Can Carpooling Clear the Road and Clean the Air? Evidence from the Literature on the Impact of HOV Lanes on VMT and Air Pollution

Proponents of High Occupancy Vehicle (HOV) lanes claim they reduce vehicle-trips by encouraging more people to carpool, but the evidence is mixed. This paper looks at attempts to understand the impacts of HOV lanes with a focus on the behavioral aspect. Many papers look at performance metrics that do not have direct welfare, congestion, or air pollution impacts, while other papers leave out important aspects of the problem such as endogenous carpool formation and induced demand. Papers on individual regions find HOV lanes may increase or decrease welfare, while more general papers find that the impact of HOV lanes depends on initial conditions. There are a few examples of papers that adequately model behavior, but they have not been applied to general circumstances