Thanks for that link. I’m 99.99% certain that the general times per zone used hasn’t changed since the feature was introduced back in 2010 (IIRC). Initially some values which the formula says should be a multiple of odd minutes were rounded incorrectly, but that was fixed ages ago. The other change was the allowance for journeys in zones 1-4, but this is catered for by using a different multiplier on the journeys involved. There are indeed some specific journeys that have a higher multiplier than the zones crossed would indicate because customers have complained that it wasn’t posssible to make valid on-time journeys without falling foul of the limit.
I also believe that where two or more routes exist for a journey the same multiplier is used based on the most number of zones. Thus Heathrow to Upminster on the District line is always classed as 11 zones, even if zone 1 is avoided. This makes sense in that the avoiding zone 1 route will usually take longer. Also, if the end station is dual zoned I understand that the reverse to fare charging takes place and the extra zone is added in to the multiplier. Thus Hatton Cross to Upminster is still 11 zones. I haven’t had official confirmation of this, but both measures make sense.
I can also understand the TOCs concerns about longer distance journeys. The ‘rules’ suggest that Gatwick to zone 1 ought to be 14 zones which means over 3 hours would be allowed. I’d have no problem with that figure being reduced as it’s clearly nonsensical. If it hasn’t been reduced I can equally understand why it would be deemed desirable to keep the data hidden. There has been no public statement as to how contactless PAYG maximum journey times are calculated, but by their nature this is done in the back-office so there could be a completely different set of rules.
The big problem that I have with the current situation is that when MJTs are exceeded for reasons outside the control of the passenger, they are hit with a financial penalty which then needs to be reversed. Because of this I believe that greater transparency is required.