There are three categories of road safety barrier: rigid, semi rigid and flexible. In general, for cars, the more flexible the barrier system the better the outcome for those that strike the barrier. However, the selection of the appropriate barrier needs to take into account a raft of factors, including; offset to hazards, horizontal and vertical alignment, severity of hazard, length of need, whole-of-life cost, consistency within a route, ability to maintain the barrier and the road/roadside and percentage of motorcyclists and heavy vehicles just to name a few.