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Red, yellow, green: Making sense of Hickory's traffic signals

Signals change to adjust to traffic flow

Robert C. Reed

Traffic Engineer Nathan Vannoy explains how Hickory’s traffic signal system works.

BY THE NUMBERS:
|:| 190 - Number of traffic lights in Hickory
|:| 85 pounds - Weight of a traffic light
|:| $500 - Cost of a new traffic light
|:| Up to $100,000 - Cost to establish a new traffic light
|:| 200 - Length of longest-cycle light in seconds
|:| 110 - Hickory's average cycle length in seconds
|:| 60 - Hickory's shortest-cycle lights in seconds (through downtown)
|:| 10 - Age of Hickory's traffic system

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By Richard Gould | Hickory Daily Record

Published: August 3, 2008

HICKORY - Sitting still at a red light in 95-degree weather, watching exhaust billow out of the truck in front, is no way to spend an afternoon.

For many Hickory residents, it's a way of life.

For the poor souls stuck inside cars without air conditioning, it's worse.

One thing most drivers seem to agree on is there are too many traffic lights and they take too long to turn green. Whether or not that's true is something many motorists ponder while sitting at one of Hickory's 190 interconnected traffic signals.

City Traffic Engineer Nathan Vannoy spends his days working to keep traffic lights optimized and traffic moving smoothly. Vannoy does one of those jobs that doesn't bring a lot of public accolades, but he's committed to serving the community.

"We can never really, fully be satisfied with our timing plans because we know things change and we have to change along with them," he said of the city's traffic signals. "We do not employ a fix-it and forget-it approach to traffic signals here. We have to stay ahead of the curve and sensitive to the needs of our citizens."

The way to keep traffic moving is to figure out exactly when, where and how long and how often to stop it. Keeping traffic moving efficiently requires the use of a signal that can detect changing traffic flow and adjust its timing to accommodate it, he said.

The most commonly used traffic detecting devices in Hickory are easy to spot at most stoplights. They're called loop sensors.

A rectangular gouge is cut into the road surface then a copper wire loop is set into it and connected to a control box. The sensors work because the current flowing through the loop creates an electrical field that's disrupted when big hunks of ferrous metal, like axles and engine blocks, pass through it.

Loop sensors are inexpensive and they work well, but Vannoy said they're the weakest link in the vehicle-detection system used by the city. He said they're vulnerable to lightning strikes, edging equipment, electro-magnetic interference and general wear and tear.

One stretch of highway where traffic signals have irritated many drivers is U.S. 321.
Vannoy said the state Department of Transportation repaved it about two months ago. When they did, he said, every loop sensor on that stretch of highway was milled up and destroyed. The cost of replacing the sensors was paid by the North Carolina Department of Transportation.

Without sensors in place, the stoplights had to be switched over to fixed, timed patterns instead of flexible sensor-driven patterns, Vannoy said. It wasn't until last week that four-man crews were able to replace the last of the sensors.

"I'm pleased to say that we do have vehicle detection capability along the U.S. 321 corridor now," he said. "The science is detecting the vehicles — the art is putting that data into use."

The next place he plans to apply his art is along the Hickory stretch of the U.S. 70 corridor. Vannoy said the area is the most heavily traveled stretch of road in the city and the last time its lights were synchronized was about five years ago. He plans to synchronize a stretch of N.C. 127, as well.

Ten years ago, Hickory's traffic signal system was state-of-the-art and was studied by municipalities throughout the Southeast that wanted to improve their systems, Vannoy said. What made the system special was its flexibility and ability to modify the length of its red-yellow-green cycles to accommodate changing traffic patterns.

Ten years later, the system is no longer cutting-edge, but Vannoy said, "Ours is one of the finest systems in this part of the country."

That may be, but many disagree.

The U.S. 321 corridor tops the list for many who want to see improvements made to the traffic-signal system.

Ryan Taylor lives in Granite Falls and works at Nissan of Hickory at 1555 U.S. 321. "If you hit one of those lights, you'll hit them all," he said.

Randy Johnson of Hudson agrees. He drives a tractor-trailer locally and wrote about the traffic signal at the intersection of U.S. 321 and 14th Aveue Circle, NW. in an e-mail to the Hickory Daily Record.

"Its location might be somewhat beneficial for traffic that needs to cross 321, but for drivers of large commercial trucks, it's a nightmare. This light is at the bottom of a rather long hill, if you are running the speed limit, it makes it just about impossible to stop without heavy braking and, at times, locking up the brakes. This is very dangerous especially if a car stops suddenly in front of the truck at a short light. This also is what causes the road to become so rough at this light."

For others, the environment is the issue.

"Considering both the cost of fuel and the area's problems with air pollution, the efficient flow of traffic is more important now than ever before," wrote Don Norwood in an e-mail.
Vannoy said his goal is to shorten trip times, minimize the number of stops and increase fuel efficiencies. "Optimizing stop times on synchronized routes usually results in a little bit of stop time for everybody."

Constant improvement and adjustment of the system is Vannoy's focus.

Loop sensors are a weak link, and Vannoy said optical technology could do the job better. He's not content to sit back and let Hickory's traffic system slide into obsolescence.

"We're planning right now for our next citywide traffic system," he said. "The plan and the development of it will take years to develop."

The new system will have the ability to monitor traffic conditions and change during each cycle, which will require tremendous processing power. It will make extensive use of fiber optic technology. Vannoy said Hickory may be five years away from having the new system.

Because the new system will not rely as heavily on loop sensors, it will be able to detect and respond to bicycles and pedestrians.

While some may suppose a truly innovative traffic-control system would make extensive use of artificial intelligence, Vannoy said that's not the case because human ingenuity, intuition and flexibility are required to operate the complexity of traffic signals.

The best traffic systems rely on good, sound decisions made by traffic engineers who can respond quickly to the ongoing data stream produced by the signals.

"We can never attain perfect satisfaction with traffic control because it's an ever-changing and evolving thing," he said.