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What is lane-keep assist?

Lane-keep assist is designed to warn and steer a driver back into line when they have drifted out of their lane or misjudged a corner


Most of us have done it; drifted out of our lane or misjudged a corner and crossed the central white line. It normally results in horn blowing but it can cause a crash or at least a smashed wing mirror.

Lane-keep assist is technology designed to warn and steer the driver back into line. It’s one of a package of electronic safety systems fitted to current cars, but the technology isn’t perfect and varies from car to car.

Most lane keeping systems use a forward-facing camera mounted at the top of the windscreen by the rear view mirror to identify the lane markings and see if they are crossed. The same camera also works with adaptive cruise control systems.

Jargon explained

Lane-keeping assistance systems are a kind of technology known as Advanced Driver Assistance Systems (ADAS). The idea is to use modern technology to help prevent accidents, rather than just making cars better at coping with collisions – after all, it’s always better to avoid an accident altogether than to have even a minor one.

Euro NCAP, probably the world’s foremost authority on car safety and provider of safety ratings for new cars, is increasingly prioritising this sort of technology in new cars. New car safety scores have a specific category for accident avoidance technology, and it contributes significantly to a new car’s overall Euro NCAP safety rating.

There are three parts to lane-related assistance systems: Lane Departure Warning (LDW), with typical warnings which include a flashing symbol on the dashboard display, an audible alert or a vibration at the rim of the steering wheel.

The next, building on LDW systems is Lane Keep Assist Systems (LKAS). These steer the car to keep a central position between lane markings. The systems will apply a small amount of steering to stop the vehicle from leaving its lane. 

The last are Emergency Lane Keeping (ELK) systems, which intervene much more aggressively.  For example, ELK will apply a large steering input if it senses that a car is about to run off the road. On tighter bends, if lane markings are poor or the driver takes their hand off the steering wheel, LKAS automatically suspends itself.

Standard fit

In July 2022, new EU regulations were introduced with the effect that all new cars and light commercial vehicles (small to medium-sized vans and pick-ups) are now required to have – amongst other things – advanced emergency braking systems, intelligent speed assistance, emergency lane‐keeping systems, driver drowsiness and attention warning, advanced driver distraction warning and reversing detection.

The UK remains aligned with the EU on new vehicle standards despite Brexit, so the new regulations apply here as well.

A lot of car manufacturers were already fitting these features to gain the maximum five-star safety rating awarded by Euro NCAP, which rates LKA and ELK based on a standard set of tests on a test track. 

Both types of system are tested against various types of road-markings, including solid lines and dashed lines, and in situations where the road edge is not marked by a line. The performance is evaluated by considering the proximity of the vehicle to the edge of a lane marking or road edge at the time of intervention. Additional points are awarded to cars equipped with a Lane Departure Warning system and a Blind Spot Monitoring system.

Are there any downsides?

No advanced drivers assistance system can allow for every situation and the driver needs to be ready to step in at any time. This similar to the semi-autonomous cars which will do a limited amount of steering for you – you still need your hands to touch the wheel.

Most people get that it’s good to have safety systems to protect you, your passengers and people outside the car but today’s lane-keeping assistance systems can still get confused.

Not all straight roads have nicely painted white lines, so some systems can’t see them anyway. Narrow crowded roadworks lanes where you really don’t want to drift very tend to have worn out markings or old lines which cross over temporary lines. The system may also not detect lane markings when driving too close to the vehicle ahead.

Heavy rain, snow and fog can limit the system’s ability to function as well as mud or dirt on the camera lens (so keep the windscreen clear). Some systems cut out below 30mph so aren’t of use in town where if you’re not paying attention you could veer into a cycle or bus lane.

Country roads can be a particular tussle for keen drivers, who if they can see the road ahead is clear like to take the cleanest line through a corner but which means going over the white line. Having the steering wheel violently fight back can be quite a distraction.

Not all as good

The only way to know whether your next car might be too enthusiastic in its corrections is to study car magazine/website road tests, especially those called ‘long term’ where a journalist has lived with a car for a few months.

The Car Expert’s road test editor Andrew Charman says: “The actual Lane-Keeping Assist devices do vary in both their function and their effectiveness – I was particularly impressed the first time I tried a Volvo system when going from the M42 to the M5 north and it calmly steered me round and over the bridge!

“Most of the major systems are effective in their use but they’re not foolproof – you (rightly) can’t use them as an excuse for not concentrating on the wheel. They’re a good safety aid for that rare moment when the concentration wavers. One or two of the systems don’t seem to react quite as accurately or as quickly as others, but I’ve not found a truly useless one yet.”

Can I get round it?

If there are unwanted or excessive lane departure warnings, or the system steers too abruptly, drivers often want to turn it off. You can do this (and the legislation has this written in), but you can’t pick which part you want to turn off, it’s the whole system apart from emergency braking.

Some cars have a button which does this but others force you to go through a series of steps on a central touchscreen, which could be dangerously distracting in itself. However, the car will default back to ‘on’ every time the ignition is switched on.

Don’t understand it? You’re not alone

The Fédération Internationale de l’Automobile (FIA) – which most famously governs Formula 1 and other motorsport categories – is also very active in road safety. In 2020 it commissioned a survey of more than 9,000 drivers to see how well they understood Advanced Driver Assistance Systems and their limitations. ‘Not enough’ was the answer for the majority and the report laid the blame both on the manufacturers, their websites and their salespeople.

It said: ‘The manuals mostly consist of all kinds of warning messages and legal disclaimers. The contents of the manuals seem to be focused more on shifting responsibility from the car manufacturer to the car driver, instead of informing the car driver. Car dealerships tend to provide quite limited amounts of information about ADAS until they notice that the customer has some level of interest in these systems.’

Nearer to home, Thatcham Research – which is Euro NCAP’s UK member organisation and funded by the insurance industry – says that ‘before we can embrace the automated mobility model of the future, it’s vital that we get Assisted Driving right and use today’s technology safely. This can only happen if consumers understand what today’s Assisted Driving systems can and can’t do – as well as remembering their own responsibilities behind the wheel.’

Last year it launched the world’s first Assisted Driving Grading, putting today’s Assisted Driving systems through their paces to independently assess their strengths and weaknesses. The top rated car of May 2022 was the Nissan Qashqai.

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Russell Hayes
Russell Hayeshttps://amzn.to/3dga7y8
Russell Hayes’ early career was 14 years of motoring journalism in print, television and online. He worked for What Car? and Complete Car magazines, the BBC's original Top Gear programme and Channel 4's Driven. Since 2007 he has written motoring history books on subjects including Lotus, TVR, the Earls Court Motor Show, the Volkswagen Golf, Volkswagen Beetle and Bus and the original Aston Martin V8. Now a full-time author, two more books are in the pipeline for 2023 and 2024.
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