There's no free lunch. Mandating more gas efficiency means you necessarily get less of other important things people like and want, such as safety and cost savi

There's no free lunch. Mandating more gas efficiency means you necessarily get less of other important things people like and want, such as safety and cost savings. One way to make cars a lot more fuel efficient would be to get rid of the weight of the roll cage...but then more people would die in auto accidents. Another would be to replace much of the metal with stronger, lighter, higher-tech alloys...but then the car would cost twice as much. That's the sort of tradeoff that makes a difference. If we could somehow get rid of all the mandates - not just the environmental ones - we'd tend to see better overall cars and a wider range of cars available with some that specialize in super-low emissions while others specialize in better safety or higher performance or whatever. But just piling on new requirements atop all the previous ones isn't going to get you major improvement - there's diminishing return on that.