Inventory is essential to a successful traffic signal program

Posted in: Bridges, Construction, Transportation

Traffic at stoplight Did you know that even one poorly maintained or operated traffic signal reduces the capacity of the roadway, resulting in unnecessary delays, backups and frustrated motorists? Building a roadway network is a huge financial investment, so maintaining optimum capacity by actively operating and maintaining traffic signals is vital. There are nine main elements of a successful traffic signal program: inventory, maintenance, funding, operations, engineering, procurement, construction, network issues, and advanced technologies. Let’s take a closer look at the first element—inventory.


You don’t know where you’re going until you know where you’ve been. It’s important to have an idea of the number and condition of the signals/flashers within your jurisdiction to begin developing your signal program. By assigning a value and life cycle to signal equipment, the total value of these field assets can be calculated and a schedule for equipment upgrades and replacements can be developed. This information provides the basic documentation to begin preparation of a budget for the signal program.

Cross referencing the signal inventory with a roadway inventory to obtain traffic volumes, high priority corridors such as evacuation routes, planned maintenance and/or roadway projects are a good basis for ranking signal equipment replacements and signal improvements. Having a map-based online inventory is a great visual tool for responding to future signal requests, assessing design needs for roadway improvement projects and corridor management planning and operations.

Signal cabinet
Inventory of Cabinet Equipment

Inventories should include the number, type, location, make and model number, serial number, and age of the equipment. While not an exhaustive list, additional items to consider when obtaining inventory information include:

Location. The inventory should have a unique identifier per location to avoid confusion. The inventory should be map-based with coordinates and include the county, city, routes, street names, and mileposts, along with any pertinent landmarks. For accurate inventory information locations should be identified consistently. Determine upfront how to identify or count locations.

General Layout. Mark up the existing signal plan or prepare a field sketch and take pictures of the signal from each approach and inside the cabinet. Some questions to ask here include: Is a copy of the signal plan in the cabinet? If so, does the plan reflect the current intersection operations? Is the plan sealed by a PE and is the date within 10 years of the current date? If there are discrepancies or the plan is over 10 years old, an engineering review of the signal should be completed.

Signal Heads. Ascertain whether the signal heads are within the cone of vision and meet minimum visibility requirements, if anything is blocking signal visibility, and whether additional signal heads are needed for safety improvements.

Cabinet. The signal cabinet should be in a location where the technician can observe traffic while making changes or performing repairs. It should be in good shape, accessible and on a sturdy foundation. Conduits should be sealed, wiring should be labeled, and contact information should be provided in case of malfunction. If a battery back-up system is in place, note the type, mounting, age and model.

Pedestrian button inaccessible
Identifying accessibility issues

Controller. The type of controller and firmware residing on the controller are key considerations, along with the life cycle. If the controller is over 7-10 years old, it will be eligible for replacement. Newer controllers have more computing power, which allows more advanced traffic operations.

Conflict Monitor. Note the make and model of conflict monitors in place. Is the conflict monitor test documentation and date in the cabinet?

Power source. Collect the utility company name and meter number, and check that the disconnect switch is provided and secured within a locked box. Also, the grounding system should be in place and fully connected.

Signal Support Poles. Include owner and pole identifiers of support poles, presence of guy cables, risers, configuration of span wire or mast arms. Measure the height of the span wire at the pole, height to bottom of signal heads over the travel lane, as there are clearance requirements.

Accessibility. We must consider whether pedestrian accommodations are provided—do pedestrian heads align with crosswalks and are buttons easily identified and accessible? Are curb ramps in place? If so, do they meet requirements? Are there any barriers to pedestrians?

Inspecting pole base

Detection. What type of detection is in place and is it operational?

Communications. Are communications in place and what type: fiber, copper interconnect, radio, cell modem, GPS unit? If so, is communications operational and monitored? List all communications devices (switches, modems are in place and on a maintenance schedule? Are traffic monitoring cameras in place or near enough for viewing signal operations?

Preemption (Railroad or Emergency Preemption). Is the signal adjacent to an active railroad crossing? If so, is signal preemption in place and operational? Is emergency preemption in place and operational? Is this information shown on the signal plan?

Maintenance Information. An inventory should identify maintenance issues for immediate or planned activities. Questions to ask include: Are there any obvious maintenance issues? Are signal support poles in good shape with no visual damage? Are signal signs in good shape?

In summary, an inventory is only a snapshot of the signal, so updates to it should become a standard operating procedure within the signal program. Therefore, any signal asset management software should include methods for updating the inventory as revisions are made. Our transportation team at Mead & Hunt is adept at completing signal inventory projects that enhance roadway capacity and elevate our communities.

Carol Jones

About the Author

As a Senior Traffic Engineer, Carol Jones understands the importance of a well-run transportation system. She is passionate about helping clients optimize roadway capacity to keep our communities running smoothly. When not at work, Carol enjoys writing children’s books, painting, sewing and cooking. She is married with 3 children and 2 grandchildren, 2 dogs, 2 cats, 2 fish and a bearded dragon!

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