Photos of cars on freeway, speeding sign

Freeway Management and Operations Handbook

Chapter 1 – Introduction
Page 1 of 2

Chapter 1 was revised in June 2006.  For more information on the extent of these revisions, see the Revision History Table at the beginning of this handbook.

1.1 Scope of Freeway Management and Operations

Civilizations have become great in part because of their transportation systems. The Phoenicians used the seas as their transportation system. The Roman Empire built roads to connect the distant parts of their empire. The British Empire used the seas to maintain their empire. The United States civilization has become great and remains so, in a large part because of its transportation system, which has contributed to a robust economy. The ability to meet society's needs for mobility, access, goods movement, security, and overall quality of life is dependent on the ability to provide for safe, reliable, and sustainable travel in an ever-changing environment with varying demands.(8)

The nation's Interstate System and other expressways – totaling approximately 55,000 centerline miles – are an integral part of the surface transportation network. For example, urban freeways make up less than 2.4% of the total urban highway mileage; yet carry approximately 20% of the traffic nationwide (1). In essence, freeways provide the basic backbone of our roadway transportation system and the highest level of service when traffic flows smoothly and safely. "Service" in this context not only refers to the commuting, commercial, and recreational movement of drivers, riders and shippers; it also refers to the ability of the freeway network to support other government agencies (e.g., emergency service providers, first responders, military and security) as they plan, react to, and recover from weather-related, natural disasters, and human-caused emergencies.

Since the 1960's, population growth and economic prosperity have led to a steady increase in the number of vehicles using the roadways – particularly freeways – across the United States. The growth in highway travel by the public can be attributed to a number of factors including: population growth, an increased number of licensed drivers and auto ownership, an increase in the number of trips per household, growth in economic activity, changes in urban land use, and increase in freight activity. As shown in Figure 1-1, vehicle-miles traveled grew steadily during the last decade, with a minimal increase in lane-mileage.

graph showing the increase in vehicle miles traveled from 1990 to 1998 with only a small increase in lane mileage

Figure 1-1: Vehicle Miles Traveled Versus Lane Mileage (Reference 10) D

This increase in demand has, unfortunately, resulted in more turbulent traffic conditions, increased congestion, and more frequent and longer traffic delays. Increased turbulence and increased vehicle demand leads to more conflicts and collisions, reducing safety. Today, the demand for freeway facilities is overwhelming, and problems have grown to an intolerable proportion in some metropolitan areas. A FHWA paper discussing TEA-21 Reauthorization (9) states: "It is has become widely acknowledged that providing effective highway-based transportation consists of three component parts:

  • Building the necessary infrastructure
  • Preserving that infrastructure (e.g., maintenance & reconstruction), and
  • Preserving its operating capacity by managing operations on a day-to-day basis.

Highway transportation can thus be likened to a three-legged stool that cannot effectively serve customer needs if any of these three parts (legs) is missing or is underemphasized (too short) relative to the others." The focus of this document is the "operations leg".

Freeway traffic management and operations is the implementation of policies, strategies and technologies to improve freeway performance. The over-riding objectives of freeway management programs are to minimize congestion (and its side effects), improve safety, enhance overall mobility, and provide support to other agencies during emergencies. The TRB Freeway Operations Committee's Millennium Paper (3) states: "Freeway operations, in its broadest context, entails a program to combat congestion and its damaging effects: user delay, inconvenience and frustration, reduced safety, and deteriorated air quality." Moreover, this "context" includes a vast array of freeway uses – the daily commute, commercial vehicle operations, personal and recreational trips, emergency service response, and evacuations during emergencies.

1.1.1 Importance of Freeway Management & Operations

When discussing the quality of day-to-day freeway operations, the terms "congestion" and "safety" are commonly used. Traffic congestion means there are more people trying to use a given transportation facility during a specific period of time (i.e., "demand") than the facility can handle (i.e., "capacity") with what are considered to be acceptable levels of delay or inconvenience. Safety is concerned with reducing the number of vehicle crashes and minimizing any injuries associated with crashes. Congestion – particularly unexpected congestion – and safety have very strong impacts on travelers' attitudes. In a series of surveys carried out by FHWA (10), traffic flow and safety topped the list of highway characteristics that should receive the most attention (followed by pavement conditions and work zones).

