An open-road test of adaptive cruise control showed that the feature, which is designed to make driving easier by continuously adjusting a vehicle's speed in response to the car ahead, does not solve the problem of so-called "phantom" traffic jams.

Human drivers are responsible for creating this type of jam, which occurs without an obvious cause. The widespread use of driver-assist technologies could help eliminate these jams.

Researchers at Vanderbilt University and Temple University said that their experiments showed that existing driver-assist systems are not yet able to overcome the worst driving behaviors of humans.

Details were presented at Cyber-Physical Systems and Internet-of-Things Week and were released in early May.

In each test, the following vehicle slowed down more than the leader, a signature of phantom traffic jam creation.The research builds on earlier work that showed that adding even a fraction of specially designed autonomous vehicles could eliminate phantom jams by keeping an optimal separation between cars and avoiding sudden stops.

Driver-assist systems such as adaptive cruise control potentially react faster 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 can anticipate changes by looking multiple vehicles ahead.

The researchers tested seven different cars from two manufacturers on a remote, rural roadway in Arizona. They simulated a range of 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, a signature of phantom traffic jam creation, the researchers said.

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 domino effect, each of the following vehicles slowed down more and more dramatically so that, by the seventh car, its speed dropped below the minimum required for the ACC system to operate.

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