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Signal Timing Manual, Second Edion Chapter 1. Introducon CHAPTER 1 INTRODUCTION CONTENTS 1.1 FOCUS FOR THE SECOND EDITION .................................................................................. 1-1 1.2 STM2 ORGANIZATION ......................................................................................................... 1-3 1.3 REFERENCES ........................................................................................................................... 1-4
Chapter 1. Introducon LIST OF EXHIBITS Exhibit 1-1 Signal Timing Outcome Based Process ................................................................ 1-2 Exhibit 1-2 STM2 Organization ....................................................................................................... 1-4 Signal Timing Manual, Second Edion
Chapter 1. Introducon LIST OF EXHIBITS Exhibit 1-1 Signal Timing Outcome Based Process ................................................................ 1-2 Exhibit 1-2 STM2 Organization ....................................................................................................... 1-4 Signal Timing Manual, Second Edion Chapter 1. Introducon 1-1 CHAPTER 1. INTRODUCTION 1.1 FOCUS FOR THE SECOND EDITION The irst edition of the Trafic Signal Timing Manual (TSTM) was written as a comprehensive guide for engineers and technicians about signal timing principles, practices, and procedures. The second edition (STM2) is a standalone document that was developed based on TSTM user feedback. Key features of this edition include ⢠Focused information written for new practitioners and those desiring a better understanding of signal timing fundamentals. ⢠Addition of four new chapters for more advanced users. ⢠Material organized so that it is presented once and referenced as needed elsewhere in the document. ⢠Inclusion of essential information only (i.e., no ânice to knowâ information). ⢠References to other documents, instead of repeated material. ⢠Expanded use of graphics to aid in the explanation of more complex topics. The STM2 has an increased focus on signal system users and their priorities. Current signal timing models tend to provide a one-size-its-all approach to signal timing, which often leads to the incorrect assumption that the model provides the optimum solution. A trafic analyst simply inputs the data required by the model, hits the optimize button, and gives the optimized results to the appropriate person for implementation. The results largely relect the modelâs priorities (generally some version of vehicle delay) for system users, which may or may not it the needs of the actual operating environment or users (including pedestrians, bicycles, and transit). The STM2 introduces an outcome based approach to signal timing (summarized in Exhibit 1-1), which allows the practitioner to develop signal timing based on the operating environment, users, user priorities by movement, and local operational objectives. Performance measures are then used to assess how well the objectives are being met. Once the objectives and performance measures are established, timing strategies and timing values can be chosen. The inal steps of the process involve implementation and observation (i.e., determining if the timing strategies and values are working), as well as sustaining operations that meet the operational objectives through monitoring and maintenance. This process was developed with an understanding that there is not a one-size-its- all method for signal timing. The approach is described in detail in Chapter 3, but brief descriptions of the eight steps in the outcome based process and associated considerations are provided below. Step 1: Deine the Operating Environment Signal timing should relect the character of the timing location, so the outcome based approach begins with an assessment of the operating environment. The operating environment goes beyond physical location characteristics and also includes goals of the local operating agency and its regional stakeholders. The second edion of the Signal Timing Manual (STM2) focuses on system users. Performance measures, such as vehicle delay, are oen mistaken as the operaonal objecves. One signal ming objecve does not fit all condions. Signal Timing Manual, Second Edi on