Other equally important considerations include:

  • Mobility: The ability and knowledge to travel from one location to another using a multimodal approach. (1)
  • Accessibility: The means by which an individual can accomplish some economic or social activity. (1)
  • Reliability / Predictability: How much the ease of movement varies from day to day, and the extent to which the traveler can predict these temporal variations.

In essence, motorists (and transit riders) want to know what to expect – such knowledge being a key attribute of "mobility". Having accurate information about roadway performance significantly improves the perception of a trip because information allows motorists to make decisions that give them the perception of having more control over their life. Knowing the extent and duration of congestion not only gives the motorist better options, it removes a significant stress point, the unknown. (For example, a father trying to reach his daughter's softball game realizes that the 10-minute delay won't force him to miss the first pitch; therefore, he can relax and approach the accident site more cautiously, without any aggressive driving or "road rage"). Thus the perception of the congestion improves significantly. Conversely, when information is not available, the anxiety associated with the unknown reason for, and length of, the delay causes the motorist to perceive the delay as longer than it really is, perhaps leads to more erratic driving behavior, and creates a much more negative opinion of both the traffic congestion and, ultimately, how well the highway agency is using taxpayer resources. (2)

These considerations of mobility, accessibility, and reliability also apply to emergency and incident management agencies (i.e., Principal Responding Agencies – PRAs), and to motorists who are affected by an emergency (e.g., the need to evacuate from an area affected by a disaster of some sort). Under such extreme circumstances, these users also need to know their options and what to expect.

In theory, problems of congestion, safety, mobility, accessibility, etc. would dissolve with increases in capacity (i.e., adding more lanes, and new facilities) and the reconstruction of existing facilities (wider lanes and shoulders, improved alignment) to improve safety. Increasing capacity and reconstructing existing facilities, however, introduces significant economical, political and societal challenges, many of which cannot (and perhaps should not) be overcome. Moreover, increased capacity may create additional demand, eventually resulting in the same problems as before. Management and operations can provide practical and cost-effective alternatives (perhaps in concert with capacity improvements) for addressing freeway problems.

The need for and importance of freeway management and operations extends well beyond any constraints on building / reconstructing conventional infrastructure. Transportation agencies and authorities, and their staffs, have the responsibility to be good stewards and responsible managers, being more proactive in addressing potential problems, rather than merely reactive. Moreover, part of this stewardship includes managing the elements of the network itself (e.g., asset management), not just the traffic flow.

Another important consideration in this regard is that transportation is becoming increasingly customer-driven, with a need to view the network at more of a regional scale. The public does not care which jurisdiction is responsible for the road on which they are currently traveling. They want and deserve a safe, reliable, and predictable trip, one that is safe from physical and mental harm, provides consistent service, and is predictable in terms of travel time that is within an acceptable variance.

Finally, technology – specifically Intelligent Transportation Systems (ITS) – is creating an environment where management and operations can take a major leap forward. The recent advances in surveillance, communications, processing, and information dissemination technologies, with an emphasis on "real time" applications, have proven a significant enabler of freeway management and operations. ITS allows for the rapid identification of situations with a potential to cause congestion, unsafe conditions, reduced mobility, etc.; and then to implement the appropriate strategies and plans for mitigating these problems and their duration and impacts on travel.

1.1.2 Wile E. Coyote and Freeway Performance

Reference 2 presents the "Wile E. Coyote Theorem of Freeway Performance" (including Figure 1-2) as follows:

"Freeway performance on congested and nearly congested roadways can perhaps best be explained by analogy to the Warner Bros. Road Runner cartoons. First, let's talk about the cartoon. In a familiar Road Runner scene, Wile E. Coyote chases the Road Runner across the mesas of New Mexico. They run along a mesa until the Road Runner simply runs off the end, into thin air. Unaware, the Coyote follows him, running on thin air. Then something happens: he looks down. The Road Runner, safe as ever, whips out a taunting sign, and suddenly the Coyote realizes he is hanging in air. Zoom! Down he plunges for hundreds of feet... ending in a small puff of dust.

This same scenario is a very good description of urban freeway operations. Detection systems now measure freeway volumes that are 20 percent greater than what was once considered their theoretical maximum. However, under these volume conditions, when any type of disturbance in flow occurs, dramatic decreases in vehicle volumes and speeds result.

