Chapter 9 – High Occupancy
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The term "High-Occupancy Vehicle (HOV)" is defined as a motor
vehicle with at least two or more persons, including carpools, vanpools,
and buses. A "High Occupancy Vehicle (HOV) Facility" is any
type of treatment that gives priority to HOVs, including freeway lanes,
park & ride lots, and other elements. Individual HOV facilities may
require different vehicle occupancy levels, which are expressed as either
two or more (2+), three or more (3+), or four or more (4+).
Priority treatments for HOVs have proven to be one of the most flexible,
cost effective alternatives for increasing the person-moving capacity
of congested metropolitan transportation systems. This "lane management"
concept emphasizes person movement rather than traditional vehicle
movement. It offers multi-person vehicles the opportunity to travel
in reserved lanes that preserve higher operating speeds and more reliable
A related strategy – and a relatively recent lane management concept
– is that of High Occupancy Toll (HOT) lanes. HOT lanes combine
HOV and pricing strategies by allowing vehicles that don't meet
passenger occupancy requirements to gain access to HOV lanes by paying
9.1.1 Chapter Scope & Objectives
The breadth of the HOV topic is too great to be handled in any detail
in this Handbook. Accordingly, the reader's attention is directed
to the following extensive references for additional information:
- The "HOV Systems Manual," NCHRP Report 414 (Reference
1), is perhaps the most exhaustive single reference on the topic. This
manual provides a comprehensive guide to developing policies, planning,
designing, implementing, marketing, operating, enforcing, and evaluating
- The Federal Highway Administration (FHWA) maintains an HOV website
at www.ops.fhwa.dot.gov/travel/traffic/hov/index.htm. It includes an inventory
of HOV facilities, a list of training resources, and links to several
technical references and reports.
- Another valuable website is the HOV Pooled Fund Study (http://hovpfs.ops.fhwa.dot.gov).
The goal of the PFS is to assemble regional, state, and local agencies
and FHWA to identify issues, select projects to address these issues,
and disseminate the results of these projects (using the website).
- The Transportation Research Board's HOV Systems Committee
also maintains a website of links and reference information at www.HOVworld.com.
- High Occupancy Toll (HOT) lanes are addressed in the "A
Guide for HOT Lane Development" (Reference 5). The guide presents
a wide range of information on HOT lanes. It addresses a wide range of
policy and technical issues that are associated with HOT lanes, focusing
on how these activities are likely to differ from those associated with
more traditional highway improvements.
9.1.2 Relation to Other Freeway Management Activities
HOV facilities represent just one potential element for managing the surface
transportation network; and as such, must be viewed from various perspectives
(e.g., users, decision makers, providers) and operational / planning "tiers"
(as discussed in Chapter 2). Moreover, as with other freeway management
strategies, the performance of HOV facilities must be continuously monitored
and evaluated. (Refer to chapter 4).
There are many freeway management activities, as discussed in other Chapters,
that relate directly to HOV treatments; and to understand the role of
HOV facilities within the freeway management spectrum, it is important
to understand the relationships between these activities and the HOV facility.
The following table itemizes those related activities and their relationship.
Table 9-1: Freeway Management and Operations Activities and Their Relationship to HOV Treatments
|Ramp Management and Control (Chapter 7)
|As an incentive for HOVs, bypass lanes are provided for HOVs at ramp meter
locations that allow the HOV to proceed in a dedicated lane without
being required to stop at the meter signal, or with a shorter queue
if required to stop.
|Managed Lanes (Chapter 8)
|HOV and HOT facilities represent a special case of lane management.
|Traffic Incident Management (Chapter 10)
|Incident management is an important element of HOV operations (i.e., maintaining the full capacity of the priority lanes / facility)
|Planned Special Event Management and Control (Chapter 11)
Emergency & Evacuation Management (Chapter 12)
|For some special events, HOV is implemented to encourage people to utilize fewer vehicles, thereby reducing congestion.
During major emergencies / evacuation, when additional capacity is needed, occupancy restrictions on HOV lanes may be removed.
|Information Dissemination (Chapter 13)
|Changeable Message Signs are used to convey the current restriction status of HOVs in some systems. CMS
are also used to identify current pricing for HOT operation.
9.2 Current Practices, Methods, Strategies & Technologies
The primary concept behind priority facilities is to provide HOVs with
both travel time savings and more predictable travel times. These two
benefits serve as incentives for individuals to choose a higher-occupancy
vehicle mode over driving alone. The person-movement capacity of the roadway
is increased by carrying more people in fewer vehicles. In some areas,
additional incentives, such as reduced parking charges or preferential
parking for carpools and vanpools, have been used to further encourage
individuals to change their driving habits (1).
