Hmmm. I have realised that there are two many variables in the electrification vs DMU building race.
What is clear to me is that electrification
willcould happen at a slower pace than the aspirations of the last few years would suggest.
Although I argued that 230s will provide an open door for replacement EMUs sooner there is a risk. The risk is that if electrification proceeds as slowly as is becoming obvious then at the end of the 230s lives new DMUs might have to be ordered anyway thus postponing the necessity to electrify. That would mean that new DMUs now might be better.
I cannot face the detail but it is a fear of mine that the current pace of electrification is getting too ambitious. We bite off more than we can chew and end up with a lot less.
The current pace of electrification is not a guide to how things will go in the future but that has been discussed elsewhere anyway.
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But once you start to join up the various electrification schemes currently in hand - which in many cases means wiring a series of relatively short connecting lines - then you start to take out an awful lot of diesel miles rather rapidly. Acting on the top priorities in the Northern task force proposals would eliminate huge areas of dmu operations in the North West and Yorkshire, never mind the other potential schemes I and The Ham mention above
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I agree and it is a hope I cling to that sooner or later we will reach critical mass and infill electrification schemes will be more relevant.
The joint rolling stock strategy document did say if the current rate of electrification continues ('current' presumed all announced schemes including MML and North TPE would be done by 2019 at the latest) that no new DMUs would be required in CP5 or CP6 but a small order may be required in CP7 as some lines will never be electrified. However, all electrification schemes have fallen behind schedule since, some by as much as 4 years.
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Thanks for reminding me. The above is what I have been keeping in mind, rightly or wrongly.
Typed the following in a rush :-
Separately I have always assumed that we have to look at the current diesel trains and services as two beasts. Loosely Suburban and Intercity - forgive the terms I am thinking door layout and speed/acceleration.
Suburban :-
I can see predominantly 170s replacing 150s which then replace 142s-144s. Later More 172s replace 150-153s. The hope was 230s would speed that up and take pressure of electrification.
Intercity :-
The 220s-222s replace 170s (a bit contentious). No case for 230s there of course.
In both the above electrification and EMUs has to fit in but goodness knows how effective that will be. The EMUS will probably obviate the need for 220-222s on inappropriate (suburbanish) routes.
EDIT :- In the above I can see it likely that 220s-222s have less use, the only thing they can do is replace HSTs (sadly in my biased mind). Of course this assumes enough electrification (or Bi-Modes) to make them spare.