Land Uses and Travel at Suburban Activity Centers

Several recent studies have focused on how land-use characteristics of suburban activity centers affect travel demand. Research indicates that low densities, single uses, small scales, and plentiful parking tend to induce drive-alone automobile usage in the suburbs for employment, residential, commercial, and institutional land uses alike. Much of this past work, however, has been fairly aggregate in scope, relying on comparisons of travel behavior between different activity centers among different cities. Usually, transportation demand, such as average vehicle occupancy levels or trip-generation rates, is gauged in terms of "averages." Few, if any, analyses have been done at a property site level (i.e., relating travel demand of workers within a building to that site's density, degree of land-use mixture, tenancy characteristics, and so on). This article aims to build upon past research by studying the relationship between land use and various indicators of travel demand for a number of office buildings at six different suburban activity centers across the United States. The data source used in this analysis was the report on "Travel Characteristics at Large-Scale Suburban Activity Centers," recently made available through the National Cooperative Highway Research Program (NCHRP). The NCHRP report is a rich source of information on a range of site and travel-demand characteristics of individual buildings -- housing such functions as offices, retail, hotels, and residences -- within six of the largest suburban activity centers in the country. The analysis that follows examines the influence of project size, density, land-use mixing, and parking facilities on three measures of transportation demand: trip generation rates, work-trip mode splits, and automobile occupancy levels. The analyses are summarized by presenting a table of land-use elasticities -- indices of how sensitive various measures of travel demand are to various indicators of site land-use characteristics. The article concludes with discussions on how land use and transportation can be more closely integrated in U.S. suburbs. The term "land use" is used rather loosely in this article, and is meant to convey more than how land is simply put to use. Here, land use refers to the overall built environment -- size and density of suburban work sites, degree to which uses are segregated or commingled, tenant mixes, and site design features, such as the amount and availability of parking. In that all of these attributes of the built environment influence travel behavior, this broader definition of land use is more compelling. Indeed, it is how land is used and organized that shapes how and along what corridors we travel.