The intent of HOV facilities is not to force individuals to make changes
against their will. Rather, the objective is to provide a cost-effective
travel alternative that a significant volume of commuters will find attractive
enough to change from driving alone to use a high-occupancy mode. Many
HOV projects have focused on meeting one or more of the following three
- Increase the average number of persons per vehicle
- Preserve the person-movement capacity of the roadway
- Enhance bus transit operations (1).
As an example of HOV system benefits, Reference 2 describes the results
of an extensive monitoring effort of HOV lane use and performance in the
Puget Sound area in 2000. Available data showed the following for most
- Substantial travel time savings exist in comparison to general
purpose lane travel.
- HOV lanes are operating much more reliably than general purpose
- HOV lanes are successfully moving large numbers of travelers,
particularly in the peak periods when general purpose lane congestion
- HOV person and vehicle volumes are increasing substantially in
the peak period.
- An increasing percentage of peak period travelers are taking
advantage of ride sharing (transit and carpool) travel modes.
- While not all HOV facilities are equally successful, taken as
a whole the HOV lane system is successfully meeting the general policy
goals of providing mobility within the limited right-of-way available.
- Some regional HOV lanes are so successful at attracting users
that they are starting to show signs of stress from high use. The most
obvious sign of stress is recurring congestion at specific locations.
At these locations, consideration of geometric improvements and/or changes
in operating conditions may be required.
Another example of the benefits and overall success of HOV systems is
the growth of this strategy. The report "HOV Facility Development:
A Review of National Trends" (Reference 3) states: "Based
on current roadway improvement program plans identified by various regions
and agencies, the number of HOV lane-miles in existence in 2001 will climb
almost 50 percent by the end of this decade. A majority of the planned
future HOV lanes will be implemented as extensions to current lanes."
9.2.3 Key Considerations During Freeway Management Program Development
HOV systems can be an important part of a freeway management and operations
program. HOV facilities have most commonly been used in roadway corridors that
are either at, or near, capacity, and where the physical and/or financial
feasibility of expanding the roadway is limited. When properly planned
and implemented, HOV facilities can offer a number of advantages. However,
HOV facilities are not appropriate for all situations, nor does their
implementation eliminate the need to pursue other complimentary strategies.
The potential use of HOV facilities should be examined thoroughly before
any such improvements are made, including demand estimation tools and
approaches for assessing the potential environmental impacts (1).
A comprehensive approach in planning, designing, implementing and operating
HOV facilities can help ensure successful projects. The NCHRP HOV Systems
Manual (Reference 1) provides a comprehensive overview of the steps involved in planning, designing, and implementing HOV facilities on freeways (as
well as in separate rights-of-way and arterial streets). Some of these
key elements are summarized in Section 9.3. It is noted that they parallel
the activities identified in the "funnel diagram" from Chapter 3 (e.g., institutional environment and stakeholders, goals and objectives,
concept of operations, performance monitoring). Moreover, Reference 1
emphasizes the need to coordinate this process with other roadway and
transit improvements to ensure an integrated multimodal transportation
9.2.4 Relationship to National ITS Architecture
The National ITS Architecture includes an "HOV Lane Management"
market package. This market package "manages HOV lanes by coordinating
freeway ramp meters and connector signals with HOV lane usage signals.
Preferential treatment is given to HOV lanes using special bypasses, reserved
lanes, and exclusive rights-of-way that may vary by time of day. Vehicle
occupancy detectors may be installed to verify HOV compliance and to notify
enforcement agencies of violations."
9.2.5 Technologies and Strategies
This section summarizes the types of HOV facilities typically found on
freeways. Ancillary facilities (e.g., park-and-ride lots, bypass lanes
at metered ramps) are also noted, as well as a discussion of HOT lanes.
Information on the planning, design, implementation, and operation of
HOVs is provided in section 9.3.
184.108.40.206 HOV Lanes on Freeways
Three types of HOV lanes are commonly found on freeways, and a variety
of different operations and approaches. These are exclusive HOV lanes,
concurrent flow HOV lanes and contraflow HOV lanes. In addition, exclusive
HOV lanes can be operated either bi-directionally or reversible. The following
describes the characteristics of the various HOV treatments (1).
