Arterial Management Program

Improving Traffic Signal Management and Operations: A Basic Service Model

About this Report

Over the last several decades, the gap between the state of the art and the state of the practice in traffic signal operation has grown. Influential studies such as the 1994 General Accounting Office report to Congress have reported improved technological capabilities that go unused in agencies that increasingly find it difficult to meet the expectations of policy makers and the public.

Managing the expectations of the agency managers and decision makers to coincide with the purpose and objective of traffic signal operations has become an increasingly more difficult task for experienced practitioners and traffic signal system managers. The lack of clearly stated operational objectives may contribute to an unrealistic expectation that traffic signals can create capacity, when in fact they can only distribute it. Yet signal operations activities such as retiming projects and traffic signal infrastructure projects are most often proposed by those same practitioners to meet the expectation of relieving congestion.

The perceived gap between art and practice has led toa number of assessment efforts. In addition to the industry councils that led to such documents as the Institute of Transportation Engineers (ITE) document A Toolbox for Alleviating Traffic Congestion and Enhancing Mobility, and external assessments such as the GAO report, more recent efforts have included the Traffic Signal Report Card and Self Assessment. All of these efforts reinforce the assumption that activities are the measure of effectiveness. Thus, agencies seek to demonstrate that they are doing all they can to alleviate congestion by undertaking prescribed activities, including projects to retime traffic signals and projects to enhance the traffic signal infrastructure. These activities often consume more resources than are available to the agency, with the result that they dominate the agency's attention and priorities. By promising results based on activities alone, agency professionals often undermine their own credibility by setting unattainable expectations and then spending resources in competition with more attainable objectives.

The industry often promises what it cannot deliver, and then fails to deliver what it could, with better commitment and resources.

In this report, the research team has adopted a different approach. By identifying archetype agencies and then gathering information from real agencies, the researchers have attempted to define what makes an agency more successful with or without an abundance of resources. The report suggests that more successful agencies are those that establish and maintain a concept of good basic service. This concept becomes the basis for how they interact with the public, how they promise results to policy makers, and how they set priorities for limited resources. It focuses on results rather than activities.

The report begins with a background discussion and a review of the literature, particularly past assessments and focusing on the Traffic Signal Report Card.

Following the literature review, the report develops case studies based on archetype agencies. These archetypes illustrate the different levels of resources and how those resources are used, whether the agency looks good in assessments and whether it gets results in terms of motorist and policy-maker expectations. From these archetypes emerges the concept of good basic service. Targeted interviews with two agency managers provide examples of how well-regarded agencies define and achieve their goals (or not).

The interviews and the archetypes then form the basis for developing a basic service concept, including the outline for a Traffic Signal Management Plan for traffic signal operating agencies consistent with that basic service concept.

The Appendix includes a discussion of signal timing versatility and how the objective of versatility contrasts with the more common objective of optimality.

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