Advanced driver assistance systems (ADAS) explained

What are driver assistance systems? Which ones are fitted to your car and how do they work? Our guide explains everything you need to know.

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By Cazoo editorial team

We all want to be as safe as possible on the road. To that end, most modern cars are fitted with advanced driver assistance systems (ADAS) that help to minimise the likelihood of an accident. These systems monitor road conditions around you and can warn you – or even intervene – if a potentially dangerous situation develops.

ADAS is an umbrella term that covers lots of different systems. They’re often referred to as driver safety features or active safety features. Many have been legally required on new cars since the early 2010s, and more are regularly mandated as legislators try to reduce road casualties. Some manufacturers also fit more features than are legally required to their models, either as standard or as extra-cost options.

It’s worth noting that the biggest factor in staying safe on the road is driving with care and consideration. ADAS features are a safety net, not a substitute for careful driving. Nevertheless, it’s good to know what the various ADAS features are and how they work because you’re very likely to experience their effects in everyday driving. Here are the features you’re most likely to come across.

What is automatic emergency braking?

Automatic – or autonomous – emergency braking (AEB) can perform an emergency stop if the car’s sensors detect an impending collision. It’s so effective at reducing the likelihood – or at least severity – of a crash that safety experts have called it the most important motoring safety advance since the seatbelt.

There are several types of AEB. The most basic can detect a stationary vehicle in front of you in low-speed, stop-start traffic. More advanced systems can work at much higher speeds and some can detect cyclists and pedestrians that could cross your path. A warning sound will alert you to the hazard but, if you fail to react, the car will stop by itself.

The stop is very sudden because the car applies the full braking force available, which you’re highly unlikely to ever do yourself. The seatbelt pre-tensioners will also be activated, pulling you very tightly into your seat and, if your car has a manual gearbox, it will probably stall unless you press the clutch.

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What is active cruise control?

Conventional cruise control systems allow you to set a particular speed that the car then sticks to, most commonly on high-speed roads like motorways. If you need to slow down, you disable the cruise control with a button or by pressing the brake pedal. Then when you are ready, you accelerate back up to speed and reactivate your cruise control.

Active – or adaptive – cruise control still operates to a maximum speed set by you, but it uses sensors in the front of the car to maintain a safe gap between your car and the vehicle in front. If it slows down, so do you. You don’t have to touch the brakes or throttle at all, you just have to steer. When the vehicle in front moves over or speeds up, your car will automatically accelerate to the speed you’d set.

More advanced systems can work in stop-start traffic, bringing the car to a complete stop then getting up to speed automatically.

What is lane-keeping assist?

There are several types of system designed to prevent your car from straying from its lane. They’re broadly separated into two –lane-departure warning, which warns you if you’re crossing the white lines on either side of the lane, and lane-keeping assist, which actively steers the car back into the centre of the lane.

Cameras in the front of the car spot the white lines and can tell if you’re crossing them without indicating. Lane-keeping assist will alert you, usually with an audible alarm, a flashing light or a vibration through the seat or steering wheel. Some cars use a combination of those warnings.

If you indicate to change lanes, the system won’t be triggered. In most cars, there’s the option to turn off the system.

What is traffic-jam assist?

Traffic-jam assist combines advanced active cruise control and lane-keeping assist to accelerate, brake and steer a car in low-speed traffic, which can take a lot of the stress out of the situation. It works best on motorways and the most sophisticated systems can even help your car change lanes if needed. However, the driver must still pay attention to the road and be prepared to retake control of the car when necessary.

What is blind-spot assist?

Blind-spot assist (also known as blind-spot warning or blind-spot monitoring) detects if there’s another vehicle in your car’s blind spot – that’s the view just over your right shoulder, which your side mirrors can’t always show. If a vehicle is there for more than a second or two, an amber warning light will show in your car’s door mirror to signal that you shouldn’t pull out into the other vehicle’s path. If you indicate while a car is there, you’ll usually hear an audible warning, see a flashing light, or both.

What is rear cross-traffic alert?

Rear cross-traffic alert uses sensors and/or cameras to detect if a vehicle, cyclist or pedestrian is about to cross your path while you’re reversing out of a parking space. It will sound a warning and, if you don’t react, apply the brakes in the same way as automatic emergency braking. Some cars also have a front cross-traffic alert system, which works in the same way at T-junctions.

What is hill-start assist?

If you drive a car with a manual gearbox you’ll know that they can roll back a little when you do a hill start, as you move your right foot from the brake pedal to the throttle. In older cars, you’d counteract that by engaging the handbrake but cars with hill-start assist will hold the brakes on for a moment after your foot leaves the brake, to stop the car rolling back.

What are active headlights?

Active – or adaptive – headlights automatically switch between full and dipped beam when they detect oncoming traffic. More advanced active headlights can redirect the lights or block out a section of the full beam so that you can still see as far ahead as possible without dazzling oncoming drivers.

What is road-sign recognition?

Road-sign recognition uses a tiny camera system mounted to the front of the car to detect and interpret road signs. You’ll then see an image of the sign on the driver’s digital display so that you know what it said even if you missed it the first time. The system specifically looks for speed and warning signs.

What is intelligent speed assist?

Intelligent speed assist uses road-sign recognition and GPS data to determine the speed limit on the stretch of road you’re driving along and sounds a sustained warning if you go over that speed. More advanced versions of the system can restrict the car’s speed to the current limit. You can override the system – in emergency situations, or if it misreads the limit – by pushing harder on the accelerator.

What is driver-attention detection?

Driver-attention detection uses sensors inside the car to determine whether the driver is paying enough attention to the road. The sensors look at head and eye position and will notice if the driver is looking at a phone, rooting around for something in the glovebox, or even falling asleep. An audible, visual or vibration warning is given to snap the driver back to attention. There may also be an image or text message on the driver’s display suggesting they take a break.

Cars have lots of other safety features that help protect you and your passengers in an accident. You can read about them here.

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