Besides, time is money, and people like to get where they are going in a timely manner. Where I live, 60 mph is an acceptable speed limit for most people considering the huge distances across country, although many exceed it. That's why lowering the speed limit won't work either. Alot of people are willing to risk getting a ticket knowing full well that the police don't have the man-power to enforce the speed limit.

People want a car that goes at least 60 mph, has some guts (peppy acceleration), feels safe, has good visibility, and handles well.

If a maximum weight and horsepower were established for non-freight vehicles, then to give cars more pep manufacturers would have to lower the vehicle weight. In doing so they would also improve fuel economy. I'm not suggesting that this system be used to reduce consumption, rather to prevent it from growing. Same with emissions. Later they can consider the merits of decreasing it further if needed (or not).