Office of Operations
21st Century Operations Using 21st Century Technologies

CHAPTER 1. Introduction and Overview

Traffic congestion on U.S. highways serving our largest metropolitan regions have reached unprecedented levels despite our heroic but, ultimately, failed efforts to build more highways in response to the nation’s insatiable demand for travel.[1] With the benefit of several decades’ worth of hindsight, the U.S. transportation policy community has pledged a renewed commitment to attacking the urban transportation problem through a combination of demand and system management strategies focused on managing our existing transportation supply more effectively and efficiently.

Some of these ideas have been around for as long as the automobile itself. A major cornerstone of transportation system management (TSM) is the High Occupancy Vehicle (HOV) lane, which was first popularized in the U.S. during World War II as part a national fuel rationing program. Highway agencies and toll authorities across the U.S. operate over 2,500 HOV lane miles, with approximately 2,500 more HOV lane-miles planned over the next thirty years.

Photo. I-15 Express Lanes in San Diego, CA.The presence of HOV lanes is an important inducement for ridesharing, which reduces vehicle trips and, in turn, lowers traffic congestion. In addition, HOV lanes – by moving high occupancy vehicles – can carry more passengers per hour than general purpose highway lanes. Today, many HOV facilities do in fact outperform adjacent general purpose highway lanes in terms of person throughput, especially during peak hours of service. By themselves, however, the extent to which HOV lanes induce new ridesharing beyond pre-existing levels is debatable and varies from region to region. Trip chaining, particularly family-related trip movements, and other factors (e.g. the scarcity of potential carpool matches) may dis-incentivize new HOV formation regardless of the presence of viable HOV express options. When new carpool formation is low, HOV lanes may go underutilized and do not meet expectations about congestion relief benefits.

Over the past decade, the commercialization of new technologies has created new opportunities to manage highways using age-old economic principles. The application of these innovative concepts have demonstrated unequivocally that congested highways can be managed more effectively and expand user choices. These applications come in a variety of names – managed lanes, high occupancy toll (HOT) lanes, Express Lanes, and smart roads. Together, they represent a growing body of evidence suggesting that efficient and effective management of existing highway assets is both achievable and sustainable.

The primary purpose of this document is to provide technical guidance and recommended practices on an increasingly popular highway system enhancement opportunity: the conversion of HOV lanes to HOT lane. The guidebook is based on industry best practices with special consideration given to applicable pricing techniques, planning, cost estimation and operational requirements, including the application of supporting Intelligent Transportation System (ITS) technologies.

1.1 What are High Occupancy Toll (HOT) Lanes?

The Federal Highway Administration (FHWA) defines managed lanes as highway facilities, or a set of lanes, in which operational strategies are implemented and managed (in real time) in response to changing conditions. Managed lanes are distinguished from other traditional forms of lane management strategies in that they are proactively implemented, managed, and may involve using more than one operational strategy.[2]

The HOT lanes concept is a managed lane that combines HOV with pricing strategies to improve facility operations. Unlike HOV lanes, HOT lanes allow single occupant vehicles (SOV) to gain access to HOT lanes if they choose to pay the applicable toll. To maintain the “improved facility operations” and the service benefits of a HOT lane, HOT lanes may employ some or all operational strategies.

1.1.1 HOT Lane Characteristics and Applications

Although HOT lane operational and policy parameters may vary from facility to facility, they share several common characteristics with respect to system design, physical configuration, operations and technology. FHWA’s “Guide for HOT Lane Development” identifies several major characteristics of HOT lanes:

  • HOT lanes typically are limited-access; normally barrier-separated highway lanes that provide free or reduced cost access to qualifying HOVs, and also provide access to other paying vehicles not meeting passenger occupancy requirements. (Note: The geometric limitations of the existing HOV facility are the primary reason HOV to HOT lane implementations are not barrier separated from the general purpose lanes. Instead striping or plastic delineators are generally used as a buffer.)

  • 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.

  • 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 sophisticated electronic toll collection (ETC) 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 variable message signs (VMS), 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, conversion of existing lanes, or converting HOV lanes to HOT lanes with additional capacity added. Since both right of way and construction funds are limited, conversion of existing HOV lanes to HOT operation is the most common approach.

Photo. Barrier – separate reversible flow facility.Occupancy requirements on HOV facilities are usually set at HOV 2+. HOV 2+ lanes represent approximately 95 percent of all HOV lane miles operated in the United States. Nationally, most HOV lanes perform within the generally accepted range of peak performance:

  • Of HOV lanes with the HOV 2+ eligibility requirement, approximately 70 percent of he nation's HOV lane miles operate with peak hour volumes between 900 and 1,500 vehicles per hour.

  • Of the remaining 30 percent, 10 to 15 percent of HOV vehicles are operating with over 1,500 peak hour vehicles, and the remaining 10 to 15 percent operate at or below 900 vehicles per hour in peak hours.

