Suggested Citation:
Handy, Susan L., Gil Tal, Marlon G. Boarnet (2010) Brief: Impacts of Connectivity Based on a Review of the Empirical Literature. Institute of Transportation Studies, University of California, Davis, Brief UCD-ITS-RR-10-54

No studies were identified that directly test the effect of a change in network connectivity on vehicle miles traveled (VMT) or greenhouse gas (GHG) emissions, though network connectivity has been considered in several studies that examine the association between the built environment and travel behavior. Connectivity in these cases is measured for residential neighborhoods, from the perspective of households, but not for areas around transit stations or trip destinations. Measuring the impact of connectivity on VMT and GHGs, while controlling for socio-demographic characteristics (e.g. income, household size), population density, and land-use mix, is challenging.

The key criterion for including studies in the research brief was reporting of the effects of network connectivity on VMT and GHGs while controlling for socio-demographic characteristics and built environment characteristics. Additional considerations included U.S. location for the data (though studies in other developed countries were also considered), published since 1990, and data collected from a sample of residents of areas both with transit supply and areas without it. There are no available studies that provide direct evidence on the effect of connectivity on greenhouse gas (GHG) emissions.

Studies meeting the criteria were Ewing and Cervero (2010), Boarnet et al. (2004), Bento at al. (2003), Cervero and Kockelman (1997), and Chapman and Frank (2004). Fan and Khattak (2008) reports person miles of travel (PMT) rather than VMT, but was included because of its U.S. location and because it is the only study to control for attitudes, in this case meaning one’s beliefs about and feelings towards transportation. Hedel and Vance (2007) was also considered, but excluded since it focuses on a non-U.S. location and does not report an average value of VMT that would enable calculation of the change in VMT associated with an increase in connectivity (though an elasticity for this study is reported in Ewing and Cervero (2010)). Specific measures used in each study and important considerations with respect to these measures are noted in Table 1.

Key words:  Vehicle miles of travel, pollutants, networks, connectivity