Is is possible to make cars significantly lighter without compromising safety? Damn skippy. But it's also hideously expensive. A Formula 1 chassis without engine or ballast could be picked up by a few guys and allows the driver to walk away from wrecks that in any current road car would leave the occupants looking like chunky salsa. But they also cost tens of millions of dollars. Each.
Even if you look at high end sports cars, thanks largely to carbon fiber, the weight is amazingly low when you consider the power it has to absorb. And crash survivability is also very good. But again, you're talking well into 6 figures to buy one.
For a typical family sedan that technology is simply not affordable. And economy of scale really won't bring the price down all that much.
Far better than screwing with CAFE standards would be to "drill baby, drill" while also building a metric crap-ton of nuclear plants and using the gas/coal saved to produce whatever "drill baby, drill" doesn't, and then use the excess power from the nukes to start making synthetic hydrocarbons and reserve all that oil for value added products like plastics, fertilizer, etc.
