Flywheel technology is creeping into motorsports as way to store energy that’s otherwise wasted. The technology ultimately makes racing cars more efficient and more powerful at the same time. However, flywheels may soon be incorporated into subway systems to bring affordable power to sprawling cities. Each time a subway train hits its brakes, a massive amount of energy is dissipated. Modern trains run their electric motors in reverse to slow down then release the energy as heat or into a grid ill equipped to absorb the surge. A flywheel, however, is able to capture that energy and effectively…