Hybrids Trains with Regenerative Braking System by Deutsche Bahn and Tognum. They have converted a diesel-mechanical power car from the VT 642 series into a hybrid vehicle. Image © wikipedia
The Hybrids Trains will use new drive system from MTU, a hybrid Powerpack, uses a generator to convert the kinetic energy generated during braking into electrical energy.
This electrical energy is temporarily stored in batteries. The benefit is the reduction in CO2 emissions and fuel consumption by up to 25%.