Potential Impact of Exempt Vehicles on HOV Lanes
Objectives of Study
The Federal Highway Administration (FHWA) sponsored this study to examine the potential impact of certain exempt vehicles on the operation of high-occupancy vehicles (HOV) facilities. The possible exempt vehicles examined in the study include environmentally friendly vehicles, and law enforcement, emergency services, and designated public transportation vehicles. The experience with the use of HOV lanes by these types of exempt vehicles is presented. Potential issues and approaches for allowing exempt vehicles to use HOV lanes are examined. This information is provided for use by state departments of transportation and other agencies in considering HOV exemption policies, and in monitoring and evaluating the use of HOV lanes by exempt vehicles.
Traffic congestion continues to be a major issue in metropolitan areas throughout the country. The agencies responsible for the surface transportation system in these regions use a variety of approaches and techniques to address concerns relating to traffic congestion, mobility, and air quality. The use of HOV facilities represents one approach in use or being considered in many urban areas.
The goal of HOV facilities is to provide travel time savings and improved trip time reliability to buses, vanpools, and carpools to encourage individuals to change from driving alone; increasing the people-moving capacity rather than vehicle-moving capacity of congested travel corridors. Currently there are some 130 HOV facilities operating on freeways and in separate rights-of-way in 31 metropolitan areas in North America.
The operation of HOV facilities has evolved over the past 30 years. Some of the initial projects were bus-only demonstration projects. Carpools became the dominant user group on many HOV lanes during the 1970s and 1980s. A three person per vehicle occupancy (3+) requirement was used on many initial projects. A two person per vehicle (2+) requirement is currently in use on most HOV facilities. Allowing lower-occupant vehicles or single-occupancy vehicles to use HOV lanes for a fee was introduced in a few areas during the 1990s as part of high-occupancy toll (HOT) and value pricing projects. In addition, the Transportation Equity Act for the 21st Century (TEA-21) provided states with the ability to allow vehicles classified by the Environmental Protection Agency (EPA) as Inherently Low-Emission Vehicles (ILEVs) to use HOV lanes without meeting the occupancy requirements to support meeting or maintaining the National Ambient Air Quality Standards (NAAQS) and/or transportation conformity regulations [40 CFR 51 and 93]. The ILEV program is no longer an active EPA initiative.
These and other changes reflect an interest in maximizing the use of HOV facilities by state departments of transportation and other agencies responsible for their operation. Ongoing monitoring programs help these operating agencies proactively manage HOV facilities to maximize use, while maintaining the travel time savings and trip time reliability needed to encourage carpooling, vanpooling, and riding the bus.
FHWA provides guidance on possible changes in HOV operations to ensure that federal investments are maintained. The most recent Program Guidance was issued in 2001 (1). The Program Guidance identifies the circumstances under which federal action is required to initiate changes in the operation of an HOV facility, and the federal review process and requirements to be used in these situations.
As noted in the Program Guidance, the source of federal funds used to design, acquire right-of-way, and construct HOV lanes will influence the ability to make changes in the operation of the facility. Some funding categories cannot be used for additional general-purpose roadway capacity. These categories include the Congestion Mitigation and Air Quality (CMAQ) program, the Interstate Maintenance Program, and Mass Transit Capital Investment Grants. In addition, other funding sources may have requirements that limit consideration of possible exempt vehicles (1).
This study examines the use of HOV facilities by possible exempt vehicles, including ILEVs, environmentally friendly vehicles, and law enforcement, emergency services, and public transportation vehicles. The study reflects FHWA's interest in determining the possible impacts of allowing a variety of vehicle exemptions to help promote the efficient use of HOV lanes, while maintaining the intent of maximizing the person-movement capacity of these facilities.
A number of activities were completed as part of this study. First, federal legislation and agency directives relating to HOV facilities and potential exempt vehicles were identified and reviewed. Second, state legislation relating to the use of HOV facilities by ILEVs, environmentally friendly vehicles, and law enforcement, emergency services, and public transportation vehicles was identified and reviewed. Third, available reports, papers, and other documents on the use of HOV lanes by these types of exempt vehicles were obtained and analyzed. In addition, information on the various definitions of HOV lane capacity and options for the use of available HOV capacity was examined. Both traditional methods and electronic search engines were used in the literature review.
Finally, additional information on selected case study examples was obtained through telephone calls and e-mails with representatives from transportation agencies and other groups. Recent HOV lane vehicle counts and clean fuel vehicle license plate registration information were obtained from a few states. No further original data was collected due to the limited project scope. The information obtained through these activities is presented in this report.
Organization of this Report
The remainder of the report is divided into four chapters. Chapter Two defines HOV facilities, discusses the capacity of different types of HOV lanes, and describes possible alternatives for using available capacity. Chapter Three examines possible HOV exemptions for ILEVs and environmentally friendly vehicles. It highlights federal and state legislation and policies relating to HOV exemptions for these types of vehicles. It describes the experience with the use of HOV lanes in California, Virginia, and other states by these vehicles and identifies issues to consider in enforcing the use of HOV lanes by ILEVs and environmentally friendly vehicles. Chapter Four examines the potential effects of providing HOV exemptions for law enforcement, emergency services, and designated public transportation vehicles, and the issues that should be examined for enforcing exemptions for these types of vehicles. The report concludes with a summary of the main points examined in the study and possible areas of further research.