The effects of local and non-local traffic on child pedestrian safety: A spatial displacement of risk

Abstract

In most places, motor-vehicle traffic volume is associated with increased risk of child pedestrian injury; however, the burden of risk is geographically complex. In some neighbourhoods, proportionally fewer drivers may be local, meaning that the moral and practical responsibility of risk to children is displaced from one place (e.g., the suburbs) to another (e.g., downtown). Using the City of Toronto, Canada, as a case study, this research asks two related questions: 1) what is the variation in traffic volume by neighbourhood of origin and socioeconomic status and 2) what is the relationship between the geographical origin of traffic and the risk of collisions involving child pedestrians and motor-vehicles? We find that low-income downtown neighbourhoods have the highest proportion of non-local traffic. We also find that while higher local traffic activity is associated with lower risk of collision, higher flow-through traffic activity (excluding traffic from major thoroughfares) is associated with higher risk of collision. We interpret the former as very likely a proxy of parents' frequency of chauffeuring children to school, and the latter an illustration of the spatial displacement of risk between Toronto neighbourhoods. Our results suggest that more attention needs to be paid to account for the externalization of harm experienced by children, particularly in low-income downtown neighbourhoods.

Introduction

Injuries remain the most common cause of death and disability for persons under 45 years of age, and are a leading cause of morbidity and mortality worldwide (Krug, Sharma, & Lozano, 2000; Mathers, Boerma, & Ma Fat, 2009). The burden of non-fatal injury is considerable, with many types of injury associated with long-term disability, chronic comorbidities, loss of income and a loss in quality of life. Economic costs of injury are also noteworthy; motor vehicle injuries alone are estimated to cost up to 2% of global GDP annually (Peden et al., 2004).

Changes in urban design, traffic engineering, legislation and driver behaviour have contributed to a dynamic geography of road traffic injury over the last century, with a noteworthy (though non-linear) decline in traffic-related injury and mortality in recent decades (van Beeck, Borsboom, & Mackenbach, 2000). Many of the greatest improvements in traffic safety have benefitted drivers—particularly in the development of motor-vehicle occupant safety technology (Graham, 1993). Some have argued that the emergence of urban features such as single-use zoning, curvilinear street design and hierarchical road plans may have contributed to a safer pedestrian experience as well (Wang & Smith, 1997). Smaller scale interventions—such as traffic calming infrastructure and intersection controls—also show some promise in reducing the risk of injury and mortality among pedestrians, particularly for children, and have been thought to explain recent declines in pedestrian injury incidence and mortality (Retting, Ferguson, & McCartt, 2003).

There is, however, an important critical discussion of the relationship between child pedestrian injury prevention efforts and declining risk of injury and mortality. First, there are questions of its empirical validity. The correlation between declining incidence and increasing environmental intervention is undeniable, but the causality is unclear. An alternative explanation for the decline in risk is simply a change in pedestrian activity; there is growing evidence of a decline in independent child pedestrian travel in recent decades (Hillman, Adams, & Whitelegg, 1990; McDonald, 2007; van der Ploeg, Merom, Corpuz, & Bauman, 2008; Roberts, 1993). A second critique concerns a curious ethical contradiction; children carry the bulk of technical and legal responsibility when collisions between motor-vehicles and children occur (Roberts & Coggan, 1994) in spite of clear evidence that they lack the cognitive ability to judge traffic speed and distance (Barton & Schwebel, 2007; Schieber & Thompson, 1996) and lack any legal or political authority over the development of the transportation environment. So while injury prevention seeks to reduce risk of injury, it does not admit the underlying structural reality—that industrialized countries implicitly allow motor-vehicles to constrain safe independent pedestrian activity among children in deference to efficient motor-vehicle travel (Roberts, 1993).

Third, emphasis on pedestrian safety may be indirectly responsible for a decline in independent pedestrian activity in children; parental fears about their children's safety may lead to reductions in independent child pedestrian activity (Dixey, 1998). Prevalence of overweight and obesity have risen in step with declining levels of active travel and injury incidence (Lobstein, Baur, & Uauy, 2004). Reversing this trend presents an important challenge to the immediate and long-term health of the population (Reilly et al., 2003). Active transportation to school—either by walking or cycling—may help to reduce rates of child obesity (Rosenberg, Sallis, Conway, Cain, & McKenzie, 2006) and may also be important for child development generally, as it provides children opportunities to build relationships, make decisions and explore their environment, all essential components in their cognitive and emotional development (Ginsburg, 2007).

Finally, while there have been declines in injury incidence and mortality in many industrialized countries, the declines are not uniform across the population. Socioeconomic disadvantage has a strong and nearly ubiquitous association with pedestrian injury risk at various scales (Durkin, Davidson, Kuhn, O'Connor, & Barlow, 1994; Oliver & Kohen, 2009; Roberts & Power, 1996), and declines in incidence and mortality are not the same across income strata (Nantulya & Reich, 2003). There are social inequalities in the effectiveness of prevention programs (Collins & Kearns, 2005) as well as income-specific differences in pedestrian injury associated with urban development (Yiannakoulias, Scott, Rowe, & Voaklander, 2011). While some prevention strategies have specifically targeted reductions of risk inequalities (e.g., Jones, Lyons, John, & Palmer, 2005), the persistent socioeconomic gradient challenges the ability of many prevention strategies to address social inequalities in injury risk.