High volumes can be compared to the Coyote running along the top of the mesa. Volumes above about 2000 vehicles per lane per hour can be viewed as the Coyote running in air. As long as nothing happens to remind him that he is doing the impossible, he's okay. And as long as nothing happens along the roadway, traffic will continue flowing.

The problem is, "things happen." Accidents occur. Even small disruptions, such as a distraction on the side of the road (a catchy billboard, a police car pulled over) are analogous to the Coyote looking down. At very high volumes, one vehicle's small hesitation can cause other vehicles to brake more heavily to avoid a collision. The disruption in flow then cascades, and suddenly both speed and throughput volume rapidly decrease. Like the Coyote, roadway performance plummets, and vehicle throughput vanishes in a small puff of dust.

And tomorrow, the Coyote will do it all again. Once again life imitates art."

cartoon representation of cars driving off a mesa and falling to a road on the plain below. It is drawn in a cartoon style with windshield eyes and front grill mouths. A sign on the mesa states: "Don't look down now!"

Figure 1-2: Cartoon Analogy of Freeway Conditions
(Reference 2)

Freeway management and operations is all about keeping the Coyote from running off the cliff in the first place; and if (and when) he does, to keep him from looking down; and if (and when) he does look down, to minimize the impact of his fall (and the resulting dust plume), so he can resume his chase of the Road Runner as soon as possible thereafter.

1.2 Purpose

This document was prepared under FHWA Work Order SA80B010 as part of Contract DTFH61-01-C-00180. The original focus was to update the Freeway Management Handbook, reflecting the changes in the state-of-the-practice that had occurred since the Handbook was last updated in 1996. Per the original task order scope, "only an update and not a comprehensive revision is required to the Freeway Management Handbook", and the "intent of this task order is to assess the current document, identify proposed changes, and perform the necessary revisions that ... are needed to represent the current state-of-the-practice in freeway management." However, after a thorough review by the project team and a task force comprised of members and friends of the TRB Committee on Freeway Operations (see Table 1-1), it was determined that a complete and comprehensive revision to the Freeway Management Handbook was required – not just an "update" – to reflect the state of the practice, as well as to better address an expanded view of freeway management and operations. Annotated Outlines of each chapter were prepared, followed by several drafts reflecting review comments made by the aforementioned Freeway Operations Committee Task Force. It should be noted that the contributions made by this group of individuals was invaluable.

Table 1-1: Handbook Contributors – Freeway Operations Committee Task Force
  • Jon Obenberger – FHWA Contract Manager
  • Joel Marcuson – Task Force Leader
  • Tom Urbanik – Project Team Reviewer
  • Walter Kraft
  • Larry Klein
  • Ron Sonntag
  • Mark Hallenbeck
  • Laurence Lambert
  • Dave Helman
  • Dave Roper
  • John Corbin
  • John O'Laughlin
  • Henry Wall
  • Brandy Meehan
  • Ken Brooke
  • Lynette Goodwin
  • Jeff Lindley
  • Les Jacobson – Review Coordinator
  • Pete Briglia – Chair, Freeway Operations Committee
  • Conrad Dudek
  • Jim Kerr
  • Mousa Abbasi
  • Ramakrishna Tadi
  • Abdul Hamad
  • Mitsuru Saito
  • Les Kelman
  • Jack Tone
  • Tip Franklin
  • Chuck Fuhs
  • Steve Balog
  • Dick McGuinness
  • Larry Corcoran
  • William Stoeckert
  • Dan Baxter

This revised "Freeway Management and Operations Handbook" is intended to be an introductory manual – a resource document that provides an overview of the various institutional and technical issues associated with the planning, design, implementation, operation, and management of a freeway network. It is not intended to be an all-encompassing, "Everything You Ever Wanted To Know About Freeway Management and Operations". Rather, it is intended to provide the user with a better understanding the wide variety of potential strategies, tools, and technologies that may be used to support management and operation of the freeway network. Additionally, beyond this obvious purpose of the Handbook, the document also attempts to address several broader issues, including:

  • The concept of "operations" as a part of the overall mission (and some might regard as a relatively new one) for transportation agencies;
  • Freeway management and operations activities (which often have a relatively short-term focus), within the context of the "life cycle" of the surface transportation network, such as relating freeway operations to a broader set of visions and goals, coordinating freeway operations with the longer-term policy making and transportation planning processes (and vice-versa), and expanding the view of freeway management and operations such that the transportation is considered.
  • The numerous institutional relationships that impact the operation of the freeway and the infrastructure itself; and similarly, how individual "operational" actions relate to one another and how, when combined, can affect the institutional framework.
  • Potential measures and procedures for evaluating the overall performance of the freeway, as well as evaluating freeway management strategies and improvements (both prior to and following their implementation).
  • Planning and engineering processes for developing and updating freeway management programs, for developing individual projects to implement the program, and for managing the program after the projects are complete.

