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.
