A version of it could be done. Probably in a newer city where the buildings and streets aren't so entrenched. But then in that case there wouldn't be a huge number of cars and people. So I guess it's not going to be practical in many places. Not to mention natural disasters like earthquakes and tornadoes and such.
But the bottom line is gonna be profit. If somebody, ie. : politicians, can get paid expect one in your town soon. Just like the Springfield Monorail.