The two G class they wrote off at Ararat some years back (517/518) was a marvellous unplanned demonstration of all sorts of things. The two crew in the moving loco applied emergency braking, then after they had done everything else possible hit the floor behind the seats prior to impact. Several thousand tonnes of mass collided at 70km/h. The crew both survived, and subsequently returned to work.
An N class struck a sand truck near Moriac a few years back. Another impact with a heavy and strong object; the cab filled with sand, the driver was behind his seat and survived (although a little sand-blasted).
In both cases, their ability to survive was based on getting out of the seat. Had they stayed in those seats, the destruction of the windscreens (which of necessity are large, but thus prone to be a weak spot) would have allowed potentially lethal objects to penetrate their space.
Getting out of the seat prior to impact and onto the floor still seems a better survival strategy than staying locked into a dangerous place as dictated by someone who will never be there. No to seat belts.
Trains are different to road vehicles, in that they can offer that additional space which can make the difference between survival or not, also that you can get to a point of doing everything possible, after which you are only a witness. Living witnesses are always better. Road vehicles are not designed with an impact of thousands of tonnes in mind.