- Exclusive HOV Facility – Facilities or lanes
built within the freeway right-of-way that are physically separated
from the general purpose freeway lanes, and are used exclusively by
HOVs for all or a portion of the day. Most of these facilities are physically
separated from the general purpose lanes through the use of concrete
barriers; although a few facilities are separated by a wide painted
buffer, with and without traffic channelizer separation. These may be
two-directional, or reversible (Figure 9-1). The latter type usually
operates inbound toward the central business district and other major
activity centers in the morning, and outbound (i.e., the reverse direction)
in the afternoon. Some type of daily set up (for reversing directions)
is required with reversible facilities.
Figure 9-1: Examples of Exclusive / Barrier-separated HOV Facility (Reversible)
- Contraflow Lane – A freeway lane in the off-peak
direction of flow (typically the innermost lane) that is designated
for exclusive use by HOVs traveling in the peak direction. Normally,
the contraflow lane is "separated" from the off-peak (or
opposite) flow by insertable cones, pylons (Figure 9-2), or movable
concrete barriers. Contraflow lanes are usually operated during the
peak periods only.
Figure 9-2: Examples of Contraflow Lanes
- Concurrent Flow Lane – A freeway lane in the
same direction of travel (normally the inside lane or shoulder) that
is not physically separated from the other freeway lanes, but is designated
for exclusive use by HOVs for all or a portion of the day. Paint striping
is a common means used to delineate these lanes. (Figure 9-3).
Figure 9-3: Example of Concurrent Flow Lane
(Courtesy Virginia Department of Transportation)
220.127.116.11 Ingress and Egress Alternatives
Ensuring that buses, vanpools, and carpools can easily and safely merge
into and out of the HOV lane is critical to the success of the facility.
A variety of treatments can be used as summarized below (1):
- Direct Merge – Used on concurrent flow HOV
lanes, this approach allows HOVs to merge directly into HOV lanes from
adjacent general-purpose lanes. Merging can be continuous along the
entire length or at specific designated points. Where designated, the
access openings are usually regulated with signs and pavement markings
in accordance with guidelines in the MUTCD.
- Slip Ramps – The at-grade slip ramps are easy and
inexpensive to build. An opening large enough for normal merge/diverge
maneuvers is placed in the barrier. This type of ramp is usually from
a park-and-ride lot to the frontage road, the freeway, or the HOV lane.
- Direct Access Ramps – Grade separated or direct
access ramps provide exclusive ingress and egress for HOVs. Further,
direct ramps may provide access from adjacent roadways, park-and-ride
lots, and transit stations.
- Direct Freeway HOV-to-Freeway HOV Connection – These facilities provide direct connections from an HOV on one freeway
to an HOV lane on another freeway.
In addition to the physical alternatives for ingress, there are operational
- HOV Bypass Lanes at Ramp Meters – This operational
strategy is used to provide priority treatment to HOVs at metered ramps.
Typically, a separate lane is provided adjacent to the general purpose
lane(s) for HOVs so that they do not have to stop at the ramp meter
signal, but rather move around the ramp queue and directly enter the
freeway. In some systems, the HOV ramp lanes is also metered, but at
a relaxed rate relative to the general purpose ramp lanes, still providing
- Priority Pricing – A variation of congestion
pricing that allows non-HOVs to use High-Occupancy Toll (HOT) lanes
for a charge. HOT lanes are discussed in Section 9.2.6.
18.104.22.168 Park-and-Ride Facilities
Park-and-ride facilities are an integral part of a multimodal transportation
system. The purpose of these facilities is to provide a location for individuals
to transfer from a low-occupancy mode of travel to a high occupancy mode
of travel. Park-and-ride facilities are typically provided in conjunction
with scheduled transit services.
Many of the HOV facilities in operation around the country are connected
either directly or indirectly to park-and-ride lots. For HOV lanes, transfers
at park-and-ride lots are usually made from an automobile to a bus; however,
transfers may also occur from other originating modes or from single-occupancy
vehicles to carpools or vanpools. There are many benefits associated with
the proper use of park-and-ride facilities, including the following (4):
- Encouragement of use of high occupancy travel to maximize the
efficiency of the transportation system.
- Improvement in efficiency of transit system by providing high-density
areas for transfers and by increasing ridership.
- Assistance with congestion management, through a reduction in
the number of single-occupancy vehicles on the freeway.
- Reduction in energy consumption and air pollution over what otherwise
would occur by not providing these facilities.
22.214.171.124 Transit Centers
Transit Centers may also be associated with HOV facilities. These centers
provide an interface between transit modes such as between buses offering
different services. These facilities may co-exist with park-and-ride lots.
