Is "Safety-in-numbers" theory applies to the pattern of pedestrian accidents in Seoul, South Korea.

Every year, about 1.25 million people die of vehicle-related accidents, among which half are pedestrians with higher vulnerability: pedestrian, cyclists and motorcyclist (World Health Organization, 2016). This urges city governments in the world to strive for pedestrian safety and to apply diverse theories to transportation planning and design. The common belief is that the number of pedestrian accidents is directly and positively associated with the volume of pedestrian, however, another hypothesis, called "safety-in-numbers" effect, tells an opposite story in that accident rates declines with increase of the volume of pedestrian. In this study, we examine first, whether the safety-in-numbers theory applies to the pattern of pedestrian accidents in Seoul, and second, further investigate environmental factors that are associated with the pedestrian safety. On the first count, we use geospatial statistical analyses of the multi-year pedestrian accident data collected by Korea Road Traffic Authority (KoRoad) and the pedestrian volume data collected by SK Telecom (SKT). With Kernel Density Estimation and Bivariate Local Moran's I, we identify spatial clustering of pedestrian accidents in the city, and examine whether those locations match with concentrations of pedestrian volume. On the second count, we use statistical analysis, tobit, poisson and negative binomial regression to investigate relationships between pedestrian volume and number of pedestrian accident for the two types of geographic areas by the results of the aforementioned analysis; Area 1- locations of high volume of pedestrian with high number of accident, Area 2- locations of high volume of pedestrian with low number of accident. For environmental factors potentially explaining pedestrian accidents, we include land use composition, number of traffic lanes, crosswalk presence, pedestrian signal, traffic island and sidewalk width in our analysis. This research will be valuable in city governments' decision making with planning guidelines and political protocols for making safer pedestrian environment.