Distances within 300-500 m of roadways affect human health. In large North American cities, 30-45% of people live near a major roadway. Patients with asthma should ideally live at least 300 m from major roadways, especially those with heavy truck traffic. In-vehicle exposure during commuting with open windows can also be very high. Air pollutants cause oxidative injury to airways, leading to inflammation, remodeling, and increased sensitization. 14% of incident asthma and 15% of all exacerbations of childhood asthma are attributed road traffic pollutants. Air pollution can cause exacerbations of pre-existing asthma but it also might cause new-onset asthma. Cities with rapid economic and population growth (China and India) have some of the worst air quality in the world. Short-term exposures to ozone, nitrogen dioxide, sulphur dioxide, PM2·5, and TRAP is thought to increase the risk of exacerbations of asthma symptoms.
This comprehensive review from The Lancet presents a snapshot of our current understanding of the relationship between outdoor air pollution and asthma (free full text after registration).
References:
Outdoor air pollution and asthma. Michael Guarnieri et al. The Lancet, Volume 383, Issue 9928, Pages 1581 - 1592, 3 May 2014, doi:10.1016/S0140-6736(14)60617-6
http://www.thelancet.com/journals/lancet/article/PIIS0140-6736(14)60617-6/fulltext
Related reading:
Two Children, One Rich, One Poor, Gasping for Air in Delhi’s Smog - NYTimes http://buff.ly/2fyuxUI
Image source: Interstate 80, seen here in Berkeley, California, is a freeway with many lanes and heavy traffic, Wikipedia, GNU Free Documentation License.
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