Lane departure warning is a driver assistance system designed to help avoid collisions that are caused as a result of drifting out of lane. The system detects lane markers and alerts the driver, usually via a warning light on the wing mirror and/ or vibration of the steering wheel. Lane departure warning signals will generally not create an alert when the driver is indicating appropriately to change lanes.

Some more advanced vehicles benefit from lane keeping assist. If this system detects a potential lane departure with no response, the vehicle will be steered back into lane. In some vehicles, the steering wheel movement will become stronger the closer your vehicle gets to the lane markers. Similarly, there is usually no alert when the driver is indicating appropriately to change lanes. 

Some lane departure systems are activated automatically when a vehicle is switched on, whilst others have to be activated by manually pressing a button within the vehicle. 

If turned on automatically, in some vehicles, the lane departure warning can be switched off, but will likely default back on again each time the vehicle is started.