Elaborating an index methodology for creating an overall road safety performance score for a set of countries

Abstract

Compared to traditional road safety research using crash data, risk factors causing crashes and casualties are studied in this research. More specifically, several risk factors (e.g., alcohol and drugs) are quantified by performance indicators (e.g., the share of road users with a blood alcohol content above the legal limit) and these indicator values are compared across countries. Given the high number of relevant road safety performance indicators, the creation of an index – i.e., a combination of indicators – is beneficial. One of the main advantages of an index over a set of individual indicators is that an overall road safety picture is presented capturing a multitude of risk information. However, to create a valuable road safety performance index in terms of communication, benchmarking, monitoring and policy supporting, a scientifically sound and appropriate index methodology is required. By critically studying the index development process in other domains (such as the environmental sustainability index) and taking the specific road safety case into account, this study describes the different steps that are essential in the construction of a road safety performance index. The selection of indicators and the data preparation are described, the issue of weighting and aggregating indicators is discussed and the robustness of the index in terms of the ranking of the countries assessed. These steps are illustrated using performance indicator data for 21 countries.