Employing regenerative braking in trains can lead to substantial CO2 emission reductions, especially when applied to full stop service commuter trains (8 – 17%) and to very dense suburban network trains (~ 30%). Regenerative braking applied to freight trains can also lead to CO2 emission reductions, albeit considerably lower than for full stop service trains (~5%). When regenerative braking is employed, the current in the electric motors is reversed, slowing down the train.
A regenerative brake is an energy recovery mechanism which slows a vehicle or object by converting its kinetic energy into a form which can be either used immediately or stored until needed. This contrasts with conventional braking systems, where the excess kinetic energy is converted to unwanted and wasted heat by friction in the brakes. In addition to improving the overall efficiency of the vehicle, regeneration can greatly extend the life of the braking system as its parts do not wear as quickly.