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Knowledge Base


Improving Traffic Signal Operations - A Primer

Traffic congestion is a major problem in cities of all sizes. People are taking more trips, and there are more vehicles on the road. The street system is often overtaxed, causing traffic to bog down. The resulting traffic congestion is costly-motorists’ time is wasted, and the environment is harmed by pollutants emitted from idling engines. Even worse, the congestion often provokes motorists into dangerous behavior, such as running red lights, in an attempt to make up lost time.


The Institute of Transportation Engineers is an international educational and scientific association of transportation professionals who are responsible for meeting mobility and safety needs. ITE facilitates the application of technology and scientific principles to research, planning, functional design, implementation, operation, policy development and management for any mode of ground transportation. Through its products and services, ITE promotes professional development of its members, supports and encourages education, stimulates research, develops public awareness programs and serves as a conduit for the exchange of professional information.

ITS America

The Intelligent Transportation Society of America is the leading advocate for technologies that improve the safety, security and efficiency of the nation's surface transportation system. Our members include private corporations, public agencies, and academic institutions involved in the research, development and design of Intelligent Transportation Systems technologies that enhance safety, increase mobility and sustain the environment.

Legislation & Regulations

This section provides descriptions and summaries a wide array of Federal, state and local legislation that establishes transportation funding sources and governs their distribution and uses, as well as information on legislation establishing and regulating the use of the finance mechanisms used for transportation improvements. Separate content has been prepared for Federal legislative issues, as well as state and local legislation. The Federal legislation section provides coverage of laws governing funding, finance and policy contained in Titles 23 (highways) and 49 (transit) of the Federal code, together with information on the seven-year Transportation Authorization Act process which is used to update Federal legislation and funding levels. The state and local authorization section addresses legislation that is needed to establish new revenue sources or powers, such as the ability collect tolls or other revenue sources, as well as the use of different types of financial tools.

Legislation, Regulations and Guidance Resources

The Federal Highway Administration (FHWA) is an agency within the U.S. Department of Transportation that supports State and local governments in the design, construction, and maintenance of the Nation’s highway system (Federal Aid Highway Program) and various federally and tribal owned lands (Federal Lands Highway Program). Through financial and technical assistance to State and local governments, the Federal Highway Administration is responsible for ensuring that America’s roads and highways continue to be among the safest and most technologically sound in the world.


The National Association of Regional Councils (NARC) serves as the national voice for regionalism by advocating for regional cooperation as the most effective way to address a variety of community planning and development opportunities and issues.

National Surface Transportation Infrastructure Financing Commission

Section 11142(a) of SAFETEA-LU established the National Surface Transportation Infrastructure Financing Commission and charged it with analyzing future highway and transit needs and the finances of the Highway Trust Fund and making recommendations regarding alternative approaches to financing transportation infrastructure.

NCHRP 572 - Roundabouts in the United States

Based on a comprehensive evaluation of roundabouts in the United States, this report presents methods of estimating the safety and operational impacts of roundabouts and updates design criteria for them. The report will be useful to geometric designers and traffic engineers who are considering improvements to an intersection.

NCHRP 599 - Default Values for Highway Capacity and Level of Service Analyses

Based on the assembly of an extensive set of field data from across the United States, this report presents valuable information on the appropriate selection of default values when analyzing highway capacity and level of service. The report will be useful to planners, geometric designers, and traffic engineers who do not have ready access to field data for an analysis. The report also describes how to prepare service volume tables, which can be a useful sketch planning technique.

NCHRP 616 - Multimodal Level of Service Analysis for Urban Streets

NCHRP Report 616: Multimodal Level of Service Analysis for Urban Streets will be of interest to public agencies responsible for the planning, design, and operation of urban streets. This report provides a method for assessing how well an urban street serves the needs of all of its users: auto drivers, transit passengers, bicycle riders, and pedestrians.

NCHRP 672 - Roundabouts: An Informational Guide, Second Edition

This report updates the FHWA’s Roundabouts: An Informational Guide based on experience gained in the United States since that guide was published in 2000. The report addresses the planning, design, construction, maintenance, and operation of roundabouts. It also includes information that will be useful in explaining to the public the trade-offs associated with roundabouts.

NCHRP Report 500 Volume 12: A Guide for Reducing Collisions at Signalized Intersections

The goal of the AASHTO Strategic Highway Safety Plan is to reduce annual highway fatalities by 5,000 to 7,000. This goal can be achieved through the widespread application of low-cost, proven countermeasures that reduce the number of crashes on the nation’s highways. This twelfth volume of NCHRP Report 500: Guidance for Implementation of the AASHTO Strategic Highway Safety Plan provides strategies that can be employed to reduce the number of collisions at signalized intersections. The report will be of particular interest to safety practitioners with responsibility for implementing programs to reduce injuries and fatalities on the highway system.

NCHRP Synthesis 403 - Adaptive Traffic Control Systems: Domestic and Foreign State of Practice

Highway administrators, engineers, and researchers often face problems for which information already exists, either in documented form or as undocumented experience and practice. This information may be fragmented, scattered, and unevaluated. As a consequence, full knowledge of what has been learned about a problem may not be brought to bear on its solution. Costly research findings may go unused, valuable experience may be overlooked, and due consideration may not be given to recommended practices for solving or alleviating the problem.

NCHRP Synthesis 409 - Traffic Signal Retiming Practices in the United States

Highway administrators, engineers, and researchers often face problems for which information already exists, either in documented form or as undocumented experience and practice. This information may be fragmented, scattered, and unevaluated. As a consequence, full knowledge of what has been learned about a problem may not be brought to bear on its solution. Costly research findings may go unused, valuable experience may be overlooked, and due consideration may not be given to recommended practices for solving or alleviating the problem.

