California Air Resources Board

Principal Investigator/Author: Patricia Mokhtarian

Contractor: University of California, Davis & Yale University

Contract Number: 11-322

Project Status: Completed

Relevant CARB Programs: Climate Change

Topic Areas: Behavioral Change, Mobile Source Strategy, Modeling, Sustainable Communities

Research Summary:

California has committed to reducing greenhouse gas emissions through coordinated transportation and land use planning as required by Senate Bill (SB) 375 and to reduce overall statewide GHG emissions by 40% below the 1990 levels by 2030 through SB 32. In order to meet both of these goals, significant changes in household transportation choices must be made.

This first part of this study (Part A) examined the impact of household demographics, individual attitudes, and residential location on vehicle ownership and usage decisions in California. The characteristics of households that voluntarily choose to own fewer than expected vehicles and travel less by vehicle were identified: they tend to be more ethnically and racially diverse, have fewer children, and live in rental units in very high density neighborhoods. Individuals with more pro-environmental attitudes and who like mass transit, biking and walking are more likely to live in zero-vehicle-owning households, while those who like driving and living in spacious homes with large yards are more likely to be in higher-than-expected vehicle-owning households. Local density has non-linear effects on travel behavior: a given increase in density is associated with larger reductions in households' vehicle miles traveled (VMT) in lower-density neighborhoods than in higher-density ones, and this difference is larger in regions of lower-density with less than one million in population. Among higher-density neighborhoods, however, density increase is associated with larger reductions in VMT for households living in light rail-served regions. These results provide useful insights for promoting the adoption of more sustainable travel behavior, and support the State's efforts to promote infill development and reduce dependence on personal vehicles, including implementation of SB 375.

The second part of this study (Part B) analyzed multiple years of statewide household vehicle registration data to explore the process of household vehicle choice, holding, and usage. Results indicate that there are important differences across households in the sensitivity of travel and vehicle choice to the price of gasoline. The researchers are the first to estimate a "portfolio effect" in household vehicle purchases, where attributes of one car affect the revealed desired choice of another. The research shows that this effect influences the turnover of the fleet, and potentially erodes energy savings from fuel economy standards. Finally, a new model of vehicle choice and driving was developed that incorporates key features of the decision-making process of forward-looking consumers. These innovations provide important insights into the effects of policies to further reduce transportation emissions in California.

Final Report: Please email research@arb.ca.gov to request the final report generated by this research contract. Contact the University of California, Davis (UCD) Economics Program for the UCD Energy Economics Program paper.