The Boynton Bicycle Railroad

That is the whole article. You click on the Read the whole article link, and you get no more info.

Seems obvious anyway that it would fail. There is no space advantage to a single bottom rail since the cars need to be about the same width as a normal car and the support structure for the top rail makes it wider than a normal 2-rail roadbed. Also, the expense of building and supporting the upper guide rail would be prohibitively expensive. I'm pretty sure that over a purpose-built 2 mile stretch of track a conventional steam locomotive of the same era could achieve 100 mph.

A bit of side info, by the way, is that there were bicycles made to run on 2-rail rail systems. At the Cass Scenic Railroad museum in Cass, WV, you can see the bicycles used by a medical doctor to visit the logging camps along the railroad.

Here is the link they took it from.