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Clayton County Traffic Signal Timing and Optimization

As a vital tool used to safely and efficiently manage vehicle, pedestrian and bicycle traffic, traffic signals are a fundamental part of nearly everyone’s lives, and must be regularly monitored and adjusted to serve ever-changing traffic patterns. In the United States alone there are approximately 300,000 traffic signals, and more than 75 percent could be improved either by updating equipment or adjusting the all-important timing.

Improved traffic signal timing and coordination offers one of the most cost-effective and expeditious ways to reduce congestion, improve traffic flow and make our streets safer. Recognizing this, the Clayton County Transportation and Development Department (T&D) selected GS&P to provide professional engineering services to develop and implement improved traffic signal timing plans for 182 intersections throughout the county.



"Clayton County was already in the midst of another project to upgrade its communications,” explains Marion Waters, GS&P senior vice president for ITS/traffic engineering and principal-in-charge on the project. “They are very progressive and understood they had the perfect opportunity to go back and retime their traffic signals, and take advantage of improved software and hardware with communications improvements already taking place.

“Their goal was to make significant traffic operations improvements throughout the county without incurring the costs that are typically associated with major capital improvement projects. So when the opportunity arose for them to apply for grant funds through the U.S. Department of Energy (DOE), they pursued the grant vigorously.”

The T&D was ultimately awarded Energy Efficiency and Conservation Block Grant Program funds by the Department of Energy to develop traffic signal timing plans that respond optimally to current traffic patterns and volumes from motor vehicles, bicycles and pedestrians. Principal goals for the project included minimizing stops, delays, fuel consumption and air pollution emissions, in addition to maximizing progression along major arterials.

Where Art Meets Science

As a principal component of the extensive project, 77 intersections—part of nine interconnected, coordinated signal systems—would be retimed. Three additional isolated intersections on SR 314 (Fayetteville Road) would also be coordinated by procuring and installing wireless communications equipment, and synchronizing the new timing plans at each intersection.

“I think the important thing to understand is that a lot of people travel down roads that have traffic signals, and it’s very frustrating to motorists when they get unduly delayed by signals that don’t appear to be operating for the traffic that’s there,” says Carla Holmes, GS&P senior transportation engineer. “When you’re idling in traffic it not only causes congestion, but it also wastes fuel and hurts the environment, and that’s where the energy conservation piece comes in. This project’s primary focus was getting all the county’s traffic signals in its major corridors timed efficiently. That essentially means you’re able to progress along a corridor without having to stop at every traffic signal, and that you’re riding what traffic engineers sometimes refer to as a ‘green wave.’

“Sometimes traffic signal timing is done every three or four years, and in that space of time you could have new development or greater traffic volumes, so it’s not really keeping up with current traffic conditions. This project involved going out there and evaluating all of the existing conditions and then timing the signals to better address those conditions.”

Recognizing that traffic signal timing can be just as much an art as it is a science, the GS&P team supplemented the science of traffic flow theory with creative problem-solving and sound engineering judgment in order to develop new timing plans that would meet the needs of the county.

Timing plans developed for each intersection within the nine interconnected signal systems (totaling 20 miles of roadway) included morning peak, midday peak, evening peak and weekend peak periods. Holiday timing plans were also developed for two of the systems—SR 54 (Jonesboro Road) and Mount Zion Road/Mount Zion Boulevard—which are heavily impacted by variations in holiday traffic.

“Just as no two people look exactly alike—even identical twins—every intersection is unique,” explains Waters. “Even intersections that are built to the same standard may have some physical differences when they’re actually put on the ground. We have a software program that can theoretically tell us what the best timing plan is for a particular intersection based on data input, but the computer is never going to know the exact radius at the intersection, or the precise length of the left-turn lane—and that’s where the art comes in rather than the science. A software program can give you the science of the solution. But having an engineer on-site, studying the way the motorist is interacting with pedestrians and is turning to the left and turning to the right, affecting the timing that’s needed at the signal—that’s the art.”

“And it’s a balancing act, too,” adds Holmes. “It’s critical that you balance the mainline progression you’re timing without causing a lot of delay on the side streets. You’re looking at giving people as much green time as possible, but that means you’ve got red time on the opposing street, so you have to look at the overall picture as well as the individual motorists.”

Documentation and Training

Throughout the comprehensive project, a series of reports was produced to fully document the timing plan development process. These reports became a valuable tool for the T&D, helping detail the existing conditions of its operations infrastructure and identify any operational deficiencies. In addition to offering vital before and after statistics, the reports also provided Clayton County administrators with justification for the project, as well as future signal timing investments.

“Because this was a block grant, Clayton County administrators had to provide a lot of documentation to the Department of Energy to prove this project was money well spent,” says Holmes. “The reports we generated were key because they showed measurable progress and the goals that were being achieved.”

