The Adelaide O-Bahn raises a peculiar problem in the case of a bus breaking down:
Hoist the bus off with a crane? Due to the nature of the terrain surrounding the O-Bahn track, this is impractical for much of the track's length.
Drive another bus up behind, and push it home? This is the solution implemented in Germany. It's awkward, and having the driver able to see obstructions is difficult and dangerous.
Just tow it off? Sure, but that means reversing down the track to get to the front of the crippled bus. There's no way to turn around on the track.
Mercedes came up with another solution...
(Front -->)
_____ _____
/ ] [ \
| [__]|===========|[__] |
/_____|___________|_____\
(| ___ ___ |)
>[_/.-.\_|_______|_/.-.\_]
|(O)| |(O)|
'-' '-'
Their special-purpose, one-of-a-kind vehicle has been nicknamed "Dumbo". Dumbo is based on a heavily modified Unimog, the transmission thus giving it six speeds in both forward and reverse. Merc 22xx series cabs were placed on both ends, with all controls duplicated in both. A towing mechanism at the back of Dumbo enables it to haul crippled buses from the O-Bahn track. There is technically no right or wrong direction to drive Dumbo, except that it can only tow in one direction. While Dumbo has 4WD, only the front pair of wheels are used in steering, and the rear wheels are locked straight. Guide wheels, the same as those fitted to the O-Bahn buses, are attached behind all four of Dumbo's wheels. Between the two cabs is a walled bed used for general storage of tools, parts, etc. The words "BUSWAY RECOVERY" are printed in black across the front of both (white) cabs, just above the grill. Although originally stationed at St Agnes depot, close to the O-Bahn, Dumbo has been kept at Mile End for the past few years.