Multi-lane HOV facilities that suffer chronic peak hour underutilization (below 900 vehicles per peak hour) comprise the pool of facilities most suitable for conversion to HOT lanes. HOV facilities that carry between 900 and 1,500 vehicles per peak hour generally do not offer sufficient residual capacity to sell to SOVs without risking lower level of service (LOS) than baseline peak conditions.[3] Experience has shown that raising minimum HOV access requirements to HOV+3 has had minimal effect on HOV lane performance since the number of HOV +3s is generally less than the number of HOV +2s that were using the HOV lanes. This condition may in fact result in underutilization of the HOV lanes. Additionally, with deflection of HOV +2s onto general purpose lanes, it is very likely that prevailing traffic congestion on general purpose lane will worsen.

Capacity is also influenced by factors such as facility geometry, the number of access points and the number of travel lanes. Consequently, HOT lane capacity varies from location to location. For example, a single HOT lane will have a lower managed capacity than a HOT facility with multiple lanes. Volumes on the Houston I-10 Katy Freeway QuickRide – a one lane, reversible-flow facility are kept to 1,500 vehicles/hour. However, the 91 Express Lanes provide two managed travel lanes in each direction and have been able to operate at acceptable conditions with flow rates of 1,800 vehicles/hour/lane.[4] The 91 Express Lanes expands the toll zone in each direction to three lanes designating two lanes for HOT and one lane for HOV+3 use. HOV+3 are required to mount transponders in the vehicles and are charged a reduced toll rate.

HOT Lane Performance

The emergence of HOT lane pricing techniques has been facilitated by the use of ETC. These techniques can range from flat toll to dynamic by time-of-day and offer a wide range of options for achieving greater performance. Electronic pricing, when introduced in the appropriate operational context, has been shown to offer a cost effective strategy for creating and sustaining net travel time benefits. The case studies presented in Chapter 5 describe how different electronic pricing applications are used to maximize and maintain peak travel time savings.

It is important to be able to evaluate the performance of the HOT lane facility against established measures of effectiveness, and estimate travel time benefits. In Chapter 2, a more detailed discussion of system performance and user benefits associated with HOT lanes is presented.

HOT Lane Benefits

HOT lanes are intended to provide a wide variety of benefits to multiple user groups. When applied in conjunction with other management tools and sensible, targeted provision of additional lane capacity, HOT lanes have the potential to generate significant improvements in congested travel corridors.

HOT lanes can also afford a wide range of secondary benefits, including:

  • New revenues that can be used to support the construction of the HOT lanes themselves or other initiatives, such as improved transit service or regional transportation initiatives;

  • Traffic service improvements on congested parallel highway mainline lanes by drawing vehicles off parallel local streets and improving corridor-wide mobility;

  • Performance reliability compared with general purpose lane during peak periods.

  • Faster highway trips for express transit services such as bus rapid transit (BRT);

  • Environmental advantages by providing opportunities to encourage carpooling, improve transit service, and move more people in fewer vehicles at faster speeds;

  • Increased efficiency of managed lane facilities making them attractive in regions that might not otherwise consider them; and,

  • Improving the utilization of HOV lanes and therefore eliminating potential pressure to convert under performing HOV lanes to general-purpose use.

1.2 Purpose of the High Occupancy Toll Lane Guidebook

The intended audience of this document includes states’ departments of transportation (DOTs), Metropolitan Planning Organizations (MPOs), policy-making agencies, enforcement agencies and others having a role in the planning, development, management, operations, monitoring, evaluation and reporting on the performance of HOV and HOT lanes. The objective of the guidebook, which explores the planning, design, implementation and ongoing operations and maintenance of HOT lane facilities converted from existing HOV lanes, is to provide:

1) Technical guidance that will assist the state and local transportation planners in determining the conditions where conversion from HOV to HOT lanes is feasible and advisable, and 2) comprehensive list of activities to be performed in the planning, implementation and operation of an HOT lane facility. Special attention is paid to institutional, system design and operational challenges that typically present themselves in the course of a conversion to HOT lane.

Three case studies of HOT implementations are provided in the guidebook to further illuminate key practical insights and lessons learned that would be of value to HOT planners. The case studies are based on information gathered from on-site visits and a focused interview methodology. Focused interviews were conducted with key managers at three HOT lane projects:

  1. MnDOT’s MnPass I-394 HOT lanes,
  2. SANDAG I-15 Express and HOT lanes, and
  3. CDOT’s I-25 Express Lanes.

1.3 Study Approach/Methodology

The approach and methodology used in developing the Guidebook included:

  • Establishing a project development framework that advances the HOT conversion project from concept to implementation;

  • Employing a combination of formal interviews with recognized industry experts and selected agencies with experience in the implementation of both managed and HOT lanes;

  • Conducting on-site focused interviews that inform three “case studies” of functioning HOT lanes; and,

  • Conducting a literature review of current industry practices.

The research and case studies focused on all elements of project implementation, including items such as planning, design, pricing strategies, construction, operational requirements, and the integration of ITS with the HOT lane application.


[1] Small, K., C. Winston, J. Yan, March 16, 2006, Differentiated Road Pricing, Express Lanes, and carpools: Exploiting Heterogeneous Preferences in Policy Design.” Back to reference 1.

[2] A Guide for HOT Lane Development, U.S. Department of Transportation, Federal Highway Administration. Back to reference 2.

[3] Ibid Chapter 6. Back to reference 3.

[4] Ibid Chapter 6. Back to reference 4.

June 2007
Publication #FHWA-HOP-08-034