The upcoming TriMet Portland-Milwaukie light rail line has been designed so that power captured from braking trains can power accelerating ones.

The concept is quite similar to a hybrid car with regenerative brakes, except the battery isn’t on board. In fact, there’s no battery at all. The Siemens Sitras SES system that’s set to be installed in Oregon actually uses a massive supercapacitor to store up juice.