Ford and Vanderbilt University show that ACC can mitigate ‘phantom’ traffic jams


Researchers from Ford and Vanderbilt University have conducted one of the largest demonstrations of its kind showing that widespread use of adaptive cruise control (ACC) could help minimize the problem of ‘phantom’ traffic jams.

The team from Ford and Vanderbilt have conducted what is believed to be the largest, most realistic demonstration of its kind, showing that existing technology could help minimize phantom traffic jams, which happen for seemingly no reason and can cause hazardous traffic backups.

Human factors, such as merging into traffic without signaling, distracted driving, poor driving habits and reaction times, or unnecessary braking, are the main causes of phantom jams. Once one driver hits the brakes, a chain reaction can occur as other drivers tap their brakes, causing the flow of traffic to halt.

On a closed Ford test track, 36 drivers simulated normal highway traffic using ACC, which can automatically slow down and speed up to keep pace with the car in front without getting fatigued or distracted. Those drivers then drove the same course, but without the technology, meaning they had to manually brake and accelerate the vehicle.

Three lanes of 12 vehicles each were tested on a closed high-speed oval simulating a highway. The lead vehicles in each lane slowed from 60mph to 40mph (96-64km/h) to mimic a traffic disturbance.

Without the ACC technology, the drivers each braked harder than the vehicle ahead, which led to a braking wave that became more pronounced further down the traffic stream. The non-ACC drivers amplified the initial braking event, in some cases to the point where traffic slowed to a crawl.

The demonstration was repeated with all vehicles using adaptive cruise control set at 62mph (100km/h), just slightly higher than the lead vehicles to ensure the vehicles remained in a constant platoon. In these demonstrations, the ACC systems outperformed the human drivers in almost every braking situation. In one run, the ACC actually suppressed the braking wave so the last car in the lane only slowed by 5mph (8km/h) instead of coming to a standstill. The team also reduced the number of ACC active vehicles to 33%. This is the low threshold researchers have long believed could help suppress phantom traffic backups. The results were similar to the full ACC demonstrations.

“For years, traffic researchers and engineers have been looking to smart vehicle technologies to reduce traffic congestion, whether that’s vehicles that talk to each other or vehicles that can predict the road ahead,” said Daniel Work, civil engineering professor at Vanderbilt University.

“This demonstration was a unique opportunity to understand how commercially-available active driver-assist technologies can be used to positively influence traffic flow. Unlike the traffic jams caused by accidents or road construction, phantom traffic jams appear out of nowhere.

“The fact that we saw a commercially-viable ACC system fully suppress the traffic backup is quite impressive. And while we know this won’t happen in every situation or in every circumstance, it’s very promising to see that commercially available ACC systems can already have a desired effect in normal, everyday driving scenarios.”

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Tom has edited Traffic Technology International (TTi) magazine and its Traffic Technology Today website since May 2014. During his time at the title, he has interviewed some of the top transportation chiefs at public agencies around the world as well as CEOs of leading multinationals and ground-breaking start-ups. Tom's earlier career saw him working on some the UK's leading consumer magazine titles. He has a law degree from the London School of Economics (LSE).