I just saw a piece on TV about the Wuppertal, Germany Schwebebahn, a suspended monorail that is over 100 years old.
It seems like a good model for the US. The trail can be suspended directly over existing roads and stay within the existing right-of-way.
And besides being a good idea, it is a visually impressive solution to the car as well.
The US needs more transportation options and something like this would add a lot of character to a city.