Perhaps the easiest way to make a car more fuel-efficient is to make it lighter. The designers of the Edison2 concept vehicle have taken auto dieting to the extreme. The car — as aerodynamic as it is anorexic — weighs less than 800 lb., which helps it get 102.5 m.p.g. That was good enough to share the Progressive Insurance Automotive X-Prize, an award set up to encourage development of production-ready cars that are super-fuel-efficient. Sadly, Edison2 team owner Oliver Kuttner says you won't see the car at your dealer anytime soon. But it's a hopeful sign for an oil-pinched future.