The key point is how the end-of-life profile of the existing fleets fits with the profile of units being made redundant by electrification.
The original plan seems to have been that electrification would render several DMU classes redundant (probably the Pacers and 153s) before 2020 so these would not require accessibility mods. Most of the electrification schemes have slipped back, but only by a couple of years. So there are several choices in respect of these classes:
- Pay for accessibility mods for units that will remain in use for only a few more years. Arguably not a worthwhile way to spend money.
- Obtain derogation from accessibility mods to minimise spend on technical life extension. Cheaper but may be politically unacceptable with disability groups or just passengers fed up with worn out Pacers, so risks having to spend even more to do the mods at short notice.
- Buy new units. This would lead to arguably premature replacement of other classes such as 150 once the committed electrification schemes are delivered. Merit of this depends on whether the 150s etc will last another few years without drastic costs or plummeting reliability, and on whether further electrifications will be authorised for delivery in the 2020s. The latter depends to some degree on whether NR can recover its current difficulties and persuade DfT that it can deliver electrification schemes.
- Buy short-life "new" units such as D78s. This is a good option if you believe the D78s will work and be suitable and attractive to passengers on the routes they are assigned to, and if you also believe the 150s etc can reasonably be kept going until the mid to late 2020s and that there will be more electrification authorised during that decade.
Most of the above are unknowns at present (to me at least). If I ruled the world I think I'd plump for the D78s, assuming the prototype is promising, to tide us over for a decade or so by which time there should be more certainty on many of them.