The Freeway Management and Operations Handbook relies heavily on other references for many of the concepts and some of the text included herein. As a general rule, the specific reference(s) is identified at the end of the associated sentence / paragraph / bullet list with a reference number in parenthesis. The references and their respective numbers are listed at the end of each chapter.

1.2.1 Why This Document Is Needed

In the late 1960s and early 1970s, highway agencies began to take steps toward active operation of the freeways that had been constructed during the intense building years of the Interstate Program. Emphases in highway transportation began to shift from building new facilities and enlarging existing ones to extracting the most from existing facilities. It was the dawn of the era of freeway operations and traffic management. Authorities began to realize that understanding how the public used freeways and how operating agencies managed that use was crucial to maintaining operational efficiency. Allowing unrestrained growth in the use of the freeway network produced congestion, which effectively reduced freeway capacity, lowered traveling speeds, reduced safety, and increased driver frustrations. Tools that could manage and reduce the congestion plaguing our highways were sorely needed. Researchers used studies of highway usage to come up with the concepts and approaches that have since evolved into freeway traffic management programs. They realized that implementing these programs could cost-effectively influence the public's use of the highway system. (3)

Over the past three decades, the practice of freeway operations has matured. Strategies have evolved, techniques have been developed, and new technologies (ITS) have emerged. Traffic operation centers have reported successes and failures as lessons learned. The intelligent transportation community has quickly incorporated those lessons, and the resultant systems have progressed with each new generation of the freeway traffic management system.

The profession's view of freeway management and operations has also changed. Freeway management strategies and concepts were initially developed to counter congestion. That is still a major goal. But freeway practitioners are also beginning to view themselves as good stewards and responsible managers, managing not only the traffic flow on the network but also the physical elements of the network itself, addressing safety and security issues, and attempting to be more proactive in addressing potential problems rather than merely reactive.

Throughout this evolution, FHWA has sponsored the development of Handbooks to document the state of the practice in freeway management. A "Freeway Management Handbook" was originally developed in 1983. The first (and current) update was initiated in 1995, with the revised document published in 1997. The evolution will undoubtedly occur, and a new and revised "Freeway Management and Operations Handbook" will likely be required in another few years.

1.3 Intended Audience

The intended audience of the revised Handbook is transportation professionals that participate in or are responsible for any phase in the life cycle of a freeway network. This includes all public or private "practitioners" (e.g., managers, supervisors, engineers, planners, or technicians) that are involved with any issue or decision (e.g., legislation, policy, program, funding, project implementation, operational scenario) that may directly or indirectly influence the performance of a freeway facility. These activities may include, but not be limited to, planning and design of freeways and other transportation facilities within the same corridor, operational strategies, programs, and services that support continuous management of travel and control of traffic on freeway facilities, and the technology infrastructure to provide these capabilities.

It is emphasized that while this document focuses on the management and operation of freeway facilities, and views freeway practitioners as the primary audience, these practitioners must not consider freeways and their operation in a singular, isolated manner. All three of the aforementioned legs of the "transportation stool" (i.e., building, preserving, operating), are integral parts of the business of most transportation agencies, and freeways are just one element of the surface transportation network. The same planning, programming, and budgeting processes are applied to all of these facilities and management attributes. This is not to imply that they are necessarily in competition with one another; rather they should be viewed as complementary – for example, the application of freeway management and operational strategies on existing facilities may defer or eliminate the need for new infrastructure; new / expanded transit service may reduce the traffic flow on the freeway and other roadway facilities; the construction / reconstruction of freeway facilities can provide the opportunity to install ITS technologies and infrastructure (that support operations) in a most cost-effective manner; and an intense program of freeway management and operations can help minimize the traffic flow impacts during reconstruction / maintenance activities.