The two types of centers are on-line, which are located on the
HOV lane and off-line stations, which are located adjacent to
or near the HOV lane.
126.96.36.199 Enforcement Areas
Enforcement of HOV facilities is discussed in Section 9.3. It is important
that the HOV design includes adequate and safe enforcement areas. To be
effective, an officer must have a safe and convenient place to issue citations
or warnings. The enforcement activity should be in view of HOV users so
that they can see when the lane restrictions are being enforced; however,
it should not interfere with traffic on the HOV and mixed-flow lanes.
9.2.6 High Occupancy Toll (HOT) Lanes
One of the most recent management concepts – High Occupancy Toll
(HOT) lanes – combines HOV and pricing strategies by allowing vehicles
that don't meet passenger occupancy requirements to gain access
to HOV lanes by paying a toll. The lanes are "managed" – that is, by using price and occupancy restrictions to manage the number
of vehicles traveling on them, HOT lanes maintain volumes consistent with
uncongested levels of service even during peak travel periods. The appeal
of this concept is tri-fold:
- It expands mobility options in congested urban areas by providing
an opportunity for reliable travel times to users prepared to pay a significant
premium for this service;
- It generates a new source of revenue which can be used to pay
for transportation improvements, including enhanced transit service; and
- It improves the efficiency of HOV facilities, which is especially
important given the recent decline in HOV mode share in 36 of the 40 largest
metro areas (5).
Figure 9-4 illustrates how the concept of excess capacity for HOV lanes
can be used to manage overall roadway congestion. The key to effective
use of this strategy is to actively manage, using dynamic toll collection,
how many vehicles can use the excess capacity. This keeps a congestion
free incentive for carpool and transit vehicles (HOV), while at the same
time fully utilizing the facility. Managing the excess capacity of a facility
is accomplished by charging a dynamic toll for access, with tolls set
by level of congestion as well as vehicle class. The motorist has the
option of paying for a congestion free restricted freeway lane or traveling
free on a congested general purpose freeway lane.
Figure 9-4: Concept of Excess Capacity D
Per Reference 5, approximately 70 percent of the nation's HOV lane miles
operate with peak hour volumes of between 900 and 1500 vehicles/hour.
Ten to 15 percent are operating with over 1500 peak hour vehicles, and
the remaining 10 to 15 percent below 900 vehicles in peak hours. This
suggests that several HOV facilities have some available capacity to allow
other user groups on the facility. However, residual capacity is quite
limited and additional traffic levels would need to be managed closely.
The combined ability of HOT operations to introduce additional traffic
to existing HOV facilities, while using price and other techniques to
better manage and control the number of additional motorists and maintain
high service levels, renders the HOT lane concept a promising means of
utilizing this available capacity.
Most HOT lanes are created within existing general-purpose highway facilities
and offer potential users the choice of using general-purpose lanes or
paying for premium conditions on the HOT lanes. HOT lanes utilize electronic
toll collection and traffic information systems that also make variable,
real-time toll pricing of non-HOV vehicles possible. Information on price
levels and travel conditions is normally communicated to motorists via
changeable message signs, providing potential users with the facts they
need in order to decide whether or not to utilize the HOT lanes or the
parallel general-purpose lanes that may be congested during peak periods.
HOT lanes may be created through new capacity construction or conversion
of existing lanes. Conversion of existing HOV lanes to HOT operation is
the most common approach.
Some of the unique attributes of HOT lanes (relative to HOV) include:
- Pricing Systems: In order to maintain superior traffic
service conditions, toll levels are set to limit the number of users
by willingness to pay. The fee structure may be fixed, varying by time
of day, or dynamic, varying in response to real-time traffic conditions.
In either case, higher tolls are charged during peak demand periods.
Information on toll levels is conveyed to motorists through variable
message signs located near entry points.
- Toll Collection Procedures: In order to avoid the
delays associated with manual toll collection, HOT lanes rely on electronic
payment systems or paid monthly passes during test pilot periods. Therefore,
only those vehicles equipped with a transponder tag or valid permit
may use the lanes.
- Vehicle Type: A range of management policies may
be implemented related to vehicle type. Depending on local transportation
goals, low-emission vehicles, motorcycles, emergency vehicles, transit
vehicles, taxis, and/or trucks may be allowed to use a HOT lane, either
at no cost or for a reduced fee.
