Adaptive cruise control (ACC)

Adaptive cruise control (ACC) is an advanced driver-assistance system that automatically adjusts the vehicle’s speed. Similarly to regular cruise control, the driver can choose their desired speed which the system then maintains. But with ACC, the car also keeps a safe distance from the cars ahead, breaking and speeding up when necessary.

For example, when a car ahead drives below the speed limit, the following car with ACC matches its speed to keep a safe distance. When the driver decides to pass this car and changes the lane, the car automatically speeds back up to the driver’s selected speed. The same is true when a car ahead breaks for any reason such as to turn or match a new speed limit.

The technologies used in ACC are nothing very new. The first ACCs offered by Mitsubishi in the 1990s used lidar or a laser to measure the distance with the car ahead. Today the most common sensor used is radar. Some ACCs use small cameras, usually on the rearview mirrors. Some combine different sensors, mostly using cameras and GPS data.

ACCs can also have additional features. Many allow the driver to select the distance they want to maintain with the car ahead. Some have a so-called stop and go function that makes it possible to automatically stop and then continue moving in a traffic jam. Predictive systems can change the car speed based on the predicted behaviour of other cars around it. Some ACCs automatically adjust the set speed to the speed limit. When the limit changes the speed adapts to it. Some systems also read the road and automatically brake or speed up in curves and at highway exits, junctions and roundabouts.

The main benefit of adaptive cruise control is improved safety. Keeping a safe distance with the car ahead, the ACC lowers the possibility of an accident resulting from obstructed view or close following distance. It also helps the driver focus on the road since they do not have to worry about their speed.

Even though ACC is a step towards self-driving cars, it does have limitations. A car with ACC is considered only a level 1 autonomous vehicle. The ACC only affects speed – turning the wheel is still the job of the driver. Also, extreme weather conditions such as heavy snow, rain or fog can confuse the system. When ACC is combined with lane centring, the car is considered a level 2 autonomous vehicle. But even in that case, the driver still needs to hold their hands on the wheel and keep their focus on the road.