Road test proves adaptive cruise control can add to traffic jam problem

traffic jam
Credit: CC0 Public Domain

A new, open-road test of adaptive cruise control demonstrated that the feature, designed to make driving easier by continuously adjusting a vehicle's speed in response to the car ahead, doesn't yet solve the problem of phantom traffic jams.

Because human drivers are responsible for the creation of this type of jam—which occurs without an obvious cause—the widespread use of these types of driver-assist technologies holds promise to eliminate these jams, if designed appropriately.

"Our experiments show that today's driver-assist systems are not yet able to overcome the worst driving behaviors of humans that lead to extremely frustrating traffic jams," said Dan Work, associate professor of civil and environmental engineering at Vanderbilt University, who helped lead the research.

The details of the multi-university team's latest experiments on ACC vehicles are available on the arXiv preprint server in a paper titled "Are commercially implemented adaptive cruise control systems string stable?"

Their work builds on earlier research that showed adding even a small fraction of specially designed could eliminate phantom jams by keeping an optimal separation between cars and avoiding sudden stops.

As vehicles with driver-assist systems such as adaptive cruise control become more prevalent, it is critical to understand how they influence traffic, said Work. While they potentially react faster and more gracefully to vehicles ahead than humans can, their sensors are not able to see beyond the vehicle immediately in front. That limits their ability to outperform human drivers, who anticipate changes by looking multiple vehicles ahead.

Work and his collaborators tested seven different cars from two manufacturers on a remote, rural roadway in Arizona. They simulated various driving conditions with a pace car changing its speed, followed by a vehicle using adaptive cruise control. The team measured how quickly and aggressively the ACC system responded to the pace car speed changes.

They drove the cars at varying speeds over more than 1,000 miles of testing, with the results always the same.

"In each test, the following vehicle slowed down more than the leader, which is a signature of the creation of phantom ," said Benjamin Seibold, associate professor of mathematics at Temple University and another lead researcher.

In one experiment, the team filled a lane of traffic with seven identical vehicles—all running the same ACC system—with a pace vehicle in front. Once all vehicles achieved a cruising speed of 50 miles per hour, the pace vehicle quickly reduced its speed by 6 miles per hour. In a , each of the following vehicles slowed down more and more dramatically so that, by the seventh car, its dropped below the minimum required for the ACC system to operate.

Team members said they hope manufacturers ultimately will design vehicle automation systems that make traffic a concern in addition to safety, comfort and fuel efficiency. Sixteen of the 20 best-selling vehicles in America already offer ACC, which demonstrates their potential for impacting traffic decades before vehicles become fully autonomous.

They said the next step is to design and demonstrate effective driver-assist features in real freeway , paving the way for the next generation of automation technologies.

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More information: Are commercially implemented adaptive cruise control systems string stable? arXiv:1905.02108 [cs.SY]
Citation: Road test proves adaptive cruise control can add to traffic jam problem (2019, May 8) retrieved 23 September 2019 from
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User comments

May 08, 2019
Adaptive cruise controls are a horrible creation. In heavy traffic, adaptive cruise controls will continually slow traffic until they cease to operate.

Unfortunately, adaptive cruise controls cannot be disabled without disabling cruise control entirely.

May 08, 2019
adding even a small fraction of specially designed autonomous vehicles could eliminate phantom jams by keeping an optimal separation between cars and avoiding sudden stops.

The reason why it doesn't work is because phantom traffic jams arise out of the average tendency of drivers to act like a compressible fluid. Adding a small number of drivers that maintain an "optimum" separation is simply changing the properties of that fluid - like adding water to treacle or vice versa. It flows differently, but it still flows according to the same rules of fluid dynamics and there will be regions of flow where the exact same type of swirls and standing waves appear - it's just going to be at a different location along the road.

You can break up a standing wave by changing the behavior of some small number of drivers going through it, but then those drivers will cause a different phantom jam somewhere else and you'd have to predict that in order to change their behavior again.

May 08, 2019
I've wondered how large trucks affect the system as their drivers try to maintain a longer cushion in stop and go traffic taking up slack to maintain speed as much a possible to minimize endless gear shifting. For those behind them it minimizes breaking and downshifting as well. Of course cars will simply dart in front of trucks during lane changes causing them to constantly slow down more to maintain that cushion. Game theory among different types of drivers probably ripples out endlessly. Only after all vehicles are automated and can communicate seamlessly and follow a strict protocol that doesn't involve gaming the system will we see any improvements in traffic flows. That level of centralized control will never happen in freedom lovin' 'merica which why China will eat our breakfast, lunch, and dinner eventually.

May 08, 2019
When you leave a large distance between your car and the car ahead of you in heavy traffic, that space is quickly filled from adjecent lanes. If you recreate the space, another car will fill the space. Adaptive cruise control continually slows you in heavy traffic.

May 08, 2019
Sounds like this article should be called, "How one dumb driver can screw up a good thing". Seriously though, any level of autonomy needs to err on the side of caution, and protect itself against erratic unpredictable drivers. Until such time as the human element is removed from the road, efficiencies will never be fully realized. I can tell them with no research money needed, lawyers will dictate the reactions of all autonomous systems, and all you need is one human driver to screw up any promising autonomous technology on the road.

May 08, 2019
The cause of traffic jams is no real mystery!! For 10 of years I commuted 25 miles on a road that was posted 55MPH. During rush hour the average speed was about 70-75 MPH and there was never a jam. The road had a high volume of traffic during those hours but everything flowed nicely.

But when they stationed a cop with a radar gun 12 miles down the road and cars slowed down to 55 MPH for 1/4 mile or so this created bumper to bumper stop and go traffic that started right at the beginning of the road. The reality of the situation was that due to the amount of cars entering the highway they had to travel at 70 for the entire distance or traffic would back up just as sand does in an hour glass.

May 09, 2019
Using the hourglass analogy, when roads are at capacity conditions any slowdown will be reflected backwards as stop and go conditions. I remember one day on the New Jersey Turnpike when they had just turned on the road hazard warning signs. There was terrible stop and go before each sign and free traffic right after for a few miles. This happened at each sign as people slowed down to read them. The irony was that the signs were warning of slow traffic ahead.

May 14, 2019
With ACC one should also have RTTI alternative routing. Works for me!

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