Thoughts on the Meaning of Mark Stevens’s Meta-Analysis

The literature on the relationship between land use and travel behavior is vast but messy. I should know, as a contributor to this literature for more than 25 (how-did-thathappen) years. Studies rarely use the same land use measures as previous ones, their travel data come from different sources, each applying its own survey method, and they employ varied statistical techniques from the simple to the sophisticated. Some studies are national in scope; others focus on particular metropolitan areas. Some rely on data aggregated to geographic units; others use individualor household-level data. No two studies are alike. Murky terminology is part of the problem. Back when I was working on my dissertation, planners used the term “land use” for what we now more commonly call the “built environment. ” “Traditional neighborhood design” became “the new urbanism,” which was somehow related to “smart growth. ” What the users of these terms meant, exactly, was not always clear. The “3Ds” then caught on as a way to describe the built environment and later expanded to the “5Ds” and even the “7Ds. ” The “D” words, though catchy, are often confusing. Diversity as a D means land use mix, but one could mistake it to mean socio-demographic mix. Design as a D means street network structure, not the aesthetic qualities that the word generally implies. Mark Stevens (2017/this issue) uses “compact development” to refer to communities with high scores on the 5Ds: density, diversity, design, distance to transit, and destination accessibility. Absentee conceptual models are another part of the problem. Researchers use density more than other measures of the built environment because the data to measure it are readily available. But how does density infl uence travel choices? Travel behavior researchers generally assume that individuals make choices that maximize their utility or, more simply, that make the most sense for them. The built environment plays a role in determining the choices available to the individual. Most fundamentally, built environment characteristics such as density, land use mix, and street connectivity determine how far individuals are from destinations, and it is the cost of this distance that infl uences where they can go, by what mode, and how frequently. This infl uence is indisputable, a physical, temporal, and fi nancial fact. But it does not mean that the built environment determines the choices made by the individual. The compact development hypothesis asserts that in communities for which destinations are closer to home (as is usually the case in communities with higher densities, land use mix, and street connectivity), residents will drive less because they do not need to drive as far to get to the nearest store (or other destinations) or because they have the option to walk or bike or take transit rather than drive. They do not have to, of course; they can choose more distant stores, they can continue to drive even to nearby stores, and they may also choose to go to the store more frequently because it is close. A reduction in driving is thus not a given for compact development, though it is a possibility. The literature largely supports the hypothesis: Residents do tend to drive less and use other modes more when they live in more compact areas, all else being equal.