• California generates 7% of the US GHGE, and is the 12th largest emitter worldwide. Within transportation, the largest emitting sector in California (38%) and personal vehicles are the largest portion of that sector (79%).  Two strategies to reduce emissions include increased use of clean emission vehicles and reducing miles driven.  The latter approach would have the public health benefit of improved health from active transportation and reduced air pollution. The authors quantified transportation strategies to reduce greenhouse gas emissions using both approaches.
• Statistics on travel patterns and injuries, physical activity, fine particulate matter, and GHGE in the San Francisco Bay Area, California, were input into a model that calculated the health impacts of walking and bicycling short distances usually traveled by car or driving low-emission automobiles. The change in disease burden was calculated in disability-adjusted life years (DALYs) based on dose–response relationships and the distributions of physical activity, particulate matter, and traffic injuries.
• Increasing median daily walking and bicycling from 4 to 22 minutes reduced the burden of cardiovascular disease and diabetes by 14% (32466 DALYs), increased the traffic injury burden by 39% (5907 DALYS), and decreased GHGE by 14%. Low-carbon driving reduced GHGE by 33.5% and cardiorespiratory disease burden by less than 1%.
• Increased physical activity associated with active transport could generate a large net improvement in population health. Measures would be needed to minimize pedestrian and bicyclist injuries. Together, active transport and low-carbon driving could achieve GHGE reductions sufficient for California to meet legislative mandates of reducing emissions to 80% of 1990 levels levels by 2050.

Neil Maizlish, PhD, James Woodcock, PhD, Sean Co, MS, Bart Ostro, PhD, Amir Fanai, CEng IMechE, and David Fairley, PhD. (2013). Health Cobenefits and Transportation-Related Reductions in Greenhouse Gas Emissions in the San Francisco Bay Area. Am J Public Health, e1-e7. doi: doi:10.2105/AJPH. 2012.300939