OBSERVATIONAL BEFORE-AFTER STUDIES IN ROAD SAFETY -- ESTIMATING THE EFFECT OF HIGHWAY AND TRAFFIC ENGINEERING MEASURES ON ROAD SAFETY

This three part monograph aims to enable road safety researchers and professionals to interpret correctly the results of one of the main sources of knowledge about the effect of road safety engineering measures, the observational Before-After Part I, Essentials - contains information the author regards as essential for forming an opinion of results obtained by others, and for planning and analyzing such a study. This is written to be accessible to all. Part II, Adaptations of conventional approaches - explains how to avoid the errors and improve the results obtained from the predominant methods currently used. This part employs algebra and statistical analysis. Part III, Elements of a new approach - presents new approaches to improve future methods of observation and analysis.