(AP) - U.S. transit agencies hope to save money by storing energy created when subways put on the brakes.
For years, subway cars have been able to recycle some of the energy created when they brake. They turn resistance into energy to help power the train or others running on the rails at the same time.
But much of the energy is wasted by the time the train stops braking. Now, transit agencies in Philadelphia, New York, Los Angeles and Washington are experimenting with ways to store that power in batteries so it can be put back into their system later.
Philadelphia's Southeastern Pennsylvania Transportation Authority is setting out on a pilot project at one of its substations and thinks it could ultimately save 10 percent on power costs.