Many costs of motor-vehicle transportation are externalized; specifically, infrastructure, social and environmental costs of driving are not paid fully by those who drive, but are either explicitly shared (for example, through the spending of public resources) or are hidden (Verhoef, 1994). In a recent report, Transport Canada estimated the social costs of light road motor-vehicle use in Canada at more than 10 billion dollars per year, roughly 25% of the total cost of light road motor-vehicle use Transport Canada (2008). These costs include estimates of the costs of accidents and pollution, but not capital or operating costs, which are also partially externalized. While this and other research has measured various externalized costs of the motor-vehicle transportation system, often at a national or regional level, it has left the displacement of these externalized costs from one place to another unexamined. For example, in their assessment of illness attributable to air pollution, Künzli et al. (2000) estimated the total health effects of traffic-related air pollution in three European countries, but did not isolate the effects attributable to specific regions. Similarly, in their study of the effects of traffic noise on hypertension in children, Regecová and Kellerová (1995) did not distinguish the relative burden of effects attributable to local and non-local traffic.

Elvik (1994) identifies three classes of externalities related to traffic-related injury, one of which—physical injury externalities—describes the external costs of one group of transportation system users on another. One example is the cost that motor-vehicle drivers impose on pedestrians in loss of life, pain etc. following a collision. In addition to being an important externalized social cost from drivers to non-drivers, this cost is also very likely to be spatially displaced. Most motor-vehicle work-commuting trips are long enough that the bulk of the driving (in terms of distance and time) occurs outside of one's own neighbourhood (Clark, 2000; Heisz & Larochelle-Côté, 2005). It follows then that the bulk of any physical injury externalities are also very likely to be experienced outside one's own neighbourhood. When combined with other attributes of place relevant to pedestrian injury—such as variations in levels of car ownership and features of neighbourhood safety—physical injury externalities are very likely to have a distinct geography that underlies both the pattern of variation in risk and responsibility.

Specific studies of the degree and nature of spatial externalization of pedestrian injury risk are lacking; however, there is some indirect evidence. Cities that experience high levels of suburbanization and urban sprawl experience high rates of pedestrian injury (Erwin, Schieber, Zegeer, 2003), but not due to higher in situ factors associated with the suburban neighbourhoods themselves. In fact, the highest risks are often associated with neighbourhoods in the older-inner city areas with higher population density rather than the suburbs (Braddock et al., 1994; Yiannakoulias et al., 2002). This results in a curious pattern; highly suburbanized cities have relatively high rates of pedestrian injury, but peripheral suburban neighbourhoods within these cities continue to have relatively low injury incidence. This pattern may emerge partly because risk to pedestrians is spatially externalized—displaced from neighbourhoods where a large share of the population uses motor-vehicles to neighbourhoods where fewer people use motor-vehicles.

Understanding spatial externalization of child pedestrian injury risk is important for several reasons. First, spatial externalization of risk is a problem of spatial equity. Research in environmental pollution (Jerrett et al., 2001) and access to resources (Talen & Anselin, 1998) in particular have highlighted the importance of understanding inequity in spatial terms, and specifically, how geographical variation in hazards and services can be a cause and consequence of structural social inequality. While this is often framed in the context of income and ethnicity, children can also represent a similarly marginalized group. In collisions between motor-vehicles and child pedestrians, there is a clear asymmetry of risk, with almost all being incurred by the pedestrian. However children are not participants in policy making that could influence the safety and suitability of the transportation environment, nor do they benefit as directly from the convenience of motor-vehicle culture in general. When children are from traditionally marginalized ethnic or income communities the consequences of spatial inequity can be further amplified; children from poor families are more likely to walk to school than other children, which increases their exposure to harm (Roberts & Power, 1996) particularly in transportation environments that favour motor-vehicles.

Second, understanding the spatial externalization of injury risk is important for developing more informed interventions. For example, if most risk to child pedestrians is attributable to local traffic, then most of the moral and practical responsibility lies with local motor-vehicle users. Traditional interventions targeted at drivers—such as awareness campaigns, or local speed enforcement measures–could be more effective if framed as a solution to a local problem with consequences directly tied to their own neighbourhoods. On the other hand, if the bulk of the risk originates with motor vehicles from other parts of the city, then responsibility is wider reaching, and different interventions may be required. Traffic costing policies (such as tolls or congestion charges) or street engineering to reduce neighbourhood traffic permeability may be effective and normatively appropriate tools for increasing local safety, and would place the burden on the source of hazard rather than the victims of the problem.

To date, the authors are aware of no empirical research studying the spatial externalization of child pedestrian injury risk. Part of the challenge of such research is that it requires considerably detailed data on the spatial distribution of traffic not simply in terms of total traffic flow, but also the origin of traffic. In this study we use journey-to-work data collected as part of the Canadian census to model and estimate the volumes of motor-vehicle commuter traffic throughout the city of Toronto. This approach allows us to distinguish between local and non-local motor-vehicle commuting traffic in each Toronto neighbourhood, and in turn, address two related research questions: 1) what is the variation in traffic volume by neighbourhood of origin and socioeconomic status and 2) what is the association between the origin of traffic and the risk of child pedestrian injury in Toronto neighbourhoods?