Fed usually use the "carrot" approach to distributing some taxes. So instead of "forcing" states to comply say to set a speed limit. They'll just withhold the funds for road repair and maintenance if speed limit is not set according to some standards. Perhaps the same goes for other things welfare money, drinking age, etc.
Some people are fiercely in favour of more state control (almost down to a religious type conviction). I never really got that. I came from Europe and when I think of "government" I think of one government entity. It operates at multiple levels but it is more or the same entity. And basic things like traffic laws, gun laws, sales taxes, etc are uniform.