What if Mass Transit Systems, as well as reducing pollution, where used for transport? What I mean is, you would be able to instantly send a unit in a city with an MTS to another city that also had MTS. This wouldn't negate railroads, which come a whole age earlier anyway, because the free move only applies to a city - not overly useful for sending troops to your border, something that can be done earlier (and easier) with a good rail system.
But if the free move is a problem, then it could simply be that it takes up 1 turn to move the unit, which, now I think about it, would probably be more realistic.
But if the free move is a problem, then it could simply be that it takes up 1 turn to move the unit, which, now I think about it, would probably be more realistic.