Does Compact Development Increase or Reduce Traffic Congestion?

Reid Ewing, University of Utah

Co-investigator:

Summary:

It is now widely held, even among many state transportation departments, that you cannot “pave your way out of congestion” (at least in the long run) due to highway induced traffic and highway induced development (sprawl). Therefore, any solution to highway congestion must be multi-faceted and must, in particular, reduce the need for so much vehicular traffic. From years of other research, we know that compact development that is dense, diverse, well-designed, etc. reduces vehicle miles traveled. But compact development also concentrates origins and destinations. No one has yet determined, using credible compactness/sprawl metrics and congestion/travel time data, the net effect of these countervailing forces.  

Using compactness/sprawl metrics developed in an earlier project at the University of Utah, and congestion/travel time data from TTI's Urban Mobility Scorecard Annual Report database, this study will determine which point of view is correct. It will do so by (1) measuring compactness, congestion, and other control variables using the best national data available for U.S. urbanized areas and (2) relating these variables to one another using multivariate methods to determine whether compactness is positively or negatively related to congestion and travel times. 

This project will be very cost-effective. The compactness/sprawl metrics have already been developed and published by the PI of this project for urbanized areas, metropolitan areas, metropolitan counties, and census tracts. They have already been used by our team to study other costs of sprawl in five peer reviewed articles. Our current sample of FHWA urbanized areas consists of the largest 162 urbanized areas, all with populations over 200,000. Our sample will be expanded to include all urbanized areas with over 100,000 population. Smaller urbanized areas are unlikely to experience major traffic congestion, and will be omitted. Control variables will be estimated using publicly available data sets, principally the American Community Survey and the National Transit Database. Congestion/travel time data are now available, for the first time, for 471 FHWA urbanized areas from INRIX, in association with TTI.

Impacts:

The results of this project are important not only for bringing planning academia closer to resolving the debate over this particular impact of sprawl, but also for policy planning. Reducing congestion is the primary objective of transportation agencies. Congestion costs Americans billions of dollars in lost productivity, and policy should reflect the best ways to avoid such inefficiency. While this is counterintuitive, expanding freeways appears to have the exact opposite effect of what is intended, increasing VMT and hence congestion indirectly, without (in this cross-sectional study) relieving congestion directly. Freeway induced traffic appears to undermine all the good intentions of freeway building. And ultimately, given the strong negative relationship between average fuel price and delay per capita, the U.S. may have to consider higher fuel taxes or congestion pricing to deal with the pervasive increases in congestion documented by TTI in the Urban Mobility Scorecard Annual Report database.

Project Details

Project Type:
Research
Project Status:
Completed
End Date:
December 31,2017
UTC Grant Cycle:
Natl Round 3
UTC Funding:
$36,416