Safety fencings are designed to contain vehicles in the carriageway in which they are traveling and prevent them from rebounding into the road and causing hazards. For normal fencing design, when vehicles crash into safety fencings, it will give way so as to absorb as much energy as possible, thus reducing the impact forces on the vehicles. Moreover, it serves to realign the vehicles along the carriageway when vehicles hit on them. However, for concrete profile barriers they are not designed to absorb energy during vehicle crashing, but to hold the vehicles hitting on them. In this connection, concrete profile barriers are designed with curved profiles so that vehicles can mount and go up partly on them, and yet they will not cause overturning of vehicles. Reference is made to Arthur Wignall, Peter S. Kendrick and Roy Ancil.
For shallow-angle crashing of cars, they would climb on the lower slope face of concrete profile barriers. On the other hand, when a car hits at a large angle to the barrier, the bumper collides with the upper sloping face of concrete profile barrier and the car rides upwards. This provides the uplift of the car whose wheels move up the lower sloping face of the barrier. It is not intended to lift the car too high, otherwise it may result in rolling. Since the friction between the wheels and barriers provide extra lifting forces, it is undesirable to design rough finish on these faces. In essence, the kinetic energy of the car during collision is transformed to potential energy during its lifting up on profile barrier and finally converted back to kinetic energy when the car returns to the road.
This question is taken from book named – A Self Learning Manual – Mastering Different Fields of Civil Engineering Works (VC-Q-A-Method) by Vincent T. H. CHU.