use flyweight to accumulate kinetic energy
consider the following mechanical system: a massive (100kg) spinning flyweight connected with the driving wheels through CVT like that: http://www.youtube.com/watch?v=kOeXQrS6WPU then, acceleration of the flyweight is a result of car slowing down (kinetic energy accumulation), and acceleration of the car is a result of transmission of the energy accumulated on the flyweight. the brake pedal will shift the transmission into a "negative" ratio, accumulating the speed of a car in the flyweight. (make sure that the flyweight turns parallel to the road, otherwise the gyro forces will flip the car turning on a traffic light) probably, a flyweight with 30cm radius and weight of 100kg spinning at 1000rpm will be enough to accelerate 1000kg a smartcar to the speed of 30 km/h this was a mechanical "analogy" for {the "breaking" magnets / inductor accelerating its rotation (and thus generating power) in exchange to slowing down the car motion} idea I presented earlier... the advantage of a hybrid between the two might result in a compact multi-purpose unit.