposed Scheme
Introduction
Six improvement strategies have been assessed at DMRB Stage 1. These are shown in Appendix A, Figure A3-1. The improvement strategies tie-in to the existing A75 within the assessment corridor at various locations and are located at varying offsets from the existing A75.
Do-Minimum Scenario
While the approach to the DMRB Stage 1 Assessment has focussed on major improvements along the A75 in the vicinity of Springholm and Crocketford, it is also necessary to consider the Do-Minimum scenario in the quantitative assessment, including economic appraisal, against which the proposed scheme is compared.
The Do-Minimum scenario reflects the most likely transport situation where the proposed scheme is not progressed and no major intervention is assumed to occur. The current road layout is largely maintained as is, with essential road maintenance continuing to be addressed and minor interventions undertaken. This allows the assessment to determine the potential impacts of not progressing the proposed scheme and allows a consistent baseline comparison against which the effects of the proposed scheme can be determined.
Examples of potential interventions that could be anticipated in the Do-Minimum scenario include improvements to the safety and operation of the route such as updated signing and lining and the installation of additional Variable Message Signs (VMS).
Improvement Strategies
Improvement Strategy 1
Improvement Strategy 1 is offline and leaves the existing A75 at Allanton Roundabout. It then runs north-west of Springholm, Auchenreoch Loch and Crocketford, before rejoining the existing A75 at Drummore Roundabout. It would involve the construction of a new carriageway between the Allanton and Drummore roundabouts. The total length of the improvement strategy is approximately 19km.
This improvement strategy would include a number of structures over watercourses including Urr Water. In addition, further structures and/or junctions may be required for the existing A75, B795, B794, A712, Core Path IRON/72/1, several C-roads and private accesses. This improvement strategy passes through areas of undulating topography and native woodland. A number of properties lie within the improvement strategy. Improvement Strategy 1 is shown in Appendix A, Figure A3-1.
Improvement Strategy 2
Improvement Strategy 2 is offline and leaves the existing A75 at a location approximately 2.7km south of Springholm. It then runs north-west of Springholm, Auchenreoch Loch and Crocketford before rejoining the existing A75 at a location approximately 0.8km north-east of the settlement of Brae. It would involve the construction of a new carriageway between the existing A75 / B794 junction and the existing A75 to north-east of Brae. The total length of the improvement strategy is approximately 12.4km.
This improvement strategy would include a number of structures over watercourses. In addition, further structures and/or junctions may be required for the existing A75, A712, Core Path IRON/72/1, several C-roads and private accesses. This improvement strategy passes through areas of undulating topography. A number of properties lie within the improvement strategy. Improvement Strategy 2 is shown in Appendix A, Figure A3-1.
Improvement Strategy 3
Improvement Strategy 3 is online and follows the route of the existing A75 from the south of Springholm to the north of the Crocketford. This includes the sections of existing A75 subject to the 30mph speed restriction. The total length of the improvement strategy is approximately 5.4km.
This improvement strategy would include the widening or replacement of the existing structures over watercourses. In addition, further structures and/or junctions may be required for the A712, several C-roads and private accesses. A large number of properties lie within the improvement strategy. Improvement Strategy 3 is shown in Appendix A, Figure A3-1.
Improvement Strategy 4
Improvement Strategy 4 is offline and leaves the existing A75 at a location approximately 0.8km south-west of Springholm. It then runs to the south-east of Springholm, parallel to the existing A75 for approximately 1.2km, before continuing south-east of Crocketford and re-joining the existing A75 approximately 0.6km north-east of Crocketford. It would involve the construction of a new carriageway between the south-west of Springholm and the north-east of Crocketford. The total length of the improvement strategy is approximately 6.0km.
This improvement strategy would include a number of structures over watercourses. In addition, further structures and/or junctions may be required for the existing A75, several C-roads and private accesses. This improvement strategy passes through areas of undulating topography. A number of properties lie within the improvement strategy. Improvement Strategy 4 is shown in Appendix A, Figure A3-1.
Improvement Strategy 5
Improvement Strategy 5 is offline and leaves the existing A75 approximately 0.4km south of the Ramhill Bridge over Urr Water. It then runs south-east of Springholm and passes south-east of Auchenreoch Loch and Crocketford and north-west of Milton Loch before rejoining the existing A75 near the settlement of Brae. It would involve the construction of a new carriageway between the south of Ramhill Bridge and the south of Brae. The total length of the improvement strategy is approximately 11km.
This improvement strategy would include a number of structures over watercourses including Urr Water. In addition, further structures and/or junctions may be required for the existing A75, the B794, Core Path IRON/72/1, Core Path URR/603/1, several C-roads and private accesses. This improvement strategy passes through areas of undulating topography and native woodland. A number of properties lie within the improvement strategy. Improvement Strategy 5 is shown in Appendix A, Figure A3-1.
Improvement Strategy 6
Improvement Strategy 6 is offline and leaves the existing A75 at Allanton Roundabout. It then follows a route south-east of Springholm, Crocketford and Milton Loch. It also passes to the east of Haugh of Urr, Hardgate and Milton, running parallel to the Old Military Road for the majority of the route, rejoining the existing A75 at the Drummore Roundabout. It would involve the construction of a new carriageway between the Allanton to Drummore roundabouts. The total length of the improvement strategy is approximately 17.2km.
This improvement strategy would include a number of structures over watercourses including Urr Water. In addition, further structures and/or junctions may be required for the existing A75, the Old Military Road, the B794, several C-roads and private accesses. This improvement strategy passes through areas of undulating topography and native woodland. A number of properties lie within the improvement strategy. Improvement Strategy 6 is shown in Appendix A, Figure A3-1.
Comparative Preliminary Cost Estimates
Due to the broadly defined nature of the improvement strategies, a detailed cost estimate has not been prepared at DMRB Stage 1. Therefore, a comparative cost assessment has been undertaken. The comparative cost assessment involved reviewing previous projects that are similar in nature to the proposed scheme to gain an understanding of which features would make the improvement strategies comparatively more or less expensive. A high level review of each improvement strategy was then undertaken, taking into consideration its relative length and whether it is generally online or offline, with online construction considered to be more expensive.
Based on the above, it is likely that the relative cost of each improvement strategy, listed in ascending order, would be as follows:
- Improvement Strategy 4 (Approximately 6km in length and generally offline)
- Improvement Strategy 3 (Approximately 5.4km in length and generally online)
- Improvement Strategy 5 (Approximately 11km in length and generally offline)
- Improvement Strategy 2 (Approximately 12.4km in length and generally offline)
- Improvement Strategy 6 (Approximately 17.2km in length and generally offline)
- Improvement Strategy 1 (Approximately 19km in length and generally offline)
Detailed cost estimates will be prepared for route options at DMRB Stage 2.