4 The Proposed Scheme
Proposed Trunk Road
4.0.1 The Proposed Scheme would involve the construction of a new section of wide single-carriageway with alternating overtaking sections (Figure 4.1). It would diverge from the existing single-carriageway at the western end of the Carrutherstown bypass, following a line to the south of the existing trunk road and rejoining the existing alignment some 50 m west of the access to Upper Mains (Figure 4.1). The total land-take would be 21.9 ha.
4.0.2 Opportunities for overtaking would be prioritised for westbound traffic between Carrutherstown and the U81a (two of the three lanes would be dedicated to westbound traffic). The priority would change in favour of eastbound traffic between the U81a and Upper Mains. There would be short transitional sections at the eastern and western tie-in points with the existing trunk road and centred on the junction with the U81a to effect the change in priority from westbound to eastbound. The relevant lengths of these and the two sections of new three-lane carriageway are detailed in Table 4.1.
Table 4.1 – Lengths of new transitional road sections
1E+1W to 1E + 2W
1E+2W to 2E + 1W
2E+1W to 1E + 1W
4.0.3 The new section of trunk road carriageway would comprise a total running width of 13.5 m and would have a design speed of 100 kph (60 mph) in accordance with Table 2 of TD 9/93 (DMRB Volume 6, Section 1, Part 1).
Proposed Local Road
4.0.4 The existing section of the A75 would be retained as a local road between Whitecroftgate and Stenries View (Figure 4.1). New sections of road would be introduced at each end of the retained section of road to provide segregated access for local traffic to Carrutherstown and to form an access between the retained local road and the proposed new section of trunk road at Stenriesgate.
Side Roads and Junctions
4.0.5 Travelling west to east, modifications to existing side roads and junctions would comprise:
- local modification to the existing staggered junction where the B725 crosses the trunk road corridor at the western end of the Proposed Scheme. The northern arm of the junction would continue to provide access off the trunk road to Carrutherstown;
- closure of the private access from Fostermeadow to the existing A75. New access would be provided by upgrading an existing track running west of the farmstead to the B725. Access to the A75 and Carrutherstown would then be via the local road and the modified staggered junction at the western end of the Proposed Scheme;
- closure of direct access from the U81a to the proposed new section of the A75. Future access for local traffic from the north would be via the existing junction onto the retained section of the declassified trunk road and along the retained road to the modified junction at Carrutherstown or the new junction at Stenries View. Access from the south would be via a realigned section of the U81a routed beneath the proposed new section of trunk road with a new junction onto the retained section of the existing trunk road and then along the retained road to the west or east as described for local traffic using the U81a from the north;
- retention of the existing junctions within the retained section of the existing trunk road that provide private access for Oakbank and for traffic travelling from the north on the U82a;
- modification of the existing private access from Nether Stenries and Stenries View onto the new section of local road at the eastern end of the Proposed Scheme;
- closure of the existing access from Stenriesgate onto the new A75 (the property would be demolished to accommodate the proposed trunk road alignment); and
- retention and modification of the existing private access for Topmuir Farm.
4.0.6 The proposals include six new structures:
- an underbridge to provide grade-separated cross movement of the U81a beneath the proposed trunk road;
- four culverts to accommodate existing watercourses flowing north to south across the Proposed Scheme corridor; and
- a concrete culvert near Oakbank to provide for the passage of wildlife.
4.0.7 The U81a under-bridge would comprise a 6 m high by 13 m wide reinforced concrete structure approximately 20 m in length.
4.0.8 The five culverts would be designed in accordance with the requirements of Volume 10, Section 4, Part 2 (Highways Agency, 2001a); Volume 10, Section 4, Part 4 (Highways Agency, 2001b); and Volume 10, Section 4, draft Part X (Highways Agency, 2007).
4.0.9 Surface water run-off for the new section of trunk road would involve over-the-edge drainage collected via filter strips in the roadside verges. The collected waters would be carried to balancing ponds prior to discharge to local watercourses (Figure 4.2). There would be two balancing ponds between the new alignment and retained local road in the vicinity of the U81a, one either side of the realigned side road. Both will discharge to the Hardgrove Burn. A third balancing pond would be located at the eastern end of the Proposed Scheme to the north of the trunk road as it rejoins the existing alignment. This would discharge to the Glen Burn.
4.0.10 Reed-beds would be established in the balancing ponds to settle out pollutants suspended in runoff. Petrol interceptors would be provided to remove hydrocarbons associated with routine use and accidental spillage.
4.0.11 Where the proposals would involve severance of existing field drains and ditches, these would be collected and diverted to avoid disruption to local agricultural holdings.
4.0.12 The existing lighting at the Carrutherstown junction would be retained and modified as part of the redesign of the B725 staggered junction.
4.0.13 Along the extent of the scheme stock proof fencing will be included, which will be timber post and wire. Accordingly, 250 m sections of wire fencing will also be provided either side of any culvert passing under the road and on both sides of the road; the first 100 m of which will include an overhang. The wire fencing is being provided to exclude badgers and otters from the highway and has being designed in accordance with Volume 10, Section 4, Parts 2 and 4 of the DRMB. Further information is provided in Chapter 7.
4.1 Landscape and Environmental Proposals
Principles and Objectives
4.1.1 The landscape and environmental proposals for the Proposed Scheme have been developed with reference to Volume 10 of the DMRB. The prime objective has been the integration of the new road into the local countryside and the avoidance, reduction or compensation of environmental impacts that would be associated with the introduction of a new section of trunk road and its associated traffic into the local area.
