Pictures

Adelaide's O-Bahn was introduced in 1986 to service the city's rapidly expanding north-eastern suburbs, replacing an earlier plan for a tramway extension. The O-Bahn provides specially built track, combining elements of both bus and rail systems. The track is 12 kilometres (7.5 mi) long and includes three interchanges at Klemzig, Paradise and Tea Tree Plaza. Interchanges allow buses to enter and exit the busway and to continue on suburban routes, avoiding the need for passengers to transfer to another bus to continue their journey. Buses can travel at a maximum speed of 100 km/h (60 mph), but have been restricted to a 90 km/h (55 mph) speed limit since 2016. As of 2015, the busway carried approximately 31,000 people per weekday.[2] An additional section including a 670-metre (2,200 ft) tunnel opened in 2017 at the city end to reduce the number of congested intersections buses must traverse to enter the Adelaide city centre.[3]

Straight from the Wikipedia. Seems like it allows busses to transfer to different parts of the city using the tram systems right of way, bypassing busy streets. They can hop on and off on certain spots. Pretty clever really.