It's extremely hard to prove culpability and very rare for a truck driver to be successfully charged. In the case of Kerang I believe the truck driver argued that the lights didn't appear to be working and nobody could prove otherwise. The Trawalla accident I can fully understand how that happened because the truck was slow, had an extremely heavy load (ten tonne block of blue-stone); it was a remote, unprotected crossing and on a corner where it was impossible to see any distance down the track; in that instance he claimed that when he stopped he couldn't see anything coming but by the time he got halfway over the track the train was on top of him and there was nothing he could do.
Benella was B-double on an unprotected crossing; as I recall there were actually three crew fatalities. There was a report at the time that indicated the B-double cab didn't allow enough side visibility of the approaching train and the crossing was on an unusual angle. There was also something in the court case about the train being 'not expected' because it was out of grain haulage season. Again, the driver got off on that basis.
It's highly unlikely that the driver will be convicted in the Cranbourne crash on the basis of the above; all you have to do is say there was some kind of extenuating circumstance ("the sun was in my eyes") and you'll get off. Sad but true, unless you're drug or alcohol affected you'll almost always get off. Even then you can be on heavy impairment prescription drugs like codeine, benzodiazpam or oxycodone and as long as your doctor gave it to you then you're in the clear.
This also extends to all other motorists. There was a coroner's inquest into a very elderly gentleman killing a cyclist in rural Victoria some years ago where the motorist had lost sight in one of his eyes due to a stroke and was also partially blind in the other one; he also had a mild dementia (as I recall). Apparently he got off criminal charges because his doctor didn't tell him he shouldn't have been driving - despite the fact that you would think it's self-evident that you shouldn't be driving in that condition. We don't have any mandatory reporting or compulsory reviews here in Victoria so unless your doctor informs Vicroads or the police pick you up for doing something stupid its likely that you could keep driving forever with almost any medical impairment.