A recent Harvard study found that compressed natural gas (CNG) affords a third more health benefits than clean diesel, but that the cost per unit of health improvement is six to nine times higher for CNG. The analysis, conducted by the Harvard Center for Risk Analysis, part of the Harvard School of Public Health, measures the public health damages of air pollution from urban transit buses in units of Quality Adjusted Life Years (QALY). The study finds that new emission controlled diesel (ECD) buses reduce health damages by 40%, and that new CNG buses cuts health damages by 55%, compared with new conventional buses. Both CNG and ECD reduce emissions of fine particles by about 75%. CNG also has a further health advantage because it reduces emissions of NOx. The cost per QALY saved using CNG would be six to nine times greater than for ECD because of the higher cost of acquiring and maintaining CNG vehicles, installing and maintaing infrastructure to fuel them and paying more for fuel to run them. Funded by International Truck and Engine Corp., the study was informed by an advisory panel of 18 academic, industry and five government experts, including five senior managers of public transit authorities from across the United States. For more information on the school log on to www.hsph.harvard.edu