Go all the way to encourage easier, safer, and more practicable biking by converting the elevated rail line into a bikeway.  Biking is clean and green, but the train would be dirty because it would run on electricity generated mostly by fossil fuels.  Another advantage of converting the rail line into a bikeway is that it could be roofed with something like Elon Musk's solar roof so that it's a source of clean energy.  

The driverless car is not far away.  In fact, driverless Uber cars have been operating in Pennsylvania for months now, although with a human in the driver's seat who can override the car's computer when necessary.  And driverless car technology is being constantly improved.  The driverless car is going to increase road capacity, especially when there's a computer system that coordinates all cars on the road.  That's the technology of the future.  By contrast, rail is obsolete technology.  The elevated line, however, can still be salvaged as a bikeway.