Traffic-related air pollution and health : a Canadian perspective on scientific evidence and potential exposure-mitigation strategies Brauer, Michael; Reynolds, Conor; Hystad, Perry
While urban areas in Canada generally experience relatively good air quality, exposure to outdoor air pollution still elicits considerable public health impacts. Recently, a growing body of evidence has emerged that specifically links traffic-related air pollution (TRAP) with health effects, including cardiovascular disease and cardiovascular mortality, respiratory disease, adverse pregnancy outcomes and lung cancer. This understanding of the importance of TRAP requires renewed focus on options to reduce population exposure, including integration with urban and transportation planning. The objectives of this document are: (a) to present an overview of the international scientific evidence linking TRAP exposure to adverse human health effects, highlighting Canadian studies and new research findings published since the completion of a critical systematic review of the literature (HEI, 2010); (b) to estimate the exposure of Canadians to TRAP and identify its potential public health implications in Canada; (c) to review current legislation and guidelines regarding urban planning, the built environment and traffic exposure; and (d)enumerate potential options to mitigate population exposure to TRAP. Canadian researchers have made important contributions to the body of evidence linking TRAP exposure with health effects, and findings from these studies have been highlighted and reviewed in detail. Recent Canadian published epidemiologic studies support the conclusions reached by the HEI panel in describing effects of TRAP exposure on respiratory heath, adverse pregnancy outcomes, cardiovascular disease and cancer. Therefore, Canadian scientific data indicates that exposure to traffic-related air pollution is a significant public health issue in Canada. Spatial analysis of the number of Canadians living in proximity to major roads quantifies the scope of potential impact of TRAP as a public health concern in Canada. We applied the finding from the HEI (2010) literature review of roadway gradients to estimate TRAP exposure and found that approximately 10 million individuals (32% of the Canadian population) live within 100m of a major road or 500 m of a highway. In addition, recent research has estimated that approximately one-third of Canadian urban elementary schools are located in zones of high traffic proximity. These estimates highlight the large proportion of the Canadian population exposed to TRAP and confirm its public health importance. Four categories of exposure-mitigation options for TRAP are described: (1) Land-use planning and transportation management; (2) Reduction of vehicle emissions; (3) Modification of existing structures; and (4) Encouraging behaviour change. Real-world implementation of policies and actions – within Canada and internationally – have been examined. These strategies tend to either reduce TRAP exposures uniformly (e.g. identifying and repairing high-emitting vehicles or making improvements to public transit), or reduce TRAP exposure spatially (e.g. separation of buildings and active transit infrastructure from busy roads, low emission zones, or the use of HVAC to reduce TRAP infiltration in buildings). In addition, the time-horizon within which a reduction in TRAP exposure is expected to take place following a specific action varies from less than a year to decades. It is recommended that municipal and local governments take these considerations into account when choosing which TRAP exposure-reduction measures to implement. Recommended approaches include the following, grouped according to the time-horizon of their expected impact. “Near-term” time horizon (months to years):• Install HVAC filter systems in buildings that house susceptible populations within 150m from busy roads (>15,000 AADT); • Limit heavy truck traffic to specific routes and times; • Target high emitting vehicles for retrofit or removal with inspection and maintenance programs; • Separate active commuting from busy roads (e.g. create bicycle routes on minor roads); • Implement anti-idling bylaws; • Implement traffic congestion reduction policies (e.g. tolls, parking restrictions, low emission zones, car-share programs, increased public transportation) to increase traffic flow (evidence suggests higher TRAP exposures with stop-and-go traffic). “Long-term” time horizon (years to decades): • Conduct integrated land use planning that incorporates health impact assessments (HIA's); • Site buildings that house susceptible populations (e.g. schools, daycares,retirement homes) at least 150m from busy roads (>15,000 AADT); It is likely that a bundle of complementary mitigation options will be required to protect the most susceptible sub-groups as well as those most highly exposed to TRAP, and to enable both near-term as well as long-term results.
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