[TimT]

I've been involved in Highway/Bridge/Heavy construction for my whole career, and have never seen aluminum used as a guide rail material. Mostly Galv. or weathering steel

That is what we call in the states "Armco" or corrugated guide rail.. There is a bit of semantics in guide vs guard language that some lawyers bickered about years ago..

Spacing of the posts typically increases the closer to a DFO (deadly Fixed Object) traffic is..

It looks like the post were spaced about 5' o/c and the car happened to hit one directly and take out its partners..

A neat thing about the corrugated guide rail, is that is overlaps....but that takes more material.$$$

Also instead of attenuating the crash, guide rail system using that construction could direct a car back onto a hot track