I’m not proposing a tax, to be clear. One problem with these sorts of taxes on driving is that drivers often see them as a ‘service charge’ they pay to use the roads and they then expect governments to plot that money into road maintenance/construction. I think it’s not great to have a tax whose revenue that people feel should be earmarked for certain things. Perhaps something like an emissions/inefficiency levy on car tax (and based on miles driven) would help but I doubt it would be politically tenable, especially with the current government trying to de-boris their policies (and so walk back on various green things).
I think part of the solution would be changing safety standards to better capture the dangers to other road users, changing liability rules/penalties to make such cars more expensive to insure (though probably the effect is too small to make much difference), having some fines scale with the value of the car (on the one hand I think people speeding, etc, in flashy cars should be particularly penalised. On the other, the UK already has some fines that are meant to scale with income and letting people off by driving smaller cars seems bad. Perhaps an alternative would be fines for certain infractions that are higher for cars that would do more damage were something to happen as a result of the driving), installing more bell bollards on corners so the people who aren’t good at staying on the road risk big dents instead of running over a toddler, and more enforcement against minor violations. Lots of those don’t specifically target oversized cars though.