New sensors on traffic lights keep vehicles moving

Posted: Thursday, August 26, 2010

The Alaska Department of Transportation recently installed new video detection cameras on top of traffic signals in the Mendenhall Valley area.

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Klas Stolpe / Juneau Empire
Klas Stolpe / Juneau Empire

However, these cameras aren't there to catch drivers running red lights. Instead, they are being used to give motorists the "green" in a more efficient way.

"The overhead cameras people will see at a traffic signal are solely for detecting the presence of vehicles to provide the best distribution of green time based on traffic demand," said Carolyn Morehouse, a traffic engineering manager for the Department of Transportation & Public Facilities' Southeast Region. "They will not change traffic signal timing patterns, video is not recorded, and there is no red-light running or speeding ticket component to the video detectors."

When a vehicle pulls up to an intersection that is equipped with video detection and the signal is red, the camera detects the presence and puts in a call for a green light.

The experimental cameras are being used because many motorcycles or bicycles do not have enough metal to trigger the detectors set in pavement, Morehouse said. Those sensors, called inductive loops, emit a magnetic field to detect a vehicle and are currently used in Juneau traffic signals to detect the presence of vehicles and distribute green light time.

"They do have multiple advantages over the older loop detectors," said John Brannan, director of sales and service for Western Systems. "Chief of which is there are no reoccurring costs if the pavement wears out and you have to do reconstruction."

Western Systems is the major supplier of intelligent transportation system communications and networking products in the Pacific Northwest.

"These devices are often used in advance problems with deer crossings or cattle or even moose," Brannan said. "They would be linked to flash warning lights if animals were in the target zones. The state here is using them as intelligent traffic systems."

According to a release by the department of transportation, they are evaluating the video detectors' effectiveness and performance in Juneau's weather conditions to determine if future video detector installations will be implemented.

The release also stated the department has had positive experiences with video detectors in the Northern Region, which includes Anchorage and Fairbanks.

• Contact Klas Stolpe at 523-2263 or

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