4.1.2 The specimen design and its related landscape and environmental measures have accordingly been developed with a view to ensuring that:
- the road alignment achieves best fit within local landform and respects existing landscape character;
- existing planting is safeguarded as far as is possible and that proposed planting enhances the existing planting structure;
- that potential visual impacts on residents and users of open space and public facilities are mitigated as far as is practicable and consistent with other design objectives; and
- that ecological resources and assets are safeguarded as far as is possible and that local biodiversity is enhanced where appropriate.
4.1.3 There are some areas where the alignment of the new road would sever parts of existing agricultural holdings, and the severed areas would be likely to prove of marginal operational and economic viability. These have been included within the Draft Compulsory Purchase Orders (CPOs) and have been used with a view to enhance integration and biodiversity.
4.1.4 Key issues addressed by the landscape and environmental design and mitigation proposals comprise:
- screening and integration of the realignment and grade separated crossing of the U81a beneath the new section of trunk road;
- differentiation and separation between the new section of trunk road and the retained local road;
- establishment of an appropriate rural character along the retained existing section of the A75 to reflect its function as a local road; and
- provision of crossings beneath the proposed new alignment to cater for established mammal movements.
4.1.5 The landscape proposals comprise a combination of earthworks, planting and grassland establishment (Figure 8.4).
4.1.6 Key mitigation measures described in Section 8.7 relate to the following.
The introduction of low mounding between the news section of trunk road and the newly nominated local road.
The extension and relaxation of embankment slopes where the proposed new trunk road would cross over the U81a. There is some available space between the line of the old road and new road to modify the essential engineering landform, soften slopes and establish a combination of dense woodland planting and scrub edge. This would achieve a balance between mass planting, which would soften and enclose the earthworks supporting the road, whilst avoiding over enclosure for users of the approach road to the underpass.
Relaxation of cutting slopes and extension embankment slopes where space permits to the west and east of the central U81a underpass.
Rounding of the crest of cutting and embankment slopes.
Introduction of hedgerows where verge widths preclude the use of denser planting to define the corridor and tie into existing hedgerows which would be severed by the new alignment.
Planting of dense woodland edge species where the new alignment would encroach into the northern edge of Braemoss Wood.
Reinforcement of existing planting at the modified western junction providing access to Carrutherstown.
Use of native tree and shrub species of local provenance throughout and of grassland species with semi-natural characteristics to enhance local landscape character and contribute to local biodiversity.
Incorporation of landscape design objectives to enhance the appearance and natural interest associated with the proposed balancing ponds whilst maintaining their prime function to regulate flows and minimise pollution discharge.
4.1.7 The Proposed Scheme would require the demolition of the existing Stenriesgate residential property and outbuildings. The property is currently vacant and is in the ownership of The Scottish Ministers.
Statutory Undertakers Diversions
4.1.8 Prior to the commencement of the main construction activities, preliminary works would be required to divert and protect public utilities. The majority of the diversion work relates to the tie-in areas where there is a Virgin Media fibre optic and various BT cables. Scottish Water require to carry out some diversion works around U81a crossroads as existing infrastructure coincides with the proposed balancing ponds. Scottish & Southern Energy (electricity) has two overhead cables crossing the A75, one at each end of the scheme, which will be diverted underground.
4.1.9 All diversions are considered minor-works that will be carried out within the standard construction period and the CPO footprint, with plant remaining within the highway boundary at all times.
4.2.1 It is anticipated that the construction period for the Proposed Scheme would be 52 weeks.
4.2.2 The programme would serve to maintain traffic on the existing A75 for the longest possible period whilst the new carriageway is built offline.
4.2.3 Typical plant and equipment used during construction are likely to include mechanical excavators, scrapers, graders and dump trucks, generators, HGV delivery vehicles, ready-mix concrete vehicles, bowsers, road rollers and compaction plant, pumps, hand tools and site staff vehicles.
4.2.4 Construction plant will use the existing A75 as it provides the only access link to the work areas. Traffic management procedures will be employed to ensure that the traffic flows along the A75 are maintained throughout the construction period so as to minimise disruption along the route.
4.2.5 It is anticipated there would be short-term disruption in the order of 4-6 weeks as flows are temporarily managed to maintain movement whilst merging the new and existing sections of road. There is also a requirement for more limited traffic management levels at the start of the construction phase to establish site accesses and set out the construction site.
4.2.6 There would be no need for the use of piling equipment or blasting techniques.
4.2.7 Working hours during construction would be limited between 7am and 7pm weekdays and 7am to 1pm Saturdays. No working is anticipated on Sundays and public holidays.
4.2.8 Additional night works outside normal working hours may be required where operations on existing roads are necessary to avoid peak traffic flows and to reduce disruption to road users; the key ones relating to the tie-in operation required around the A75 and the B725.
Construction Environmental Management Plan (cEMP)
4.2.9 The EIA has identified a number of construction specific mitigation measures which the contractor/s for the construction of the Proposed Scheme would be required to incorporate into their methods of working. There are also many mandatory and good practice requirements and guidelines related to the safeguarding of environmental resources and interests which the contractor would be required to observe during construction. The contractor would be required to demonstrate that these commitments, requirements and guidelines are formally incorporated into their working practices in the form of a Construction Environmental Management Plan (cEMP) for which they are responsible. The contractor would accordingly be required, under the terms of the contract, to submit and obtain approval of the cEMP prior to the commencement of the works.