6.9.10.4 West Wiltshire Corridor: Salisbury  to Chippenham

A number of options were considered for the West Wiltshire corridor to meet demand for travel from Melksham to other urban centres such as Bristol, Bath Spa, Chippenham and Swindon. The options reviewed an hourly Westbury service operating to either Chippenham or Swindon and an hourly  Salisbury to Chippenham service. These options would significantly enhance the service provision on the route and offer faster journey times to London through an interchange at Chippenham. Should the service terminate at Chippenham, the construction of a bay platform at Chippenham would be required. Should the service be extended to Swindon, no additional infrastructure would be necessary.

The Draft for Consultation presented the appraisal results for these options. The  Salisbury to Chippenham service failed to achieve the necessary BCR to enable the RUS to recommend it, however, the other options for a service from Westbury to Chippenham or Swindon both achieved a sufficient BCR to be able to recommend the proposals subject to operational viability. However, during the consultation period, respondees raised concerns with regard to the accuracy of the analysis and in particular the assumptions on the number of rail passengers who currently travel to and from Melksham. This is due to an earlier discrepancy with ticket purchases at Melksham station for travel between Trowbridge and Bath which was rectified in September 2008.

The initial appraisal used ticket sales data from April 2007 to March 2008 which contained the ticket anomaly. The analysis has been revised using data from April 2008 to March 2009, which shows a 29 percent fall in passenger numbers as a result of the rectification in September 2008. However, only six months of accurate ticket sales data is available. The revised appraisal results using the April 2008 to March 2009 data are presented in Figure 6.18. This shows that the Westbury to Swindon option achieves a BCR of 1.7 and is recommended as it requires no infrastructure. However the Westbury to Chippenham option only achieves a BCR of 1.7 and is therefore unable to be recommended due to the requirement to achieve a BCR of 2 or above for schemes which require additional infrastructure.

However, it is recognised that the appraisal results are particularly sensitive to current demand and the number of new passenger journeys stimulated by the scheme. For example, only an additional 30 passenger journeys by rail per day to Melksham over and above what is already assumed in the business case would be required to achieve the necessary BCR of 2. It is also recognised that MOIRA may not be able to predict demand accurately when the station currently has a low footfall and the proposed service proposition is significantly different from existing.

The RUS therefore recommends the further development of these proposals by the scheme promoter, Wiltshire Council, to include local area research to understand the demand potential and optimum service proposition and a detailed timetable study to assess the operational viability of the proposals with predicted future growth. The RUS recommends that any further work is undertaken in conjunction with the West of England Partnership as scheme promoter for the Bristol Metro.

The proposals will need more detailed modelling and operational verification to understand the timetable viability with the mix of passenger and freight services and any performance implications particularly given the emphasis placed on the freight diversionary route via Melksham as part of the Strategic Freight Network.

The Great Western document published by Network Rail says lines could benefit from more trains, better connectivity and shorter journey times, especially in key growth areas.