electricity/train

Anyone know anything more about this? CTA tattler tells us:

Through regeneration, AC propulsion offers power savings. Some of the power used to accelerate the train can be recovered and put back into the power (third) rail when stopping the train. This provides additional power to accelerate other trains and reduces the total amount of energy required to run the system. On trains using DC propulsion systems, the braking energy is dissipated as heat.

Sounds pretty amazing!