Introduction

High-occupancy vehicle (HOV) lanes are reserved for vehicles with a driver and one or more passengers. These lanes, which often run parallel to general purpose (GP) highway lanes, have been implemented in over 30 U.S. cities since they first appeared in the late 1960s and early 1970s. HOV lanes were originally conceived as a means to encourage carpooling and therefore increase person throughput in the transportation system. The restrictions in these lanes limit traffic demand, which can provide travel time savings along a corridor when compared to adjacent general purpose lanes. This travel time advantage is an incentive to drivers to form carpools in order to bypass congestion.

HOV lanes are one possible solution to increase transportation system efficiency. However, in practice these lanes do not always provide the advantages they advertise. Because occupancy restrictions are discrete (2+, 3+, etc.), it is difficult to achieve utilization balance in these lanes. Ideally, HOV lanes would carry between 1,500-1,800 vehicles per hour per lane, which roughly corresponds to Level of Service C conditions and operating speeds of 45 mph or higher. This level of flow would ensure a high degree of vehicle throughput, and greater overall system efficiency. However, in some areas around the country, occupancy guidelines prove to be too restrictive, resulting in empty lane syndrome, where HOV lanes experience very light demand. In other areas, peak period demand from eligible carpools can actually overwhelm the HOV lanes, leading to congested conditions. Situations with too many, or too few, vehicles using the facilities have left several HOV operators seeking solutions to improve the performance of their HOV lanes.

Fortunately, a number of policy solutions do exist to improve utilization rates in HOV lanes. The planning team has developed the Policy Options Evaluation Tool for Managed Lanes (POET-ML) to evaluate potential changes to existing HOV facilities. This tool is intended for use by HOV owners who are considering changes to their current operating policies. It will allow them to see the impacts of various alternatives and to compare these alternatives to one another. The methodology behind POET-ML is outlined in this paper.

December 2008
FHWA-HOP-09-031