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How exactly does Lane Keeping Assist work?



Driver assistance and safety systems help prevent accidents. At VisionZeroWorld we explain how ABS, ESP and other safety-related systems work. This time it’s the turn of Lane Keeping Assist.

A long and tiring day at work has come to an end: time to clamber into my car and head for home at last! I hardly even notice the quiet background music on the radio as I drive along the almost empty country roads. I’m starting to feel drowsy. The car gradually edges left, approaching the lane marking and threatening to stray onto the wrong side of the road. But then, as if by magic, it gets itself back on course and stays in lane – thanks to the lane keeping assistant. The first manufacturers started to install this these systems into their customers’ cars as an optional extra shortly after the turn of the millennium.

Driving is much safer with Lane Keeping Assist on board. Graphic: Continental


The Nissan Cima was the first car to feature Lane Keeping Assist (LKAS), a further development of the lane departure warning system (LDWS), as of 2001. With both of these technologies, integrated video cameras track the road markings and detect any change in the distance to either side of the vehicle. A camera, like the Multi-Function Mono Camera offered by Continental for example, is normally mounted behind the windshield of a car, from where it registers not only lane markings but road signs as well. It is usually concealed in a casing behind the rear-view mirror. If the vehicle threatens to veer out of lane, the lane departure warning system, also offered by Continental, alerts the driver by means of an acoustic or haptic alarm. Depending on the make of car, the steering wheel or the driver’s seat will vibrate, or an acoustic warning will sound, prompting the driver to get the vehicle back on course. According to a study carried out by the German Federal Ministry of Education and Research, these systems can prevent more than half of all accidents caused by straying out of lane.


The LKAS system goes a step further: Lane Keeping Assist can actively intervene to keep the car in lane. Depending on the distance to the curb or median strip, the system intervenes to a different extent – in most cases by electronically amplifying the steering force. Audi for example offers Active Lane Assist for its A6 mid-series sedan, which uses image processing software to evaluate the data from the on-board camera and then eases the car back on course with discreet steering interventions. If a lane marking is crossed, by way of additional warning the steering wheel starts to vibrate. The lane keeping assistants in the Ford Focus or the Lexus LS, for example, work in a similar way.


Lane keeping systems can normally be used at speeds of 60 to 180 km/h and must be activated by the driver. Internal algorithms determine whether the person behind the wheel is alert and attentive. If not, the systems first give the driver a warning and then switch themselves off; this ensures that the responsibility remains with the driver. Also, the camera-based systems only work when the windshield is clean and the road markings are clearly visible. For this reason, Mercedes combines its camera-based Steering Assist with a radar system that is activated when another vehicle is driving in front, which it then tracks. Citroën does without cameras, and since 2004 has used infrared sensors that detect road markings and trigger a warning signal for the driver.


Small camera, large gain in safety: the Multi-Function Mono Camera from Continental. Photo: Continental


Whether it be cameras, sensors or radar, all of these technologies can make our roads safer. After all, according to the German Federal Statistical Office, one third of accidents occurring outside built-up areas are the result of vehicles “veering off the road”. Lane Keeping Assist can help eliminate this type of accident – not least after a long, tiring day at work.