A:
Air Fares - Quarterly airline prices since the first quarter of 1995 [U.S. Department of Transportation (DOT), Bureau of Transportation Statistics (BTS)]

D:
Domestic Airline Fares Consumer Report - Includes quarterly airfares by origin and destination pair [U.S. Department of Transportation (DOT)]

G:
Government Transportation Financial Statistics - Transportation revenues and expenditures for Federal, state and local governments. In addition, the GTFS contains data by revenue source, expenditure type, and by mode of transportation. [U.S. Department of Transportation (DOT), Bureau of Transportation Statistics (BTS)]

S:
Surface Transportation Board industry data - Traffic, financial, employment reports on freight railroads reported (annual and quarterly). [U.S. Department of Transportation (DOT), Surface Transportation Board]

T:
Transportation Energy Consumption Surveys - Vehicle energy supply and consumption surveys compiled by the Energy Information Administration (EIA) [U.S. Department of Energy (DOE), U.S. Energy Information Administration (EIA)]

Transportation Services Index - Seasonally adjusted index that measures the movement of passengers and freight in the US (monthly) [U.S. Department of Transportation (DOT), Bureau of Transportation Statistics (BTS)]