Daniel G. Chatman
The consequences of sprawl for travel behavior remain unclear. Theory suggests at least two possible commuting outcomes. As jobs decentralize and central employment areas congest, workers might shorten their commutes in time and distance by relocating to the suburbs. Or, the average commute could grow if residential choice is relatively inelastic with respect to job location, amenity explanations for residential and job location dominate, or as dual-worker households in polycentric labor markets become the norm.
Evidence on these questions is surprisingly rare and dated. For data on individual travel behavior, we use the American Housing Survey, a detailed individual-level panel survey for most major metropolitan areas of the U.S. for several years between 1985 and 1997. Commute distance is regressed on a reduced form travel demand model, including U.S. Bureau of Economic Analysis measures of metro-wide employment deconcentration at the one-digit SIC industry level. The model specification conforms to urban form theory, the model estimation uses panel techniques, and the potential endogeneity of wages and land costs -- as compensations for commute costs -- is addressed statistically.
We find that the more suburbanized is employment -- that is, the more sprawl -- the shorter the average commute. There are strong differences by industry, however, that may reflect a combination of industry agglomeration effects, differential job location stability by industry, and historical transitions.
Perhaps the clearest structural evolution of metropolitan areas continues to be the decentralization of both employment and residents. During some periods, U.S. central cities have grown at a lower rate than their suburbs; in others, the decline has been in absolute numbers. The overall trend is fairly strong, particularly over the past century:
Many questions remain regarding the consequences of this pattern of decentralization and deconcentration or, to use a broader term, urban sprawl. Much of the debate concerns environmental resource issues, such as the excess conversion of open land to urban uses and pollution problems associated with overdependence on cars. The potential social impacts are also widely discussed; for example, one of Putnam's (2000) "sprawl" explanations for social capital decline is that the suburban commute leaves less time and energy for social interaction.
Given continuing concerns with sprawl-related transportation issues, it is surprising how little is known about what sprawl means for driving behavior. On the other hand, it is less surprising given the complex nature of the relationship. For example, urban deconcentration consists of many different phenomena, including reduction in employment density, reduction in residential density, and a greater prevalence of discontinuous patterns of developed and undeveloped land. In this paper we focus on decentralization rather than deconcentration; in particular, the extent to which employment is decentralized, or dispersed, versus being clustered in the built-up portion of cities. More specifically, do people drive more or less when employment decentralizes?
We find that both the theoretical and empirical literatures reveal significant gaps. In general, theory provides several hypotheses but few if any hard conclusions, while empirical studies rarely formally test those hypotheses directly.
This paper addresses these gaps in several ways. It builds on established theories of urban structure and transportation behavior to develop the hypotheses of interest. These are tested on a rich data set for U.S. metropolitan areas over the period 1985 to 1997. The model specification conforms to urban form theory, the model estimation uses panel techniques, and the potential endogeneity of wages and land costs is considered.
In brief, we find that the more suburbanized is employment -- that is, the more sprawl -- the shorter the average commute. There are strong differences by industry, however. The suburbanization of construction, wholesale, and service employment is associated with shorter commutes, while manufacturing and finance deconcentration (weakly) explain longer commutes. These results may reflect a combination of industry agglomeration effects, differential job location stability by industry, and historical transitions. While travel behavior is thus complex and nuanced, there is no evidence in these data that job decentralization lengthens the average journey to work. It appears to do the opposite.
Section 2 summarizes the theoretical and empirical literature. The following section discusses our data, while Section 4 describes those data in several key respects. Section 5 presents the empirical strategy. We analyze our results in Section 6, followed by conclusions.