A diesel electric train is not a hybrid in the same sense a car is. The diesel-electric train just uses the electric motor as a transmission, and when it brakes, the brake pressure is converted to electricity and then exhausted as heat through the top of the train (though the noise is very similar to regenerative braking on a hybrid). A true hybrid train would get little efficiency gain from regenerative braking, because it spends so little time actually braking relative to the distance it travels, and most of the time it is operating under full engine load (unlike a car). Only purely electric trains use regenerative braking, and even then the effect is mostly limited to other train using the same catenary system.