Potential Impact of Exempt Vehicles on HOV Lanes
This report examines the potential impact of exempt vehicles on HOV facilities. The use of HOV lanes by ILEV, environmentally friendly, law enforcement, emergency services, and designated public transportation vehicles not meeting occupancy requirements is discussed. Potential issues associated with allowing these types of vehicles to use an HOV lane and possible issues associated with enforcement are presented. In addition, information on the capacity of different types of HOV lanes and options for using available capacity is summarized.
The report is intended for use by state departments of transportation and other agencies interested in maximizing the use of HOV facilities, while maintaining the travel time savings and trip time reliability for carpoolers, vanpoolers, and bus riders. The report reflects FHWA's interest in providing operating agencies with information on potential approaches to optimize use of HOV facilities, while not degrading their basic purpose of maximizing the person-movement rather than vehicle-movement capacity of congested freeway corridors.
Information from the 10 states with legislation allowing ILEVs to use HOV lanes without meeting occupancy requirements indicates that the registration of ILEVs and the use of HOV lanes by ILEVs is low. As a result, it appears that few ILEVs are using HOV lanes in states where they are allowed. In addition, the ILEV program is no longer an EPA initiative, which may influence the future market for vehicles meeting this classification.
However, it does appear that allowing hybrids to use the HOV lanes in Virginia has contributed to an increase in sales of hybrid vehicles in the state and to their use of HOV lanes. The number of clean special fuel license plates issued in the state has increased significantly since hybrid vehicles became available. Hybrids currently account for some 95 percent of the total clean special fuel license plates issued in the state. Monitoring data of hybrids vehicles using the HOV lanes in northern Virginia indicates that in the fall of 2003, hybrid vehicles accounted for between 2 percent and 12 percent of the peak-period volumes in the HOV lanes in northern Virginia. In the fall of 2004, hybrid vehicles accounted for between 11 percent and 17 percent of vehicles in the I-95 HOV lanes during the three-hour morning peak-period. The actual number of hybrids during the morning peak period ranged from 844 to 1,422 and the corresponding total vehicle volumes in the HOV lane ranged from 7,994 to 8,450 (25).
The Virginia HOV Enforcement Task Force report in January 2005 indicates that the volumes of vehicles with special clean fuel license plates, which are primarily hybrids, are eroding the performance of the HOV lanes in northern Virginia. As a result, the Task Force recommended that the HOV exemption for vehicles with clean special fuel license plates not be extended past the current expiration date of July 1, 2006. The Task Force also recommended that other possible actions be taken if the HOV lanes become too congested prior to the expiration date. (25).
The experience in northern Virginia, where the operation of the HOV facility has been degraded, illustrates the potential impact of allowing hybrid vehicles to use HOV lanes without meeting occupancy requirements. This experience emphasizes the need to adequately evaluate each HOV lane to determine whether capacity exists on the facility prior to granting an exemption to hybrid vehicles.
Allowing law enforcement and emergency-service vehicles that are clearly marked and equipped with rooftop emergency lights and a siren to use HOV facilities without meeting occupancy requirements is not currently reported as a problem in any area. Experience in Houston suggests that marked law enforcement, emergency services, and authorized operating agency vehicles accounted for slightly less than one percent of the HOV lane volume from 6:30 a.m. to 8:00 a.m.
Issues do emerge when unmarked law enforcement and emergency-service vehicles use HOV lanes, and when law enforcement and emergency personnel use the lanes in their personal vehicles. The use of HOV lanes by unmarked law enforcement and related vehicles and personnel from these organizations driving their own personal vehicles has been identified by the Virginia HOV Enforcement Task Force as a significant problem in northern Virginia. It has also been identified as a concern on the Gowanas Expressway HOV lane in New York. Observations from Houston indicate that these types of vehicles may account for some two percent of the HOV lane volumes from 6:30 a.m. to 8:00 a.m.
It is common practice to allow designated public transportation vehicles to use HOV lanes when deadheading or in non-revenue service without meeting occupancy requirements. Private charter and tour buses, school buses, taxicabs, airport shuttles, vans, and vehicles for agencies serving special population groups are not allowed to use HOV lanes without meeting minimum-occupancy requirements.
Areas for Further Research
Additional research would be of benefit in the following areas to better examine the potential influence of exempt vehicles on HOV facilities.
- The role of enforcement in maintaining the operating standards of HOV facilities when any HOV exemptions are under consideration.
- Enhance monitoring of existing exempt vehicles use of HOV lanes.
- Conduct surveys of environmentally friendly vehicle owners in selected areas to better understand the influence of the HOV exemption on the decision to purchase these types of vehicles.
- Develop tools and methods for estimating the demand for environmentally friendly and other exempt vehicles use of HOV facilities.
- Examine potential equity and environmental justice issues associated with environmentally friendly vehicle HOV exemptions.
- Examine occupancy levels for environmentally friendly vehicles using HOV lanes. Explore if drivers of environmentally friendly vehicles likely to carpool.
- Examine violation trends on HOV facilities, including those related to exempt vehicles, in more a detailed synthesis report.
- Conduct longitudinal studies on the impacts of exemptions for different types of vehicles and user groups.
- Examine performance measures and policy guidance associated with data collection and monitoring the use of HOV facilities by exempt vehicles.
- Examine and test improved technologies for enforcement of different types of exempt vehicles, as well as vehicle-occupancy levels.
- Examine institutional and policy issues associated with the enforcement of exempt vehicles and identify effective approaches for addressing these concerns.