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Travel Time Index
The Travel Time Index is the ratio of travel time in the peak period to the travel time at free-flow conditions. A value of 1.35 indicates a 20 minute free-flow trip takes 27 minutes in the peak. Free-flow speeds (60 mph on freeways and 35 mph on principal arterials) are used as comparison threshold.
Methodology and data sources have been changed in 2015; these figures are not comparable to those in past editions of NTS. Population group is based on 2014 population.
KEY: NA = not applicable; R = revised.
Very large urban areas – 3 million and over population.
Large urban areas – 1 million to less than 3 million population.
Medium urban areas – 500,000 to less than 1 million population.
Small urban areas – less than 500,000 population.
(a) Rank is based on the calculated point change with the highest number corresponding to a rank of 1.
(b) Averages weighted by Vehicle Miles Traveled.
1982-2014: Texas Transportation Institute, Congestion Data for Your City, Excel spreadsheet of the base statistics for the 101 urban areas and population group summary statistics (College Station, TX: 2015), available at as of Nov. 19, 2015.
2015-16: U.S. Department of Transportation, Federal Highway Administration, Urban Congestion Reports, Personal Comunication, Aug. 19, 2017.