As millions of people travel the freeways this Thanksgiving, many will encounter areas of stationary traffic for no apparent reason — no construction or accidents. Researchers say the problem is you.
Human drivers just don’t do a good job of navigating heavy traffic, but an experiment using artificial intelligence in Nashville last week means help could be on the way. In the experiment, specially equipped cars were able to reduce rush-hour congestion on Interstate-24, researcher Daniel Work said Tuesday. As well as reducing driver frustration, Work said fewer stops and starts means fuel savings and, by extension, less pollution.
The Vanderbilt University civil and environmental engineering professor is one of a group of engineers and mathematicians from American universities who studied the problem of phantom traffic jams after a simple experiment in Japan a dozen years ago. ‘years showed how they develop. The researchers placed about 20 human drivers on a circular track and asked them to drive at a constant speed. In no time, the traffic went from a smooth flow to a series of stops and starts.
“Ghost traffic is created by drivers like you and me,” Work explained.
A person presses the brakes for some reason. The person behind them takes a second to respond and has to brake even harder. The next person has to brake even harder. The wave of braking continues until many cars come to a standstill. Then, as traffic clears, drivers accelerate too fast, causing more braking and yet another traffic jam.
“We know that a car suddenly braking can have a huge impact,” Work said.
Last week’s experience showed that a few slow and steady cars could also have an impact, for the better.
The experiment used 100 cars that traveled in a loop on a 15-mile section of I-24 from about 6 a.m. to 9:45 a.m. each morning. Assuming that if 5% of the cars on the road acted together they could reduce the prevalence of phantom traffic, the researchers equipped these 100 cars to communicate wirelessly, sending traffic information back and forth.
They also took advantage of adaptive cruise control which is already an option on many new vehicles. This technology allows the driver to set a car to travel at a certain speed, but the car automatically slows down and speeds up as needed to maintain a safe distance from the car in front. In the experiment, adaptive cruise control was tweaked to react to overall traffic flow — including what was happening far ahead — using artificial intelligence.
Decision-making for the cars happened at two levels, Work said. At the cloud level, information about traffic conditions was used to create an overall speed plan. This plan was then broadcast to the cars, which used artificial intelligence algorithms to determine the best action to take. Researchers were able to assess the effect of connected cars on morning traffic flow using a special 4-mile stretch of I-24 equipped with 300 pole-mounted sensors.
The experiment is a project of the CIRCLES consortium, a group that includes several automakers and the US Departments of Energy and Transportation. Other principal investigators are based at the University of California, Berkeley; Temple University; and Rutgers-Camden University.
Liam Pedersen is assistant general manager for research at Nissan, a CIRCLES consortium partner who was in Nashville last week for the experiment. He said one of the exciting things about it is that it builds on technology already found in many new cars.
“It’s not self-driving,” he said. “That’s something we could achieve very soon.”
Asked if automakers would be willing to cooperate to ease traffic, Pedersen said: “I certainly hope so, because the system works best when many cars participate.”
Last week’s experiment built on work and colleagues conducted in 2017 at the University of Arizona. This repeated the Japanese experience, this time with a single self-driving car thrown into the mix. The autonomous car made it possible to streamline traffic so that there were 98% fewer brakes. This resulted in a 40% increase in fuel efficiency and a 14% increase in distance traveled.
Researchers are still crunching the numbers from last week’s experiment, but Work said it “demonstrated that these traffic jams can be reduced with the new automated vehicle technologies we’ve developed. There’s no denying that improved automotive technology can significantly reduce phantom traffic jams when implemented on a large scale.”
Still, he cautioned that technology isn’t going to suddenly eliminate congestion.
“When there are more cars on the road than the road can handle, there will always be traffic,” he said. “But it can make that congestion less painful.”
Photo: Vanderbilt University researchers monitor live interstate traffic images and data screens Nov. 17, 2022, in Nashville. They say they have successfully used artificial intelligence in a cluster of wirelessly connected cars to help reduce rush-hour traffic on a freeway in Nashville. The aim is to reduce phantom traffic – start-and-stop congestion on congested roads that has no obvious cause. (AP Photo/Mark Humphrey)
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