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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 and were applied retroactively to past years; 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.


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.