Advanced driver assistance
systems on the road

The anti-lock braking system (ABS) has been around in some form or other for 100 years or so, having first been developed for aircraft in the 1920s. These systems, while effective, were entirely mechanical and developmental light years away from today’s electronically controlled four-channel, four-wheel ABS set-ups.

The basic components of ABS are wheel speed sensors, switchable valves in the hydraulic lines, a pump and an electronic control module. The system works by monitoring wheel speeds and sensing the rapid wheel deceleration immediately prior to a lock-up, then briefly reducing then reapplying the hydraulic pressure in a pulsing action. It mimics the pedal-pumping cadence braking action that was once taught to drivers as a skid-avoidance technique, but at a much higher frequency – around 15-20 times per second in current systems.

As we’ve previously mentioned in this ‘What is ADAS?’ series, the hardware became a primary enabler for other ADAS functions, and developments of the ABS pump and control module remain at the heart of many key safety systems today.

The advantages of ABS are so widely acknowledged that it has been mandatory on all new cars sold in the European Union since 2004. For most drivers ABS tends to shorten stopping distances on most road surfaces, primarily by removing any uncertainty about how much brake pedal pressure should be applied, particularly in emergency braking scenarios. ABS’s key advantage, however, is that it allows a vehicle to be steered around an obstacle during heavy braking, a manoeuvre that would otherwise result in locked wheels and the vehicle carrying straight on – although poor driver education means that this fact is lost on some end users. Some early studies of accident statistics involving ABS-equipped cars even concluded that while ABS reduced the risk of multiple-vehicle accidents, the risk of single-vehicle accidents involving the car leaving the road actually increased. A 2002 study by the American National Highway Traffic Safety Administration (NHTSA) found a 28% increase in fatal run-off-road rollover crashes in vehicles with ABS. It was concluded that drivers of non-ABS vehicles entering a corner too fast were more likely to lock their wheels in a panic-braking situation, with a resultant tangential departure from the road and a survivable head-on collision. ABS-equipped vehicles, meanwhile, would tend to leave the road in a less predictable manner with an increased likelihood of a potentially more injurious or fatal rollover. The NHTSA was cautious about its findings, however, noting that advances in ABS technology could mitigate the risk of such accidents.

Even so, ABS wasn’t mandated in the United States until 2013, and then in conjunction with electronic stability control (ESC).

While ABS hardware provided an early gateway to other ADAS functions, it was ABS’s direct successor, electronic stability control (ESC) that has done most to enhance safety of vehicles on the road today, either directly or through further developments and refinements of its components and systems.

ESC (many car manufacturers have their own names for essentially the same system) monitors vehicle stability and intervenes to maintain control when a likely directional anomaly is predicted that appears contrary to the driver’s inputs. Interventions usually take place while cornering, either due to excessive entry speed or erroneous control inputs, and during evasive manoeuvres or sudden direction changes. By combining ABS hardware with a steering wheel position sensor, yaw rate sensor and lateral acceleration sensor, ESC is able to compare the vehicle’s movements with the presumed intention of the driver in order to prevent a loss of control that might otherwise result in the vehicle leaving the road and possibly rolling over.

Essentially the system works by momentarily braking individual wheels to offer a torque reaction about the vertical axis contrary to the unintended vehicle movement. In some instances, and with some systems, ESC is also able to reduce engine torque, by ignition retardation, control of the fuel supply, spark suppression or direct throttle actuation, to further mitigate the predicted loss of control. Much of the time ESC’s intervention is very subtle or even unnoticed by the driver, but its effectiveness at reducing accidents, injuries and fatalities is universally acknowledged.

ESC has been mandatory on all new cars sold in the United States since 2012 and in Europe since 2014. Prior to that, in 2004, an NHTSA study concluded that ESC reduced accidents by 35%, while in 2007 the UK’s Department for Transport found that cars with ESC were 25% less likely to be involved in a fatal accident. In 2014 Global NCAP went on to call for ESC to be made mandatory worldwide.

While it is often marketed as an independent feature, today’s traction control systems (TCS) are essentially a subsidiary function of ESC. TCS is basically the reverse of ABS: if a driven wheel is rotating too quickly under acceleration, i.e in excess of measured road speed, torque to that wheel will be suppressed until traction is regained.

Like ABS, cruise control is such a familiar feature on today’s cars that it’s often taken for granted as a ‘driver assistance’ feature, although it should be noted that not all drivers favour its use.

In its basic form cruise control automatically maintains a pre-set vehicle speed by taking control of the throttle and adjusting it when necessary to compensate for gradients. The driver must set the desired speed manually via controls usually mounted on the steering wheel or on stalks immediately behind it, and the system must deactivate as soon as the driver touches the brake pedal.

