Wednesday, December 22, 2010

Trends in Traffic Congestion, Emissions and Health

Evaluation of the Public Health Impacts of Traffic Congestion: A Health Risk Assessment (12 page pdf, Environmental Health, 9:65, Oct. 27, 2010)

Isolating the impact of traffic’s impact on health from that of ambient and roadside air quality is challenging but the article under review attempts that and also projects this impact two decades into the future for more than 80 cities in the USA.  Although this article projects lower health impacts over the next decade, a slight increase is seen after that point as vehicle-miles traveled continue to increase. In addition, no allowance is made for the health and economic impacts arising from climate change which may be significant.

A similar study by the City of Toronto’s Public Health estimated that in that city about 1/3 of the mortality due to air pollution can be attributed to traffic as reported in Impact of Traffic Air Pollution on Health in Toronto

Key Quotes:

“Congestion arises when a roadway system approaches vehicle capacity, resulting in numerous negative impacts ranging from wasted fuel and time to increases in tailpipe emissions..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”

“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)”

“In total, across the 83 urban areas modeled, VMT [Vehicle-Miles Travelled] is projected to increase 33% from 2000 to 2030 (an increase from 2.97 billion daily VMT to 3.94 billion daily VMT), closely paralleling projected population growth in the urban areas of 32%… Whereas 18 of the 83 urban areas were estimated to have 50% of time in congestion in 2000, 40 urban areas reached this threshold by 2030…Overall, approximately 48% of the impact over the 83 urban areas is attributable to NOx emissions, with 42% attributable to primary PM2.5 emissions and 11% attributable to SO2 emissions”

“whereas the public health impacts contributed approximately 34% of the total cost of congestion in 2000, this decreases to 14% by 2030”

“when comparing traveling conditions of congestion and freeflowing traffic in which the estimated average speed is similar, emissions during congested driving conditions are 50% higher”

“the monetized value of PM2.5-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“

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