1.4 Overview

1.4.1 The Problem

Demand for highway travel by Americans continues to grow as the population increases, particularly in metropolitan areas. Construction of new highway capacity has not kept pace with this growth. For example, between 1980 and 1999, route miles of highways increased 1.5 percent while vehicle miles of travel increased 76 percent. The effects of this disparity are captured in a number of measures and perceptions, including visible and consistent roadway congestion, the loss of personal and professional time, environmental degradation, and general traveler frustration – in essence, a reduction in overall mobility and accessibility. Some statistics are provided below:

  • The Texas Transportation Institute (TTI) estimates that, in 2000, the 75 largest metropolitan areas experienced 3.6 billion vehicle-hours of delay, resulting in 21.6 billion liters (5.7 billion gallons) in wasted fuel and $67.5 billion in lost productivity. (4)
  • Each year, more than 42,000 people die on the nation's highways and 5 million are injured. A recent report from the National Highway Traffic Safety Administration put the economic costs of highway crashes at more than $230 billion per year including medical and emergency services costs, lost productivity, legal costs, travel delay and property damage. Additionally, highway crashes are the leading cause of death of Americans 6 to 28 years of age. (13) The fatality rate on the Interstate System has been relatively steady after falling early in the 1990s. The number of fatalities on Interstate highways has increased over the past decade, but so has the level of traffic, as indicated by the number of vehicle miles traveled (VMT) (5).
  • Congestion is growing in areas of every size. TTI's 2001 Annual Urban Mobility Report shows more severe congestion that lasts a longer period of time and affects more of the transportation network in 1999 than in 1982 in all urban population categories. The average annual delay per person climbed from 11 hours in 1982 to 36 hours in 1999. And delay over the same period quintupled in areas with less than 1 million people. The time to complete a trip during the congested period also continues to get longer. (2)
  • Another measure of congestion – the travel time index – indicates how much more time it takes to travel during a peak period than at other times of day. This measure is based solely on the regular traffic congestion on the roadways. It provides a measure of how much of the change in traffic congestion is due solely to more cars using the roadways. During the past decade, the travel time index on Interstates increased by about 12 percent. This statistic provides information about drivers' experiences as well as the level of congestion on the road because it accounts for delays due both to the traffic demand on the road and to roadway incidents (e.g., crashes). (5)

The growth in demand has also impacted the temporal aspects of freeway operations. As discussed in Reference 2 and shown in Figure 1-3, traffic levels initially grow immediately before the start of the workday and immediately after the end of the workday (the green line). As traffic reaches the roadway's capacity during those times, travelers begin to leave 10 or 15 minutes earlier or later in the day to avoid the resulting congestion or they allow more time for travel. This spread of travel demand soon creates a true "peak hour" of volume. As growth continues, like it has in most major cities, the "peak hour" becomes the "peak period," since limitations in roadway capacity allow growth in traffic to occur only at the beginning and end of the "peak period" (see the red line in the figure). The sharp morning or afternoon peak in travel thus becomes a wide mesa. In many areas, particularly suburban areas, these peak movements stop being one-directional (people traveling from the suburbs to the central city in the morning and back in the afternoon) and become two-directional as people travel among multiple suburban locations. As the evolution of congestion continues, travel on heavily used (and frequently congested) roads actually becomes almost constant throughout the day. Finally, as growth pressure continues, congestion in the peak periods can become so severe that average peak period volumes actually decline because congestion decreases the volume of vehicles a road can accommodate. (2)

graph depicting changes in traffic volume during a typical weekday

Figure 1-3: Typical Plots of Volume vs. Time-of-Day (Reference 2) D

Delays (resulting from freeway congestion) at particular locations in a transportation network are certainly aggravating to those using the system; but these delays are part of a much larger picture of how a transportation system allows people and goods to move around a metropolitan area. The consequences of congestion are much more serious to a community. For example:

