I had an idea of using a strong spring that is a coiled band, like a watch spring, to recover the coasting energy when a bicycle is stopped. When the brake is applied, the outside of the coil connects to the wheel and the spring winds up as the wheel slows down. When the bike stops it locks in place to prevent the spring from uncoiling and pushing the bike backwards. Now the coasting energy is stored in the coiled spring. A sproket that is attached to the center of the wheel, is also attached to the center of the coiled spring. The energy in the spring wants to turn this sprocket in the forward direction. When the brake is released this sprocket turns forward as the coiled spring unwinds, and it pushes the wheel making it turn forward. So as the spring unwinds it is using its energy to push the bicycle forward, so the coasting energy of the bicycle is now transfered back into the forward motion of the bike. When the coil is unwound completely, the bicycle wheel simply wratchets past the sproket in the center of the spring, and the wheel turns free of that sprocket.
I condsider this an engineering and metalurgy problem that could be solved by trial and error, and experimentation. The right kind of spring would need be developed and mechanical engineering would be needed to connect it together correctly.
If you could get it to work for a bike, you might be able to get it to work for a small car.
Changing the brakes might involve installing a new coiling spring.