Adaptive cruise control (ACC) is a safety feature available on newer vehicles. It is an advanced version of previous cruise control features that uses sensors to keep the vehicle at a preselected following distance from the vehicle ahead. This eliminates an annoyance from earlier versions of cruise control, where the driver would have to repeatedly reset the cruise control when the vehicle ahead slowed down. ACC also maintains the vehicle’s position within the lane of travel.
ACC was meant to turn cruise control into a “set it and forget it” feature. Maintaining following distance and lane position are newer features that have safety benefits.
Unfortunately, human nature is still an issue. According to a recent study by the Insurance Institute for Highway Safety (IIHS), drivers with ACC tend to set the feature at a speed higher than the limit.
“ACC does have some safety benefits, but it’s important to consider how drivers might cancel out these benefits by misusing the system,” says the study’s lead author. “Speed at impact is among the most important factors in whether or not a crash turns out to be fatal.”
It’s important to keep in mind that ACC is not a fully automated driving system. Drivers should never take their attention from the road when using this feature, as it is not capable of navigating certain road features or handling some driving scenarios.
In order to test whether ACC actually reduces crash risk or encourages speeding, the IIHS researchers analyzed data that had been collected by the Massachusetts Institute of Technology’s Advanced Vehicle Technology Consortium.
Forty drivers from the Boston area were provided with either a 2016 Land Rover Range Rover Evoque or a 2017 Volvo S90, both of which had ACC or Volvo’s Pilot Assist, which combines the features of ACC with a lane-centering feature.
The study determined that the drivers were 24% more likely to speed when using ACC or Pilot Assist. They also sped more when using the system than when it was turned off.
Drivers tended to exceed the speed limit by the largest margin when the speed limit was 55 mph. The speeders averaged about 8 mph over the limit in a 55 mph zone, versus 5 mph over the limit in a 65 mph zone.
Ultimately, drivers in a 55 mph zone were likely to travel at 1 mph faster when using ACC than when it was turned off. That doesn’t sound like a very big difference, but a common formula used to predict probable crashes estimates that this 1 mph difference increases the risk of a fatal crash by 10%.