From the user’s standpoint, system performance is based on an individual trip. Travel time to work refers to the total number of minutes it normally takes a person to get from home to work each day, including time spent waiting for public transportation, picking up passengers in carpools, and on other activities related to getting to work [USDOC CENSUS 2014b]. In 2000 average travel time as measured by the decennial census was 25.5 minutes, which was an increase of 3.8 minutes (17.5 percent) from 21.7 minutes in 1980, and an increase of 3.1 minutes (13.8 percent) from 22.4 minutes in 1990 [USDOC CENSUS 2014b]. In 2012, based on the American Communities Survey, the average travel time stood at 25.7 minutes [USDOC CENSUS 2013].

From the operator’s perspective, congestion can also be measured by the yearly hours of delay. Table 5-1 shows that annual delay per commuter has increased by 6 hours (18.8 percent from 32 hours in 1990 to 38 hours in 2011). This is extra time spent traveling at congested speeds rather than free-flow speeds by private vehicle drivers and passengers who typically travel in the peak periods [TAMU TTI 2013]. The Travel Time Index (TTI) is another important indicator for system operators and is discussed in detail in this chapter.