Source: U.S. Department of Transportation, BTS.
Home-to-work commuting profiles are a core dimension of urban mobility since they represent movements related to employment and revenue generation. They include the length, time and speed of a commute, which underline an increasingly challenging context for urban mobility, particularly after 1995. Beforehand, commuting was generally improving in terms of speed, even if the average commuting distance was increasing. The suburbanization of housing and employment was taking place at a quick pace, but its impacts on congestion remained marginal.
From the 1990s the context started to shift rapidly with a vicious circle of congestion implying longer trips as well as of a longer duration of those trips. In several large American cities, a process of space/time divergence is taking place with a growing amount of time spent to travel a similar distance. The average commuting speed has been steadily decreasing. How far this process will go remains uncertain since, at some level of congestion, there are pressures to improve infrastructure as well as to develop alternatives such as public transit.