'Round here (in the US generally) we'd probably run the risk of being arrested for possible terrorist activity or other such nonsense for attempting to photograph the mechanicals of a public bus like that.
I wish you luck; I think it'd be interesting to see what the frame and hitch arrangement looks like there. IE do they have a dropped sub-frame for the engine cradle area, or is it single-piece, and how's the hitch arranged. If buses towing mail trailers is really so commonplace there, it wouldn't surprise me for said buses to have been designed for that purpose. Their construction would then be different to the RE school buses we're talking about, which makes it an unfair comparison (designed for towing vs retrofitted). In any case there could be some things we might learn by looking at their example.