Air carrier, domestic, scheduled service (passenger):
U.S. Department of Transportation, Bureau of Transportation Statistics, Office of Airline Information, TranStats Database, T1: U.S. Air Carrier Traffic and Capacity Summary by Service Class, available at http://www.transtats.bts.gov/DL_SelectFields.asp?Table_ID=264&DB_Short_N... as of Aug. 31, 2015 and Air Carrier Financial Reports, Schedule P-1.2, available at http://www.transtats.bts.gov/databases.asp?Mode_ID=1&Mode_Desc=Aviation&... as of Aug. 31, 2015.
1990-2001: American Public Transportation Association, 2011 Public Transportation Fact Book (Washington, DC: 2011), tables 2 and 42 (passenger fares / passenger miles).
2002-13: U.S. Department of Transportation, Federal Transit Administration, National Transit Database, Data Tables 19 and 26 (Washington, D.C.: Annual reports), available at http://www.ntdprogram.gov/ntdprogram/data.htm as of Aug. 31, 2015.
Intercity / Amtrak:
1990-2002: National Passenger Rail Corporation (Amtrak), Amtrak Annual Report, Statistical Appendix (Washington, DC: Annual Issues) (transportation revenues / passenger-miles).
2003-13: Association of American Railroads, Railroad Facts (Washington, DC: Annual Issues), p. 77 and similar pages in previous editions (passenger revenue/revenue passenger miles).
2014-2015: Amtrak, Monthly Performance Review for September 2015 (November 13, 2015), Tables A.2-2, A4-2, available at https://www.amtrak.com/ccurl/322/821/Amtrak-Monthly-Performance-Report-S... as of May 31, 2016
Consumer Price Index:
U.S. Department of Labor, Bureau of Labor Statistics, Consumer Price Index-Urban, U.S. All Items Indexes (series id CUUR0000SA0), available at http://www.bls.gov/cpi/ as of Aug. 31, 2015.