New DMUs for UK
The availability and deliverability of a new DMU for the UK market is perhaps less of a technical consideration and more of a political and commercial consideration concerning future electrification strategy, residual economic life in the existing DMU fleets, future assumptions about growth and continuing encouragement of rail as well as the commitment of resources to the design and development effort, of which delivering Stage IIIB emissions compliance forms a key part.
The long term stated objective of the UK Department for Transport (DfT) is to increase significantly the extent of electrification and the use of EMU rolling stock. Residual value risk and an uncertain economic life for any new DMU vehicle are therefore seen as prohibitive risks by the ROSCOs and at odds with the higher development costs that are likely to be encountered for producing these types of vehicles, particularly if ordered in small quantities.
However, there is a growing appreciation that there is a need for some new DMU vehicles for the UK. The electrification schemes generally leave a residual DMU operation, and the net vehicle count (EMUs and DMUs) tends to increase to accommodate both growth and an inefficiency that can arise from the carefully optimised DMU workings not being replaceable completely vehicle-by-vehicle with a corresponding EMU operation. Furthermore, despite the lower costs of continuing the operation of older stock, its functionality, quality and performance is increasingly under pressure from the state-of-the-art technology and facilities expected and provided by new DMU products.
In order to minimise the barriers for a new DMU solution, a widely usable (diesel ‘S-Stock’) design of DMU platform for the UK networks would appear to be beneficial and necessary to increase the potential new build order quantity and spread the development costs (including for incorporating a Stage IIIB engine) to an extent that the procurement can be justified and competitive. An electric transmission and final drive with on-board energy storage would seem to provide a path to recovery / re-use of braking energy, reduction in the installed diesel power requirement and potentially a future conversion to electric traction supply – helping to assuage the residual value concerns.