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

1. Introduction

Establishing, implementing, and maintaining optimally timed traffic signals is not a simple task. Even when the process is applied to a single, isolated controller, the path to optimum signal timing is paved with problems. One area of the process has been the focus of much academic research over the years, signal timing optimization. As a result, the practicing Traffic Engineer has many optimization models to choose from when retiming traffic signal. Transyt-7F, Passer II, and Synchro are examples of these models. The advent of the Closed Loop System (CLS) and all modern, area-wide traffic signal systems provide the capability of downloading traffic controller timing parameters which has helped problems associated with deployment of new signal settings. Other areas have had less success; data collection and data management are two areas that exhibit opportunities for improvements to the process.

This report considers the entire signal timing process, defines specific areas where progress has been made, identifies the interfaces between these areas, and identifies specific areas where additional research may be expected to improve the signal timing process. This background provides the basis for the identification of specific areas for improvement. Specifically, this report identifies five distinct procedures (Optimization, Deployment, Evaluation, Data Management, and Documentation) associated with the signal timing process. Each of these procedures is examined and evaluated. As important as each of the five procedures is to the process, the interface between each of these procedures is at least equally important and likely provide fruitful opportunities to improve the overall Signal Timing Process.

1.1 Purpose

The purpose of this report is to identify the steps that are required to time traffic signals, and to identify areas that will result in improved traffic signal timing. These steps define a continuing process that may be manual, semi-automated, or fully automated. In the abstract, the process is as applicable to a single isolated controller as it is to a fully integrates city-wide traffic signal system. The process itself can be defined as a series of procedures (steps). This report defines these procedures, identifies the inputs and outputs used by each procedure, examines the boundaries between each procedure, and identifies opportunities for improvements in the process.

1.2 Signal Timing Overview

It is useful to consider the Signal Timing as a process that uses four distinct procedures and one interrelated procedure: Data Management, Signal Timing Optimization, Field Deployment, and Performance Evaluation are the four quadrant procedures of the Signal Timing process. Documentation is the common element that encompasses the other four procedures. This concept is shown graphically on Figure 1.

The four quadrants are depicted simplistically as independent bubbles in Figure 1. Each quadrant receives data from one bubble and sends data to another bubble. The center bubble, Documentation, is central to the process and serves as the repository of information regarding the process.

This structure is used to provide a framework for this analysis. We are able to focus on specific elements of the process without losing the overall perspective. Our emphasis is on not only the four quadrants, but also on the interface between them. In fact, the boundaries between the quadrants are areas that are likely to provide the most potential benefit.

Diagram of the signal timing process, showing four procedures. Data management provides model input to signal timing optimization, which provides controller settings to field deployment, which provides traffic flows to performance evaluation, which provides traffic measures for data management. Documentation links these procedures.
Figure 1. Signal Timing Process.

1.3 Report Outline

Following this Introduction section, the report provides a description of the signal timing process as practiced today by many agencies. This review provides a practical foundation for the remaining sections of this report. We begin with a description of the existing signal timing process followed by many agencies.

Signal timing can not be implemented in an abstract environment; it must be installed in various specific hardware configurations. The next section of the report examines the hardware environment which serves as the host for the signal settings. The two basic approaches to system operation, central control and distributed control are explained and their impact on signal timing is discussed. This is followed by a discussion of the operation of the traffic signal controller – the host environment for the results of the process.

The next section provides a review of literature. This review concentrates on recent, relevant research and is organized using the four element structure previously described. This abstract view is convenient to categorize past work; it is also useful to consider how the signal timing task is approached by the typical agency.

The following section identifies twelve specific concepts which could be developed into projects to improve the overall signal timing process. The final section of the report evaluates the twelve proposed projects and identifies three as having the top priority. The priority selections were made on estimates of the basic need and probability of success.

Office of Operations