For information on concepts, definitions, and data sources used in GTFS, see Measurement of Government Transportation Financial Statistics 2012 (below). Note that the data tables in the 2012 publication are not current. Current data are available here.
In the 2012 publication, BTS deflated GTFS current-dollars using the overall Government expenditures and investment price index from the Bureau of Economic Analysis' (BEA) National Income and Product Accounts (NIPA) (Table 3.9.4 Line 1). Starting with the 2019 publication, the deflation method changed to use more detailed price indexes that better reflect and improve alignment with price movements at the transportation level by government. BTS now uses the government expenditures and investment (by function) price indexes for Federal transportation (NIPA Table 3.15.4 Line 19) and for State & Local transportation (NIPA Table 3.15.4 Line 31) for all chained-dollar tables. The resulting chained-dollar measures at the overall aggregate level (Federal combined with State & Local) now reflect the use of the Fisher ideal chained quantity index.