These particular units are called Velocities and run as 3 car sets. The end carriages have a driver's cab. The centre one has no cab but you can walk through. Each of the 3 has it's own motor. They often couple 2 sets together to make a 6 car train
They are are only passenger rail service from Echuca to Melbourne.
The reason for trucking them rather than railing then is to do with the changes after privatization. The owner of the broad gauge tracks is either VicTrack or Metro. At the moment all standard gauge track is the responsibility of ARTC. So v/line don't own the tracks they run on and pay an access fee.
As part of this all new rolling stock has to be accredited before it can run on the tracks amongst other trains. So the trains are trucked to where they can be put on track at one of V/lines workshops so it can be tested and accredited in a 'private area'.
The same happens for equipment going to South Australia, NSW and elsewhere as it's cheaper and less paperwork to move them as an oversize load than the paperwork and exemptions to rail them.
Hiding in the shed covered in grease and muck - want a coffee?