Harnessing the kinetic energy of subway trains

    Why not capture the kinetic energy of subway trains and use it to supplement the power the trains consume during startup.
    The system would operate through a variation of regenerative braking. A flywheel attached to the rail system would harness the energy of trains as they slow for a station, converting it to electrical power. The harnessed power could then be used to give the train a boost to get moving again.