Maximizing the Benefits of Urban Bus Retrofits

Urban buses belch unhealthful fine particulate matter, and installing diesel particulate filters is a common retrofit considered by transit authorities. Susan L. Greco, a doctoral student in environmental health at the Harvard School of Public Health, and colleagues did a case study of 25 Massachusetts Bay Transportation Authority bus routes and determined the "intake fraction"--an expression of the emissions-to-public exposure relationship--for all road segments in the Boston area. They imagined that funds were available to retrofit only half the buses and compared the public-health benefits of retrofitting half the buses on each route to the benefits of retrofitting the same number of buses but exclusively those on the high-intake-fraction routes. The latter course of action increased net benefits by 77 percent.