With the proposal to take away the TPE 170s earlier than envisaged I'm trying to work out what stock will be freed up and which new services have been committed to needing extra stock.
By my reckoning:
December 2014 -
* Manchester Airport to Liverpool services go over to EMUs
* Extra DMUs required to extend hourly Victoria-Todmorden service to Blackburn via Burnley
2015 -
* Other Chat Moss services go over to EMUs
May 2016 -
* Liverpool to Blackpool service could go over to EMU
December 2016 -
* Manchester Airport to Blackpool service could go over to EMU
* Hazel Grove to Preston service could go over to EMU
* Manchester Victoria to Blackpool service could go over to EMU
* Victoria-Huddersfield stopper withdrawn
* 2 x Northern services extended from Victoria to Manchester Airport via new Ordsall Chord
* TPE Airport services routed via Ordsall Chord
* New Piccadilly-Selby semi-fast service, with Piccadilly-Hull service also seeing extra stops to compensate for withdrawal of Victoria-Huddersfield stopper.
* Other North TPE changes may or may not go ahead at this stage, as could running electric services between Manchester and Lancaster in lieu of diesel services to Barrow/Windermere.
* Chat Moss services can once again run through to Stalybridge (as electric services.)
So if we forget about some of the "aspirational" stuff (like an hourly service through Denton) we might be okay if the 170s don't go south until 2016.
However, the Oxford services (which Chiltern need units for) are scheduled to start in around eighteen months.
Given that we know there are 317/7s going spare, we could probably chop a few current DMU services to allow EMUs to run part - e.g. terminate the Cleethorpes services at Manchester Piccadilly so that EMUs can shuttle from Pic to Manchester Airport... split the Preston - Hazel Grove service at Piccadilly for similar reasons (317s running to Hazel Grove)... maybe that gives us a Cleethorpes - Preston DMU service?
Whilst the 350s should release enough 185s to replace 170s on a one-for-one basis, there's obviously a need for more 185s for the "fifth path". By my reckoning, the new service will "cost" around five units (since it's effectively a new Liverpool - York service, then replacing the current TPE path from York to Newcastle), so we'll need half a dozen extra units.
Come 2016, when the North West Triangle is completed (around the same time as busy DMU routes like Falkirk High), there'll be more "breathing space". However, if Chiltern want the 170s from the opening date for their Oxford route then things look rather frustrating.
(I'm basing this on the assumption that no DMUs will be freed up by electrification elsewhere over the next eighteen months - the Whifflet/ Cumbernauld DMUs are more of a "rounding error" and will presumably stay in Scotland for capacity reasons - the rewards of CP5 electrification will generally take a couple of years to kick in)
PS: If we are going to "lose" any DMUs in northern England then I suppose that the 170s are a fairly weak link - a small non-standard fleet, relatively low seat numbers when compared with a 155/156/158 - would have rather that they remained though!