Urban Highway Travel Times
Box 3-A
Travel Time Index
Developed by the Texas Transportation Institute, the Travel Time Index is the ratio of peak period
travel time to free-flow travel time. A value of 1.0 indicates that traffic is moving freely. A
value of 1.3 indicates that it takes 30 percent longer to make a trip than in free-flow conditions.
If, say, a trip takes 20 minutes in free-flow conditions and the index is 1.3, then the trip would
take, on average, 6 minutes longer to complete during a peak period.
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