I was going to have the O-Bahn bus system as a puzzle one day, but del78 has bet me to it.
The city of Adelaide, in Australia has had this system in place for years. The only countries that have, or had it, as far as I know are Germany, somewhere in South America and Australia. As far as I know, it was a system designed by Daimler Benz, and they were (I think) the civil engineering consultants during the construction of these.
I've ridden on the Adelaide system (1st photo). What happens is that the buses operate throughout the city, and when they get to the outskirts, they can then enter the O-Bahn, which is a system of specially designed concrete tracks for the buses to run along. In the second photo, you can see the little guide wheels that sit in front of the front wheels. What happens is that when the bus is on the tracks, the driver switches the bus over to O-Bahn mode, the little jockey wheels flick out to the side and over ride the conventional steering (2nd photo); this can be a little worrying, as the driver is sitting on about 80kph, takes their hands of the steering wheel and sits back. This was all very high-tech for Australia back in the 70's, and it's still being used today.
