Geography and social networks in transportation mode choice

In this paper we explore the effects of social influence on travel behavior and utilize an instrumental variables approach to address the potential endogeneity related to similarities in the choice environments of socially connected individuals. We expect individuals to use a mode of transportation that is used by others in their social network. However, other factors important to mode choice, such as commute characteristics or transit access, may influence multiple members of a social network at the same time. Thus it is necessary to estimate the effects of social influence while taking into account the potential effects of shared environmental characteristics. We hypothesize that social influence is relevant to transportation mode choice, even when accounting for shared environmental characteristics among members of a social network. We explore this hypothesis, utilizing survey data collected from a sample of university students, in Davis California. The survey collected information about respondents' social networks, the transportation mode choices of their social contacts, and geographic information for the respondent and their social network. We estimate models using instrumental variables measuring neighborhood characteristics of the social contacts. Results provide evidence that social processes are important to travel behavior, even when accounting for similarities in behavior that may be attributed to similar choice environments.