The efficiency of a car can be vastly improved, as you say. However, there is still a limit to how much it can be improved. Energy that would otherwise be wasted, via braking or suspension movements, or even noise and heat, can be recovered, at least partially. There will still be a minimum amount needed to propel the car, that cannot be recovered or reduced, without affecting the movement of the car by slowing it down. Because the thermodynamic efficiency of internal combustion engines is pretty bad, there is plenty of room for reduction of energy use - perhaps to the order of 80-90%, as you say. But my point was that even if you had a drive system that is 100% efficient, and you recovered all possible energy from vibrations and oscillations in the car structure, from braking and from the suspension movements, etc., your drive system would still have to supply some energy to overcome aerodynamic drag, frictional drag, climate control, radio, lighting, power-assisted steering etc. in the car. There is a lot of room for improvement, but travel will never happen without some energy being consumed in the process, and this is the minimum limit of the energy needed to propel a car.