Infrastructure
Amey have costed proposals for changes to the infrastructure to enable the upgraded service
Reinstate the 3rd platform at Chippenham for local services
Remodel Thingley junction to reduce the time taken for an up train from Melksham to clear the down main
Provide a passing loop on the Melksham branch (possibly at Melksham station)
Cost
£2-5M (track & signalling work including 2 new crossovers, a small amount of station work)
£1-2M (relocation of 4 crossovers by about 500m)
£5-10M (assuming it would require a new platform and new Access For All bridge)
Chippenham Platform 0:
Reinstatement of the existing south-side platform as a west (Bristol) facing bay platform with a new turnout at the west (down) end of the station. This would allow local/stopping services from Bristol/Bath and from Trowbridge/Melksham to terminate at Chippenham and turn back. It would also keep the through platforms clear for freight and inter-city services, creating significant additional capacity.
This bay platform option would be far more affordable than reinstating the disused platform as a through platform as half the number of points and signals would be required. Local through-services to/from Swindon could still use the existing platforms but with two intercity services an hour in each direction stopping at Chippenham and Swindon, using Chippenham as an interchange may be a much better use of the capacity available on the network.
Click image to view tracks
Thingley Junction Remodelling:
A significant capacity constraint for services on and off the Melksham branch is the distance between the turnout onto the branch and the crossovers between the junction and Chippenham station. This means that up services towards Chippenham have to travel approximately 1km up the down main at relatively slow speed before they can move over onto the up main. This blocks the down main for a significant period of time, constraining capacity in the area.
A new crossover between the down and up main at the site of the junction would allow trains to cross straight over onto the up main, providing a huge capacity improvement.
Click image to view tracks
Melksham branch passing loop:
The Melksham branch is a long single line and has to be completely cleared in one direction before another train can enter from the other direction. A passing loop on the branch would allow much greater flexibility over the timetabling of services and also provides greater performance resilience by allowing trains to clear the mains lines at either end during times of disruption.
Greatest flexibility and performance benefit is generally achieved by a passing loop being built at a station, however this does increase the cost due to the need for a second platform and (typically) the provision of an accessible footbridge as well. The optimum location for a new passing loop would be subject to an options study looking at land availability, costs and benefits.
Click image to view tracks
Westbury platform 0:
A scheme already being considered (see Network Rail's Wiltshire Strategic Study and the Devizes Gateway Interim Feasibility Study) to reinstate the historic platform face on the south (down) side of the station to create capacity for an hourly Paddington to Bedwyn service. This will also provide improved capacity for all services through Westbury including our proposals for a half-hourly Chippenham to Frome service.
Click image to view tracks
Frome passing loop and new platform:
A scheme already being considered (see Network Rail's Wiltshire Strategic Study) to provide a passing loop and a new or extended platform to create capacity and reduce freight conflicts for "the extended Swindon to Westbury" service. This would support our alternative proposals for a half-hourly Chippenham to Frome service.