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Fri, Oct. 18

Seeing Red at the Stoplight: Technology drives city’s traffic lights

Walter Davis, city traffic signal technician, monitors a computer inside a traffic signal cabinet for timing and functionality. Despite what it feels like, no light under the city’s control stays red for more than two minutes.
Photo by Aaron Ricca.

Walter Davis, city traffic signal technician, monitors a computer inside a traffic signal cabinet for timing and functionality. Despite what it feels like, no light under the city’s control stays red for more than two minutes.

The timing of traffic signals lies in technology and furiously punching your steering wheel in a fit of rage won’t change that fact.

While the bottleneck of Stockton Hill Road might not compare to the gridlock of Phoenix, it’s still a mess and the only way to deal with it – and any other stoplight in town – is to be patient.

The City of Kingman Public Works Department is responsible for lights on all of Stockton Hill Road and Andy Devine Avenue between Grandview Avenue and Michael Street (lights north and south of those boundaries fall under the responsibility of the Arizona Department of Transportation).

Stockton Hill traffic between Detroit Avenue and Gordon Drive might seem like a mess, but according to Jack Plaunty, city street superintendent, the lights

are timed to expedite the flow of traffic, provided there isn’t much, and everyone is moving at the same pace.

“If you’re doing the speed limit, you’ll catch every green light,” he said, and is well aware that Stockton Hill is saturated with traffic. “To improve the level of service, we’d have to make physical improvements.”

That would mean adding lanes on already existing property, something some businesses have already dedicated space for, but that’s a different story.

The lights run on a combination of timing and sensors, depending on the time of day. From 7 a.m. to 7 p.m., the lights are timed by a signal cabinet – those shiny silver boxes near each intersection – depending on the size of the intersection, speed limit and volume of traffic.

“The minimum and maximum times a light will change is based on coordination of the signals,” Plaunty said.

Each intersection runs on a two-minute cycle of red, yellow and green lights, starting with a green light for one direction and working around an intersection. Every intersection has a minimum of three-second yellow lights to let all traffic pass before turning red, and all four directions are red at the same time for exactly two seconds so that no vehicle (theoretically) is passing through. Those cycles only apply to through traffic on the main roads.

Times will vary during peak hours, such as morning and evening rushes and lunchtime and will also change for traffic coming off of side streets.

For example, the left turn lane from Detroit Avenue will last longer when Kingman Middle School lets out. The same goes for other intersections.

Loop Detectors

In between the 7-to-7 window, lights are controlled by a loop detector – a sensor buried beneath the asphalt that can detect when a vehicle is stopped at a crossing. They relay information to the signal cabinets, a light turns green, and the cycle starts all over. Motorcyclists, fear not! Science is at work here.

“There’s an inductive current that creates a magnetic field and the loop amplifiers pick that up,” Plaunty said.

“If there’s not enough metal or someone’s not close enough to the loop, it might not pick them up.”

Emergency Services

Emergency vehicles, more specifically the Kingman Fire Department, use preemptive technology for expedient access to a call.

GPS trackers on both firetrucks and signal cabinets “talk” back and forth to calculate the speed and distance of an emergency vehicle and proximity to the call. Once the vehicle gets within range of the light, a preemptive sequence begins, which starts by allowing pedestrian and civilian traffic to finish the cycle in progress. Once the emergency vehicle is at a certain point, all lights turn red except for that of the direction of access. When passed, the interchange resumes normal operation.

If you’re one of those people who flick your headlights on and off thinking it’ll magically change the signal in your favor, you’re wrong.

“They used to be run by strobe lights on a certain wavelength,” Plaunty said. “Not anymore.”

Getting More Lights

Some parts of town might seem like they could use more signals – we’re looking at you, Hualapai Mountain Road.

Drag strip speeds aren’t enough to merit building another light. The public works department has to meet an engineering warrant, which is usually the result of a large volume of fatalities or accidents related to side street traffic trying to get onto a main thoroughfare.

More lights won’t necessarily slow traffic.

“It actually increases speed,” Plaunty said. “People get impatient and hurry to the next light.”

ADOT controls the more frustrating intersections

Both Plaunty and Walter Davis, city traffic signal technician, reiterated that the Interstate 40 and West Beale Street exit for Las Vegas-bound traffic falls on ADOT, not the city.

The same goes for Route 66 and Airway Avenue.

All that being said, taking a chill-pill is the best respite.

“You’ll never have to wait more than two minutes at a red light,” Davis said.

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