It wouldn't be realistic to expect everyone to give up their cars, but it can at least be argued that reducing the general need for private vehicles is a realistic target, is it not?
Lets assume something like a mid-range family car, that you buy new and keep. The ownership of such a car tends to cost in the £400 a month for the car, insurance, tax, servicing, consumables (tyres etc) (personal leasing over 3 years without final payment). If you don't outsource the parking to the council you are spending some of your land parking the car too. You can buy second hand, but that leads to more unknown costs.
If you get 45mpg, that costs about 12p a mile in petrol.
If you drive 1000 miles a year you end up spending £4800 + £120 = £4920 = £5 per mile.
If you drive 10000 miles a year you end up spending £4800 + £1200 = £6000 = 60p per mile.
If you drive 30000 miles a year you end up spending £4800 + £3600 = £8400 = 20p per mile.
So the marginal cost of a journey is about 12p a mile, it makes sense to use the car.
If you could instead rent a car from your own driveway, based on the above prices, but with the total cost spread over 30,000 miles, you'd pay 20p a mile. Add in extra wear+tear, cleaning, profit, etc and call it 40p a mile.
Drive 1000 miles, you spend £400
Drive 10000 miles, you spend £4000
Drive 30000 miles, you spend £12000 per year
It would only make sense to own a car if you drive a lot. If you only do 10,000 miles a year it's cheaper to rent.
Once you have that decided, each trip becomes 40p/mile.
Want to go to a nearby city about 50 miles away, the train might cost 30p a mile - £30 return. Currently if you have a car it will cost £12, plus say £5 parking is £17. If there's two of you then it's £60 return on the train, and £17 on the car.
If you instead pay 40p a mile and avoid parking (point-to-point rental), it comes out to be £40 return. The train is now cheaper than the car (£30 vs £40), and you're still paying less than you would before, with an expensive asset rusting away in the driveway.
Even while for two the train is still more expensive, it's not 3.5 times the price as it is now, and the ease of using the train may be worthwhile (especially adding in family or two together railcards)
If the cost of using a car can be more correctly spread as a per mile cost, and no, or limited, fixed cost, I suspect the number of trips it makes sense to use the car on will fall considerably, even with no other changes.