Show almost anyone in the world a red, yellow and green light, and they’ll instantly associate the colorful trio with a traffic signal. But add another color to the mix, and many will be left in the dark—or, let’s be honest, totally and completely confused—about what it’s supposed to mean.
That’s exactly what’s happening in some parts of the United States: Drivers have spotted the addition of a bright blue light mounted near traffic signals. Yes, blue. But what is its purpose, and does it change how you should approach the intersection? Because remember: Just because you don’t know a traffic rule, it doesn’t mean you can’t get a ticket for it!
To get us all up to speed on this new rule of the road, Reader’s Digest spoke with David A. Noyce, executive associate dean of the College of Engineering and the Arthur F. Hawnn Professor of Transportation Engineering at the University of Wisconsin–Madison. Read on to find out what those little blue lights mean—and what you should do when you see one.
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What does it mean if you see a blue traffic light?
A blue light—often called a confirmation light or red-signal indicator—is designed to help law enforcement monitor, from a distance, whether the traffic signal is displaying a red light. Yep, its whole purpose is to let a copper know if someone’s run a red.
In case you’ve never seen one of these yourself, it’s not an extra circle in the red, yellow, green lineup. The blue light will typically be mounted above the traffic signal or, in some cases, higher up or to the side on the overhead mast arms.
How does this work, exactly?
What do these blue lights mean?
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These blue lights are electrically linked to red lights on one or more of the approaches to the intersection. “Police use them to ‘observe’ the red light when they cannot see the actual red light directly,” Noyce explains. “Therefore, when the red-light traffic signal indication is illuminated, so is the blue light.”
Here’s the benefit: At signals without a blue light, an officer often has to be positioned near the same side of the intersection as a driver to confirm that they’ve run a red light. With a blue confirmation light, officers positioned at different angles or whose views are partially obstructed, perhaps by a tree branch, can verify that a signal is red by looking for the lit blue light, making it easier to spot drivers who fail to stop. Plus, it’s more efficient, since you need fewer officers to keep their eyes on the same stretch of road.
“The confirmation light is used to support a traffic law common in many states that requires a police officer to physically witness a violation to issue a citation,” Noyce says. “With the blue confirmation light, the police officer can physically witness red-light-running from anywhere in the intersection.”
Plus, according to a Federal Highway Administration research and technology report, these lights reduce the need for officers to cross the intersection against a red to pursue a driver who has run the signal. That makes the situation a whole lot safer for officers.
Are there any benefits for drivers?
While nobody likes getting a ticket, better enforcement of red-light violations can prevent future crashes by identifying and stopping drivers who repeatedly blow through red lights as well as make others tempted to do the same think twice. And that can save lives—not only those behind the wheel and their passengers, but pedestrians and bicyclists too. According to the Insurance Institute for Highway Safety, more than 141,000 people were injured in red-light-running crashes in 2024, and 1,119 were killed. Of the fatalities, about half were pedestrians, bicyclists or occupants of vehicles struck by drivers who ran reds.
Why was blue chosen for these lights?
Partly to avoid sending mixed signals. The Federal Highway Administration’s Manual on Uniform Traffic Control Devices advises that these lights “should be designed such that they do not confuse drivers,” meaning “they should not be red, yellow or green.” And since blue is not recognized as a standard traffic signal indication, Noyce notes that drivers are less likely to mistake it for a signal telling them to stop, slow down or go.
Plus, he adds, blue LEDs are relatively uncommon in the roadway environment and produce a highly visible and saturated light that stands out against the glow of headlights, streetlights and other signs, which tend to fall in the white, yellow, amber and red portions of the spectrum during the evening hours. Blue also has a strong association with law enforcement, reinforcing its purpose.
Where can you find blue traffic lights?
There’s no national database tracking where blue lights have been installed in the U.S., and they’re not part of the federal standard traffic signal system. As a result, confirmation-light usage is scattered, at best, and remains a locally adopted enforcement tool rather than a coordinated national practice, similar to blue stop signs. Since blue lights are not mandated by the federal government, local police departments and transportation agencies are usually the ones that decide to give them a try.
Based on his research and experience, Noyce says blue lights are most prevalent in Florida and Colorado, though they’ve also appeared in a handful of other states. In Minnesota, for example, the city of Maplewood installed the lights, and other communities followed, after the state’s Department of Transportation launched a formal safety study of Florida’s confirmation-light system and its effectiveness in 2014. That study found that crashes caused by red-light runners dropped by 33%.
And while social media may make blue lights seem like a newfound law-enforcement gadget, these devices have actually been around for years. They were reportedly in use as early as 2007 in Marysville, Washington. In general, though, because the devices are often installed in one intersection at a time—and not uniformly citywide—they tend to receive only sporadic local-news coverage.
What should you do if you see a blue traffic light?
The same thing you always do: Obey the normal traffic rules. It’s not there to convey anything to you—it’s strictly for police officers. (That said, blue-confirmation lights don’t necessarily indicate a cop is around.)
For the average driver, bicyclist or pedestrian, they “mean nothing from a ‘rules of the road’ standpoint,” Noyce says. “But, perhaps, some drivers will react differently by deciding not to run a red light when in other instances they may have considered it.”
Sources:
- David Noyce, PhD, executive associate dean of the College of Engineering and the Dr. Arthur F. Hawnn Professor of Transportation Engineering at the University of Wisconsin–Madison; email interview, July 2026
- Insurance Institute for Highway Safety: “Red Light Running”
- Federal Highway Administration Research and Technology: “Safety Evaluation of Red-Light Indicator Lights at Intersections”
- HeraldNet: “Those Blue Lights on Traffic Signals Help Nab Red-Light Runners”
- Crossroads: “Six Effective Low-Cost Safety Improvements for Roads”
The post Here’s What It Means If You See a Blue Traffic Light appeared first on Reader's Digest.
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