We have very safe cars but they're also very heavy as a result. Granted gains can be made with expensive and exotic materials, but how about CHEAP and LIGHT cars that could be had for just a few grand, and get 80-100MPG?
Cars don't need to be made much lighter to get incredible gas mileage. I drive a 20 year-old car that has airbags, side-impact beams, crumple zones, etc, terrible aerodynamics, and it gets 37MPG (US) hwy (and drivers report even better real-world results). Why? Because the engine is 85HP. It accelerates onto the freeway just fine, passes most other drivers going up hills, and I've taken it up to 100MPH without breaking a sweat.
These days, engines have improved DRAMATICALLY. Engines 20% smaller, develop DOUBLE the horsepower (just one example I looked up). But instead of selling cars with sub-1.0 litre engines, they sell cars with incredibly excessive power, and terrible fuel economy as a result.
A dirt cheap car should be able to get 80MPG these days. But instead the cheapest, tiniest cars have more HP than you need to tow a 30' travel trailer...