Traffic Control Systems Handbook: 1. Introduction
1.1 Scope and Objectives
Figure 1-1. Rochester N.Y. Regional Traffic Operations Center.
In 1985, the Federal Highway Administration published the second edition of the Traffic Control Systems Handbook to present basic technology used in planning, designing, and implementing traffic monitoring and control systems for urban street and freeway applications. That publication presented a compendium of applicable technology, concepts, and practices in the traffic control field. It proved useful in:
- Fostering understanding and acceptance of such systems, and
- Implementing proven advances in traffic monitoring and control.
This handbook was updated in 1996. In addition to describing signal system improvements since 1985, the 1996 edition provided considerable information on freeway management techniques and equipment.
The current edition updates signal system technology and broadens it into other methods for achieving surface street traffic management. Much of the freeway related material has been removed or abridged as the material is currently covered in the newly revised Freeway Management and Operations Handbook (FMOH) (1).
This updated version of the Traffic Control Systems Handbook maintains the following major objectives:
- Provide a compendium of existing traffic control system technology,
- Aid understanding of the basic elements of traffic control systems,
- Broaden the viewpoint of the traffic management field,
- Serve as a basic reference for the practicing traffic engineer in planning, designing, and implementing new and effective traffic control systems, and
- Serve as a training aid in the field of traffic control systems.
The Handbook targets a wide range of potential users - administrators, roadway designers, and traffic operations engineers, both experienced and newly assigned.
1.2 Summary of Handbook Contents
This section summarizes the contents of each Handbook chapter.
CHAPTER 2 - AVAILABLE AND EMERGING TRAFFIC CONTROL SYSTEM TECHNOLOGY
This chapter presents an overview of control and management functions. It discusses the issues involving inter-agency coordination and identifies potential needs and issues in selecting a traffic system. The chapter also introduces a classification system for traffic signal system categories and discusses likely future developments.
CHAPTER 3 - CONTROL CONCEPTS - URBAN AND SUBURBAN STREETS
This chapter addresses the following topics:
- Basic variables associated with surface street traffic flow and their properties.
- Capacity, cycle length and split.
- Signal phasing.
- Need for signal coordination and off line signal timing software.
- Categories of coordinated control.
- Signal timing strategies and guidance for applying strategies.
- Special control situations.
- Benefits and measures of effectiveness.
CHAPTER 4 - CONTROL AND MANAGEMENT CONCEPTS FOR FREEWAYS
This chapter provides a brief summary of the nature of freeway congestion, the types of freeway management and the relationship to surface streets. The newly revised Freeway Management and Operations Handbook (1) should be consulted as the primary reference on freeway control.
CHAPTER 5 - CONTROL AND MANAGEMENT CONCEPTS - INTEGRATED SYSTEMS
This chapter covers the non-traditional surface street control functions that are currently becoming more widely implemented.
CHAPTER 6 - DETECTORS
This chapter summarizes detector technology that is applicable to signal systems as well as installation requirements. The newly revised Traffic Detector Handbook (2) is the primary source of information on this subject.
CHAPTER 7 - LOCAL CONTROLLERS
This chapter covers the following major topics:
- Type of controller operations.
- Controller operation under isolated and coordinated control.
- Controller timing parameters.
- Phasing options and sequences.
- Controller types (NEMA, ATC and Model 170).
CHAPTER 8 - SYSTEM CONTROL
This chapter discusses architectures for conventional traffic control systems and adaptive systems, and covers time base coordination. The functions of signal system traffic management centers and some examples of the characteristics of these centers are provided.
CHAPTER 9 - COMMUNICATIONS
This chapter provides an overview of communications alternatives for surface street systems. It also briefly discusses the National Transportation Communications for ITS Protocol (NTCIP). The primary source of information for traffic system communications is the newly revised Communications Handbook for Traffic Control Systems (3).
CHAPTER 10 - TRAVELER INFORMATION SYSTEMS
This chapter provides an overview on the use of static signs and changeable message signs for surface street systems. It also discusses other types of motorist information devices. The primary source of information for traveler information systems is the Freeway Management and Operations Handbook (1).
CHAPTER 11 - SELECTION OF A SYSTEM
Chapters 11, 12 and 13 provide an overview of the systems engineering process life cycle.
After providing an introduction to federal aid requirements, this chapter describes the steps in the development of high level system requirements (scoping). Methods for evaluating candidate alternatives, utility cost analysis and benefit cost analysis are discussed.
CHAPTER 12 - DESIGN AND IMPLEMENTATION
The material in this chapter:
- Places system design, procurement, and installation tasks in perspective with respect to total system planning and implementation
- Describes alternative approaches to the procurement of systems, including contractor selection
- Describes the various elements of the design process, with particular emphasis on the contents of bid documents
- Describes elements of an approach to manage system installation.
