Learn what a traffic signal warrant study is, how it works, and why it matters for traffic safety and efficiency in transportation planning.

Warrant studies are a reactive tool in transportation planning. They are designed so that motorist throughput is prioritized unless a certain threshold of crashes, injuries, and deaths is surpassed. Only then are safety improvements considered. Unsurprisingly, advocates for Complete Streets and Vision Zero policies often view them as obstructions, as government officials will cite warrants as excuses to make no changes that might slow or stop motorists.

What is the purpose of a traffic signal warrant study?

Traffic signals are one of the most common and effective ways to control the flow of vehicles and pedestrians at intersections. However, installing and operating traffic signals can be costly and complex, and not every intersection needs or benefits from them. How do transportation planners decide whether a traffic signal is warranted or not? This is where a traffic signal warrant study comes in.

1 What is a warrant study?

A warrant study is a systematic and objective analysis of the existing and projected traffic conditions at an intersection, based on a set of criteria and guidelines. The purpose of a warrant study is to determine if a traffic signal is justified and feasible, and to identify the optimal timing and phasing of the signal. A warrant study does not guarantee that a traffic signal will be installed, but it provides the necessary data and justification for the decision.

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Kevin H. Posey
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Warrant studies are a reactive tool in transportation planning. They are designed so that motorist throughput is prioritized unless a certain threshold of crashes, injuries, and deaths is surpassed. Only then are safety improvements considered. Unsurprisingly, advocates for Complete Streets and Vision Zero policies often view them as obstructions, as government officials will cite warrants as excuses to make no changes that might slow or stop motorists.

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2 What are the criteria and guidelines?

The criteria and guidelines for a warrant study are typically based on the Manual on Uniform Traffic Control Devices (MUTCD), the national standard for traffic signs, signals, and markings in the United States. The MUTCD defines nine different warrants for traffic signals, each with specific thresholds and conditions. For instance, Warrant 1 considers the total traffic volume on the major and minor approaches during eight hours of an average day, while Warrant 2 considers the total traffic volume on the major and minor approaches during four hours of an average day. Warrant 3 focuses on the traffic volume and delay on the minor approach during the highest hour of an average day. Additionally, Warrant 4 looks at pedestrian volume crossing the major street during any four hours of an average day, and Warrant 5 evaluates safety and convenience of school children crossing the major street near a school.

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Lisa Marie Glover MST, ENV SP

Multimodal Transportation Management Professional
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The warrant study is critical to the installation of traffic control devices and signage. There are MUTCD criteria that a study has to meet to warrant the placement of equipment and signage.

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3 How is a warrant study conducted?

A warrant study is usually conducted by a qualified transportation engineer or planner, who collects and analyzes the relevant data for the intersection. The data may include traffic counts, vehicle speeds, turning movements, pedestrian counts, crash history, signal coordination, and future land use. The engineer or planner then compares the data with the MUTCD criteria and guidelines, and evaluates whether any of the warrants are met or not. The engineer or planner also considers other factors, such as the physical characteristics of the intersection, the environmental impacts, the public input, and the agency policies.

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4 What are the benefits of a warrant study?

A warrant study can provide several benefits for transportation planning and management, such as enhancing safety and efficiency by reducing crashes, delays, and emissions. It can also support rational and transparent decision-making by providing clear and consistent criteria and evidence for the installation or removal of traffic signals. Furthermore, a warrant study can help optimize resources and performance by allocating funds and resources for traffic signal projects, as well as monitoring and evaluating the performance of existing and proposed signals.

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5 What are the challenges of a warrant study?

Conducting a warrant study for transportation planning and management can present certain challenges. It may need to be updated or revised periodically to account for changing conditions, such as population growth, land use development, travel behavior, and technology. Additionally, a warrant study must be able to balance multiple objectives and perspectives, including mobility, safety, equity, environment, and economy. It must also consider the impacts and preferences of various users and stakeholders. Finally, it is important to remember that a warrant study is only the first step in the process of installing and operating traffic signals. More detailed design, engineering, and construction activities may be necessary, as well as ongoing maintenance and operation costs and responsibilities.

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6 Here’s what else to consider

This is a space to share examples, stories, or insights that don’t fit into any of the previous sections. What else would you like to add?

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What is the purpose of a traffic signal warrant study?

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1 What is a warrant study?

2 What are the criteria and guidelines?

3 How is a warrant study conducted?

4 What are the benefits of a warrant study?

5 What are the challenges of a warrant study?

6 Here’s what else to consider

Transportation Planning

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What is the purpose of a traffic signal warrant study?

1

2

3

4

5

6

1 What is a warrant study?

2 What are the criteria and guidelines?

3 How is a warrant study conducted?

4 What are the benefits of a warrant study?

5 What are the challenges of a warrant study?

6 Here’s what else to consider

Transportation Planning

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