I think it's one problem at a time. Curbing driving is a separate goal. Reducing pollution from tires is potentially a smaller and direct goal. Either people drive less or use tires that don't shed. That's why I think the tax should be related to the composition of the tire. I agree that people may end up driving on bald tires, and we don't want that. I'm British but live in the US and I think it's utterly insane that vehicles aren't required to have annual or bi-annual safety checks. An emissions test is not a safety test. A safety test involves breaks, tires, and headlamp alignment. I really wish we had headlamp alignment tests in the US. I want the 'freedom' to drive knowing the other cars are safe or the other driver is going to be charged if they are caught or are involved in an accident.