CHAPTER 13 - SYSTEMS MANAGEMENT
This chapter describes the functions involved in managing a traffic system and a traffic operations center and the staffing resources required. Maintenance requirements and staffing issues are discussed. The need for system evaluation and techniques for accomplishing it are also described.
CHAPTER 14 - ITS PLANS AND PROGRAMS
This chapter discusses ITS America and TEA-21, and provides an overview of the ITS planning process at the national, regional / statewide and agency levels.
1.3 Role and Impact of Traffic Control Systems
The traffic signal impacts virtually everyone every day. Even on uncongested routes, stops at traffic signals punctuate an urban or suburban area trip. School children obediently wait for a traffic signal to interrupt traffic so they can cross a busy thoroughfare. Drivers confidently place their own and their passengers' physical safety in a signal's allocation of right-of-way.
People accept and in some cases demand traffic signals to assure safety and mobility. Drivers usually assume that the responsible agency can efficiently operate signals, so motorists usually report only the most obvious failures. Inefficient operation annoys some motorists but produces no strong public reaction. However, inefficiencies silently steal dollars from the public in increased fuel cost and longer trip times. Users normally perceive signals as working if they turn red and green; if they operate suboptimally, this becomes a concern, not a crisis.
Research and application demonstrate the effectiveness of signal system improvements in reducing:
- Delays,
- Stops,
- Fuel consumption,
- Emission of pollutants, and
- Accidents
The systematic optimization of signal timing plans in most signal systems represents an essential continuing element of traffic control system management. This optimization is labor intensive and costly for many existing traffic control systems. As a result, the number of timing plans and the frequency of updating the timing plans are often limited by the resources available to perform these functions.
Certain traffic systems have been termed adaptive, i.e., they have the capability to automatically change signal timing in response to both short term and longer term variations in traffic. These systems not only provide more effective control of traffic but also require fewer human and financial resources to update the system's database. However, they often require more intense deployment of traffic detectors.
1.4 Travel Demand Management (TDM)
A highly developed system of streets, highways, freeways, and some form of public transportation serves most North American cities. Growth in travel demand, however, seems to outpace the ability to provide new or expanded facilities and service. This pressure places great emphasis on reducing travel demand to reduce the loading of facilities, particularly at peak hours.
The wide spectrum of TDM actions includes:
- Promotion of non-auto modes of travel,
- Preferential treatment for high occupancy vehicles (HOV),
- Preferential parking for HOV,
- Incentives to reduce peak period travel,
- Telecommuting,
- Non-standard work week such as four 10-hour days, and
- Transit and paratransit service improvements.
Many TDM measures impact or depend on the efficient and effective use of:
- Traffic signal systems,
- Freeway traffic management systems, and
- Traveler information systems.
Efforts to promote transit usage become less effective if buses meet unnecessary delay from inefficiently operated signals. Vanpool and transit usage become more attractive if these vehicles can travel on uncongested high occupancy vehicle freeway lanes.
Thus, urban and freeway control systems and traveler information systems can prove critical to the operational effectiveness of multimodal transportation facilities.
1.5 System Evolution
The development of traffic control systems for urban streets has paralleled the development and use of the automobile. After World War I, rapid growth in automobile traffic led to requirements for special personnel, signals and systems to address the problem.
In typical urban areas, approximately two-thirds of all vehicle-miles of travel, and even a higher percentage of vehicle-hours of travel, take place on facilities controlled by traffic signals (4). To a major extent, therefore, the quality of traffic signal operation determines urban vehicular traffic flow quality.
Traffic signals originated with signaling system technology developed for railroads. In 1914 (5), Cleveland, Ohio installed the first electric traffic signal in the United States. In 1917, Salt Lake City introduced an interconnected signal system that involved manually controlling six intersections as a single system (6). In 1922, in Houston, Texas, 12 intersections were controlled as a simultaneous system from a central traffic tower. This system proved unique in its use of an automatic electric timer.
The year 1928 saw the introduction of a flexible-progressive pretimed system. Municipalities quickly accepted these pretimed systems and widespread installation followed in virtually every U.S. city.
Their success resulted from:
- Simplicity (almost any electrician could understand them),
- Reliability (rugged components resulted in minimum maintenance), and
- Relatively low cost.
However, early pretimed systems had limited flexibility. They could respond only to predicted traffic changes via preset changes on a time clock. But predicting traffic conditions proved difficult because of the needed data collection efforts. Agencies usually avoided timing changes because of the staffing and time resources required to make changes at each local intersection controller.
