That's what is done in good old Europe since decades. It is also the main reason that we have much less heavy SUV's over here. For the average consumer they guzzle too much expensive gas.

Money is a powerful aide to steer the population. The popularity of diesel cars here has financial origins as well. Diesel is taxed less (thanks to the trucking and transportation lobby), driving a diesel car pays twice: It consumes less and its fuel is less expensive.

Markus