📖 The Quick Answer
A camera behind the rearview mirror sees the painted lane lines. If the car starts to cross a line without a turn signal on, the electric power steering applies a small corrective torque to nudge the wheels back into the lane. Some systems vibrate the wheel or seat as well.
⚙ How It Works (Sensors and Algorithm)
The forward camera runs lane-line detection at about 30 frames per second. The ADAS computer estimates the car position within the lane and the rate of drift. If the car is about to touch or cross a line without turn signal, the electric power steering motor applies torque (usually 1 to 3 Nm) in the opposite direction. Many systems combine this with Lane Centering Assist, which continuously steers to stay in the middle of the lane rather than only reacting near the edge.
🛡 What It Protects Against
Drowsy-driver lane departures, distracted-driver drifts, single-vehicle run-off-road crashes, and head-on collisions caused by crossing the centerline. IIHS estimates LDW/LKA reduce single-vehicle, sideswipe, and head-on crashes of all severities by about 11 percent.
⚠ Limitations and When It Fails
Faded or missing lane lines, snow-covered roads, construction zones with conflicting paint, sharp curves, and night driving with poor contrast all disable or weaken LKA. The system will not work if the windshield is dirty in front of the camera or if it has been replaced without proper ADAS calibration. LKA also does not steer around obstacles or change lanes for you.
🚗 Which Vehicles Have It
Standard on most 2018+ vehicles. Common brand names: Honda Sensing Road Departure Mitigation, Toyota Lane Tracing Assist (LTA), Subaru EyeSight Lane Keep Assist, Ford Lane-Keeping System, Hyundai/Kia Lane Following Assist (LFA), Nissan Steering Assist, Mazda Lane-keep Assist System (LAS), Tesla Autosteer.
🔧 Related TSBs and Recalls
Several Toyota TSBs address LTA pulling toward one side after a windshield replacement and call for camera recalibration. Honda Sensing TSBs cover unexpected steering inputs on grooved pavement. If LKA fights you on a specific road, check for software updates.