  • Local Traffic Impacts: When faced with congested conditions, many drivers quickly look for ways to bypass the freeway bottleneck. These often include making their way through arterial streets and residential neighborhoods not designed to handle through traffic. Such bypass traffic often becomes the focus of neighborhood complaints. (1)
  • Economic Growth: Efficient transportation access to employment and shopping sites is an important consideration to business and developers when considering expansion opportunities. A good transportation system is an important selling point to communities that desire to attract development. In addition, good transportation is very important to the movement of goods and services and thus has a direct impact on sound economic growth and productivity. (1) With respect to the last point, commercial freight carriers notice the growing lack of travel reliability even more. These companies experience increasing costs from having to pay large quantities of overtime because their trucks are stuck in unexpected traffic. Costs also increase from an inability to schedule work for their vehicles over the complete workday, as the companies lengthen expected delivery times just to ensure that they don't have to pay overtime. Inefficiencies caused by unreliable roadway travel times add to the costs that slow moving traffic create by making each trip last longer. (2)
  • Quality-of-Life: To some people, congested (and unsafe) highways are a symptom of deteriorating quality-of-life in a community. In many cases, and in particular in suburban communities, residents moved to their community to escape urban problems like traffic jams. Now facing this congestion has once again become part of their daily routine. Another aspect of this quality-of-life characteristic is the role transportation plays as a key element of getting and keeping a job. (1)
  • Environmental Quality: Congested road conditions can have a detrimental effect on the environment, in particular air quality. Making improvements to the transportation system or trying to change travel behavior has been an important objective of those wanting to improve environmental quality. (1)

There is also an institutional and political aspect to all of this. Addressing the performance of the transportation network and the mobility needs of a community has become, in several cases, a litmus test for effective leadership. Because the public sector is viewed as having the major responsibility for solving transportation problems, community officials are often the focal point for citizens' interest concerning traffic congestion, safety, and mobility needs. (1)

1.4.2 The Future

There are a number of demographic trends that are likely to affect travel patterns and congestion in the future, including:

  • Rising affluence and increased income – Rising incomes will likely translate into increased auto availability and use, increased number of trips per household, and increased average trip lengths. The rising affluence is partly due to the fact that many households now have multiple workers. When multiple workers reside in a single household, it then becomes more difficult for each to live in close proximity to their work; thus the need to choose some compromise location that meets both workers' needs as well as the needs of other household members (e.g., good schools, nice parks, etc.).
  • Democratization of mobility – Privately owned auto transportation is becoming more accessible to previously car-less households. This increased access to personal mobility via personal auto is mostly among Americans living in center cities. In many instances, this newfound personal mobility carries them to where employment is easy to find—the booming suburban areas that require longer vehicle trips. (2)

Traffic demand – both passenger and freight – is expected to increase. Estimates that FHWA uses indicate passenger traffic will increase by 17 percent from the end of 2001 through 2010—an increase from 2.7 trillion vehicle miles traveled to 3.1 trillion. In addition, states and FHWA data indicate that truck traffic is expected to increase in the future. Estimates used by FHWA show freight movement by truck increasing by 28 percent from the end of 2001 through the end of 2010. Finally, an alliance of primarily southern and southeastern states released a 2001 study that estimates a 6.9 percent annual increase in Latin American truck traffic in the United States (resulting in almost a doubling over the 10-year period). Ninety-six percent of this truck traffic will be on Interstates. (5)

1.4.3 Homeland Security and Other Emergencies

Another (and relatively new concern) is that of homeland security, which can be expected to exact new demands on the U.S. surface transportation system. Research by the Federal transit Administration indicates that 58% of international terrorist attacks were on transportation targets, and of these 92% were on surface transportation. The ability of our system to cope with such contingencies requires capability to detect catastrophic incidents, to facilitate first responder communications, to quarantine roads, and to effectively route evacuations from major metropolitan areas; all while maintaining the appropriate balance between these transportation security needs and the efficiency of the transportation network. Freeway practitioners must be prepared to go beyond the normal day-to-day management activities to support emergency service providers and the military during large-scale response and recovery activities – not only terrorist attacks, but natural and weather related disasters such as hurricanes, forest fires, blizzards, earthquakes, etc.

