Doesn’t sound very sustainable to me - taxes can’t keep going up
It depends, for example you could make the railways a lot cheaper to run if you didn't have to have a lot of staff selling tickets, other staff checking tickets, more staff catching people without tickets and yet more staff issuing refunds due to trains running late. That's before you consider the costs of managing all those people, providing training and providing uniforms for them.
Likewise, if people didn't have to pay for public transport buses would be able to run faster as each stop would take less time. Also with far less being spent on car ownership (a lot of it going overseas in buying fuel and paying for cars which aren't made in the UK) then there would be more money for people to spend on other things.. In addition, the savings could mean less debt, which again further increases the amount of money available to be spent on other things. Finally with it being easy to go places to find employment you could find that the economy is larger as Pele are more able to find work/find higher paid work without worrying about the cost of their travel.
It would also save the costs of taking payments (be that card payments or handling cash).
There could even be other cost benefits, for example older people would be less likely to be isolated and all people are likely to be fitter (even walking a little bit to catch the bus rather than driving, would make people a little healthier) and so save the NHS in diseases associated with inactivity. As well as the health benefits from reduced car use and the massive amount of time lost due to road congestion.
It then comes down to would it be cheaper overall to the tax payer to try and squeeze every penny out of passengers or to allow every passenger to travel for free and the cost savings that would produce?
I don't know the answer, but I ask the question to challenge the assumption that we have to reduce the subsidy by users paying more for it.
In a similar vein people can get upset about the increasing benefit costs and so say that we need to encourage people into work - only the largest cost of benefits to those not currently working are to those who are planning on never working again. Should we force them into work?
However, when you look at what is the reason for the big increases in benefit payments, it turns out the pensions are that largest cost and the pensioners would get grumpy if they had to go back to work.
Sometimes the narrative isn't as clear cut as it appears at surface level and I wonder if public transport subsidies is one of those examples.