Economic impacts will tend to increase approximately proportional to delay time, but public health impacts will have somewhat different dependencies, including relationships with population size and age distribution (both of which will also influence traffic demand). On the former point, when density is close to capacity, small increases in traffic volumes generally lead to larger increases in delays (i.e., congestion follows a non-linear function). Multiple factors can complicate the comparison between economic and public health impacts, including some of the non-linearities in the system and variability across urban areas. Thus, the public health implications of congestion could be appreciable and merit further investigation. They find strong evidence for a causative role for traffic-related air pollution on mortality, particularly from cardiovascular events. Recently, an expert committee summarized the available epidemiological literature on exposure to traffic-generated air pollution and adverse health effects. PM 2.5 has been associated with premature mortality in multiple studies, and health impact assessments have demonstrated PM 2.5-related damages on the order of hundreds of billions of dollars per year. While this represents a substantial economic loss, there are multiple externalities from congestion that have not been previously characterized, including the public health impacts of excess air pollutant emissions during periods of congestion.įine particulate matter (PM 2.5) is influenced by motor vehicle emissions of both PM 2.5 and particle precursors, with source apportionment studies finding vehicles contributing up to one-third of ambient PM 2.5 in urban areas in the US, with an even greater contribution if secondary sulfate and nitrate are considered. Multiple studies have modeled congestion in urban areas and assigned economic values to the excess fuel consumption and time wasted in traffic, concluding that congestion leads to annual economic burdens ranging from $83 billion to $124 billion. Our analyses indicate that the public health impacts of congestion may be significant enough in magnitude, at least in some urban areas, to be considered in future evaluations of the benefits of policies to mitigate congestion.Ĭongestion arises when a roadway system approaches vehicle capacity, resulting in numerous negative impacts ranging from wasted fuel and time to increases in tailpipe emissions. Across cities and years, the public health impacts range from more than an order of magnitude less to in excess of the economic impacts. In future years, the economic impacts grow (to over $100 billion in 2030) while the public health impacts decrease to $13 billion in 2020 before increasing to $17 billion in 2030, given increasing population and congestion but lower emissions per vehicle. We estimate that the monetized value of PM 2.5-related mortality attributable to congestion in these 83 cities in 2000 was approximately $31 billion (2007 dollars), as compared with a value of time and fuel wasted of $60 billion. Marginal concentration changes are related to a concentration-response function for mortality, with a value of statistical life approach used to monetize the impacts. We link traffic volume and speed data with the MOBILE6 model to characterize emissions of PM 2.5 and particle precursors attributable to congestion, and we use a source-receptor matrix to evaluate the impact of these emissions on ambient PM 2.5 concentrations. We evaluate 83 individual urban areas using traffic demand models to estimate the degree of congestion in each area from 2000 to 2030. In this study, we evaluate the public health impacts of ambient exposures to fine particulate matter (PM 2.5) concentrations associated with a business-as-usual scenario of predicted traffic congestion. Moreover, the relative magnitudes of economic and public health impacts of congestion would be expected to vary significantly across urban areas, as a function of road infrastructure, population density, and atmospheric conditions influencing pollutant formation, but this variability has not been explored. Previous analyses have estimated the economic costs of congestion, related to fuel and time wasted, but few have quantified the public health impacts or determined how these impacts compare in magnitude to the economic costs. Traffic congestion is a significant issue in urban areas in the United States and around the world.
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