Since the guide wheels steer the bus, the driver only has to apply accelerator/brake and there is no chance of the bus deviating off the track at high speed. So

Since the guide wheels steer the bus, the driver only has to apply accelerator/brake and there is no chance of the bus deviating off the track at high speed. So it can travel at a faster speed more safely. The track is also more compact than an equivalent two-lane dedicated bus roadway - especially given the safety margins roadways need when you have high-speed vehicles travelling on them. Being more compact meant the O-Bahn route could follow the Torrens creek which gave it an unobstructed route from the outer suburbs right to the CBD without expensive land purchases etc.