In workpackage 2 (WP 2) of RipCord-Iserest two instruments have been researched, both intended to provide this insight: Accident Prediction Models (APM) and Road safety Impact Assessments (RIA). An Accident Prediction Model is a mathematical formula describing the relation between the safety level of existing roads (i.e. crashes, victims, injured, fatalities etc.) and variables that explain this level (road length, width, traffic volume etc.). A Road safety Impact Assessment is a methodology to assess the impact of plans on safety. This can be major road works, a new bridge etc. that may or may not be intended to raise the safety level. A RIA can also concern a wider scheme i.e. be intended to make plans for the upgrading the safety level of a total network or area. This report gives recommendations for the way in which these instruments can be used by practitioners. It is based on two earlier published reports regarding the state-of-the art on APMs and RIAs, and the results of pilot studies. Both are available at the RipCord-Iserest website (wwwsicord-iserest.com; see section References). Traffic volumes (vehicles per day) and road lengths (km) are the most important explanatory variables in an APM, both for road sections and intersections. The parameters of the model, however, can vary considerably between road types and countries. The reason is that road characteristics can differ considerably and so can road user behaviour, vehicle types etc. It is therefore recommended to make APMs per country and road type and use these to compare the safety level of a road against the value of the APM for the road type and traffic volume under consideration. APMs can thus also play an important role in identifying black spots. For a RIA on single (major) road works several methods are available. It is best to use as much scientific evidence as possible, using handbooks, cost-benefit analyses and taking into account network effects. For RIAs on wider schemes or even national levels specific recommendations are given on methodology. In general a RIA is best used in comparing policy options and setting ambitious but realistic road safety targets. Absolute numbers that are predicted are usually not very reliable and in general highly dependant on high quality databases that are usually not available. (Author/publisher)
Samenvatting