📖 The Quick Answer
You set a speed and a following gap (usually 1 to 4 bars). The car maintains that speed when the lane is clear and automatically slows when it detects a slower vehicle ahead. Once the lane clears, it accelerates back to your set speed. Full-speed-range ACC will even come to a complete stop in traffic and resume.
⚙ How It Works (Sensors and Algorithm)
A 77 GHz long-range radar in the grille measures the distance and closing speed to the car directly ahead. A forward camera classifies what is in front and helps the radar pick the correct target through curves. The ADAS computer commands the throttle (or regen on EVs) and brakes to hold the chosen gap. On stop-and-go systems the car can fully stop, then either auto-resume within a few seconds or after a tap of the accelerator or RES button.
🛡 What It Protects Against
Rear-end collisions caused by inattention or fatigue, and reduces the workload of long highway drives. Combined with AEB, ACC has been shown to reduce rear-end injury crashes by more than 50 percent.
⚠ Limitations and When It Fails
ACC does not steer. It can react slowly to a sudden cut-in from another lane, and on some systems it does not see stopped vehicles at highway speed (this was the cause of several early-Tesla and early-Mobileye-based crashes). Heavy rain, snow on the radar cover, or a damaged front emblem (many radars sit behind the badge) can disable ACC. ACC also is not a self-driving system, you must remain attentive and ready to brake.
🚗 Which Vehicles Have It
Standard or optional on nearly every new 2020+ vehicle. Common names: Honda Sensing Adaptive Cruise Control with Low-Speed Follow, Toyota Dynamic Radar Cruise Control, Subaru EyeSight Adaptive Cruise, Ford Adaptive Cruise Control with Stop-and-Go, Hyundai Smart Cruise Control (SCC), Nissan Intelligent Cruise Control, Mazda Mazda Radar Cruise Control (MRCC), BMW Active Cruise Control, Mercedes Distronic, Tesla Traffic-Aware Cruise Control.
🔧 Related TSBs and Recalls
Toyota TSS 2.0 had a 2020 software update for false braking on overhead signs. Honda Sensing has TSBs for ACC dropping out on grooved concrete. Always check that the front radar bracket is straight after even a minor front-end repair.