A solution is to tax vehicles based on the ratio of number of seats to weight, with a massive tax premium for massively heavy vehicles.

Obviously at the moment (certainly here in the UK) there are loop holes when trucks and vans are "commercial vehicles" with different tax levels, many not used for commercial purposes. They need to be closed off, maybe include cargo volume in the equation so an oversized heavy pickup with little carrying capacity is penalised over a commercial van.

We are also overdue ending significant tax breaks for electric vehicles. We have reached the point where we are over the hump needed to shift the market to EVs.