"Driver 'on His First Day' Rips Roof off Double Decker School Bus"

From The Daily Mail:
A driver on 'his first day,' ripped the roof off a double-decker school bus by smashing into a railway bridge - despite pupils' warning shouts, in a crash that has left three children in hospital with serious injuries and 13 more needing treatment.
Around 70 pupils were on board the Stagecoach bus, heading towards Henry Beaufort School, in Winchester, when its roof collided with a bridge just after 8am...
I enjoy a 'bus hits bridge' story as much as the next man, but not when people are seriously hurt. 'Car hits house' stories are inherently not funny.
I really don't get it. All you need is the low tech solution of setting up a gantry before the entrance to the bridge or tunnel (or car park etc) and dangling chains from it so that the ends dangle slightly lower than the maximum height of the bridge or tunnel. The high vehicle hits those first and hopefully the driver gets the message, passengers can scream in good time etc.
There are other more sophisticated warning systems, as explained in this article, but the dangling chains seem to be cheapest and best.