This is an experimental single rail gyro train . It was stabilized by using a gyroscope. You can read all about it here:
http://www.absoluteastronomy.com/topics/Gyro_Monorail
You can build a simple single wheel gyro car that runs on a single rail made of bandsaw blades. Read all about this DIY project here:
Dave, I can see this adding single rail to the continuing argument of 2 rail v. 3 rail. Bruce Baker
Looks like it needs a kickstand. How hard would it be to make a toy one like that?
Thanks Dave, You always have neat items. Ralph
Naw, that would just mean that 3-rail track would now be dual-gauge.
I wouldn’t think that gyro train would have much traction. In fact, it’s not clear to me what “problem” it was meant to solve.
That is the Brennan monorail, patented in 1903 and demonstrated in 1909. The advantage claimed was that it was useful for a military railroad since track could be laid quickly. The 1962 version was by Swinney and looked more like a rocket.
“In fact, it’s not clear to me what “problem” it was meant to solve.” Spoken like a true engineer! 
Still pretty cool looking, though.
Now the next item of business: how to build a model of it, and, specifically, how to power it. Two rails would seem to be the minimum for an electrical circuit; but I think we can do it with one:
Make the conducting surface of the rail in segments, for example, 3/4 inches long, with a little plastic in-between so that a wheel doesn’t short two adjacent segments together. Power alternate segments with the two wires of the transformer circuit. Put a pickup assembly on the monorail vehicle with three fingers or rollers spaced 1/2 inch apart. We can show that one side of the circuit will always have two fingers and the other side will always have one. Connect each finger to two rectifier diodes, one pointing from the finger to a positive node, the other pointing from a negative node to the finger. Those two nodes are the rectified DC source for the motor (and e-unit). Put at least two such assemblies on the monorail vehicle, as far apart as possible, so that any necessary break in the rail-segment pattern affects only one of them at a time. The fingers can also have other spacings, such as 1 inch and 2 inches. With luck one of these spacings will match the wheel spacing so that we can use the wheels instead of fingers.
Brilliant!
That is pretty brilliant (but we expect no less from you, Bob!) However, what do we think of using catenary? It might not be prototypical, but it would be cool. That way, you could have your two separate power wires-one in the rail, one in the cat. That still doesn’t help in keeping it upright, though…