6. North Corridor Option 2
At 7.0km in length, North Corridor Option 2 is an offline solution which enables much of the existing A90/M90 between Ferrytoll Junction and Masterton Junction to be left insitu, allowing it to act as a local distributor road. An indicative layout of this option is provided in Appendix 4.
As a substantially off-line corridor, it was recognised that this corridor option had little potential for optimising the extent of its improvement within its overall extent.
The North Corridor Option 2 mainline is to be constructed to motorway standard. The mainline carriageway descends on viaduct from the northern bridgehead, passing through the eastern extents of St Margaret’s Marsh (SSSI) before crossing the B981 southeast of Dunfermline Waste Water Treatment Works.
Located to the west of the existing corridor through Ferrytoll, North Corridor Option 2 requires a new junction to be constructed at this location maintaining access to the B980, B981 Ferrytoll Road and the existing A90.
North of Ferrytoll Junction, the corridor climbs Castlandhill before sweeping northeast. The topography of the area requires the provision of a cut and cover solution in the vicinity of Castlandhill Steadings, masking the corridor’s presence. Upon exiting the cut and cover section, the corridor crosses the A90 on structure, south of Admiralty Junction, and continues on a north easterly bearing towards Belleknowes Industrial Estate. Continuing north, the corridor climbs out of the valley containing Belleknowes Industrial Estate, intersecting the M90 north of Masterton Junction. The tie in to the existing M90 is achieved east of Duloch Farm. The scheme terminates at Halbeath Interchange.
In the consideration of North Corridor Option 2, two mainline motorway cross sections were considered, D2M and D3M.
6.2 Engineering Issues
A number of engineering constraints were identified which require assessment to allow further development should this option be progressed. Principally these are:
- Carriageway Cross Section.
- Route Corridor, Structural Requirements and Topographical Effects.
- Junction Provision and Future Transport Developments.
- Geotechnical Assessment.
6.2.1 Carriageway Cross Section
In considering the most appropriate cross section for implementation, the scheme objectives dictate that two lanes of general traffic in each direction are required. It was recognised that there may be an opportunity to consider additional High Occupancy Vehicle (HOV) lanes in the early years following construction, prior to a possible future introduction of a public transport multi-modal facility.
Whilst effective in dealing with all means of transport provision, it was considered that the provision of a D3M cross section in tandem with the retention of the existing A90/M90 as a local distributor road would be unnecessary. Future traffic growth and the potential for HOV provision could be catered for through the use of the existing A90/M90 and the new mainline carriageway at D2M standard with effective junction provision. Given this, it is thought that the additional costs and impacts associated with the D3M cross section outweigh any benefits.
A dual two lane motorway (D2M) was therefore taken as the working assumption over the extent of North Corridor Option 2 with a design speed of 120kph.
6.2.2 Route Corridor, Structural Requirements and Topographical Effects
Situated offline, North Corridor Option 2 has a greater effect on the coastal landscape than North Corridor Option 1. Situated west of the existing A90/M90 route corridor, it further impacts the existing landscape through its assent of Castlandhill, with a complex cut and cover solution likely to be required in the establishment of the corridor through this section. Sweeping northeast across the A90/M90 route corridor, further new structures will be required to support the corridor with a sizable structure being required in the vicinity of Belleknowes Industrial estate, carrying the mainline over the A921 and the Fife Circle Railway Line. Continuing north the mainline carriageway connects to the M90 north of Masterton Junction.
In contrast to North Corridor Option 1, the new offline mainline carriageway allows a fully DMRB compliant horizontal and vertical geometry design to be considered, subject to the topographical constraints detailed and junction design. However, the provision of this option would still encompass Departures from Standard through the retention of the existing A90/M90.
6.2.3 Junction Provision and Future Transport Developments
The provision of an offline mainline carriageway and the retention of the existing A90/M90 only requires a new junction at Ferrytoll with the existing arrangements at Admiralty and Masterton being retained for local access.
(a) Ferrytoll Junction
The provision of a new offline mainline carriageway dictates that Ferrytoll Junction must be reconstructed. The junction will, as a minimum, replicate the movements of the existing layout.
As with North Corridor Option 1, Ferrytoll Junction is considered the most practical place to terminate the multi-modal aspect of the project.
Connectivity to the Forth Road Bridge must also be considered in the development of this junction, thus catering for any future role for which the existing bridge might have.
(b) Local Access Provision
To satisfy the scheme objectives, it is necessary that connectivity be maintained to both local and national routes. Therefore, the retention of the existing A90/M90 and the junctions at Admiralty and Masterton is necessary to facilitate access to Rosyth, Inverkeithing and Dunfermline.
A set of north facing slip roads are proposed between Masterton Junction and Halbeath Interchange to facilitate access between the proposed mainline and the existing M90.
6.2.4 Geotechnical Assessment
The recent ground investigation found that the ground conditions associated with North Corridor Option 2 predominantly comprise variably weathered glacial till overlying bedrock consisting of dolerite or sedimentary rocks including sandstone, siltstone, mudstone, limestone and coal seams. Based on the available information there would appear to be no significant geotechnical issues.
6.3 Environmental Considerations
North Corridor Option 2 being predominantly offline has the greatest land take of the northern route corridor options. Therefore, this option is anticipated to have the greatest potential for overall land use impacts. The significance of impacts on watercourses, designated sites of geological importance, ecological impact to habitats and species, landscape, visual and effects, footpaths and community severance are also likely to be increased compared to all other northern route corridor options.
North Corridor Option 2 is also considered to be less compliant with policy objectives than North Corridor Option 1 due to potential impacts on policies protecting Belleknowes Industrial Estate, which is designated for brownfield development.
6.4 Transportation Considerations
The provision of a D2M cross section encompassing two lanes of general traffic in tandem with the continued use of the existing A90/M90 route corridor as a local distributor road and potential HOV corridor is expected to provide the following benefits:
- increased levels of service for private, road based modes of transport;
- improved performance to the wider road network through improved connectivity;
- improved journey time reliability;
- improved accessibility and social exclusion through the provision of complementary transport measures; and
- minimal impact on the effective operation of the transport network during times of maintenance.
6.5 North Corridor Option 2 Recommendation
An indicative layout of North Corridor Option 2 is contained within Appendix 4. If carried forward to DMRB Stage 2 Corridor Assessment this option could encompass the following:
- a dual two lane motorway (D2M) mainline cross section;
- a reconstructed Ferrytoll Junction, providing:
- connectivity between the new mainline, local roads and the existing A90/M90; and
- connectivity for future transport modes;
- provision of north facing connectivity between the proposed mainline and the existing A90/M90 north of Masterton Junction.
In addition, the following junction improvements could also be considered:
- connectivity to the Forth Road Bridge.