The onboard electronics of a modern car no longer simply correct the driver’s mistakes the moment they occur. Alongside the well-established driving control systems such as ABS, TCS and ESP, which react once grip has already been compromised, a second family of devices has established itself: ADAS, short for Advanced Driver Assistance Systems. The difference between the two is a substantial one. The former read only the state of the vehicle (wheel speeds, steering angle, accelerations) and correct a situation that is already under way; the latter observe what is happening outside the cabin and act in advance, so that the critical situation never arises in the first place. Nor is this equipment reserved for premium cars: European Regulation 2019/2144 makes several of these systems mandatory on all newly type-approved vehicles.
How the car perceives its surroundings
Before any assistance function can exist, the car has to build a representation of what surrounds it. That task falls to four types of sensor, each with its own clear strengths and limits:
- Radar
- Cameras
- Ultrasonic sensors
- Lidar
Radar emits radio waves and measures the returning echo, deriving the distance, relative speed and direction of objects. It is the most reliable sensor in poor visibility, rain or darkness, but it cannot identify the nature of what it has detected. Cameras do the opposite: they interpret shapes and colours, which makes them indispensable for reading road markings, recognising traffic signs and telling a pedestrian from a cyclist; they are, however, affected by glare, fog and a dirty windscreen. Ultrasonic sensors, housed in the bumpers, measure very short distances and only at low speed: these are the ones behind parking sensors. Lidar, finally, uses laser pulses to reconstruct a high-resolution three-dimensional map of the surroundings; it is extremely accurate but expensive, and for that reason still uncommon on production cars.
None of these sensors is enough on its own. The control unit therefore relies on what is known as sensor fusion, the combination of data coming from different sources: if the radar and the camera agree in identifying an obstacle, the probability of a false alarm falls dramatically. It is on this perception that today’s most widespread assistance functions are built:
- Adaptive cruise control
- Lane keeping
- Automatic emergency braking
- Blind spot monitoring
Adaptive cruise control
Conventional cruise control holds the set speed and ignores the traffic. Adaptive cruise control (ACC) adds a second objective: maintaining the distance from the vehicle ahead. A front radar, often working alongside a camera, continuously measures the distance and the relative speed of the car in front; the control unit then acts on engine output and, when necessary, on the braking system, in order to keep the gap chosen by the driver. Once the lane is clear again, the car returns to the set speed. The most advanced versions, known as Stop & Go, also handle congested traffic: they slow the car to a complete standstill and pull away again automatically if the halt is a brief one. The deceleration delivered by ACC is deliberately moderate, however, designed for comfort on the move rather than for an emergency.
Lane keeping
This is the family of functions that causes the most confusion, because three different levels of intervention live behind similar commercial names. Lane Departure Warning does no more than signal that the car is leaving its lane, with a sound or a vibration through the steering wheel. Lane Keeping Assist, by contrast, is a corrective system: it acts on the steering only when the car approaches the line or crosses it, bringing the car back inside before ceasing its action. Lane Centering is the step above: it corrects the trajectory continuously to hold the vehicle in the middle of the lane, even when there is no drift under way. In all three cases the reference is provided by the camera reading the road markings: if the lines are worn, covered or absent, the function switches off and warns the driver accordingly.
Automatic emergency braking
Automatic emergency braking (AEB) is the function with the greatest impact on safety, and it is now mandatory in Europe on newly type-approved cars. The system compares the speed of the car with the distance and relative speed of the obstacles detected ahead of it, calculating the time remaining before a possible impact. When that value drops below a critical threshold, the intervention comes in stages: first an audible and visual warning, then a pre-charge of the braking system that takes up the free play and shortens response times, and finally, if the driver does not react, autonomous braking at the maximum deceleration the available grip allows. The most recent versions also recognise pedestrians and cyclists. The goal is not always to avoid the impact altogether, but rather to reduce the impact speed and therefore the severity of the consequences.
Blind spot monitoring
The blind spot is the portion of road to the side and rear of the car that the mirrors cannot cover. Two radars placed in the corners of the rear bumper watch the adjacent lanes and signal an approaching vehicle by means of a warning light in the exterior mirror; if the driver operates the indicator anyway, the warning becomes audible and, on some models, the system applies a slight corrective action to the steering. The same sensors feed the rear cross traffic alert, useful when reversing out with the view obstructed by parked cars.
The SAE levels of automation
To place these functions correctly there is an international classification, standard SAE J3016, which identifies six levels of automation. Level 0 involves no automated intervention in driving at all, at most some simple warnings. Level 1 assists on a single axis of control, either longitudinal or lateral: adaptive cruise control used on its own is a case in point. Level 2 combines the two axes, managing acceleration, braking and steering together. From level 3 onwards responsibility for driving passes to the vehicle: the driver may look away, but must remain ready to take back control when the system requests it. At level 4 the vehicle is autonomous within a defined operational domain, and at level 5 in any condition whatsoever.
Virtually every car on sale today stops at level 2. That means the driver remains fully responsible for the conduct of the vehicle, must keep their hands on the wheel and their eyes on the road, and that the car actively monitors their presence and attention. The few level 3 approvals granted so far operate within very tight limits of speed, road type and weather conditions, and their take-up remains marginal. Talking about autonomous driving in relation to a production ADAS is therefore inaccurate: this is assisted driving, and the adjective makes all the difference.
One practical aspect is often overlooked: ADAS need maintenance. Replacing a windscreen, repairing a bumper or altering the ride height all call for the sensors to be recalibrated, and without that the system risks misreading what it perceives.