Travel Time Index per Year, Selected American Cities, 1982-2020

Travel Time Index per Year Selected American Cities 1982 2020

Source: Texas Transportation Institute. The Urban Mobility Study.

The Travel Time Index (TTI) is the ratio of the travel time during peak hours over the time it takes to undertake the same trip under normal conditions. A value around and above 1 is indicative of recurring congestion levels since the travel time is above the average. TTI is related to the urban population, implying that the larger the population, the higher the congestion level. In the 1980s and the 1990s congestion significantly deteriorated in major American cities. Major factors linked with this deterioration were related to urban sprawl, a growing fleet of trucks and automobiles, and the difficulty in providing additional road infrastructures. Commuters were spending an increasing amount of hours in congestion. However, since the mid-2000s, the TTI has leveled off and has declined in some cases. This underlines a saturation in vehicle ownership and use. The Covid-19 pandemic impacted travel time as congestion levels were reduced due to fewer commuting flows. The index dropped by 11%.