Overload is the major reason. But the white van did make a mistake to squeeze between 2 trucks. Will the truck behind hit the truck in front if white van were not there? Yes. Will the truck brake in time if it were not overloaded(no white van)? Barely. Will the truck brake in time if it were not overloaded with white van there? Needs luck. The best outcome of this situation is ugly braking scream and angry cussing. White van does have responsibility.