At what point do pollutant concentrations return to background levels near a heavily traveled road? To answer this question, researchers from STI and UC Davis synthesized 30 years of published work on near-road pollution measurements. We evaluated data from over 40 studies and 13 countries; the analysis encompassed more than 700 air pollutant concentration measurements. Findings showed that most pollutants decay to background within 300-400 m from the edge of a major road, and virtually all pollutants decay to background by approximately 600 m. Changes in pollutant concentrations with increasing distance from the road fell into one of three groups: at least a 50% decrease in peak/edge-of-road concentration by 150 m, followed by consistent but gradual decay toward background; consistent decay or change over the entire distance range away from a road; or no trend with distance. Study findings will help agencies:
  • Plan land uses to minimize pollution exposure
  • Inform the public about near-road pollution problems
  • Guide smart growth planning
  • Identify higher-risk areas or building sites for potential mitigation efforts