This type of cruise control, while common, is best suited to open motorway or highway use with relatively light traffic flow, meaning its safe operation is limited on some smaller countries’ more congested road networks.

More recently, active cruise control (ACC), very much a modern-day ADAS function, has broadly addressed the issue of using cruise control on more heavily congested roads. ACC combines existing cruise control hardware with front-facing sensors, either radar or a stereo camera set-up, to monitor traffic ahead and adjust the vehicle’s speed in order to maintain a safe following distance.

ACC is recognised as offering Level 1 autonomy, and it is widely regarded as a stepping stone to higher levels of self-driving functionality. As already mentioned, today it is increasingly common for ACC to be packaged with other systems, such as lane keeping assist to offer Level 2 autonomy or beyond.

Forward collision warning (FCW) and autonomous emergency braking (AEB) are two separate but closely associated functions that are usually presented together.

FCW/AEB’s primary role is to prevent or lessen the severity of rear-end collisions – a type of accident that is extremely common on busy urban roads and in stop-start queues of traffic. Using a forward-facing sensor or sensors, TCW monitors the road ahead and warns against the possibility of a collision with vehicles in front, specifically those that are slowing down or moving more slowly than the car to which the system is fitted. When a collision is deemed likely, the FCW system alerts the driver to the possibility with a series of increasingly urgent audible, visual and sometimes haptic alerts. At the same time some systems pre-charge the braking hydraulics in preparation for a possible emergency stop, either autonomously or by the driver. If the driver takes no action then further warnings might include a sharp but momentary application of the brakes. Finally if no action is taken, the system will intervene with a full application of the brakes, either avoiding a collision completely or at least lessening its severity.

Many FCW/AEB systems also include an element of pre-collision preparation, such as automatic pre-tensioning of seatbelts (which can also serve as a FCW alert in itself) and closing windows, and even a degree of steering control under certain circumstances.

As with a number of ADAS functions, many car manufacturers market FCW/AEB under their own preferred name, such as City Safety (Volvo), Active City Stop (Ford) or Front Assist (Volkswagen). Use of the word ‘city’ in some names is suggestive of the speed parameters within which the systems are claimed to be effective, typically up to around 30kmh/19mph in early systems. Later systems are increasingly active at up to 50kmh/30mph or even 80kmh/50mph, while Volkswagen’s Front Assist is claimed to detect stationary objects ahead at speeds of up to 200kmh/125mph. Some of the city-based systems use Lidar sensors, the current effective range of which remains limited for now in ADAS applications, while others use radar alone or a combination of radar and camera sensors.

As sensors and detection/classification algorithms have become more effective, FCW systems are increasingly able to be used specifically for cyclist, pedestrian and animal identification as well as traffic. In some cases and as a result, certain systems are being specifically marketed as pedestrian avoidance functions.

Such is the acknowledged effectiveness of FCW/AEB at reducing the severity or frequency of accidents that it has been mandatory on all heavy goods vehicles sold in Europe since 2015. Additionally, it is expected that nearly all cars sold in the United States will have FCW/AEB as standard by 2022, and, as already mentioned, the European Commission has expressed its desire to see FCW/AEB mandated for all new cars sold in the EU by 2021.

A blind spot monitor is a system that uses radar sensors mounted on the sides and to the rear of the vehicle, usually within the door mirror housing and also within the bodywork, to detect vehicles approaching from the rear and those already passing but ‘hidden’ from the driver’s view in the area not covered by the rear-view or door mirrors. A blind spot monitor’s sensors usually have an operating range of around three metres, and the system is particularly useful on multi-lane roads and highways where lane changes are likely.

The system usually provides a series of escalating alerts to the driver, initiated when a vehicle enters the area covered by the sensors. First, a visual warning is given by means of a flashing light, often mounted within the door mirror. If a manoeuvre is commenced or continued nonetheless, often in response to the activation of the turn signal, then an audible and/or haptic warning may be given, finally followed, in some cases, by steering intervention.

Blind spot monitoring systems are sometimes marketed as lane-change assist systems, and are increasingly common on today’s vehicles. Volvo first introduced its Blind Spot Information System (BLIS) in 2007, with other manufacturers following suit in the years that followed.

