It’s well-established that density and mixed-use development reduce driving. Right? But strategies like those don’t work the same way everywhere, according to new research published in the Journal of Transport and Land Use. While in major cities, denser development is linked to lower rates of driving, researchers found that in smaller cities it might not have much effect at all. The research suggests that for smaller cities, a focus on reducing block sizes and improving street connectivity may be the most effective way to cut down on driving, though the authors caution that more research is needed to draw universal conclusions.
According to new research, block sizes help explain why some people drive less than others in Norfolk, Virginia. Photo: Joey Sheely, Wikimedia
The research team, sponsored by the Federal Highway Administration, sought to drill down and identify how urban characteristics affect driving levels in different types of places. They looked at four different case studies: Seattle, WA; Richmond-Petersburg and Norfolk-Virginia Beach, VA (grouped together as one case study); Baltimore, MD; and Washington, DC. Using travel surveys and land use information, they modeled the impact on vehicle miles traveled (VMT) of five factors: residential density, employment density, mixed-use development, average block size (which they use as a stand-in for “measuring transit/walking friendliness”), and infill development (or distance to city center).
While the authors knew from previous research that these five factors all contributed to reducing VMT, they found that the Virginia regions didn’t follow the same patterns as the other three. In the smaller urban areas of Richmond-Petersburg and Norfolk-Virginia Beach, they found, mixed-use development did not have a significant impact on reducing driving.
“This is probably because in smaller urban areas, even those living in neighborhoods with well mixed land development may still need to travel far to reach work and non-work destinations,” the researchers write. “In other words, mixed development areas are less likely to be self-sufficient in smaller urban areas.” Mixing uses proved to be a good way to reduce driving in the larger metros.
These findings would seem to show a major weakness of New Urbanist-style “town centers” developed in otherwise suburban areas. A small walkable area isn’t enough to actually spark a real shift in transportation habits – the urban area has to be big enough that most people’s needs can be satisfied without a car. But lead researcher Lei Zhang said the findings don’t warrant that conclusion. “The paper has a small sample size,” Zhang said. “I wouldn’t want to generalize the results to other places.”
Zhang and his team are working on another paper that broadens the scope of their analysis to 20 urban areas. They hope this bigger data set will help planners evaluate land-use plans and how those decisions affect driving rates in different types of places.