Trafƒc is a major source of air pollution in urban areas worldwide (Colvile et al., 2001). In urban areas of Asian developing countries, high and uncontrolled growths of vehicle ©eets in conjunction with slow increases in road surface areas and improper trafƒc management often lead to trafƒc congestion, hence further deteriorating air quality. In Bangkok, the capital city of Thailand, over the period from 1994 to 2006, the vehicle ©eet grew at a rate of 5% per annum (Developing Integrated Emissions Strategies for Existing Land-Transport [DIESEL], 2008). In Hanoi, the motorcycle ©eet alone increased by 16% per year during 2000-2008, reaching above 2 million units by 2008 (Hanoi’s People Committee [HPC], 2008). Pollutants emitted from vehicles accumulate at high concentrations along streets before dispersing to other locations inside and outside cities. Narrow streets bordered with high buildings in most urban centers limit atmospheric dispersion and enhance pollution buildup at high levels in streets and at roadsides (Kim Oanh et al., 2008; Truc and Kim Oanh, 2007). Commuters as well as those working and dwelling along busy roads are thus at risk of exposure to hazardous air pollution levels (Saksena et al., 2008).