Are subwaw trains All-Wheel Drive?

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.

Any ideas?

AFAIK, all subways use traction motors on each axle.

The three primary reasons:
Great gobs of torque to move the train in direct proportion to the length of the train. You don’t have to worry about needing to adding another engine when you add cars for rush hour.
Great gobs of braking power to control and stop the train, again, neatly in proportion to the train length.
Flexibility in setting up trains - no need to worry about which car has the motors, or which needs to be at the front of the train.

Accoring to this Wikipedia entry, the latest generation of New York City subway vehicle have traction motors powering each axle. I cannot offer guarantees about other systems and eras.

The Skytrain system in Vancouver uses zero wheel drive. The wheels are simply bearings to support the load and guide the cars along the rails. Propulsion is provided by field effects between linear induction motors on the underside of each car, and the track surface beneath.