Lane support systems can assist and warn drivers when they unintentionally leave the road lane or change lane without indication.
Several manufacturers have developed technologies which warn the driver when their car is getting close to the lane marking. Different systems use different warnings: some give an audible signal, while others use a vibrating steering wheel to simulate the feeling of the car running over a 'rumble strip'. The intention is simply to make the driver aware that the car is in danger of crossing the line. Some systems need a line only on one side of the car, while other systems rely on having a distinct marking on both sides.
Lane departure warning systems rely on distinct lane markings: their effectiveness is reduced if lines cannot be clearly distinguished such as in heavy rain or fog, or if the road markings are obscured by mud or snow. In such cases, an indication is given to the driver that the system is unable to assist.
Lane Keep Assist systems address similar crash situations to the lane departure warning. However, whereas warning systems rely on the driver to take corrective action, lane keep assist proactively steers the car back into the lane. When the car is close to a marking, the system gently steers the car away from the line until it is safely within the lane. The system can steer the car either by applying gentle braking to one wheel, or in the case of electric steering systems, by applying a direct steering input.