In areas where cities are dense enough for public transportaiton to make sense, adding a new line does indeed lead to induced demand. For cities that are spread out and unwalkable (read: almost all US cities), public transit isn't efficient enough to move enough people from point A to B, due to A and B being very far away -- never mind the fact that once you get to B, you can't even walk to many destinations due to the city being designed in such a sprawly, pedestrian hostile way.
For public transportation to work, we first need to make our cities denser. The best way of doing this is by outlawing use-based zoning and moving to form-based zoning. That means getting rid of the concept of a "single family zone" and a "commercial zone", etc. and just specifying stuff about the materials and shapes of buildings. It also means outlawing parking minimums. Many cities around the world (and even a few in the US, re: Philadelphia, NYC) have this kind of zoning which allows for much denser development.
For public transportation to work, we first need to make our cities denser. The best way of doing this is by outlawing use-based zoning and moving to form-based zoning. That means getting rid of the concept of a "single family zone" and a "commercial zone", etc. and just specifying stuff about the materials and shapes of buildings. It also means outlawing parking minimums. Many cities around the world (and even a few in the US, re: Philadelphia, NYC) have this kind of zoning which allows for much denser development.