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Cyclists’ Exposure to Traffic-Related Particulate Matter (USA)
This research paper, published by the Oregon Transportation Research and Education Consortium in July 2011, found that moving cyclists just a few feet from automobiles can make a big improvement in their exposure to ultrafine particles given off by automobile engines.
Urban residents spend a considerable amount of time in transportation microenvironments as pedestrians, bicyclists, public transit users, residents and workers situated along roadways, and
automobile commuters. Within these microenvironments, vehicles powered by carbon-based fuels (e.g., gasoline, diesel) have a negative impact on air quality. Vehicular exhaust is the source
of a multitude of air contaminants, including particulate matter (PM). Particulate matter of concern ranges in size from the largest PM10 (diameter<10μm) and PM2.5 (diameter<2.5μm), to
microscopic ultrafine particles (UFP). Ultrafine particles have diameters smaller than 0.1μm.
The majority of UFP present in an urban environment are the result of traffic emissions (Zhang and Morwaska, 2002; Kittelson, 1998; Ristovsk et al., 1998). Significant adverse human health
impacts have been connected to UFP number concentrations.
UFP levels that would be experienced by cyclists in roadway environments were used in this study to characterize urban residents’ exposure to traffic-related pollution. Additionally, the study focused on the evaluation of mitigation strategies to lower an urban road user’s exposure.
The first strategy evaluated decreasing proximity of cyclists to motor vehicles in a downtown urban corridor environment, and the second evaluated the use of sound wall barriers as a
shielding technique to lower exposure in a freeway/bike facility microenvironment.
The major findings of this research can be summarised as:
- An original method was developed to measure and compare simultaneous UFP exposure for cyclists in a traditional bicycle lane and a cycle track. UFP number concentrations were significantly higher in the typical bicycle lane than the cycle track for all study days, and nearly all study periods within those days.
- A cycle-track roadway design may be more protective for cyclists than a traditional bicycle lane in terms of lowering UFP exposure concentrations. This, of course, must be balanced against other considerations such as vehicle-bicycle conflicts at intersections and other design factors. Based on these initial findings, understanding roadway and traffic effects on exposure levels can help guide bicycle facility design, and pinpoint locations in which mitigation of exposure levels by placement of facilities such as cycle tracks may be most important.
- Using concurrent traffic, wind and air quality measurements, UFP levels were found to be significantly higher along multiuse paths placed in front of noise barriers (on the freeway side) than those behind the noise barriers (on the residential side). The shielding effectiveness of the noise barrier varied by study site and day, but the effectiveness did not appear to relate to traffic or wind conditions. Increased UFP exposures can be partially mitigated by placing the multiuse path on the side of the noise barriers away from freeway traffic.
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