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Did You Know: Freeway Traffic Flow Determined By Pavement Wires

By Nadine Arroyo Rodriguez
Published: Friday, February 13, 2015 - 4:34pm
Updated: Thursday, February 19, 2015 - 1:47pm
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Nadine Arroyo Rodriguez/KJZZ
The ADOT Traffic Operation Center in Phoenix.

Ever wondered how we are able to tell you where there are freeway back-ups at any given time of the day? Well, there’s a system dedicated to this science.

The freeway management system will continue to grow this year. ADOT has a sensor and camera installation project underway along I-17 north of Loop 101 and along Loop 202 in the Chandler area.

Overhead message boards, social media notices and news station information are ways we often know when there are back-ups on our road system. Did You Know…the information we receive is gathered electronically?

“It really comes down to it being a wire that is actually embedded in the pavement itself," said Doug Nintzel, spokesperson for the Arizona Department of Transportation.

“And there are series of wires that wind-up being put into the pavement across the width of the freeway and as you’re driving along the freeway you’re traveling over those sensors," he said.

I bet you’ve seen those sensors. They look like a set of three to four consecutive black stripes on the road.  ADOT calls them loop detectors. They’re placed at key points along the freeway, like major interchanges. The electronic wires are attached to a metal box on the side of the freeway. Each time vehicles run over them, the sensors send data to the box. Each wire provides different data including the number of vehicles passing by, their speed and the space between them.

“Welcome to our world of the control room within the traffic operations center," Nintzel said.

The room looks like a little NASA mission control center. There are 40 video monitors on a wall. Live video of Valley freeways is streamed and captured on each one. There are two to three traffic operators on duty during any given shift, including a DPS officer. The center operates 24 hours a day, seven days a week.

While watching the operators work, I glance up at the monitors and see a back-up on east bound I-10, near 27th Avenue. An accident just occurred.

Nintzel said once traffic data from the sensors is transmitted, operators can zoom in the on the troubled area. The pavement sensors and the video cameras are part of more than 150 mile freeway management system that keeps all of us up-to-date on freeway conditions.

“This is all about computer technology, so it’s nearly instantaneous that you’re able to have that information into a computer system and it’s all real time out there," he said.

The data is also used for future planning. Depending on how many cars and commercial vehicles area traveling the roads, for example, ADOT can decide if there’s a need for additional lanes or road improvements.

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