My understanding is that there are significant differences between those rail replacement bus/coach services which can be planned well in advance (in some cases many weeks/months) and those that are very short term, truly emergency situations.
I guess also, sometimes situations morph between the two. So for example, a landslide or failed bridge may be sudden and cause an emergency rail replacement bus, but it may take many months to repair and so the rail replacement bus becomes more long-term and more planned.
The planned use of buses/coaches for rail replacement work (such as Blackpool recently, and Derby shortly) is using vehicles over a specified route, with individual fares paid [albeit initially to the TOC], and operating to an agreed timetable. For these planned operations a vehicle needs to meet PSVAR legislation.
In which case, I wonder why so many coaches in use as rail replacement buses in such circumstances are inaccessible at the moment.
Coaches that were first used on or after 1st January 2005 are subject to PSVAR now (if used on scheduled services at separate fares, as per the above.)
I had a quick look at the website of the main provider of coaches locally for Northern's rail replacement buses for e.g. their industrial action days and currently on Windermere. Over half of their coaches were manufactured after 2004. Unhelpfully, whilst their website lists whether each one has a toilet, air conditioning etc etc., it doesn't mention whether each coach is wheelchair accessible; but the pictures, and Northern's communications with me, suggests that they are not.
As I mentioned above, it's quite likely that there will be insufficient disabled-friendly *coaches* from 2020 but the early ex-National Express vehicles that comply with PSVAR have already moved on to smaller operators and, in any event, there are numerous *buses* around.
That's good news. (I originally asked about buses and coaches, not just coaches.)
I guess that on the bigger rail replacement work there only needs to be 1 compliant coach out of the 5-6 that might be covering one train journey.
The other 4 or 5 being accessible buses?
I don't think the PSVAR differentiates between situations where one bus, or several buses, run to the same schedule - my understanding is that PSVAR would apply to all the vehicles covering the one journey (provided it's got a published schedule etc.)