I notice that the latest plans for redeploying dmus from the Thames Valley after electrification appear to have changed. At least one source is suggesting that the air-conditioned Class 166s are now to remain at Reading for the Gatwick services, and only the Class 165s will now move to Bristol.  I wonder if this means that the Cardiff-Portsmouth service will be covered by the rather unsuitable non-airconditioned Class 165s with 5-a-side seating ?  Definately a step in the wrong direction IMHO^▸ (in my humble opinion).

David

I believe FGW^▸ (First Great Western) have already indicated informally that they are negotiating to acquire the Class 387/1s.  The expected delivery rate of Class 700 units to Thamesllink should allow all 29 Class 387/1s to be released from Thameslink by December 2016 when the Oxford & Newbury electrification is due to be completed.

At present FGW uses (approx.) 36 Class 165/1 units and 21 Class 166 units.  Quite a few of these are used on diagrams over routes that will not be electrified under current plans (eg Reading-Gatwick, north of Oxford etc).  Additionally quite a few 166 diagrams will be worked by Class 800 IEPs^▸ (Intercity Express Program / Project.) (eg Cotswold services).  So it is not inconceivable that the 29 Class 387/1s would be sufficient to cover the electrified Thames Valley local services on the GWML^▸ (Great Western Main Line).  The only uncertainty is what will be used on the electrified branch services to Marlow which will need to be 2 car units.

David

After some further reading, I have to correct myself here. It seems that a 2x5car IEP bi-mode train working on diesel will have much higher power at the rail (2x2MW) than a 2+8 HST (1x1.3MW) so that there should be no performance loss compared with present day services. Moreover there is very little performance difference on electric between the bi-mode and all electric versions which have the same power at the rail, although the bi-mode unit is slightly heavier and has fewer seats.
David

Unfortunately, as I understand, the performance of the bi-mode IEP when in diesel mode will be significantly inferior to present day HSTs, so that services worked by these trains are likely to be slower than present day services. While this may not matter for short extensions from eg Bristol to Weston or Swansea to Carmarthen, it becomes a more serious issue for Newbury-Penzance or Oxford-Hereford, or Swindon-Cheltenham.  So I anticipate that Devon and Cornwall will continue to be served by HSTs for many years. The all diesel version of the IEP has apparently been dropped.

Incidentally, I am told that the plan is to use bimode IEPs on a semi-fast service from Paddington to serve Hungerford, Bedwyn and probably Pewsey and Westbury. On the other hand, it seems that electrification from Newbury to Bedwyn in the inital phase  is not entirely ruled out.

A further downside of the electrification plan is that the new dmus for the Bristol area which were due to enter services from 2011-12 have also been cancelled and it will now be 2017-18 or so before any significant improvements are made to the Cardiff-Bristol-Portsmouth services, using second hand turbos from the Thames Valley.

David