Over the last two decades, dozens of studies ha ve been directed at air pollution and negative health impacts along high volume traffic corridors in cities around the world. These studies have examined a variety of vehicle-related air pollutants such as fine particulate matter (PM2.5), ultra-fine particles (UFP), nitrogen dioxide (NO2), carbon monoxide (CO), black carbon, and particle-bound polycyclic aromatic hydrocarbons (PPAH). They have been directed at a variety of populations including adults, children, the elderly, pregnant women and newborns. They have addressed a broad range of health impacts including asthma, lung function, strokes, heart attacks, a variety of cancers, and several reproductive effects. They been directed at traffic corridors with varying volumes of traffic (i.e. 10,000 to 100,000 vehicles per day), at traffic corridors with different types of traffic (i.e. different ratios of diesel-fuelled trucks to gasoline fuelled cars), and at different distances between traffic corridors and sensitive land uses such as homes and schools (i.e. 50 to 500 metres).

In 2007, when Brugge, Durant and Rioux reviewed the air quality and health studies directed at high volume traffic corridors, they concluded that:

Air levels of UFP, BC, CO and nitrogen oxides ( NOx ) are all elevated along high volume traffic corridors with greater than 30,000 vehicles per day;

) are all elevated along high volume traffic corridors with greater than 30,000 vehicles per day; People living beside these highways are likely to receive much higher exposures to traffic-related air pollutants than people living beyond 200 metres from highways;

Evidence from a variety of sources suggests that vehicle-related air pollutants have adverse effects on cardiovasular systems; and

There is strong evidence linking traffic corridors to the development of asthma and reduced lung function among children.

These researchers declared that: “The most susceptible and overlooked population in the US subject to serious health effects from air pollution may be those who live near major regional transportation routes, especially highways.”

In 2008, Boothe and Shendell reviewed 29 traffic corridor studies conducted between 1999 and 2006 and found statistically significant associations between residents who live in close proximity to traffic corridors and at least one of the following:

Increased prevalence and severity of symptoms of asthma and other respiratory diseases;

Reduced lung function;

Adverse birth outcomes;

Childhood cancer; and

Increased risk of premature death.

While these reviewers acknowledged that a number of uncertainties make it difficult to prove that traffic corridors are causing these health effects, they concluded that: “…public health can be better protected through enhanced precautionary land use; smart growth; and transportation policies…”

In 2010, the Health Effects Institute (HEI) released a special report on traffic-related air pollution which reported that:

Traffic emissions are the principal source of variation in the levels of air pollutants wthin many cities;

Traffic emissions have an impact on air quality at an urban and regional scale as well as a local scale; and

Air pollution associated with traffic corridors can extend up to 300 to 500 metres from a highway depending upon factors such as traffic volume, wind direction and wind speed.

The HEI concluded that the health evidence:

Indicates that traffic corridor pollution aggravates asthma;

Suggests that traffic corridor pollution can lead to the development of childhood asthma, non-asthma respiratory symptoms, impaired lung function, total and cardiovascular mortality, and cardiovascular disease.

The HEI Panel declared: “…exposures to traffic-related pollution are likely to be of public health concern and deserve public attention.”

Since these reviews were conducted, a number of new studies have been released. For example, a study conducted in Montreal suggests that traffic-related air pollution might be associated with an increased incidence of post-menopausal breast cancer (Crouse et al., 2010), while a Danish study based on 53,000 participants in the Danish Diet Cancer and Health cohort, suggests that traffic-related air pollution might increase the risks of cervical and brain cancer (Raaschou-Nielsen et al. 2011).

As the body of evidence linking traffic corridors to negative health impacts grows, there is increasing pressure for a variety of policy responses. While new vehicle emission standards that are being being rolled out over the next decade will ensure that cars and trucks emit fewer air pollutants than those built in previous years, these gains could be off-set by the growing number of vehicles on the roads, the growing number of vehicle kilometres travelled (VKT) by Canadians each year, and by the increasing congestion on some road in Canada.

Brugge D. et al. “Near-highway pollutants in motor vehicle exhause: A review of epidemiological evidence of cardiac and pulmonary health risk”, Environmental Health. No. 6. August 2007.

Boothe V. and D. Shendell. “Potential Health Effects Associated with Residential Proximity to Freeways and Primary Roads: Review of Scientific Literature, 1999-2006”, Journal of Environmental Health. No. 8, April 2008.

Health Effects Institute (HEI). “Traffic-Related Air Pollution: A Critical Review of the Literature on Emissions, Exposures, and Health Effects”, Special Report 17. January 2010.

Crouse, D. et al. “Postmenopausal Breast Cancer Is Associated with Exposure to Traffic-Related Air Pollution in Montreal, Canada: A Case-Control Study”, Environmental Health Perspectives. October 2010.

Raaschou-Nielsen, O. et al. “Air Pollution from traffic and cancer incidence: a Danish cohort study”, Environmental Health. No 10. July 2011.

Prepared by Kim Perrotta

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