Crash barrier end terminals

I've seen these from the car as they have been introduced in the UK over the last decade but I managed to get up close at this one beside Thirlmere. I had imagined that the end plate would have been on some sort of compressible piston, but that isn't the case. It seems that the car crumbles the steel frame, ripping the steel and thus dissipating the car's kinetic energy. The wide end of the crash barrier spreads the force over a bigger area so there is less pressure and the end of the barrier is less likely to puncture the passenger compartment. There is a steel cable behind the first sections of the barrier. One source said it is to keep the end section in tension during a side impact. I couldn't figure out the mechanism. Sources included https://en.wikipedia.org/wiki/Traffic_barrier#Barrier_end_treatments and http://www.wsdot.wa.gov/publications/fulltext/design/RoadsideSafety/ImpactHeads.pdf