Before and after studies documented in these reports determined that the annual savings to motorists from retiming all of the intersections in each of the nine systems resulted in more than $5 million in cost savings for the public, thanks to reduced stops, delays and fuel consumption.

Not subject to pre- and post-project studies, an additional 102 isolated intersections throughout the county were also retimed. The improved timing of these isolated intersections also greatly enhanced traffic operations at these locations.

Another important element of the project was the training of staff. The GS&P team developed a one-day training workshop to teach T&D personnel how to perform traffic signal timing tasks efficiently and how to maintain equipment as the need arises. The agenda of the program covered topics that would benefit newer staff members, as well as provide refresher training and more advanced instruction to experienced engineers and traffic signal technicians.

“After we completed the project, the county wanted to be able to maintain the timing without always having to ask consultants to do it for them,” explains Holmes. “They provided us with the topics they wanted to learn about, which included maintenance, diagnostics and the timing of the controller equipment.”

Sending the Right Signals

At the outset of the project, GS&P had initially proposed to use BlueTOAD (Bluetooth Travel-time Origination and Destination) travel time monitoring system devices on a demonstration basis at two locations. Once additional grant funds were made available to the county, the T&D decided to expand the use of BlueTOAD by procuring 25 permanent devices and installing them at key locations. Using cost-effective and non-intrusive technology, the BlueTOAD system would be used to accurately monitor travel times by detecting anonymous Bluetooth signals broadcast from mobile/vehicle devices, such as smartphones, headsets and music players.

“There are four different systems like this in the nation, but the one that’s the most widely used in this region is BlueTOAD,” explains Waters. “When a set of units is deployed along a roadway, the BlueTOADs are able to match a vehicle’s Bluetooth MAC address—either from the vehicle itself or Bluetooth-enabled devices within—from point-to-point and determine the exact travel time it took that driver to get from point A to B. And by having the distance and time between those two points, you can calculate the speed.”

“The procurement of this equipment enables the county to monitor and respond to changing traffic conditions more efficiently,” adds Holmes. “It provides near real-time, accurate information to the County. That information is also available on a website so they can see what the traffic conditions are like on a particular corridor and then make adjustments to the timing if needed.”

Also as part of the BlueTOAD installation, GS&P purchased a three-year operations package and had a T1 line installed in the Clayton County Traffic Control Center to provide communications for the system. The GS&P team worked closely to coordinate all procurements and to make sure they met stringent DOE “Buy America” requirements.

“All of the equipment that we purchased for the project had to be American-made,” says Holmes. “The DOE was very strict about that requirement, and we were able to put together some extremely effective systems that satisfied those constraints. And of course it all goes back into the economy.”

The Perception of Timing

Whether they’re mounted on mast arms, sitting on a pole or suspended by a wire, traffic signals exist for one principal reason—to keep people safe. And if that safety can be augmented by a more streamlined and cost-effective system, then motorists, pedestrians and cyclists get the best of both worlds. But if that delicate synthesis of safety and efficiency appears out of sync, end users will ultimately look to their transportation officials for answers.

“Signal timing is one of the most customer-sensitive areas that departments of transportation face,” says Holmes. “People might not see or understand the inner workings of the equipment, but they’ll know how long it takes to stop at a signal. And that’s where the motorists are getting their perception of how well their DOT is operating.”

“If it’s right, most people don’t notice it. But if it’s not, the DOTs will get more complaints about that than just about anything else,” adds Waters. “You’ll remember every signal that you stopped at, but you won’t remember the ones that you just cruised on through.

“With this signal timing project, we were not only trying to enhance the safety of the community, but we were also trying to help the economy of the community. If a person is spending $50 a week on gas, they’re extremely conscious of when they have to wait on two traffic signals. So, one of our goals was that even at the traffic signal with the longest delay, a motorist won’t have to wait more than one full cycle to get through it.

“Our professional ethics and responsibility call for us to do that type of job, and when we quit doing that it’s time for us to quit being engineers. I think this project fulfills that message because we were constantly asking ourselves, ‘How can we make the county just a little better? How can we make a person’s commute just a little better?’ And if we’ve made just a tiny bit of difference in people’s lives, then we’ve really done our job.”


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Project Info

  • Client: Clayton County Department of Transportation and Development
  • Location: Clayton County, GA, USA
  • Market: Transportation
  • Services: Engineering, Planning
  • Team:
    • Marion Waters, P.E., PTOE Principal-in-Charge
    • Carla Holmes, P.E., PTOE Project Manager
    • Jay Bockisch, P.E., PTOE Project Professional
    • France Campbell, P.E., PTOE
    • Nithin Gomez, P.E.
    • Josh Williams, P.E., PTOE
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