I know that there were some test done on concrete barriers by scientists here in australia, and they are really dangerous, they line our highways/dual carriageways if there isnt a gap of about 10 metres. anyhoo, a car doing 120 km/h can hit a wall at a 20 degree angle or such, and it will go literally, flying! Its because concrete can't absorb the energy as well as other barriers. for example, you can have plastic barriers filled with water or metal railings that will actually stop the car, instead of bouncing all the energy back...