How do steel beam barriers (e.g. tension/untensioned beam barrier and open box barrier) function to contain vehicles upon crashing?

Steel beam barrier consists mainly of horizontal rails and vertical posts. When a vehicle hits the steel beam barrier, the kinetic energy is resolved in three components, namely vertical, normal to barrier and parallel to barrier. The vertical and normal components of kinetic energy are dissipated through deformation and bending of beam and supporting posts. As such, the remaining component (i.e. parallel) guides the vehicle back to the carriageway in a direction parallel to the barrier.

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.