An inside look at Brentwood’s Traffic Operations Center

Photo: Martin Yates at his desk in Brentwood’s Traffic Operations Center

By LANDON WOODROOF

People often take traffic lights for granted. When they do think of them it is usually out of annoyance over a short-lived green light or a seemingly endless red one. 

Most people do not consider that, as frustrating as gridlock can be in Brentwood, it would be indescribably worse without a carefully designed system of traffic signals and a group of people to oversee them.

In fact, Brentwood’s traffic signal system is complex and involves a great deal of planning and oversight to operate. It is not just as easy as buying traffic lights, hanging them at intersections and plugging them in. Traffic signals have to be regularly evaluated and their timings modified to accommodate changing traffic patterns and to account for unforeseen events like accidents. Even then, a lack of understanding of how signals work can lead to driving practices that impede traffic flow.

“There’s a lot more to signals than people think,” Brentwood’s Director of Engineering Mike Harris said Friday afternoon at Brentwood’s Traffic Operations Center.

A quick look around the room confirmed that. Four large television sets lined the wall, each displaying live camera footage of four different signalized intersections around town.

At a desk, Traffic Operations Coordinator, Martin Yates sat in front of two more screens. One showed a map of the city’s signals and the other showed images from the video detection system the city uses to more closely monitor specific intersections.

Yates is the main person charged with overseeing Brentwood’s 46 signalized intersections. Generally, during peak travels hours Yates will monitor the video feeds of those intersections to make sure there are not any incidents that need his intervention. If a light malfunctions, he receives an email.

There are several types of cases where he will intervene. Often, he will step in when there is a bad accident. A wreck on I-65, for instance, will cause many drivers to get off the interstate and use Franklin Road.

“It places a heavy priority on Franklin Road to try to keep the cars moving,” Harris said.

In response, Yates can change signal timings to make those on Franklin Road stay green longer to help clear the excess traffic because of the wreck. Of course, that means that roads leading on to Franklin Road will experience longer red lights.

“It’s a balancing act,” Harris said.

“If you’re giving something more green time you’ve got to rob Peter to pay Paul,” Yates agreed.

Some of this variation is built into the system, especially for areas of frequent congestion. That is why many signals in the city vary in their timings throughout the day.

Again, Harris used Franklin Road as an example.

“Along Franklin Road [in the a.m.] you’re gonna want more green time for northbound,” he said. “You want to synchronize the signals so that they’re more efficient for northbound traffic. In the p.m., when everybody’s going back the other way you want it be more efficient going southbound.”

Another way the city optimizes traffic flow is by synchronizing certain signals concentrated along the same route.

“Almost everywhere in town where you have a group together they’re synchronized,” Harris said.

By that he means that the timing plans of these lights are interconnected. Ideally, the way it works is that if you are at one end of a synchronized group of lights and a light turns green you should be able to make it through the succeeding lights on green lights as well.

The city uses a program to come up with this synchronized timing.

“You tell it how many signals there are, what the measured distance between the two signals is,” Harris said. “It will generate for you what it considers to be the ideal timing plan.”

Harris said this level of coordination between traffic lights close together on the same road is absolutely necessary.

“If you just let them do their own thing it would be a complete disaster,” he said.

Yates agreed.

“Traffic would be backed up to the state line,” he said.

One of the pillars of the city’s traffic control operations is its detection system. The detection system consists of the sensors placed at signalized intersections. These sensors relay the message to the computer controlling the lights that a car is present.

“In order for a signal to work efficiently you have detection, which is just what it says, it detects a vehicle in that lane,” Harris said.

This is essential because in many cases lights will change faster if a car is waiting at an intersection.

“In areas…where the traffic can vary, the detection is very important,” Harris said. “If it’s not maintained and you have problems with it it’s gonna result in more delay and driver frustration. There’s nothing more frustrating than to be stopped [at a traffic light] and there’s nothing on the other side.”

Although some people think that sensors help control the lights by sensing the weight of an approaching car, that is actually not true.

The city has two main methods of detection that work in different ways: loops and video cameras.

Loops are just what they sound like, wire loops implanted underneath pavement. Loops use electromagnetic waves to sense when a car has reached an intersection.

Loops have the advantage of being cheaper to purchase than cameras, but they are also prone to problems. Freeze and thaw cycles can mess them up as can roadwork.

“If you’ve ever gone to a signal, and it stops you, and it sits there and no one else is around, a lot of times the loop has gone bad,” Harris said.

The city has been transitioning to video camera sensors as its preferred method of detection. Yates can watch these cameras’ feeds from his desk. A green rectangle flashes up on his screen whenever a car comes near a camera sensor.

The information these detectors provide can be valuable in determining cycle lengths, the amount of time it takes for a traffic light to go through all of its signals (the longest cycle length in Brentwood is at the Maryland Way and Franklin Road intersection: two-and-a-half minutes). That is because Yates can see if, for instance, a light stays green for 20 seconds but there are only cars moving through it for 10 seconds. If he sees that happening again and again at the same intersection, he can shorten the length of that green light.

“That’s what it’s all about, keeping the timing appropriate for the level of traffic that you have,” Harris said.

At some times, if the sensors are working properly, lights should not stray from green at all.

“If you’re driving down Franklin Road at 2 in the morning, unless someone pulls up on a side street it should not change,” Harris said.

Brentwood’s centralized traffic operations make adjustments to signal timings much easier.

“We’re kinda blessed here,” Harris said. “Every signal has a computer that runs all the lights.”

Those individual computers communicate back to a central computer, meaning that Yates can make changes to things like timing plans either from the Traffic Operations Center or even using his smartphone.

“If he’s got internet access he can do it from his boat while he’s fishing on a lake,” Harris said.

Other cities that lack this centralized system are forced to send workers individually to traffic lights. There they can open the cabinet that holds the signal computer and manually key in changes.

Despite the significant amount of effort that people like Yates put in to make driving around Brentwood as pleasant as possible, there is only so much the city can do. Brentwood has grown a lot in recent years, and there is going to continue to be unwanted traffic.

Still, Harris shared some thoughts on ways that drivers could cut back on roadway frustration, and they all have to do with gaining a better understanding of how traffic signals work.

“There are things the everyday driver can do to make the system work better,” Harris said.

The first has to do with the detection systems discussed earlier. These systems are designed to sense cars that stop just behind the white lines at the edge of intersections. These lines are called stop bars.

“People will say, this light never changes, and I ask, Did you stop at the stop bar, and they’ll say, What’s that?” Harris said.

If people go too far over the stop bar, “it will not know you’re there,” Harris said.

Another suggestion pertains to situations where distracted drivers might not notice a light has turned green. The car in front of them goes through the intersection, but they lag behind.

“If someone is distracted for whatever reason and doesn’t move on through the intersection it can cause the light to turn red prematurely,” Harris said.

People in the field of traffic control call this “gapping out.”

This happens when a gap in traffic is left “long enough so the system thinks all cars are gone,” Harris said.

On a related note, Harris had an interesting statistic on the traffic delays that can follow from just one distracted person not reacting promptly to a green light.

“For every second someone delays responding to a green light, three cars could have gotten through,” he said.

For all the challenges that traffic presents, Yates is perfectly content trying to get a handle on the problem as best he can. He’s been with the city for 15 years and has done this kind of traffic work for 10 years.

“I eat, dream and live this because I love what I do,” he said. “You never know what you’re going to get into the next minute.”

You can check Brentwood’s live traffic cameras here. For more information on the city’s Traffic Operations Center visit its page on the city’s website.