Thought about, but never built.
You realize that monorails come in several different flavors:
The one I was thinking about would have been a narrow straddle type, loosely based on a mineral tram that ran in the Mojave Desert a century or so ago. (The prototype didn't do anything a cableway couldn't have done - but cableways 40 miles long are somewhat impractical.) It's still on my list of, 'someday, maybe,' projects - a couple of lines below the operating TBM eating its way through Haruyama (the mountain, not the station named after it.)
Chuck (modeling Central Japan in September, 1964 - when TBM's were a brand new idea)