WHY ARE LANEKEEPING SAFETY SYSTEMS ALWAYS SWITCHED ON?

QWe hired a Toyota Yaris while on holiday and thought it had a steering problem, pulling across the road as though the brakes were binding. It turns out that it features a lane-departure warning system. You can turn it off each time you drive, which I will now do, but why is this not by default, so that we can switch it on if we choose? – KW

ASince 2015, the inclusion of lanedeparture warning (LDW) – where the car beeps at you or wobbles the steering wheel if you cross a white line – has been a necessity for obtaining the top Euro NCAP safety ratings, which explains its proliferation. Since 2017, so has emergency lane keeping (ELK), which wrests the steering wheel from your hands in order to forcibly keep the car in its lane.

If a system is well set up, you shouldn’t notice it – it should only come into effect when you’re about to stray into danger. If you’re noticing it enough to want to switch it off, it’s not a well-executed system. The trouble is that versions of these systems that aren’t well engineered can end up making your driving more dangerous, rather than safer. If, for example, you overtake a cyclist and neglect to indicate because the road is otherwise empty, the car will sense you crossing the white lines and nudge you back into your lane – towards the cyclist you’re passing. I speak from (panicked) experience.

But not all of these systems are created equal. Certain manufacturers’ versions seem to perform much better than others; in my experience, higher-end systems from the likes of MercedesBenz, Volvo and BMW tend to be far less intrusive than, for example, those from the Volkswagen and Hyundai groups.

There are several possible reasons for this, according to Matthew Avery, of Thatcham Research, the British safety and security organisation that’s part of the Euro NCAP crash testing and safety regime. First, the way the system is calibrated by the manufacturer – some are more risk averse, hauling you back into your lane at the first sign of trouble; others are less nannying, only cutting in when you’ve crossed the line, rather than when you’re approaching it.

The quality of the system plays a part, too. Euro NCAP recommends that manufacturers use a system that includes cameras to detect white lines along with radar to detect oncoming or overtaking traffic. Unfortunately, many manufacturers use only camera-based systems, which are cheaper, but can only tell when you’re about to cross white lines, regardless of what’s around you – and it’s these that react most frequently.

When a system creates too many “false positives” (meaning that it activates when there’s no need), the driver tends to switch it off, which makes it pointless having the technology in the first place.

Your frustration with the fact that the system turns itself back on every time you start the car is understandable. However, to fit Euro NCAP’s definition of an ELK system, the technology has to behave this way and is specifically required to default to “on”.