As for the problem of where cars will go: much as I dislike any "anti-car" measures, such as "price motorists off the road and force them on to public transport", I would be in favour of more car-pooling schemes: cars that you can easily rent when you need them, (emphasis on "easily"), so you don't have to own one. There are lots of these in big cities like London, but almost none outside. Sometimes the worst place to be is in small towns just outside a big city like London: the "magnificent London public transport" is not in walking distance, so you need a car or infrequent bus to reach the Underground stations (and TfL keep selling off the station car parks), yet there are none (that I know of) of these car-pooling schemes in towns outside London.
When you own a car, it's expensive not to use it. It's a sunk cost fallacy. Public transport is then an expensive, slow and unpleasant "luxury". Also, as we are being nudged towards using electric cars, they are still very expensive to buy and repair; so people (like me) hang onto their petrol cars. Once somebody has invested in electric, and paid a few thousand pounds to be able to charge it at home, they are not going to want to use expensive public transport. This is what the powers that be keep overlooking. What we need is for each town to have easily accessible communal electric cars, like the bikes in London, that people can use when they need.
Suppose a family of four wants to travel to visit grandparents. The choice is often as follows: car journey, about £10. Train journey, £60+, probably slower, less reliable, and they still have to pay their ongoing car costs. Tough decision, innit?