Car Advice

What is lane-departure warning and how does lane-keep assist work?

As drivers are becoming more distracted behind the wheel, our vehicles are becoming more active. So, what is lane-departure warning and how does lane-keep assist work?

According to collision statistics, each year around 30% of all accidents involving a motor vehicle occurred when it left the road. Inattention is also a growing cause of collisions with figures out of Europe suggesting one in four collisions are caused by fatigue. That’s where vehicle technology like lane-departure warning and lane-keeping assist is intended to help. But we need to separate the two systems as one is often confused for the other and vice versa.

What is lane-departure warning?

Lane-departure warning has been around since the early 1990s but it’s still not common fitment although it’s becoming more readily available, with entry models being offered with cost-optional safety packs that include things like lane-departure warning. This is less because of car makers and more because of NCAP organisations making it harder for new vehicles to achieve five-star collision ratings without a greater range of standard-fit active safety systems.

Lane departure warning systems range from camera-based to infrared sensors and or a radar and sometimes a combination. The idea is that you have ‘something’ monitoring the lane markings on the road and when your vehicle veers across the lane marking there is a warning, be it a visual one, an audible one and sometimes even a physical one where the steering wheel will vibrate. This is intended to prompt the driver to return to the middle of their lane.

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The systems are usually clever enough to know if the driver has intentionally crossed a lane marking although most systems will still warn you. The system will deactivate itself when the indicator is used and will also deactivate if you’re travelling along a road where it can’t detect a lane marking.

And, if you’ve ever driven in a car with lane-departure warning you’ll know there are situations where it won’t work, like often in heavy rain where the camera simply can’t see the lines. Unfortunately, almost every system I’ve sampled won’t tell you if it’s unable to detect the lane markings except for Subaru’s EyeSight system which will tell you it’s not working because of adverse conditions, be it heavy rain or even direct sunlight dazzling the camera. And sometimes the system will react to phantom lines on the road (this is the same for lane-keeping assist too), although most new-release versions are better at weeding out these situations.

What is lane-keep assist?

This is the next step up from lane-departure warning and most vehicles with one will have the other, although that’s not always the case in cheaper vehicles. Most drivers don’t mind lane departure warning and it can generally be deactivated by the driver but make mention of lane-keep assist systems and the Internet will go into meltdown.

Feeding off the lane-departure system, lane-keep assist is intended to help you stay centred in the lane. And depending on your vehicle the system may have several levels of severity that can be adjusted according to the kind of intervention you want, the system on the Ford Everest offers this adjustability which is good because in its highest setting, the steering assist is very aggressive. But I’m getting ahead.

The idea with lane-keeping assist is that should you nudge a lane marking, you’ll be warned visually that you’ve crossed a lane marking on either the left or right but instead of leaving it up to the driver to move the steering wheel, the ‘lane-keeping assist’ will nudge the steering and re-centre the vehicle in the lane.

This sensation, at first, can be a little disconcerting and, if I’m being honest it’s not something you totally get used to. And for some drivers it can become annoying. Fortunately, this ‘intervention’ can usually be switched off.

Personally, I’m all in favour of safety systems that make us safer on the road but I’m not totally convinced by the majority of lane-keep assist systems. And that’s because they’re usually intended as a short-burst intervention. Meaning they will ‘wrench’ the steering wheel and give the sensation that they’ve in some cases over-corrected causing the driver to push back against the wheel and once the system lets go can cause you to jerk back in the direction the lane-keep assist has tried to steer you away from.

But not all systems are created equal. While most are active for a second or two and won’t work if your hands aren’t on the steering wheel. Some will stick around and feel more natural in the way they work even while taking more control from the driver. For instance, Audi’s lane-keeping assist system, to name just one, is able to keep the vehicle centred on a bend and the intervention from the system doesn’t feel like a fight or a panic counter steer.

So, how do the systems work?

Quite simple, and they break into two camps. Some car makers, like Mercedes-Benz have systems that will issue an audible, visual and physical warning and if the driver takes no action will apply the brakes to the opposite wheels to cause the vehicle to move back into the centre of the lane. Other systems will piggy back off the electric power steering pump and counter steer via that rather than the vehicle’s brakes. It’s these systems, depending on the calibration, that can feel like the steering wheel is jerking in your hands.

Are there any drawbacks?

Not really. Sure, sometimes the systems can be tricked by faded lane markings or patches in the road causing the system to react to a ‘phantom’ lane marking. But anything that helps to make our roads a little safer is a good thing. That said, some car makers still only include this sort of system as part of a cost-optional ‘safety’ pack, so, if you’re keen on having it, make sure you check the fine print.

Question: Do you have lane-departure warning or lane-keep assist on your vehicle? If so, do you use it or do you switch it off? See you in the comments.


Isaac Bober

Isaac Bober

Isaac Bober was born in the shadow of Mount Panorama in Bathurst and, so, it was inevitable he’d fall into work as a motoring writer. He began his motoring career in 2000 reviewing commercial vehicles, before becoming editor of Caravan & Motorhome magazine. He then moved to MOTOR Magazine before going freelance and contributing to Overlander 4WD, 4×4 Australia, TopGear Australia, Men’s Health, Men’s Fitness, The Australian, CARSguide, and many more.