The pollution performance of state school buses varies widely depending on fleet age, fuel choice, and investments in retrofits and cleaner fuels. This report analyzes the amount of pollution released from the average state school bus.18 Each state received a letter grade (A, B, C, or D) for modeled tailpipe soot pollution; we also evaluated tailpipe emissions of smog-forming pollution and state programs for cleaning up school buses, assigning each state a rank of Good, Above Average, Average, or Poor for its perfor-mance in these secondary categories.
DATA COLLECTION AND EVALUATION
We contacted each state’s director of pupil transportation to collect information on the age distribution and fuel choice of the state’s school bus fleet. If the director was not responsible for maintaining this information, we contacted the agency responsible for overseeing school bus safety (such as the state police) or for collecting vehicle information (such as the transportation department).
Thirty states and the District of Columbia provided data on the age distribution of their school buses.19 Some of the states only had data on buses transporting public school students, while other states also included data for private schools. Where we could not locate reliable state data, we used a national database prepared by r.L. Polk (2005) that culled model year data from each state’s motor vehicles department. In addition, we contacted state environmental agencies to discuss ongoing or planned school bus cleanup programs, and often spoke with local agencies and schools to gather project-specific data. For a list of data sources, see the appendix.
Fuel Choice and Annual Mileage
Twenty-three states, comprising about 36 percent of the nation’s school bus fleet, provided annual mileage data. These buses traveled an average of 11,400 miles per year—15 percent higher than the value in the EPA’s MOBILE6 vehicle emission model. We assume the higher value reported by states represents the national average.
Twenty-one states, comprising 40 percent of the nation’s school bus fleet, provided fuel choice data. On average, five percent of the fleet in these states is powered by gasoline, so, for states that did not provide fuel-use data, we assume five percent of the fleet is gasoline and 95 percent is diesel.20This assumption is supported anecdotally by many state directors of transportation.