Federally, all of them. I dont think it is a role for the federal government. The only plausible authority it the continued in proper use of the commerce clause to justify all federal action.
At the state level I think the only regulations should be those around direct safety concerns (like air bags, lights, etc). Efficiency or other non-safety related regulations should be disallowed. Further safety regulations should be limited safe operations for other drivers sharing the road, not passenger protection (outside of regulations on truth in advertising, product defect)... passenger protection should be a market dynamic, coupled with greater tort reform to be able to hold liable manufacturers for their marketing claims.
At the state level I think the only regulations should be those around direct safety concerns (like air bags, lights, etc). Efficiency or other non-safety related regulations should be disallowed. Further safety regulations should be limited safe operations for other drivers sharing the road, not passenger protection (outside of regulations on truth in advertising, product defect)... passenger protection should be a market dynamic, coupled with greater tort reform to be able to hold liable manufacturers for their marketing claims.