What system actively steers a car to stay within lane markings?

The system that actively steers a car to stay within lane markings is lane keeping assist.

Lane keeping assist uses a forward-facing camera, usually mounted near the windshield, to detect painted lane boundaries. If the vehicle begins drifting without a turn signal, it can apply corrective steering. Some systems also use selective braking or other vehicle-control inputs.

It is commonly confused with lane departure warning. That system primarily alerts the driver through sounds, vibrations, or dashboard messages; it does not necessarily steer the car. Lane-centering assistance is related but generally provides more continuous steering to keep the vehicle near the middle of the lane.

The technology became widespread as part of modern driver-assistance packages, but it remains an assist rather than an autonomous-driving system. Faded markings, snow, construction zones, sharp curves, or blocked cameras can prevent it from working reliably, so the driver must continue monitoring the road.