Current generation adaptive cruise control systems do not prevent phantom traffic jams.
University researchers tested adaptive cruise control (ACC) systems on a rural roadway in Arizona.
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Road Test Shows Some Adaptive Cruise Control Systems Can Amplify Phantom Jams: Taking Driver-Assist Technology Past Comfort and into Traffic Relief


Adaptive cruise control (ACC) systems are now a near-standard feature on newer model cars. ACC systems automatically vary the speed of the vehicle to maintain a safe following distance from the car in front. However, ACC systems are primarily designed to improve safety and their effect on congestion dynamics is not well understood.

To better understand how ACC systems effect congestion researchers "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[s] using adaptive cruise control." They then used these results to calibrate various mathematical models designed to measure the overall impact of ACC systems on congestion.

Lessons Learned

Open-road tests show that adaptive cruise control systems can amplify breaking behaviors, potentially causing "phantom jams."

  • After the initial car slowed down each car following it showed a "progressively more extreme braking response"
  • ACC system amplified initial disturbances by as much as six times
  • Manufacturers of these systems should consider traffic impacts when designing ACC systems along with safety.


See also: Gunter, George, et al, "Are Commercially Implemented Adaptive Cruise Control Systems String Stable?," ArXiv, May 2019.

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