Changing your usual travel patterns to walk or cycle away from major roads has been shown to significantly reduce exposure to harmful air pollutants from traffic, according to a recent study by  Sustrans and a number of other organisations

News article: http://www.sustrans.org.uk/resources/in-the-news/greenways-to-cleaner-air?dm_i=6EB,NVTV,1571MG,1XGPG,1

London Greenways Report: http://www.sustrans.org.uk/assets/files/london/2010%20London%20Greenways%20Monitoring%20Report_final.pdf