Adaptive cruise control (ACC) is a driver assistance technology that sets a maximum speed for vehicles and automatically slows the speed of the car when traffic is sensed in front of the vehicle. The technology is also known as autonomous cruise control.
Standard cruise control allows the driver set a steady speed and take a foot off the throttle, but requires driver intervention to turn off cruise control when that set speed is no longer possible. Adaptive cruise control allows for smart, reactive management of a vehicle's speed without driver intervention. ACC automates responses in situations that would have otherwise required action on the part of the driver. Without required driver intervention, the technology can reduce driver discomfort and fatigue more than standard cruise control while safely maintaining distance from vehicles ahead on the road.
Most ACC systems are based off a radar module in the vehicle's front bumper, although some car manufacturers like Subaru use a paired laser and camera set up. These sensing technologies measure the speed of traffic in front of the vehicle relative to the controlled vehicle. A driver sets a maximum speed with + and - and the distance, within reason, to follow. When a driver presses set the system actively locks onto the vehicle in front. ACC then maintains the set parameters by reducing speed or applying 50% of the maximum braking force. In situations approaching the limits of ACC, chimes sound and brake or brake now warning lights come on.
Although ACC is a key component in autonomous driving systems, it does not necessarily indicate autonomous driving capabilities. Some systems in the low end (starting around $500) are only operable at speeds exceeding 25Mph. More advanced setups can handle full stop-and-go traffic. It is important to note that the sensor range and speed that most adaptive cruise control systems use are not adequate for collision protection from vehicles that are not traveling in the same direction. This means that side or head-on collisions are not reduced by these systems but only by more advanced driver assistance in the semi-autonomous to fully autonomous range.