Lane Departure Warning Systems

To reduce crashes caused by unintentional lane departures, lane departure warning systems (LDWS) monitor the position of a vehicle within a roadway lane and warn a driver if the vehicle deviates or is about to deviate outside the lane. LDWS are forward-looking, vision-based systems that use algorithms to interpret video images to estimate the vehicle’s lateral position, lateral velocity, heading, and roadway alignment. These LDWS use a forward-facing camera that is mounted to the windshield in the cab of the vehicle. The systems also include an electronic control unit and a warning indicator.

Some LDWS may issue directional warnings to alert the driver to which side of the lane the vehicle is drifting. A directional warning may be audible, such as rumble strip sounds in left or right in-cab speakers, or tactile. LDWS may graphically indicate on a user interface display how well the vehicle is centered in the lane on a time-averaged basis.

LDWS warn the driver of a lane departure when the vehicle is traveling above a certain speed threshold and the vehicle's turn signal is not in use. However, LDWS do not take any automatic action to avoid a lane departure or to control the vehicle. Therefore, the driver remains responsible for the safe operation of the vehicle.

Although traditional LDWS do not take any automatic action to avoid a lane departure or to control the vehicle, some emerging systems actually incorporate the use of a steering shaft actuator. If the driver does not react appropriately to a lane departure warning, the system automatically applies torque to the steering wheel and steers the vehicle back within the lane boundaries. These are known as Lane keeping systems. Some new models incorporate this feature, but it has yet to attain widespread adoption.

LDWS are valuable in situations where road visibility is limited and in conditions such as rain, fog, and falling snow when lane markings are present. In some cases, however, LDWS will not be able to recognize lane markings for reasons such as lack of or poor quality of lane markings, poor visibility, or a dirty/icy windshield. When lane markings are not visible on roads covered by mud, ice, or snow, the lane tracking indicator will show that the system is inactive.

The European Commission funded project eIMPACT studied the benefits of the combining Lane Departure Warning (LDW) together with the Lane Change Assist (LCA), which is an extended functionality of Blind Spot Monitoring. It has been found that if all vehicles in Europe were fitted with LDW and LCA, 5,500 deaths, would be avoided per year.[1]

LDWS may be installed both directly by the fleets as an aftermarket accessory or by truck Original Equipment Manufacturers (OEMs) when the vehicles are manufactured. The costs of LDWS vary greatly depending on the number of units wanted. The list price of a single unit is normally in the $1,000 to $2,000 range, but this price steadily decreases with additional units.

[1]European Comission, Vehicle Safeyt systems,, (January 20, 2021)