A study of safety effects of road infrastructure improvements under Israeli conditions.

A study aimed at developing a uniform methodology for evaluating potential safety effects of projects on road infrastructure improvements, is presented. The final product of the study is a computer program, which enables to perform cost-benefit analysis of different variants of a project, from the viewpoint of associated accident savings, and serves as an assistance tool for road and traffic engineers. The core element of the system is a database on values of expected safety effects from various road infrastructure improvements. To provide this database, the study included the following steps: (a) developing a summary of safety effects as these appear in the international experience (based on reviews on the subject published over the last decade, some 250 summary values were evolved); (b) developing a method for evaluating safety effects of road infrastructure improvements under local conditions; (c) collecting data on road infrastructure improvements performed on the Israeli road network through the 90s, building examples of treatment types for analysis (in total, some 400 interurban and some 500 urban projects were recorded in the database from which more than 30 examples of treatment types evolved); (d) evaluating the effects of these treatments, based on accident statistics in "after" as opposed to "before" periods. Based on the comparative review of the known methods for evaluating safety effects, the method proposed in the current study, accounts for confounding factors such as regression-to-the-mean, time-trend, changes in traffic volumes but at the same time, stays relatively simple and accessible for wide application. To combine the study findings with the previous experience, decision rules were developed which enabled the inclusion of some 20 estimates of safety effects in local conditions, to the required database. (A) For the covering abstract of the conference see ITRD no 207828. The reprints are also available at the web - http://www.vti.se/pdf/reports/K18APart1.pdf; http://www.vti.se/pdf/reports/K18APart2.pdf and http://www.vti.se/pdf/reports/K18APart3.pdf.