Benefit/cost analysis for the selection of roadside safety alternatives

In EU, the new Standards EN 1317-1/2 define the performance classes of road restraint system and induce a growing interest for roadside safety. However, analytical procedures are not used for the selection of specific roadside safety features at specific locations or for the development of warrants, policies, and guidelines on a system-wide basis. In this paper, a new benefit/cost analysis procedure, based on an encroachment model, is presented. The new model, called SAFBAR, represents an improvement of the existing procedures and is very useful for selection of performance classses of safety barriers because it takes into account the effective performance level of road safety barriers, basing on the comparison between the impact conditions of the full scale crash tests performed according to the CEN standards and the real world impact conditions. The behavior of the safety barriers in relation to the impact conditions has been studied by performing non-linear dynamic finite element analysis of collisions of HGV against steel road safety barriers. As a result of the study, analytical relationships between barrier’s containment capacity and impact conditions have been obtained. The expressions allow to evaluate the number of vehicles correctly redirected from the safety barriers in relation to the type of road, to the geometrical characteristics of the road, to the traffic volume and composition and to the safety barriers containment level. The procedure allows to compare different types of measures, as relocation of utility poles and protection of utility poles with safety barriers, or measures of the same type carried out with different expenditure, as the installation of safety barriers with different performance levels.