NCHRP Web-Only Document 128: Multimodal Level of Service Analysis for Urban Streets: Users Guide

An urban street is unique among the various facility types operated by public agencies, because its right-of-way is shared by multiple modes of travel, each using their assigned portion of the right-of way. To adequately evaluate the quality of service provided by the facility, one must consider the implications of facility design and operation on the auto driver, the bus passenger, the bicyclist and the pedestrian.

NCHRP Web-Only Document 94: Appendices to NCHRP 572

The following contains a comprehensive review of each source, by country of origin followed by a summary indicating how useful the insights from this review were in guiding the current research effort.


NSPE keeps its members in touch with the latest in their field through respected publications and information resources, opportunities for mentoring and continuing education, and through a national conference and meetings, where members can meet and share ideas with colleagues.

Pedestrian and Bicycle Information Center

The Pedestrian and Bicycle Information Center (PBIC) is a national clearinghouse for information about health and safety, engineering, advocacy, education, enforcement, access, and mobility for pedestrians (including transit users) and bicyclists. The PBIC serves anyone interested in pedestrian and bicycle issues, including planners, engineers, private citizens, advocates, educators, police enforcement, and the health community.


The mission of the National Transportation Library (NTL) is to maintain and facilitate access to statistical and other information needed for transportation decision-making at the Federal, State, and local levels and to coordinate with public and private transportation libraries and information providers to improve information sharing among the transportation community. NTL was established in 1998 by the Transportation Equity Act for the 21st Century (TEA-21).

Roundabouts: An Informational Guide

The guidance supplied in this document, Roundabouts: An Informational Guide, is based on established international and U.S. practices and is supplemented by recent research. The guide is comprehensive in recognition of the diverse needs of transportation professionals and the public for introductory material through design detail, as well as the wide range of potential applications of roundabout intersections. The following topics are addressed: definition of a roundabout and what distinguishes roundabouts from traffic circles; public acceptance and legal issues associated with roundabouts; consideration of all user modes, including heavy vehicles, buses, transit, bicycles, and pedestrians; a methodology for identifying appropriate site for roundabouts and the range of conditions for which roundabouts offer optimal performance; methodologies for estimating roundabout capacity, delays, and queues with reference to the Highway Capacity Manual; design principles and guidance on safety and geometric design, with reference to applicable national standards such as the AASHTO Policy on Geometric Design of Highways and Streets; guidelines for control features such as signing and pavement markings, with reference to the Manual on Uniform Traffic Control Devices; illumination; and landscaping.

Signal Timing on a Shoestring

The conventional approach to signal timing optimization and field deployment requires current traffic flow data, experience with optimization models, familiarity with the signal controller hardware, and knowledge of field operations including signal timing fine-tuning. Developing new signal timing parameters for efficient traffic flow is a time-consuming and expensive undertaking. This report examines various cost-effective techniques that can be used to generate good signal timing plans that can be employed when there are insufficient financial resources to generate the plans using conventional techniques. The report identifies a general, eight-step process that leads to new signal plans: 1) Identify System Intersections; 2) Collect and Organize Existing Data; 3) Conduct a Site Survey; 4) Obtain Turning Movement Data; 5) Calculate Local Timing Parameters; 6) Identify Signal Groupings; 7) Calculate Coordination Parameters; and 8) Install and Evaluate New Plans. The report examines each of these steps and identifies procedures that can be used to minimize costs in each step. Special emphasis is placed on the costs of turning movement counts. The report develops a “tool box” of procedures and provides examples of how the tool box can be used when there is a moderate signal timing budget, when there is a modest signal timing budget, and when there is a minimum signal timing budget.

Signal Timing Under Saturated Conditions

This report provides guidance to practitioners on effective strategies to mitigate the effects of congestion at signalized intersections. The scope is limited to single intersections and does not address network-level strategies. The strategies are defined in terms of their underlying objective. Under congested conditions, traditional objectives and performance measures shift from progression and minimizing delay to maximizing throughput and managing queues. Experts were interviewed to identify the strategies and tactics they used to address congested intersections, a discussion of their methods is presented. Select strategies were studied further, particularly the belief that longer cycles are more efficient, and the effects of buses on signal timing in grid networks. The research revealed that long cycle lengths may not be more efficient at intersections where long queues starve turn lanes. In grid networks, the cycle length that is just long enough to reliably serve busses from a near-side stop was found through simulation to prevent the development of residual queues.

Signalized Intersections: Informational Guide

This report complements the American association of State Highway and Transportation Officials' (AASHTO) Strategic Highway Safety Plan to develop guidance on safety of nonsignalized and signalized intersections. The goal is to reduce the annual number of highway deaths. This guide is a comprehensive document that contains methods for evaluating the safety and operations of signalized intersections and tools to remedy deficiencies.


As a national centre of transportation expertise, and a not-for-profit association, our goal is to provide a neutral forum to gather and exchange relevant ideas and information on technical guidelines and best practices. We actively promote the importance of transportation to Canada’s economic well-being, as well as safe, secure, efficient and environmentally and financially sustainable transportation services.

Traffic Analysis Toolbox Documents

The Traffic Analysis Tools Program was formulated by FHWA in an attempt to strike a balance between efforts to develop new, improved tools in support of traffic operations analysis and efforts to facilitate the deployment and use of existing tools. FHWA has established two tracks under the Traffic Analysis Tools Program: the deployment track and the development track.

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