I will say that I've been around tractors, trailers, and farm equipment, as well as construction equipment my whole life. There are danger zones such as being between a vehicle and a trailer where one may have to be at times, but one has to be extremely vigilant during those times.

Staying alive requires communication, and expecting it to move any time, and paying attention to both the diver and the vehicle.

Someone mentioned previously that buses often take off, hammer down (but at a speed safe for the passengers).

It is hard to imagine being in the situation without actually being in the situation, but if I saw a sign of a 20 ton vehicle moving, I wouldn't stick around long enough to see if the driver eventually noticed the error.