The latest ‘active’ lane change assist systems, such as Mercedes-Benz’s Active Lane Change Assist and Tesla’s Auto Lane Change, are able to complete a full lane change manouevre, thus elevating the technology into the realms of Level 2 autonomy. These systems augment existing blind spot monitoring sensor inputs with camera sensors (to detect and recognise lane markings) and automated steering assistance. Once the active lane changing system is activated by the driver, a manoeuvre is instigated by manual operation of a turn signal. When the system determines that it’s safe to change lanes, i.e. that no vehicles are alongside and none are approaching imminently from the rear, then it assumes full control of the steering for the duration of the manoeuvre.

Ostensibly, lane departure warning (LDW) and lane keeping assist (LKA) systems appear similar in function to blind spot assistant systems, but the sensor hardware they employ is different.

LDWs use a camera, usually mounted behind the vehicle’s windscreen ahead of the rear-view mirror, to scan the road immediately ahead, and image processing software is used to identify lane markings. If the vehicle appears to be straying out of its lane without the driver activating a turn signal, a warning is given, usually a flashing light, an audible alert or a vibration through the seat or steering wheel, or a combination of all three, depending on the particular system and the degree of deviation from the intended lane.

LDW systems were initially developed for heavy goods vehicle, but have been available on cars since the early-2000s. Since then they have become increasingly commonplace, as ever filtering down from higher-end and premium models to become cost options and even standard equipment on more affordable cars.

LKA systems augment the basic LDW by adding a degree of steering intervention or control. LKAs can work either by reacting when a measured deviation occurs, or by continuously providing small steering inputs to actively keep the vehicle in the centre of the lane. This latter approach is sometimes marketed as lane centring or lane centre assist.

LKA is increasingly being combined with active cruise control and traffic sign and speed limit recognition functions to offer Level 2 autonomy driver assistance under certain conditions.

As with blind spot monitoring systems, parking assistance systems are another ADAS function that, in many cases, have evolved from a relatively simple set of sensor-instigated alerts into far more complex active assistance systems. Initially they were conceived as a luxury or premium convenience feature but they have become increasingly commonplace as the near-field visibility from even quite mundane cars has been compromised by evolving crash and safety requirements. Aftermarket devices are also widely available.

Basic systems employ bumper-mounted short-range sensors, often ultrasonic although increasingly radar, designed to detect objects nearby during low-speed parking or turning manoeuvres. The driver is alerted to obstacles through a series of audible alerts, which usually escalate in volume and frequency as the distance to the obstacle decreases.

Advancements in parking assist technology have included the augmentation of a basic sensor set-up with a rear-view, reversing or back-up camera, which gives a mirror-image view of the area immediately behind the car on a dashboard-mounted display or within the rear-view mirror. Some of these systems feature display-screen graphics showing directional guides for the vehicle according to steering wheel position.

More recently, rear-view cameras have been supplemented by wide-angle cameras mounted on the sides and front of the vehicle. Images from these are then spliced together on-screen to provide a bird’s-eye or so-called surround view image of the environment immediately around the vehicle, aiding parking and close-quarter manoeuvring.

Other recent developments have included active parking assistant functions, which fuse various sensor inputs with autonomous operation of the vehicle’s controls to parallel or reverse-park into an available space. Depending on the system, these are able to variously manoeuvre into a parking space identified by the driver, or autonomously detect and then park the car, either assuming full control of the steering, brakes, gears and throttle, or with some inputs provided by the driver following on-screen and/or spoken-word prompts.

Cross-traffic alert is a short-range object detection system initially designed to aid drivers reversing out of parking spaces but since developed to include forward-facing systems for use not only in car parks but also at junctions with limited or restricted visibility.

Cross-traffic alert systems use short-range sensors, usually radar, to detect vehicles, cyclists and pedestrians approaching from the vehicle’s sides. The sensor hardware can either be shared with or independent of that used for the blind spot assistance systems described earlier, and the audible alerts to the driver of approaching hazards may be augmented by cameras providing an in-car view of the area behind the vehicle – although it’s perhaps more accurate to say that the cross-traffic alert is a later augmentation of the standalone rear-view camera. In most cases the cross-traffic alert system is passive and only provides an alert to the driver, but some systems will actively brake the car in order to avoid a collision. This latter function is sometimes referred to as reverse autonomous emergency braking, or reverse AEB.

The turning assistant is a relatively recent development of blind spot alert/cross-traffic alert technology that is designed to prevent a vehicle from turning right (in right-hand-drive vehicles) or left (in left-hand-drive vehicles) across the path of oncoming traffic into a side road.

Turning assistant employs front-mounted sensors, usually a combination of radar and camera, to scan ahead for oncoming traffic when a driver is stationary, indicating and waiting to turn. The system will brake the car to a stop if manoeuvre is commenced in the face of an oncoming vehicle and a collision is imminent.