The Gyro Monorail

The gyro monorail, gyroscopic monorail, gyro-stabilized monorail, or gyrocar all denote a single rail land vehicle, road or rail, which uses the gyroscopic action of a spinning wheel, which is forced to precess, to overcome the inherent inverted pendulum instability of balancing on top of a single rail. The principal advantage of the monorail cited by Schilovski is the suppression of the Hunting oscillation, which was a speed limitation encountered by conventional railways at the time. Also, significantly reduced radii of turn are possible compared with the 7km typical of modern high-speed trains, e.g. TGV. This is possible because the vehicle will bank automatically on bends, like an aircraft, so that no lateral centrifugal acceleration is experienced on board.

Very interesting wiki article. Too bad there never was anymore development on this. It seems very promising. Even though it looks unsafe, it's actually quite safe. If all power fails the gyros will still be spinning for a long time and the train can slowly slow down. One track also means much cheaper railway tracks.