摘要：Objectives. We examined the extent to which differential traffic volume and road geometry can explain social inequalities in pedestrian, cyclist, and motor vehicle occupant injuries across wealthy and poor urban areas. Methods. We performed a multilevel observational study of all road users injured over 5 years (n = 19 568) at intersections (n = 17 498) in a large urban area (Island of Montreal, Canada). We considered intersection-level (traffic estimates, major roads, number of legs) and area-level (population density, commuting travel modes, household income) characteristics in multilevel Poisson regressions that nested intersections in 506 census tracts. Results. There were significantly more injured pedestrians, cyclists, and motor vehicle occupants at intersections in the poorest than in the richest areas. Controlling for traffic volume, intersection geometry, and pedestrian and cyclist volumes greatly attenuated the event rate ratios between intersections in the poorest and richest areas for injured pedestrians (−70%), cyclists (−44%), and motor vehicle occupants (−44%). Conclusions. Roadway environment can explain a substantial portion of the excess rate of road traffic injuries in the poorest urban areas. Injuries resulting from road crashes are leading causes of death and disability worldwide. 1 Although the number and rate of road deaths have decreased in industrialized countries, they remain a major public health burden, with approximately 40 000 and 3000 road deaths annually in the United States and Canada, respectively, and thousands more injuries. 1,2 For pedestrians, decreases may reflect a reduction of the exposed population, as, currently, fewer people walk as a mode of transportation. 3–5 There are significant social inequalities in road crashes, injuries, and deaths between and within countries. 1,6–8 Within countries and cities, motor vehicle injury and death rates have been shown to vary according to individual and neighborhood socioeconomic positions, with greater rates among the least well off. 9–13 Although many different factors, related either to individuals, vehicles, or the environment, contribute to creating such social inequalities, they should be understood in light of some mechanisms involved in the occurrence of road traffic injuries (RTIs). First, moving vehicles are the primary cause of road crashes: deaths and injuries result from the transfer of a motor vehicle's kinetic energy at a rate that exceeds the human body's protective capacity. 14 Second, the burden of RTIs on population health is related to exposure to risk of crash. 1 Risk exposure can be estimated by distance traveled for drivers or traffic volume for streets and intersections. 15,16 Two California studies on neighborhood exposure to motor vehicles showed a greater likelihood of higher traffic volumes in the poorest census block groups and around schools in deprived areas. 17,18 Third, the number of injured pedestrians and cyclists is also related to the number of people exposed. 19,20 Thus, in a given environment, the more people walking, the more injured pedestrians. Fourth, the physical environment has a strong influence on the likelihood of injuries. 21 Road widening increases crashes, whereas traffic calming and 20 mile per hour zones greatly reduce their occurrence. 22–26 In London, United Kingdom, the deprived areas have a larger proportion of traffic-calmed roads, 27 whereas in Montreal, Canada, urban environment safety for pedestrians and cyclists is associated with greater neighborhood affluence. 28 Two broad categories of factors—individual and contextual—can explain neighborhood inequalities in RTIs. 12,13 Although income and education levels are well-documented individual factors, a recent multilevel analysis demonstrated that the socioeconomic characteristics of individuals and communities exerted independent and additive effects on risk of road death. 9 Cross-sectional surveys have shown that children from lower income families and those living in downtown areas cross more roads, encounter more motor vehicles every day, and have a higher risk of injury. 29–34 Several ecological investigations have shown the influence of population characteristics and environmental context on the geographical distribution of pedestrians and cyclists injured in urban settings. 13,35–46 In the United States, at the county level, urban sprawl and lower density—which are known to generate more traffic—have been associated with a greater incidence of pedestrian fatalities. 35 Within a city, it is generally observed that the per capita or per road kilometer rate of injured pedestrians in a neighborhood increases with population density. 36–41 However, 1 study showed an inverse relationship when other factors were taken into account. 42 Urban areas with better public transit availability, 43 more traffic, 38,41,44 greater density of major roads, or more traffic-generating activities 37,42,45 have a higher incidence of injured pedestrians. In some studies, the proportion of low-income households, the proportion of people without access to a motor vehicle, or an index of multiple deprivation were independent risk factors for pedestrian injury. 13,39,41,43,46 The ecological design of these investigations precludes conclusions about relationships at the street or intersection level. 47 At the intersection level, estimates from mathematical models have shown that the mean number of pedestrian crashes is approximately proportional to the square root of vehicle volume. 48–50 The influence of road geometry is also widely acknowledged. Vehicle speed, road crashes, and fatality frequencies are higher on wider major roads (“arteries”), and in general there are more conflict points, crashes, and injuries at 4-legged intersections than at 3-legged, T-intersections. 22,48,50–52 Although many studies point to the important role of traffic volume and street geometry in explaining RTIs, few studies have examined the variables explaining socioeconomic inequalities related to RTIs. 11–13,43,53 When included in multivariate analysis, socioeconomic position is treated as an additional risk factor to be controlled. Therefore, we examined whether differential traffic volume and road geometry can explain socioeconomic variations in the rate of pedestrian and cyclist injuries within an urban area. To improve generalizability to other road users, we also included injured motor vehicle occupants in our analyses.
