Safety-in-numbers is a phenomenon whereby the crash risks of road users decrease when their numbers increase. Although several previous studies have confirmed safety-in-numbers at a microscopic level (e.g., intersection), few studies have investigated safety-in-numbers at a macroscopic level (or zonal level). In this study, safety-in-numbers is investigated at a larger scale unit, the metropolitan statistical area (MSA), which is usually composed of multiple counties in the U.S.A. Various pedestrian and bicyclist exposure data were obtained from the U.S. National Household Travel Survey (i.e., trips, miles, and hours). A series of Bayesian Poisson lognormal models confirm safety-in-numbers with the different exposure variables at a large-scale geographic level (i.e., MSA). The findings imply that regional travel behavior and cultures of respect for vulnerable road users play a key role in determining the level of pedestrian and bicyclist safety. In addition, the results reveal other factors important to vulnerable road user involved crashes, including but not limited to the climate, demographic, socioeconomic, and travel characteristics of the study regions.
Autonomous Vehicles and Vulnerable Road-Users—Important Considerations and Requirements Based on Crash Data from Two Countries
