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Advanced driver assistance systems (ADAS) are a set of sensors, cameras and software that monitor the area around the car, warning you of a potential hazard or intervening in specific conditions by braking, steering or adjusting speed. Before buying, it is not enough to see a system's name in the specification sheet; ask exactly what it does, when it stops working and how to try it safely.
These systems usually rely on a camera behind the windscreen near the rear-view mirror, a radar behind the grille or front bumper, radars in the corners of the rear bumper, plus parking sensors and cameras around the body. The car's computer combines their signals to estimate distances, speeds and the car's position between the lane markings.
They differ from the anti-lock braking system (ABS) and the traction control system (TCS); those two monitor the wheels themselves, while ADAS monitors the road, vehicles and pedestrians around you, and many of these systems use the same brake system when they intervene.
The US National Highway Traffic Safety Administration (NHTSA) explains in its guide to driver assistance technologies that some systems are designed only to warn you, while others take action to avoid a crash, and that manufacturers use different trade names for the same function; so rely on the function described in the owner's manual rather than the name.
| System | What it does |
|---|---|
| Forward Collision Warning (FCW) | Warning only when you close in quickly on a vehicle ahead. |
| Automatic Emergency Braking (AEB) | Intervention: supports your braking or brakes automatically if a collision appears imminent. |
| Lane Departure Warning (LDW) | Warning only when the car leaves its lane without a signal. |
| Lane Keeping Assist (LKA) | Intervention: gently corrects the steering to bring the car back into its lane. |
| Blind Spot Warning (BSW) | Warning by a signal in the mirror when there is a vehicle you cannot see. |
| Adaptive Cruise Control (ACC) | Intervention: adjusts speed to keep a distance from the vehicle ahead. |
| Rear Cross Traffic Warning (RCTW) | Warning while reversing of a vehicle approaching from the side. |
| Surround-view camera | Visibility aid: a combined image of the car's surroundings while parking. |
| Driver attention monitoring | Warning when signs of drowsiness or distraction appear. |
Having a warning system does not mean a matching intervention is fitted; a trim may include blind spot warning without any steering or braking intervention, so ask for the system list for the exact trim and model year you will buy.
The NHTSA page on active braking technologies explains that these systems use radar, cameras and other sensors to detect vehicles, pedestrians or objects in front of the car, increasing braking force if your braking is insufficient, or braking automatically if you do not respond to the warning, with the aim of avoiding a collision or reducing its severity. This does not mean they prevent every collision in all conditions.
Ask when buying: does the system detect pedestrians and cyclists, or only vehicles? Does it work when reversing? And what speed range does it operate in according to the owner's manual? Never test it by deliberately approaching a car, a person or an obstacle.
The warning system only gives a sound or a vibration in the steering wheel when the car drifts across the lane markings, while the assist system gently corrects the steering, and in some cars may brake one of the wheels. Lane centring, by contrast, steers the car continuously while it is active, and usually works together with adaptive cruise control.
These systems depend on the camera seeing the road markings, so their performance weakens when the lines are faded or missing, as on some desert roads and in diversion zones, and many cars alert you if you take your hands off the wheel while they are active.
Standard cruise control keeps a fixed speed that you set, whereas the adaptive version slows down if you approach a slower vehicle, then returns to the set speed when the road clears, and in some cars it can stop and move off again in traffic.
Before using it, learn how to choose the following distance and how to cancel it with the brake pedal or the cancel button. Its braking ability is limited, and it may not respond as you expect to a stationary vehicle or a car that cuts in suddenly; so stay ready to brake yourself.
Blind spot monitoring alerts you with a light in the side mirror, some systems add a sound if you signal towards a lane with a vehicle in it. Rear cross traffic warning is useful when reversing out of a parking space between large vehicles that block your view.
The surround-view camera shows a combined image as if you were seeing the car from above, but it can distort distances at its edges and does not replace the mirrors and turning to look yourself.
Alongside the general steps in our new car buying guide, set aside part of the test drive for the assistance systems:
If a message says the system is unavailable, continue driving carefully without relying on it, clean the sensors with water and a soft cloth while keeping high-pressure water away from them, and if the message persists, have the car inspected.
The camera and radar are mounted at a precise angle, and even a small change can make the system misjudge distance or lane position. That is why the manufacturer may require the sensors to be checked or calibrated in cases such as:
Before any repair, ask the service centre about the calibration requirements for your car, and ask for proof that it was carried out. With a used car, ask whether the windscreen has been replaced or the bumper repaired, and whether the sensors were calibrated afterwards.
No. NHTSA's classification in the guide mentioned above makes clear that the driver remains responsible for driving and attentive at all times, even with systems that combine speed control and steering. Even driver attention monitoring is a reminder to stop and rest, not a substitute for rest; if you feel drowsy on a long journey between cities, stop in a safe place.
Driver assistance systems add a useful layer of protection when you understand what each system does and its limits, and keep the sensors clean and calibrated after any repair. When browsing the cars listed by Saleh Cars Group, compare the assistance systems in each trim and ask how they work before you decide, because the final decision on the road always remains yours.