This report is concerned with the development of criteria for the installation of central reserve safety fences on 60 and 70 mph all purpose dual carriageways. For this purpose personal injury accidents were examined on over 350 kilometres of such roads in England, of which 142 kilometres have a safety fence. Safety fences are primarily intended to reduce accidents where a vehicle crosses into the opposing carriageway; however, because of possible effects on general safety, all types of accident were considered. The report presents tabulations of accidents by frequency, severity and by type of interaction with the central reserve. Accident frequencies are further considered in relation to traffic flow and site characteristics, the latter including road geometry and layout. Regression equations were developed for use in criteria for the justification of safety fences in particular circumstances. A combined accident prediction/cost model is demonstrated and general results illustrated. The effectiveness of safety fences is underlined by the study to the extent that their installation is shown to be warranted at traffic flows below those suggested by past guidelines.
Abstract