There are already many driverless subways in existence (especially at airports). Many driven subways (BART in SF) are actually driverless, with a driver there just to close the doors and in case of emergencies.
Good luck implementing totally driverless subways on currently driven subways, though. Unions will totally block the necessary incremental steps, so it would have to be an all-or-nothing back room skunkworks project from a public transit authority.
http://en.wikipedia.org/wiki/List_of_driverless_trains#Unatt...
Good luck implementing totally driverless subways on currently driven subways, though. Unions will totally block the necessary incremental steps, so it would have to be an all-or-nothing back room skunkworks project from a public transit authority.