... Even most modern trains are not level with platforms (although I've read that the new ones in East Anglia are, which makes me wonder why it isn't a requirement for new stock), so some assistance is needed in getting on and off come what may.
Up to now, the whole industry seems to have judged that "too hard" and not really tried to do it. But now Stadler have taken it seriously, so their FLIRT trains for
GA▸ do offer level boarding. This involves a number of factors, all specific to the
UK▸ .
The British gauge has evolved with platforms high enough and coming far enough out for one step up into the train, and as a result it is narrower at platform height and below (unlike continental ones). The floor has to be above platform height for this to work - but at least that allows for level floors throughout the train and enough space for bogies underneath - just. Lower continental platforms can be level with the floor downstairs on double-deckers, or between bogies, but you need steps or steep ramps to get between cars (and upstairs, obviously).
Stadler have shaved the floor depth over the bogies (shared or Jacobs ones for FLIRT) enough to get the whole floor level, and to match platform heights*. It has to be narrower at floor level than other trains, and to fill the gap there is a motorised gap-filler (not really a ramp or a step as it's level!). For the bimodes, the engines now can't fit under the floor, so they go in a dedicated short semivehicle, but that brings the advantage of not distorting the engine/cooling systems to fit a shallow space.
Obviously that gap-filler, being mechanical, can fail - we'll have to see about that. And it does still leave a small gap, rather than pushing out until it meets the platform edge. But Stadler, being Swiss, come with a reputation for engineering quality even higher than the Japanese - and have not just set up a factory here from scratch - so we'll see! And we'll also see how much this alters thinking for other train procurements or designs; will everyone want ones like this? It would certainly push the balance between new build and rebuild even further towards the former.
For more on this, there's an informative
PR▸ video here from Railway Gazette International, and
another of Geoff Marshall having a go on one - he's quite a fan.
*I'm still not 100% sure of either, as platform heights do vary, and there appear to be steps in the floor but I think only right at the ends and under the seats over the wheels.