Figure 4-5a Travel Time Index (TTI): July 2013–June 2015
FIGURE 4-5b Planning Time Index (PTI): July 2013–June 2015
Figure 4-5c Congested Hours: July 2013–June 2015
NOTES: The reports utilize vehicle probe-based travel time data from FHWA's National Performance Management Research Data Set (NPMRDS). The reports are currently using data from 52 urban areas in the U.S. Congested Hours are computed as the average number of hours during specified time periods in which road secti ons are congested — speeds less than 90 percent of free-flow speed (e.g., 54 mph if free-flow speed is 60 mph). This measure is reported for weekdays (6:00 a.m. to 10:00 p.m.). Averages are weighted across road sections and urban areas by VMT using volumes from FHWA's HPMS.
Travel Time Index is the ratio of the peak-period travel time as compared to the free-flow travel time. This measure is computed for the AM peak period (6:00 a.m. to 9:00 a.m.) and PM peak period (4:00 p.m. to 7:00 p.m.) on weekdays. Averages across urban areas, road sections, and time periods are weighted by VMT using volume estimates derived from FHWA's HPMS.
Planning Time Index is the ratio of the 95th percentile travel time as compared to the free-flow travel time. The measure is computed during the AM and PM peak periods as defined in the TTI, and averages across urban areas, road sections, and time periods are weighted by VMT using volume estimates derived from FHWA's HPMS.