There were a lot of interesting transportation experiments going on in the 60s/70s and quite a few of them focused on the idea of an elevated guide way on which a vehicle could move on. Though seen as futuristic at the time, I think most of those examples didn't quite pan out the way they had hoped. As a result, the remaining systems seem to be expensive to operate vs. more traditional transport systems (cars, trains, buses etc.).
Of course, my personal favorite example would be the WVU PRT (Personal Rapid Transit). Though, many people would argue that it isn't personal, it is seldom rapid, and hardly qualifies as transit.
Look at that little guy go. He's adorable.
Walt was definitely an incredible visionary. I'd love to have seen more of his ideas come to fruition.
Side note: I've finally gone over 1000 posts! It only took me 10 years!