Traffic-actuated local controllers using pressure detectors became available during the period 1928-1930. These controllers proved a first step toward traffic-actuated control but applied only to isolated intersections.
In 1952, Denver, Colorado advanced the state-of-the-art of traffic control systems by developing and installing an analog computer control system. This system applied some actuated isolated intersection control concepts to signalized networks. Sampling detectors input traffic flow data, and the system adjusted its timing on a demand rather than time-of-day (TOD) basis. Over one hundred systems of this type were installed in the United States in the period 1952-1962.
In 1960, Toronto conducted a pilot study using a digital computer to perform centralized control functions (7). The amount of traffic data available from this form of control proved a fortunate by-product. While the computer used for the test was archaic by today's standards - an IBM 650 with about 2,000 words of drum memory - the success of this control system approach encouraged Toronto to proceed with full-scale implementation. The city placed 20 intersections under computer control in 1963, and later expanded the system to 885 intersections by 1973.
International Business Machines (IBM) began a cooperative development in 1964 with the City of San Jose, California, to further develop a computer traffic control system (8). The project used an IBM 1710 computer. Control concepts developed and implemented proved successful in significantly reducing stops, delays, and accidents.
Beginning in 1965, the City of Wichita Falls, Texas, contracted for the delivery of an IBM 1800 process control computer for traffic control. This system was placed in daily operation in 1966, controlling 56 intersections in the central business district. It was later expanded to include 78 intersections. San Jose, California, shortly thereafter made a transition to an IBM 1800 computer, and similar systems were installed in Austin and Garland, Texas; Portland, Oregon; Fort Wayne, Indiana and New York City. In these systems, traffic signals were controlled by using stored timing plans developed off-line.
In 1967, the Bureau of Public Roads, currently the Federal Highway Administration (FHWA), began to develop the Urban Traffic Control System (UTCS) Project. The system was installed in Washington, D.C., to develop, test, and evaluate advanced traffic control strategies (9). Completed in 1972, it contained 512 vehicle detectors whose outputs determined signal timing at 113 intersections. Extensive data processing, communications, and display capabilities were made available to support traffic control strategy research. Later efforts produced the Extended and Enhanced versions of the software package that implemented these concepts.
The 1970s also saw continuing research and development of software packages and models for digital computer and microprocessor based traffic control systems. The Transport and Road Research Laboratory (TRRL) in Great Britain developed the advanced centrally controlled traffic system, Split, Cycle and Offset Optimization Technique (SCOOT), in the 1970s with implementation taking place in Glasgow and other cities in the 1980s. SCOOT has been installed in several North American cities including Toronto, ON. Another advanced system, Sydney Coordinated Adaptive Traffic System (SCATS), developed in Australia, has been implemented in many cities throughout the world. SCOOT and SCATS initiated the deployment of responsive control systems. Adaptive control techniques, represented by Optimized Policies for Adaptive Control (OPAC) and RHODES, have also begun to be implemented.
Figure 1-2 summarizes the historical development of coordinated traffic control systems.
The experience gained during this evolution shows that substantial reductions in travel delays, stops, fuel consumption, and vehicle emissions can accrue from control system efficiency and aggressive traffic signal management. However, in conventional (non-adaptive) systems, full realization of benefits depends on the frequent updating of timing plans to optimize traffic flow.
The ACS-Lite program is a current FHWA research initiative that seeks to migrate certain techniques used in adaptive systems into the environment of simpler closed loop systems.
Figure 1-2. Interconnected Traffic Control System Chronology.
Driver information systems have expanded as well, using a whole spectrum of media including:
- On-freeway and on-street dynamic signing and highway advisory radio,
- Commercial media,
- Displays at major traffic generators,
- Internet, and
- In-vehicle information and displays.
1.6 Present Status — Traffic Surveillance and Control
The 1980s and early 1990s have witnessed widespread acceptance and implementation of advanced traffic control and management systems for both freeways and urban streets. Use of the computer has become the accepted way to control streets and highways and has been accelerated by the revolutionary advances and associated cost reductions in computer, communications and electronic technology. Local microprocessor controllers have virtually eliminated operational constraints previously imposed by hardware capability. Today, constraints on effective system operation are generally not technical but institutional, jurisdictional or financial.
Present activity in traffic monitoring and control systems has advanced beyond experimentation to deployment of effective operational tools. Basic control concepts have been refined through the experience of multiple users. An effective network of system designers, manufacturers, and suppliers exists to offer choices in system selection. The cooperative participation of governmental agencies (Federal, state, local) and commercial and professional organizations (manufacturers, consultants) continues in the development efforts of hardware and software. Prime examples include the development of the 2070 Advanced Transportation Controller, which provides an open architecture for controller hardware and software and the National Transportation Communications for ITS Protocol (NTCIP), which facilitates equipment interoperability.
