Curious if each car of a subway/elevated train provide power to moving the train or if only the lead car pulls the train? I am specifically thinking of the subway trains in Chicago and realize that this may be different for different systems in different cities. I cannot think that having all the cars providing driving power would be efficient or useful. Wouldn’t it be really hard to get all the drive wheels spinning at exactly the same rate? If they didn’t some wheels would be spinning too fast and others too slow either of which I imagine would not be good or helpful.
Then again looking at the subway cars in Chicago they all seem to have the equipment on board to drive themselves around. This also seems like a waste as it has to add significantly to the cost of the car rather than having no engine that is meant to be pulled around by another car.