Average U.S. Car Weight Increasing

Why is that a problem? Approximately 10% reduction in vehicle weight can reduce the fuel consumption by about 5-6%. The average vehicle weight has been increasing for over a decade now. However, several issues get confounded with the story.

Government studies say these giant vehicles are increasing the overall number of deaths in accidents, mainly because of the threat they pose to people in cars they hit in collisions. The administration's plan does suggest that manufacturers be pressed to slim down the heaviest of the heavyweights, like the Hummer.

As I have noted previously, the arguments against the proposed changes in CAFE standards are weak. Of course, even if weight based standards were applied to the light-trucks (not to cars) as NHTSA proposes, the increase in CAFE standard would be small (~0.5 to 1.5 m.p.g. over three years). Further, lightweighting the heaviest of the vehicles will only improve overall safety. This is completely consistent with the NRC report on CAFE.

Two more points. If light-truck standards were made class based, american companies, notably GM is likely to benefit, as it leads in fuel economy in several of those categories.
Secondly, Mr. Shosteck's statement that if all vehicles were made heavier, it would have a positive impact on safety, is nuts. We would all be safe if we all drove buses.