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Nov 06, 2023

What are those blue lights in Boulder on top of traffic lights?

Bob from Boulder writes, “What’s driving you crazy? Driving around town,

Bob from Boulder writes, "What's driving you crazy? Driving around town, especially at night while stopped at traffic signals, I have noticed on the pole a blue light. What are those for?"

Those blue lights are called confirmation lights, or sometimes a Red-Light Indicator, and they are used by law enforcement to know when the traffic light on the other side of the traffic signal is red so they can watch for red light violators in a safe place. Because the light is high up in the air, when the confirmation light turns on, it's visible from any intersection approach.

The lights come in several colors, but blue and clear are the most prevalent.

Traffic signal technician Joseph Grijalva provided video for this story and calls himself, "TikTok's and Instagram's most famous signal tech." During his work day near Dallas, Grijalva records and narrates over dozens of very interesting videos on his "Over The Road" social media channels, showing not only how to change the lightbulb for a confirmation light but also showing viewers how tall can a traffic signal be and how cities count vehicles that pass through intersections.

Grijalva said the confirmation lights are mounted behind or sometimes on top of a signal mast arm — the pole that hangs over the street where all the equipment, including traffic signals, are attached.

MORE: Read more traffic issues driving people crazy

"The confirmation light is wired in with the red signal lights’ circuit, allowing it to simultaneously come on," Grijalva said. "This means only one officer is needed to monitor red light runners for all four directions of an intersection, even if he can't physically see the red signal light from a safe spot."

"Without this supplemental indicator, it is difficult for an officer to safely enforce red light-running violations," added Mike Sweeney, the civil engineering senior project manager at Boulder's Transportation and Mobility Department. "A good example of this light in Boulder is at the Foothills Parkway and Arapahoe intersection. It is very apparent at night."

The State of Minnesota has installed many of these lights and said the combination of confirmation lights and extra enforcement efforts has reduced their number of red light violators. One of their concerns, though, was the possibility of increasing the number of rear end crashes as a result of drivers making a greater effort to stop at the red light, similarly to what happens at intersections equipped with red light cameras. Literature on the subject indicates that there is no indication yet of that being the case with confirmation lights.

Officials with the state added that the low-cost of these confirmation lights allows for more of them to be installed in problematic intersections, thereby increasing enforcement efficiency.

Grijalva said his TikTok video showing him changing a bulb in a confirmation light is his most viral video with nearly 14 million views in just over four months.

"The installation and maintenance of the light is fairly straight forward, as long as you’re not afraid of heights," he said. "And surprisingly enough, the light bulb is just a normal LED light bulb you’d find at almost any store."

Denver7 traffic anchor Jayson Luber says he has been covering Denver-metro traffic since Ben-Hur was driving a chariot. (We believe the actual number is over 25 years.) He's obsessed with letting viewers know what's happening on their drive and the best way to avoid the problems that spring up. Follow him on Facebook,Twitter or Instagram or listen to his Driving You Crazy podcast on iTunes , Stitcher , iHeart, Spotify or Podbean.