Very true, but how many people who use the train daily will experience IEP▸ based improvements?
When the London Suburban services get new electric trains the Turbos will be cascaded to Bristol, which I assume will increase capacity and give longer trains so that should reduce overcrowding.
The 15X's will go further west, I assume, increasing capacity there.
My understanding of current plans (some of which should probably be in the Rumour Mill!) ...
The first 3 car turbos to be cascaded will take over services on the Severn Beach line. The current trains from the Severn Beach line will allow four to six 15x carriages to be released to reform other trains operating out of St. Philip's Marsh. However - there's competition as ever for stock; all 153 units were supposed to go back to their
RoSCOs▸ in May for redeployment in places that are neither great nor western, but the timing of part of that move may be varied. The loss of all 153s over - let's say - the next 13 months will force all
GWR▸ trains currently running with a single carriage up to 2 carriages; with one or two diagrams, that may lead to overcapacity but in certain cases it will allow the brakes to be taken off promotion and passenger growth which has been stifled by people finding other ways to travel.
Hard to say if these are indirect "IEP based" or "387 based" improvements; it depends on the inward flow of new bi-mode and electric units, how far the electrification has got, and political decisions as to whether the more flexible IEP units take over services such as Oxford and the Cotswolds (in which case 16x units are released) or other services (in which case
HSTs▸ are released for shortening and cascading across a very much wider area).