In addition to the benefits normally associated with HOV (travel time
savings, trip time reliability) HOT lanes can provide additional benefits (5):
- Revenue Generation: HOT lanes can provide an additional
source of revenue to support transportation improvements such as the
construction and operation of the lanes themselves, or to address corridor
transit needs or other local demand management strategies. In areas
with funding constraints, certain improvements might not be possible
without the additional revenue provided by HOT lanes.
- Utilization of Excess Capacity: HOT lanes may provide
an opportunity to improve the efficiency of existing or newly built
HOV lanes by filling "excess capacity" which would not otherwise
- Remedy for Under-Performing HOV Lanes: In some areas
there has been increasing pressure to convert under performing HOV lanes
to general purpose use. HOT lane applications have the potential to
increase the number of vehicles traveling on underutilized facilities
and possibly reduce pressure to convert them to general-purpose use.
Given that the HOT lane concept is relatively new and has not yet been
widely deployed, it is important to recognize the contexts into which
HOT lanes can be most effectively introduced. These include (5):
- High density corridors typical of larger metropolitan area with
limited travel options and a lack of parallel highway routes where a new
HOT facility can appeal to several travel markets;
- Newly created HOV facilities where HOT operations can maximize
use of the expanded lane capacity;
- Congested HOV facilities where a transition from HOV 2 to HOV
3 eligibility provides available capacity for HOT users; and
- Underutilized HOV facilities where paying SOV users can utilize
the excess capacity with level of service maintained by pricing.
While it is possible to allow limited scale HOT lane use on single-lane
HOV facilities, it is preferable to implement HOT operations on facilities
providing more than one travel lane per direction.
9.2.7 Emerging Trends
The report "HOV Facility Development: A Review of National Trends"
(Reference 3) presents several trends in the future HOV lane development,
- Augmenting the use of occupancy restriction with pricing, where
vehicles are allowed to travel in the HOV lane for a fee, if they do not
satisfy the minimum occupancy requirement established for a particular
time period for an HOV lane (i.e., HOT lanes, as discussed in the previous
- The concept of managed lanes is just now emerging as a topic
in a number of major metropolitan areas where significant roadway improvements
are being planned within major freeway corridors. The role of the HOV
concept is broadening. Occupancy is one of a number of operational strategies
that could be applied in a managed lane application and it will continue
to be explored in more freeway corridors and metropolitan areas around
the country. Some agencies are now considering operational strategies
that serve express traffic, trucks, inherent low emission vehicles, and
pricing (i.e., HOT lanes) as a means of managing demand.
- The viability and operational benefits of HOV lanes will continue
to come under greater and greater scrutiny from various advocacy groups,
general public and elected officials as the severity of congestion grows
in metropolitan areas. While public perceptions from recent unpublished
surveys in Seattle and Los Angeles (2001) still strongly support a commitment
to HOV lanes, these same surveys also report that individuals feel that
HOV lanes are not adequately used. This finding suggests that operating
agencies will need to expend greater effort in attempting to both promote
awareness and continuously improve the operation of each HOV lane and
its related system.
- Monitoring, evaluating, and reporting of HOV lane performance
will play a greater importance in the operation, planning, decision making,
provision of travel condition, and benefit information to the general
public. If greater emphasis is not placed on performance monitoring, reporting,
and the proactive management and operation of HOV lanes to make adjustments
in the operating policies in some locales, the viability of the concept
of HOV lanes as a whole could continue to be eroded.
- Proactive management and operation will be important. This could
involve adjusting the hours of operation, combining operational strategies
with occupancy (e.g., pricing, vehicle type), or some combination. Other
changes that may be appropriate could involve significantly altering or
terminating the operation of some poorly performing HOV lanes. In locations
where the demand to use HOV lanes exceeds the capacity, it may be necessary
to provide additional lanes, raise the occupancy requirement, or pursue
the use of other additional operational strategies.
Finally, while no means of automating the occupancy enforcement of HOV
lane occupancy requirements has yet emerged, work continues, Reference 6 identifies the basic functions of such a system:
- Collect and transmit video images of vehicle license plates and
vehicle compartments for all HOV lane users to a remote computer workstation.
- Perform automatic license plate character recognition on the
license plate video image.
- Synchronize captured video images of vehicle occupants with license
- Search a license plate database containing vehicle occupancy
histories and, based upon failure to meet set criteria, display the vehicle
license plate number and vehicle compartment images on a computer monitor
for review and enforcement purposes.
Until such an automated system is perfected and accepted, enforcement
presence will continue to require a continued commitment of the necessary
staff and resources.