This paper summarizes the literature on the effectiveness of employee ridesharing programs. It provides the conceptual and empirical basis for our evaluation of AQMD's mandatory ridesharing ordinance, Regulation XV. We review the literature on the following topics: 1) employee ridesharing behavior and attitudes, 2) relationships between workplace characteristics and ridesharing behavior, 3) impacts of public programs on ridesharing behavior and, 4) effectiveness of employer-based ridesharing programs. We begin with a brief introduction on the origins of the current policy interest in ridesharing and the development of Regulation XV.

Trip reduction policies are increasingly utilized in U.S. metropolitan areas to address congestion and air quality problems. These policies typically focus on the journey to work and are aimed at reducing the amount of drive-alone commuting by providing transit and ride-sharing incentives. Severe air quality problems in Southern California have prompted the air pollution control agency for the Los Angeles metropolitan area to enact Regulation XV. The regulation requires employers to develop and implement a trip reduction program to achieve specified ride-sharing goals. It is the most ambitious and far-reaching such program implemented to date, and offers a unique opportunity to determine whether such programs can significantly affect travel behavior. This paper presents results from the first year of Regulation XV's implementation.

Regulation XV of the South Coast Air Quality Management District in Southern California requires all work sites at which there are 100 or more employees to implement a ridesharing program by which the organization's "average vehicle ridership" is intended to be increased to a specified target level. This paper summarizes the requirements and procedures required by the regulation. It also presents the first evaluation of the results of this far-reaching program after more than one year of experience. The preliminary evaluation is based on a small number of observations comprising a sample of employment sites which is less than fully representative of all sites affected by the regulation. The early results are encouraging, and show that there has been a small but significant increase in average vehicle ridership, and a corresponding decrease in commuting by single-occupant automobile. Most of the change is found to be the result of increased carpooling, while the use of compressed work hours and walking and bicycling also increased. The research reported here is ongoing and will in time should yield more definitive results.