There is an interesting study on the increase in pulmonary health risks as a result of those people living in close proximity (200 meters) to a major highway. Studies referenced in the article below demonstrated that pollutant levels increased five fold within the first 30 meters of a major highway. Other studies show that ultra-fine particles (those most likely to be inhaled) condensed and grew larger at 90 meters. Larger particles are more easily filtered out by the body and less likely to reach deep into the lungs, so the increase in ultra-fine particles would pose a health hazard.