1.7 National ITS Architecture
The National ITS Architecture (10) provides a common framework for planning, defining, and integrating intelligent transportation systems. It is a mature product that reflects the contributions of a broad cross-section of the ITS community (transportation practitioners, systems engineers, system developers, technology specialists, consultants, etc.). The architecture defines:
- The functions (e.g., gather traffic information or request a route) that are required for ITS.
- The physical entities or subsystems where these functions reside (e.g., the field or the vehicle).
- The information and data flows that connect these functions and physical subsystems together into an integrated system.
The National ITS Architecture defines the user service bundles and user services shown in Table 1-1. Figure 1-3 shows an overview of the physical architecture. Key components of the National ITS Architecture are summarized below:
Figure 1-3. Overview of Physical Entities.
Logical Architecture
The Logical Architecture defines the processes (the activities and functions) that are required to provide the required user services. Many different processes must work together and share information to provide a user service. The processes can be implemented via software, hardware, or firmware. The logical architecture is independent of technologies and implementations. The logical architecture is presented to the reader via data flow diagrams (DFDs) or bubble charts and Process Specifications (PSpecs).
Market Packages
Market packages represent slices of the physical architecture that address specific services like surface street control. A market package collects several different subsystems, equipment packages, terminators, and architecture flows that provide the desired service. Table 1-2 identifies the market packages.
| Service Area | Market Package | Market Package Name |
|---|---|---|
| Archived Data Management | AD1 | ITS Data Mart |
| AD2 | ITS Data Warehouse | |
| AD3 | ITS Virtual Data Warehouse | |
| Public Transportation | APTS1 | Transit Vehicle Tracking |
| APTS2 | Transit Fixed-Route Operations | |
| APTS3 | Demand Response Transit Operations | |
| APTS4 | Transit Passenger and Fare Management | |
| APTS5 | Transit Security | |
| APTS6 | Transit Maintenance | |
| APTS7 | Multi-modal Coordination | |
| APTS8 | Transit Traveler Information | |
| Traveler Information | ATIS1 | Broadcast Traveler Information |
| ATIS2 | Interactive Traveler Information | |
| ATIS3 | Autonomous Route Guidance | |
| ATIS4 | Dynamic Route Guidance | |
| ATIS5 | ISP Based Route Guidance | |
| ATIS6 | Integrated Transportation Management / Route Guidance | |
| ATIS7 | Yellow Pages and Reservation | |
| ATIS8 | Dynamic Ridesharing | |
| ATIS9 | In-Vehicle Signing | |
| Traffic Management | ATMS01 | Network Surveillance |
| ATMS02 | Probe Surveillance | |
| ATMS03 | Surface Street Control | |
| ATMS04 | Freeway Control | |
| ATMS05 | HOV Lane Management | |
| ATMS06 | Traffic Information Dissemination | |
| ATMS07 | Regional Traffic Control | |
| ATMS08 | Traffic Incident Management System | |
| ATMS09 | Traffic Forecast and Demand Management | |
| ATMS10 | Electronic Toll Collection | |
| ATMS11 | Emissions Monitoring and Management | |
| ATMS12 | Virtual TMC and Smart Probe Data | |
| ATMS13 | Standard Railroad Grade Crossing | |
| ATMS14 | Advanced Railroad Grade Crossing | |
| ATMS15 | Railroad Operations Coordination | |
| ATMS16 | Parking Facility Management | |
| ATMS17 | Regional Parking Management | |
| ATMS18 | Reversible Lane Management | |
| ATMS19 | Speed Monitoring | |
| ATMS20 | Drawbridge Management | |
| ATMS21 | Roadway Closure Management | |
| Vehicle Safety | AVSS01 | Vehicle Safety Monitoring |
| AVSS02 | Driver Safety Monitoring | |
| AVSS03 | Longitudinal Safety Warning | |
| AVSS04 | Lateral Safety Warning | |
| AVSS05 | Intersection Safety Warning | |
| AVSS06 | Pre-Crash Restraint Deployment | |
| AVSS07 | Driver Visibility Improvement | |
| AVSS08 | Advanced Vehicle Longitudinal Control | |
| AVSS09 | Advanced Vehicle Lateral Control | |
| AVSS10 | Intersection Collision Avoidance | |
| AVSS11 | Automated Highway System | |
| Emergency Management | EM01 | Emergency Call-Taking and Dispatch |
| EM02 | Emergency Routing | |
| EM03 | Mayday Support | |
| EM04 | Roadway Service Patrols | |
| EM05 | Transportation Infrastructure Protection | |
| EM06 | Wide-Area Alert | |
| EM07 | Early Warning System | |
| EM08 | Disaster Response and Recovery | |
