> But I really like the idea of setting different speed limits for different weight classes of vehicles. Driving a Toyota Corolla? Let's call it a Class A vehicle (2,000-2,999 lbs), with a highway speed limit of 70mph. Driving a Jeep Grand Cherokee? That would be Class C (4,000-4,999 lbs), with a speed limit of 50mph.

This seems more dangerous, not less. Change a lane and all of a sudden you need to slam on your brakes because you didn't realize how much slower the other vehicle was going. Hopefully the person behind you can react quick enough. I see near accidents from this sort of thing fairly often with less of a speed difference.