Chapter1-2 1. Introducon Step 2: Identify Users The process continues with the identiication of primary users at the focus intersections. This approach allows all users (people on foot, riding on bikes, riding transit, driving trucks, and driving cars) to be considered in the signal timing process. Step 3: Establish User and Movement Priorities Priorities should relect the local operating agency and regional stakeholder goals for mobility. Priorities should be established by movement for the primary users and by location and time of day. For example, in a central business district (CBD), pedestrians might have the highest priority, while in a suburban environment, through vehicle movements on an arterial might have the highest priority during peak hours and a lower priority off-peak. Step 4: Select Operational Objectives Once priorities are established, the process requires the establishment of operational objectives (e.g., pedestrian safety or vehicle mobility) by location and time of day. Non-vehicle-oriented operational objectives are often more dificult to assess because of their qualitative nature; however, performance measures can be selected for qualitative as well as quantitative assessment. Step 5: Establish Performance Measures Traditional optimization tools generally focus only on simple vehicle-oriented performance measures because they are easy to quantify and, therefore, easy Exhibit 1-1 Signal Timing Outcome Based Process Signal Timing Manual, Second Edion
Chapter 1. Introducon 1-3 to âoptimize.â However, vehicle stops and delay may be less important than transit and pedestrians in a CBD, as well as other existing or developing areas with signiicant pedestrian, bicycle, and transit activity. The practitioner needs to make appropriate adjustments to the trafic signal timing process to account for the operating environment and user priorities. Step 6: Develop Timing Strategies and Timing Values Once operational objectives and their associated performance measures have been determined, the process continues with the development of signal timing strategies (i.e., minimizing cycle length or favoring arterial through trafic) and selection of appropriate timing values. Step 7: Implement and Observe The next step is implementing the signal timing values and making inal adjustments to the timing parameters. Step 8: Monitor and Maintain After implementation, a successful program requires ongoing monitoring and maintenance. Collecting periodic (at least annual) volume data at a mid-block location on each arterial or subsystem is essential when determining if shifts in trafic characteristics occurred or if further investigation is necessary. A good maintenance management system can help an agency identify issues beyond the signal controller, including communication and detection issues, which are often signiicant contributors to poor operations. 1.2 STM2 ORGANIZATION The outcome based approach not only guides the development and implementation of signal timing plans, but also guides the organization of the STM2. As shown in Exhibit 1-2, the manual has 12 chapters. Chapters 1 through 4 address signal timing fundamentals, providing guidance on the elements used to support a successful signal timing program, as well as concepts necessary for understanding modern trafic signal operations. Because a poorly designed signal can never operate at its full potential, Chapter 4 focuses speciically on signal design. Chapters 5 through 8 are focused on basic signal systems, presenting the detailed, practical information necessary to appropriately time a trafic signal controller and to operate it in a system with multiple controllers. These chapters include important information about controller features that are often overlooked because they are not included in signal timing optimization tools. The information presented in Chapters 5 through 8 is intended to help new practitioners achieve locally appropriate results and to serve as a reference for more experienced practitioners. Guidance on advanced signal systems and applications is provided in Chapters 9 through 12. The material begins with a brief introduction to Systems Engineering, a process that reduces risk by clearly deining needs and the speciic requirements to meet local needs. These chapters conclude with speciic information about managing competing priorities in a multimodal system. Signal Timing Manual, Second Edion
Chapter1-4 1. Introducon It should be noted that the STM2 relies on a number of important reference documents for details. It is intended to complement policy documents such as the Manual on Uniform Trafic Control Devices for Streets and Highways (MUTCD, 1) and is not intended to replicate or replace the Highway Capacity Manual (2), or national or local engineering documents on signal timing, nor is it intended to serve as a standard or policy document. The manual has been structured and written as concisely as possible, and because the manual only references these external documents, it should not become out-of-date as those documents are updated. Practitioners are cautioned to consult current documents for changes. For example, documents such as the MUTCD (1) are periodically updated, and some guidance in this document is based on the 2009 edition. 1.3 REFERENCES 1. Manual on Uniform Trafic Control Devices for Streets and Highways, 2009 Edition. United States Department of Transportation, Federal Highway Administration, Washington, D.C., 2009. Exhibit 1-2 STM2 Organizaon Signal Timing Manual, Second Edion
Chapter 1. Introducon 1-5 2. Highway Capacity Manual 2010. Transportation Research Board of the National Academies, Washington, D.C., 2010. Signal Timing Manual, Second Edion
