Abstract
Traffic accidents are caused by a variety of factors, including human error, road hazards, and vehicle defects. They are also enormously influenced by the social changes associated with population growth, urbanization, and motorization. Smeedʼs Law, proposed by R. J. Smeed in 1949, is an empirical rule relating traffic fatalities per vehicle （D/N） to per capita vehicle registrations （N/P）. According to Smeedʼs Law, increased motorization, as represented by per capita vehicle registrations, results in a decrease in the traffic fatality rate, which he defines as the ratio of traffic deaths to registered vehicles. Researchers have since conducted analyses using Smeedʼs Law to assess the traffic accident situation in various countries. In this study, statistical data were used to analyze the transition of traffic accidents in 34 countries in the International Road Traffic and Accident Database （IRTAD） in an effort to verify the ongoing applicability of Smeedʼs Law. It was found that Smeedʼs Law remains valid for accidents occurring over an extended period but that the transitions vary depending on a countryʼs economic development. Multiple regression analyses were conducted to examine the relationship between the accident fatality rate and various social context factors. Results of the analysis indicated that gross domestic product （GDP） per capita and the proportion of elderly in the population were the significant social factors, each having a p-value ＜0.005 and a negative coefficient. Evaluating the situation in countries with high GDP using the D/N measure in Smeedʼs Law was found to be particularly difficult since the traffic environment and automobile usage conditions can change substantially depending on the level of economic growth. Overall, it was judged to be all but impossible to conduct a meaningful uniform analysis of all countries simultaneously; rather, it is necessary to evaluate countries according to their individual conditions.
