N11
As It happens I saw a car hit the Red and White plastic Barriers that used to be at Kilmacanogue. The car flipped over and landed on it's side.
The driver walked away from it, a bit shaken, but no serious injuries (that I could see).
Not sure if he'd have walked away from a smack into concrete.
5th Gear on Channel 5 did a test of smacking soem small cars into concrete barriers at 70mph. The cars stood up to it pretty well. A Smart car actully cracked the concrete, so there is some absorbtion in the concrete.
The cars would have physically protected the occupants fairly well, but the decelaration would have killed them.
-Rd