3 Alternatives Considered 3.1 Scheme 1 3.2 Scheme 2 3.3 Scheme 3 3.4 DMRB Stage 2 Assessment Conclusions 3.5 Scheme Modification
3 Alternatives Considered
3.0.1 The Initial DMRB Stage 1 assessment involved the consideration of the entire A75 between Gretna and Stranraer and identified short, medium and long term projects to improve the safety and strategic value of the route. One of the sections considered by this report was the section identified as Hardgrove to Kinmount.
3.0.2 The Stage 2 process started by extending the corridor to cover the entire section of the A75 between Carrutherstown and Annan. Three strategies were developed with varying directions of overtaking and overtaking section lengths and concluded in demonstrating that the second of the three corridor strategies provided the best perceived advantage of uphill overtaking in both directions at Hardgrove; the key accident spot. This strategy was therefore taken forward as the preferred alternative at Stage 2 through considering three overlapping sub-strategy scheme improvements between Carrutherstown and the western end of the Annan Bypass.
3.0.3 Online improvements were developed for these three schemes (as shown in Figure 3.1 sheets 1 to 3 inclusive) which where subject to assessment under Stage 2 of the DMRB.
Scheme 1 provided westbound overtaking opportunities over the western half of the section and eastbound opportunities over the eastern half. The scheme provided for transitional two lane sections at each end and centrally along the section to effect the transition in overtaking priority. The overall length of the scheme was 3.3 km and essentially covered the length of the Proposed Scheme.
Scheme 2 commenced with the easternmost two lane section of Scheme 1 followed by a three lane section providing for westbound overtaking. It then provided a two lane transitional section of road followed by an additional three lane section with priority for eastbound overtaking and a final two lane transitional section at Kinmount East. The overall length of the scheme was 3.2 km.
Scheme 3 commenced with the easternmost two lane section of Scheme 2 followed by a three lane section providing for westbound overtaking. It then provided a two lane transitional section of road followed by an additional three lane section with priority for eastbound overtaking and a final two lane transitional section at Annan. The overall length of the scheme was 3.9 km.
3.0.4 A summary of the Stage 2 assessment is presented below. Given the overlap between the schemes the range of potential impacts was broadly consistent.
3.1.1 Existing known cultural heritage assets potentially affected by Scheme 1 included the Whitecroft Gate Piers and Braehill Fort Settlement and Enclosure, the latter of which is important at the national level. Historic Scotland (HS) also indicated that there would be the potential for exposure of other currently unknown features of archaeological interest and value during road construction.
3.1.2 A preliminary site appraisal of sensitive habitats and fauna associated with the scheme corridor identified woodland and grassland habitat, wetlands, waterbodies and peatland habitats. Faunal records indicated the presence of badgers and otters. The assessment also concluded there was the potential for bat and water vole activity within the area. Of the three schemes, Scheme 1 was anticipated to result in the least impact on the ecology and nature conservation of the area.
3.1.3 Predicted impacts on landscape character were identified as being slight and negative taking account of the potential for mitigation. Predicted impacts on locally sensitive visual receptors were assessed as varying between slight to moderate with the potential for the significance of the impact to be reduced overtime as the mitigation, in the form of planting, would become established and mature.
3.1.4 It was predicted that there would be a moderate to slight negative impact in terms of agricultural land losses; primarily as a result of the implications for existing access.
3.1.5 The assessment identified potential impacts associated with surface water discharge to Glen Burn and changes in the quality of discharges to the Kelhead Quarry surface water network. Assuming the adoption of best practice during construction and the implementation of drainage proposals in accordance with current standards it was concluded that potential impacts on the watercourses and surface water quality would be slight and negative.
3.1.6 The assessment concluded that impacts associated with construction could be appropriately mitigated for a construction period of approximately 52 weeks.
3.2.1 Existing known cultural heritage assets potentially affected by Scheme 2 included Kinmount House Designed Landscape. There is also the potential for exposing unknown archaeological features during construction.
3.2.2 A cluster of moderately important habitats at Kinmount Farm and Kelhead Moss Plantation resulted in Scheme 2 having a higher ecological impact overall above Scheme 1.
3.2.3 Predicted impacts on landscape character were identified as being slight to moderate and negative taking account of the potential for mitigation. Predicted impacts on locally sensitive visual receptors were assessed as varying between large/moderate to slight/moderate and reducing as potential mitigation in the form of planting would become established and mature.
3.2.4 It was predicted that there would be a slight to moderate negative impact in terms of on agricultural land losses.
3.2.5 The impact on water resources was considered the same as Scheme 1.
3.2.6 Construction would also last for approximately 52 weeks.
3.3.1 Existing known cultural heritage assets potentially affected by Scheme 3 included Ladyfield House and Justenlees Enclosure (the latter is located within an archaeological consultation zone) and Kinmount House Designed Landscape. The risk of encountering hitherto unknown archaeology is also a potential.
3.3.2 The potential ecological impacts were assessed as being identical as Scheme 2.
3.3.3 The potential impact on the landscape character and visual receptors were assessed as being identical as Scheme 2.
3.3.4 The land use impacts were assessed as being identical as Scheme 2.
3.3.5 The impact on water resources was considered the same as Schemes 1 and 2.
3.3.6 Construction would also last for approximately 52 weeks.
3.4.1 The Stage 2 assessment concluded that there were no marked differences between the three alternative schemes in relation to the majority of the environmental interests associated with the local area. It did identify that Scheme 1 would be likely to involve lesser impacts on ecological, landscape and visual interests due to a reduced land-take.
3.5.1 Forward of this stage it was realised that large sections of the route between Carrutherstown and the western end of the Annan Bypass provided ‘safe’ overtaking opportunities in both directions. Thus reconfiguring the entire carriageway section to only favour overtaking in one direction would effectively prejudice traffic in the other direction, which would increase driver stress and journey travel times overall. The only exception was a section of the A75 covered by Scheme 1.
3.5.2 However, in reviewing Scheme 1 in 2005 it was recognised that there would be merit in considering further alternatives involving the construction of a new offline section to accommodate a wide-single carriageway with three lanes to cater for the safer overtaking opportunities necessary for this section of the A75.
3.5.3 This also provided the ability to retain the existing carriageway as a local road whilst also allowing a safer means for the local traffic that currently use the U81a to cross under the A75 via a newly constructed underpass. There would also be potential benefits related to construction that would improve the economic viability of the scheme, simply as much of the scheme could be built offline with minimum disruption to traffic flows along the existing A75 and the requirement for costly traffic management.
3.5.4 It was recognised that the new offline scheme would need to be aligned to the south of the existing road; there being fewer environmental constraints within this area in comparison to the area immediately north of the existing road. Thus the Proposed Scheme was developed.