a Locomotives used in Amtrak intercity passenger services are not included.
b Full-size buses have more than 35 seats; mid-size buses have 25-35 seats; small buses have fewer than 25 seats.
KEY: U = data are not available.
SOURCE: U.S. Department of Transportation, Federal Transit Administration, National Transit Database (Washington, DC: Annual issues), table 28 and similar tables in earlier editions.