KEY: NTTA = North Texas Tollway Authority; HCTRA = Harris County Toll
Road Authority; AVI = automatic vehicle identification.
SOURCE: U.S. Department of Transportation, Federal Highway Administration,
Toll Facilities in the United States: Bridges-Roads-Tunnels-Ferries, Washington,
DC: June 2001, available at http://www.fhwa.dot.gov/ohim/tollpage.htm
as of Feb. 18, 2002.