Can carpooling clean the air? The economics of HOV lanes, hybrid cars and the Clean Air Act

Private vehicles are a significant source of air pollution in many areas of the United States. Areas with already high levels of air pollution are required by the Clean Air Act to take steps to reduce automobile use and the associated emissions. The behavioral implications of many travel demand management techniques are poorly understood. In this dissertation I focus on carpooling. Policy makers encourage commuters to carpool through High Occupancy Vehicle (HOV) Lanes, free parking for carpoolers, attempts to connect carpoolers, and casual carpoolers (often called slugging). Despite these efforts, carpooling rates have been falling over time.

One reason for the decrease in carpooling rates, is that carpooling comes with an additional set of personal costs. These costs include reduced route flexibility, assembly costs, and a loss of privacy when another person shares the car. Encouraging carpooling may not improve traffic conditions as much as advocates claim since new carpoolers may be people who would otherwise not have driven. Encouraging carpooling does not eliminate the root of all traffic problems: under- or un-priced road space.

Traditional travel demand models take carpool mode share as exogenous. In this dissertation, I make the decision to carpool endogenous, and build a traffic equilibrium model based on the micro-economic foundations of individual route choices. I then use my model to evaluate High Occupancy Vehicle (HOV) lanes. I apply insights from these studies to a particular policy in California that sought to allocate space on HOV lanes to buyers of hybrid cars as an incentive to adopt this new technology.

My dissertation is divided into four chapters. In Chapter 1, I review current models of carpooling behavior and route choice. In Chapter 2, I develop my microfoundation model of carpooling behavior. In the Chapter 3, I apply and extend my model to the study of HOV lanes. In Chapter 4, I use data from the used car market to understand what happened when California allocated space in HOV lanes to hybrid car owners.