As I have pointed out previously, you can build railcars and locomotives like (military) tanks, but when they hit a solid obstruction, the damage to contents (people) will still be catastrophic -- due to inertia. The contents of the cars keep moving while the cars come to a sudden halt.

This accident -- like many catastrophic accidents -- appears to have been the result of a number of unfortunate unfavorable factors. Had the train hit the construction truck on an open line, it would have shoved the truck down the track, and, even if the train cars derailed, they would have skidded to a stop over some distance. Instead, the train and obstruction struck the tunnel walls.

It will probably take some time for an investigation to determine the exact sequence of events.

-- Ernest