How’s That Diet Working: Performance of Virginia Road Diets

About the report:

 In 2018, the Virginia Department of Transportation (VDOT) initiated this study to improve its understanding of past road diets in Virginia.  Of interest were how road diets have been analyzed, how their performance has been quantified, how other states and localities have optimized their practices relating to road diets (e.g., public participation processes), and which Virginia localities—including those that maintain their own roads—have recently implemented road diets.  In addition, VDOT’s Transportation and Mobility Planning Division (TMPD) requested an analysis of recently completed road diets on VDOT-maintained roadways in Fairfax County, Virginia, to determine their effectiveness in order to provide planners with data that could be useful in public participation processes across Virginia. 

The purpose of this study was (1) to compile an inventory of road diets completed in Virginia since 2010, and (2) to analyze a selection of road diets completed in Fairfax County in the last 5 years to determine if they are working as intended.  The scope was limited to lane-removal projects (i.e., road diets), excluding lane-narrowing projects (i.e., lane diets).  Safety analyses (e.g., crash analyses) were outside the scope of the study but could be included in future efforts.  The study tasks included (1) reviewing existing literature including before-after studies of road diets, case analyses, modeling and simulation studies, guidance, and performance measures; (2) developing an inventory of Virginia road diets; and (3) collecting data and analyzing operational effects of recent road diets in Fairfax County.

The study found that road diets have been incorporated into broader concepts and initiatives such as complete streets, bikeway selection, bicycle networks, context-sensitive design, and tactical urbanism and the literature has continued to document their effectiveness.  Virginia localities reported generally positive views about their road diet projects.  A working inventory developed in this study represents approximately 39 miles of Virginia road diets across 66 projects.  Although most studies reported by localities were conducted before road diets and data from those studies were generally unavailable, survey respondents reported that road diets did not generally create traffic congestion problems and that, in their opinions, most road diets had met their primary goals.  The Fairfax County road diets studied did not result in practically significant changes in mean speeds; one indicated that the road diet might have reduced unsafe behavior by people walking and biking.  Additional research on topics such as crash modification factors or the application of new data sources to road diets would be beneficial.

The study recommends that TMPD maintain a statewide inventory of completed road diets and of candidate segments for future road diets.  This could inform decision-making in the VDOT resurfacing program by having an easily accessible inventory of comparable past projects and potential future ones.  TMPD should also develop guidance for road diets including processes for evaluating the feasibility of a road diet on a VDOT-maintained road, stakeholder and/or public participation, implementation, and evaluation.  In addition, TMPD should work with VDOT districts to facilitate the implementation of road diets through the resurfacing program.  To gauge interest in developing crash modification factors for specific road diet types, VDOT’s Northern Virginia District should prepare a new research problem statement for presentation and discussion with the Virginia Transportation Research Council’s Traffic and Safety Research Advisory Committee.

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