26
Levels of ambient air pollution according to mode of transport: a systematic review
(www.sciencedirect.com)
Interpretation
Proximity to traffic and high air interchange increased the exposure to air pollution of commuters using motorised transport. Larger inhalation rates and commuting time increased inhaled dose among active commuters. Benefits of active commuting from physical activity are larger than the risk from an increased inhaled dose of fine particles.
I've often wondered about the net effect. Interesting.