Two reports issued within days provide contrasting takes on the enduring issue of highway traffic congestion. One report from traffic-data firm Inrix is an update of previous scorecards that rank world cities for highway delay, calculated by aggregating travel times slower than free flow. In contrast, Transportation for America’s new report looks closely at how the frequently-employed solution of highway capacity expansion has worked, and finds it wanting.
In pursuit of congestion relief, the United States added 63 percent more urban freeway lane-miles between 1990 and 2017. That rate far outstripped the 46 percent growth in urban population. It didn’t work. As widely reported last month, the Texas Transportation Institute’s Urban Mobility Report has returned after a five-year hiatus.
There’s new evidence, from academia and a prominent real-world case, that ever-expanding highway capacity is a futile strategy for reducing congestion. Crosstown, a data-analysis project at the University of Southern California, looked at vehicle speeds on the 405 over five years, capturing the last year before the new lanes opened and the period since. One example does not confirm the Fundamental Law of Road Congestion, but the 405 case is consistent with that theory, as is a new comprehensive study of induced demand, by Kent Hymel of Cal State Northridge.
Since passage of S.B. 743 in 2013, California agencies have wrestled with questions around the added travel and emissions resulting from land use and transportation projects. On the land use side, see SSTI’s recent webinars about land-use review reforms in San Jose and Pasadena. On the transportation side, the National Center for Sustainable Transportation has developed an induced travel demand calculator designed to calculate the percentage of additional annual VMT when highways are widened.
A newly released study sponsored by CalTrans offers a thorough review and analysis of research and practice related to the limitations of existing travel forecasting models. The authors focus on limitations in forecasting induced vehicle travel generated by adding lane miles during a capacity expansion. Acknowledging that many practitioners may not have access to more advanced travel models capable of capturing induced demand, the authors recommend project staff in these cases rely on general elasticities while acknowledging the shortcomings in the analysis.
A commonly cited strategy to achieve lower emissions and energy use is highway capacity expansion intended to reduce delay. But, as a new brief from UC-Davis and hosted on the Caltrans website points out, congestion relief is usually short-lived, due to “induced demand” or “induced travel.”
In the October 2011 issue of the American Economic Review, authors Gilles Duranton and Matthew A. Turner review traffic data from the years 1983 to 2003. Their article, “The Fundamental Law of Road Congestion: Evidence …