Traffic density as a surrogate measure of environmental exposures in studies of air pollution health effects: Long-term mortality in a cohort of US veterans

doi:10.1016/j.atmosenv.2005.09.027

Atmospheric Environment

Volume 40, Issue 1, January 2006, Pages 154-169

https://doi.org/10.1016/j.atmosenv.2005.09.027 Get rights and content

Abstract

Vehicular traffic is an ubiquitous source of air pollution in developed nations, yet relatively few epidemiology studies have considered its long-term health effects. This paper uses an areal measure of traffic density as a surrogate index of exposure to vehicular traffic. We present associations between county-level traffic density (annual vehicle-km traveled km⁻²), ambient air quality, and mortality in a cohort of about 70,000 male US veterans (the Washington University-EPRI Veterans Cohort) who were enrolled in 1976 and followed through 2001. Traffic density is seen to be a significant and robust predictor of survival in this cohort, more so than ambient air quality, with the possible exception of ozone. Stronger effects of traffic density are seen in the counties that have ambient air quality monitoring data, which also tend to have higher levels of traffic density. These proportional-hazard modeling results indicate only modest changes in traffic-related mortality risks over time, from 1976–2001, despite the decline in regulated tailpipe emissions per vehicle since the mid-1970s. This suggests that other environmental effects may be involved, such as particles from brake, tire, and road wear, traffic noise, psychological stress, and spatial gradients in socioeconomic status.

Section snippets

Introduction and background

The past decade has seen substantial growth in the publication of studies of the health effects of ambient air pollution. All of the regulated pollutants have been implicated in these various studies, and in many cases it has been difficult to distinguish their separate contributions (Stieb et al., 2002). Moreover, urban air pollution is a complex mixture of thousands of compounds, of which there has been limited characterization. One way to simplify this problem is to analyze health effects in

Measures and indicators of vehicular emissions

The general classifications of vehicular emissions include combustion products, fuel additives and impurities, detritus from wear and degradation of specific components (including road surfaces), and noise. Some of these are unique to vehicles but, in general, noise and gaseous combustion products are not. Their respective chemical and physical properties vary greatly, as do their rates of human physiological uptake and retention and the types of health impacts that may be involved. In

Comparison of density variables

VKTA is highly correlated with population and housing densities and thus could be considered a measure of congestion in general. Data on population and housing densities are available by zip (postal) code for the Veterans Cohort and thus are better measures of any true density effect, which can be obscured by local density variations within a county, as discussed above. As shown in Table 3A, the RRs of county-level traffic density consistently exceed those of population or housing densities at

Discussion

The low risk estimates for CO in this study have been seen in other long-term studies and may be due in part to the localized nature of this pollutant, which can lead to exposure errors when data from centralized monitors are used to represent an entire county. It is also likely that the health effects of CO are non-linear and exhibit a threshold. The RRs indicated for LVKTA are generally higher than those seen for traffic-related air pollutants in short-term time-series studies, in contrast to

Conclusions

Traffic sources have been implicated in recent air pollution epidemiology studies, but uncertainties remain as to the specific agents and thus causal mechanisms that might be involved (in part because of uncertainties in estimated exposures). In ecological studies from previous decades, increased mortality was associated with population density, which could also implicate traffic density. Since then, traffic levels have about doubled, but pollutant emissions per vehicle and average ambient

Acknowledgments

Funding for this study was provided by the Electric Power Research Institute (EPRI). Portions of the research described in this paper were funded by the US Department of Energy through the National Energy Technology Laboratory. We thank Dr. S.C. Morris for help with the zip-code density data and two anonymous reviewers for helpful comments.

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View full text

Traffic density as a surrogate measure of environmental exposures in studies of air pollution health effects: Long-term mortality in a cohort of US veterans

Abstract

Section snippets

Introduction and background

Measures and indicators of vehicular emissions

Comparison of density variables

Discussion

Conclusions

Acknowledgments

Journal of Urban Economics

Accident Analysis and Prevention

Science of the Total Environment

Lancet

Journal of Environmental Economics and Management

Life Sciences

Science of the Total Environment

Atmospheric Environment

Extending SAS Survival Analysis Techniques for Medical Research

Association of air pollution with increased incidence of ventricular tachyarrhythmias recorded by implanted cardioverter defibrillators

Environmental Health Perspectives

Traffic air pollution and mortality rate advancement periods

American Journal of Epidemiology

How do the indoor size distributions of airborne submicron and ultrafine particles in the absence of significant indoor sources depend on outdoor distributions?

Indoor Air

PM10 and asthma medication in schoolchildren

Archives of Environmental Health

Traffic density in California: socioeconomic and ethnic differences among potentially exposed children

Journal of Exposure Analysis and Environmental Epidemiology

Inner city air pollution and respiratory health and atopy in children

European Respiratory Journal

Estimation of long-term average exposure to outdoor air pollution for a cohort study on mortality

Journal of Exposure Analysis and Environmental Epidemiology

Health effects caused by noise: evidence in the literature from the past 25 years

Noise and Health

Triggering risk factors for ischemic stroke

Neurology

Air Pollution and Human Health

Climate, traffic-related air pollutants and allergic rhinitis prevalence in middle-school children in Taiwan

European Respiratory Journal

A Statistical Study of the Macroepidemiology of Air Pollution and Total Mortality

PM₁₀ and asthma medication in schoolchildren