A car that uses natural resources to replenish itself. So solar panel roof for example, to recharge batteries, KERS like F1 cars, a wind a tiny super economical 500cc 2 cylinder engine with a turbo and a supercharger to aid the batteries in moving the car, as well as driving a powerful alternator to recharge the batteries while on the go. Could also use downhills to recharge and save fuel, so coasting downhill whilst maintaining a constant speed with the alternator still spinning and recharging. The car could run off LPG, or even hydrogen to be even more eco friendly.
I think a super eco friendly car is what the future wants, as petrol will eventually run out/cost too much.