| EM09 | Evacuation and Reentry Management | |
| 1M10 | Disaster Traveler Information | |
| Maintenance & Construction Management | MC01 | Maintenance and Construction Vehicle and Equipment Tracking |
| MC02 | Maintenance and Construction Vehicle Maintenance | |
| MC03 | Road Weather Data Collection | |
| MC04 | Weather Information Processing and Distribution | |
| MC05 | Roadway Automated Treatment | |
| MC06 | Winter Maintenance | |
| MC07 | Roadway Maintenance and Construction | |
| MC08 | Work Zone Management | |
| MC09 | Work Zone Safety Monitoring | |
| MC10 | Maintenance and Construction Activity Coordination |
ITS Standards
ITS Standards are fundamental to the establishment of an open ITS environment, the goal originally envisioned by the U.S. Department of Transportation (USDOT). Standards facilitate deployment of interoperable systems at local, regional, and national levels without impeding innovation as technology advances and new approaches evolve. The National ITS Architecture is a reference framework that spans all of these ITS Standards activities and provides a means of detecting gaps, overlaps, and inconsistencies between the standards. The National ITS Architecture references specific applicable standards sites and provides connections to them.
1.8 Relationship to Other FHWA Handbooks
This handbook is one of a series of FHWA handbooks that have been recently issued or revised. The following handbooks provide information which is closely related to a number of chapters in the Traffic Control Systems Handbook (TCSH):
" Freeway Management and Operations Handbook (FMOH) (1) " Traffic Detector Handbook (TDH) (2) " Telecommunications Handbook for Transportation Professionals: The Basics of Telecommunications (TH) (3)Table 1-3 summarizes the relationship of the material in those handbooks to this document.
| Traffic Control Systems Handbook (TCSH) Chapter | Other FHWA Handbooks | Relationship |
|---|---|---|
| 1 Introduction | FMOH | FMOH provides additional information on the National ITS Architecture. |
| 4 Control and Management Concepts for Freeways | FMOH | FMOH is the prime source on this subject. TCSH provides a brief overview. |
| 6 Detectors | TDH | TDH is the prime source on this subject. TCSH material is primarily related to installation issues. |
| 8 System Control | FMOH | FMOH provides additional information on traffic management centers. |
| 9 Communications | TH | TH is the prime source on this subject. TCSH discussion is limited to the relationship of communication technologies to surface streets. |
| 10 Traveler Information Systems | FMOH | FMOH is the prime source on this subject. TCSH provides information on static signing, use of CMS on surface streets, summary of advantages and disadvantages of different technologies. |
| 11 Selection of a System | FMOH | FMOH provides additional information on the system design cycle. |
1. Neudorff, L.G., J.E. Randall, R. Reiss, and R. Gordon. "Freeway Management and Operations Handbook." Federal Highway Administration Report No. FHWA-OP-04-003, Washington, DC, September 2003.
2. Klein, L. "Traffic Detector Handbook." Federal Highway Administration Report, Washington, DC. To be published.
3. Leader, S. "Telecommunications Handbook for Transportation Professionals: The Basics of Telecommunications." Federal Highway Administration Report No. FHWA-HOP-04-034, Washington, DC, September 2004.
4. Wagner, F.A. "Overview of the Impacts and Costs of Traffic Control System Improvements." Federal Highway Administration Office of Highway Planning, Washington, DC, March 1980.
5. Mueller, E.A. "The Transportation Profession in the Bicentennial Year - Part II." Traffic Engineering, Vol. 46, No. 9, pp. 29-34, 1976.
6. Sessions, G.M. "Traffic Devices - Historical Aspects Thereof." Institute of Traffic Engineers. Washington, DC, 1971.
7. Irwin, N.A. "The Toronto Computer-Controlled Traffic Signal System." Traffic Control Theory and Instrumentation. Plenum Press, New York, 1965. (See also: Casicato, L., and S. Cass. "Pilot Study of the Automatic Control of Traffic Signals by a General Purpose Electric Computer." Highway Research Board Bulletin 338, 1962).
8. "San Jose Traffic Control Study." IBM Corp., March 1965 (Initial Report).
9. "The Urban Traffic Control System in Washington, DC." Federal Highway Administration, U.S. Department of Transportation, Washington, DC, September 1974.
10. "The National ITS Architecture, Version 5.0." Federal Highway Administration, 2003.
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