1.4.4 Potential Solutions

As previously noted, providing effective highway-based transportation consists of three component parts: construction, preservation, and operations. In addition to these primarily "supply"-oriented solutions, there is also "demand" aspect; and numerous agencies have implemented solutions for managing the demand for the highway network. Construction

Construction, whenever it is feasible, often seems to be the first choice of most politicians and many transportation agencies. It provides a visible increase in vehicular capacity. Whether it is politically popular depends on the cost of the construction project and its impacts on land uses and the environment. Construction does have several drawbacks. There isn't enough funding to address the growing demand. Moreover, construction is becoming increasingly difficult to do. In urban areas, where congestion tends to be greatest, land prices, public resistance, and environmental mitigation requirements severely limit the size of capacity improvements. They also increase the time required to gain the necessary permits, thus raising costs dramatically. These problems limit both the public's acceptance of new construction and their willingness to pay for those roads. Under these circumstances, new construction may only moderate existing congestion rather than eliminate it because building sufficient capacity to meet existing levels of demand is not feasible. Operations

Since new construction is often not feasible or insufficient to significantly reduce congestion and improve mobility, transportation agencies are turning to operational improvements to reduce / limit the growth of congestion, improve safety, and / or increase the number of people the existing roadway will carry. A variety of strategies have been used successfully to improve roadway operation. Among the most common are: traffic incident detection and management, traveler information, managed lanes (e.g., preferential treatment to high-occupancy vehicles), ramp management, and Intelligent Transportation Systems.

Freeway management applications have had a positive effect on freeway operations leading to benefits such as increased safety, improved traffic flow, and reductions in traffic delays. A summary of measured benefits associated with freeway management is provided in Table 1-2. (More detailed information on the benefits and costs of freeway management strategies, and ITS technologies in general is available "Intelligent Transportation Systems Benefits and Costs – 2003 Update" (Reference 15). Information in that report is drawn from the ITS Benefits and Unit Costs Databases, a regularly updated repository of information, available at

Table 1-2: Measured Benefits of Freeway Management (Reference 6)
Measure Benefit
Travel Time Decrease 20% to 48%
Travel Speed Increase 16% to 62%
Freeway Capacity Increase 17% to 25%
Accidents Decrease 15% to 50%
Fuel Consumption Decrease of 41% in congested areas
Emissions Decrease HC emissions 1400 tons annually
Decrease NOx emissions 1200 tons annually

Each of the various operational strategies works effectively under specific conditions, but most improvements individually achieve only modest reductions in congestion. Their real contribution is to significantly improve the efficiency of the existing infrastructure, while increasing the reliability and safety of the transportation system operation. Demand Management

In the broadest sense, transportation demand management (TDM) is any action or set of actions intended to influence the intensity, timing, and spatial distribution of transportation demand for the purpose of reducing the impact of traffic or enhancing mobility options (1). A variety of government- and employer-sponsored programs can be designed to reduce vehicle trips during congested periods and in congested locations. These include flexible work schedules that allow employees to travel off-peak (or work at home), amenities to improve the safety and efficiency of biking and walking, ridematching services for vanpools and carpools, community-based carsharing, employer-subsidized transit passes, guaranteed emergency rides home for transit users, and incentives to decrease employer-paid parking. Discussion

The transportation phenomenon is the result of demographic and market forces that are difficult to change. In addition to the supply and demand-oriented solutions noted above, there is also the issue of managing the land use and development patterns that influence when and where travel demand occurs over the long term. To be effective within this context, one needs to examine how the various actions complement one another over the long run.

A coordinated mobility, congestion reduction, and safety enhancement program should consist of several tools and elements from all of these categories of potential solutions. The specific structure of such a program depends, of course, upon funding and the feasibility of implementing such actions in the local political environment. Attributes of a mobility / congestion / safety program include:

  • Provide the most cost effective transportation system improvements that enhance mobility, increase safety, and reduce traffic congestion while being consistent with community goals. The improvements can include operational changes to improve the performance of the existing network and services, and the physical expansion of the highway system or the addition of transit services.
  • Examine better ways of managing transportation demand, especially if the opportunity for substantial gains in system performance through expansion or operational improvements is limited.
  • Explicitly consider long-range strategies that will provide the foundation for avoiding similar problems in the future. This implies an important role for considering future land use/development patterns and their impact on travel.
  • Deal with institutional arrangements and funding requirements for implementing the program. This is especially important where the transportation services are housed in separate units. (1)

It also bears mentioning that while all of these potential strategies can reduce congestion, enhance safety, and improve mobility; they will rarely be implemented in enough magnitude to completely eliminate congestion in urban areas. The goals, then, are more typically to manage congestion, provide travel options, and improve travel reliability and safety.