Beyond the Company Carpool: Disadvantage and Informal Automobile Sharing Within and Between U.S. Households

Planners increasingly recognize connections between traveler constraints, automobile access, and travel behavior. The limited ability to travel via car—for economic or other reasons—greatly reduces mobility for many Americans, who overwhelmingly rely on automobiles for access. Yet public policy efforts to reduce excessive automobile travel often prioritize public transit, ignoring the high rates of private automobile sharing among U.S. travelers. Relatedly, few researchers have studied informal sharing and its relationship with traveler disadvantage, particularly for noncommute trips. To address this research gap, I analyze U.S. trip diary data from 2017. I use multinomial probit modeling to explore the relationship between disadvantage and informal automobile sharing. My definition of disadvantage includes people who have low incomes, travel-limiting physical conditions, and/or limited automobile access. I define several categories of informal automobile sharing to account for different dimensions of interhousehold and intrahousehold sharing. I find that transportation disadvantage is associated with most types of informal sharing, particularly borrowing cars and receiving rides from nonhousehold members. However, trip purpose—particularly noncommute trips—predicts the choice to share better than disadvantage does. Further, trip purpose has a stronger association with sharing among nondisadvantaged travelers. These findings suggest that informal sharing benefits disadvantaged travelers, but social and situational contexts also influence decisions to share transportation. I recommend policies to enhance automobile-based access for low-income travelers, including subsidies for carshare, ridehail, and private car ownership.