Advanced driver assistance systems
Advanced driver assistance systems, or ADAS, is the term used to describe the growing number of safety functions designed to improve driver, passenger and pedestrian safety by reducing both the severity and overall number of motor vehicle accidents. ADAS can warn drivers of potential dangers, intervene to help the driver remain in control in order to prevent an accident and, if necessary, reduce the severity of an accident if it can’t be avoided. In short, ADAS compensates for our mistakes, be they inattentiveness, erroneous control inputs or, up to a point, downright stupidity. As uncomfortable as humans are with admitting it, we’re not perfect – but ADAS is here to help. At least that’s the idea.
As the associated ADAS technologies are developed and refined, and as car manufacturers look to appeal to customers with an increasing range of safety- and convenience-focused features, the umbrella under which ADAS resides has got bigger and bigger. Today the term ADAS covers an increasingly broad, and increasingly common, range of passive and active systems that are offered as options or as standard on a growing number of new cars and commercial vehicles. Some ADAS functions are so well proven and effective that they have become mandatory in certain regions across the globe. Today ADAS extends from day-to-day driver and passenger comfort and convenience features to accident and injury mitigation and prevention. The lines are, in fact, becoming a little blurred, and at times it can be hard to determine where ADAS’s remit begins and where it ends.
To say ADAS is becoming ‘increasingly common’ is, in fact, a little disingenuous. ADAS has been playing an important role in the development of safer vehicles for some decades, but the early incarnations of automotive driver-assist technology are now so well-developed, effective and familiar that we often take them for granted. The most commonplace and familiar of all is the anti-lock braking system, or ABS. Various incarnations of ABS have been developed and trialled by automotive manufacturers since the middle of the 20th century, but an electronically controlled four-wheel anti-lock braking system first saw service as an option on the Mercedes-Benz W116 S-Class of 1978. ABS’s benefits in terms of reducing accident frequency and severity are so widely recognised and well documented that it has been mandatory on all new cars sold in the European Union since 2004.
ABS aside, traction control systems (TCS) and electronic stability control (ESC, sometimes called electronic stability program, or ESP, or dynamic stability control, DSC) have also entered the realm of everyday automotive reality. Again, the proven benefits of each system are well known, and ESC, like ABS, is now mandatory in the EU. In fact, ESC is widely acknowledged as being the single most important contributor to vehicle safety due to its ability to reduce the number and severity of accidents, specifically those involving a vehicle rolling over and leaving the road – a scenario that often results in serious injuries or even fatalities. In 2016 ESC’s inventor, former Bosch engineer Anton van Zanten, described it, perhaps with understandable bias, as “the single most important part of ADAS and the basis for all future systems”. [*citation: https://spectrum.ieee.org/cars-that-think/geek-life/profiles/van-zattan-wins].
ESC and TCS also set a precedent for future ADAS development by combining the functionality of an existing system with new developments to further assist the driver. In order to carry out their specific tasks, both TCS and ESC use the ABS control module to apply retardation to individual wheels under prescribed conditions as part of their particular remits.
Today such integration of ADAS functionality is common, but while the growing capabilities of increasingly complex systems are furthering vehicle safety, a distinction must be made between ADAS, which is designed assist with the task of driving, and autonomous or self-driving functionality, which is ultimately intended to take control of the vehicle away from a driver. The former is readily available now, the latter is not.
Why have ADAS?
In short, ADAS means safer roads. As already mentioned, the role of ADAS is to reduce road deaths and injuries by cutting the number of road accidents overall and reducing the severity of those that can’t be avoided. A number of studies have already gone some way to proving the efficacy of ADAS in real-world driving situations, and the general consensus, both within the automotive industry and in wider legislative circles, is that the technology should be promoted and adopted on as broad a scale as possible – and sooner rather than later.
A 2016 report by wholesale insurance provider Swiss Re looked at accident statistics provided by the UK’s Department for Transport. It concluded that a hypothetical (and admittedly unrealistic) 100% adoption of forward collision warning, blind spot detection and lane departure warning by 2020 would reduce motorway accidents by 16.3% and accidents on other roads by 11.6%. Factoring in more sophisticated systems such as lane-keeping assist, autonomous emergency braking, night vision and multi-feature packages of combined ADAS functions, these figures rose to a 45.4% accident reduction on motorways and a 27.5% reduction on other roads. [*citation: www.swissre.com/library/The_future_of_motor_insurance.html]
More realistically, and taking into account the projected real-world uptake of ADAS packages that remain, for now, relatively expensive options or standard only on more costly premium models, Swiss Re concluded that an overall accident reduction of 4.3% could be expected by 2020.
While Swiss Re’s figures are based on reported accidents, i.e. those involving deaths or serious injuries, other studies have looked at insurance claim data, which includes minor accidents that result in damage to vehicles but not necessarily any harm to occupants, pedestrians or other road users. A study by the Swedish car maker Volvo, in co-operation with insurers If and Volvia, looked at the effectiveness of the manufacturer’s ‘City Safety’ autonomous emergency braking system, which has been offered as an option since 2006 and fitted standard on all new Volvos since 2008. It was concluded that cars fitted with City Safety were involved in 28% fewer accidents. [*citation www.volvocars.com/uk/about/our-innovations/city-safety]
The evidence of ADAS’s effectiveness is so irrevocable that many functions have become mandatory on new cars sold in various regions around the world. Euro NCAP has embraced ADAS and it continues to adapt its assessment procedures to address the growing number of systems and technologies. Indeed, Euro NCAP’s championing of occupant and pedestrian protection over the past couple of decades has led to widespread consumer awareness of the benefits of safer cars. It’s expected that Euro NCAP and its testing and rating system will play a similar role in promoting ADAS and its industry-wide adoption.
It is already the case that Euro NCAP’s ‘safety assist’ tests assess forward collision warning/autonomous emergency braking systems (in various scenarios), as well as lane departure warning systems, lane-keep assist systems and speed assist systems, and it includes ratings for these functions in its overall assessment of new cars. By doing so, the models with more standard ADAS equipment, providing it performs appropriately, will inevitably climb higher in Euro NCAP’s rankings, pushing less well-equipped models further down the scale. And as has already been seen with the occupant and pedestrian protection measures that have become commonplace, other manufacturers will inevitably follow suit by adopting the new technology. It shouldn’t be underestimated how effective this consumer-facing programme has been both in improving vehicle safety and raising consumer awareness of available new technologies, and ADAS is expected to benefit similarly with accelerated uptake over the coming few years.
As mentioned earlier, several ADAS functions are already mandatory on new vehicles in various regions around the world, with others set to become so in the near future. ABS has been mandatory on all new vehicles sold in the European Union since 2004, and electronic stability control became mandatory in the region in 2014, such are the proven benefits of the two systems. Autonomous emergency braking, meanwhile, has been mandatory on all commercial vehicles sold in the EU since 2015, while rear-facing or reversing cameras with a dashboard display screen have been mandatory on all new cars sold in the United States since May 2018.
Also in May 2018 the European Commission published a list of 11 new safety features it wants mandated on new cars by 2021. The list includes several existing ADAS functions, specifically autonomous emergency braking, lane keeping assistance, intelligent speed assistance system and a reversing camera/rear detection system.
For all of ADAS’s benefits, however a caveat should be made. While ADAS development is advancing all the time, it is the self-driving or autonomous cars of the future that are proving particularly adept at making news headlines. This has led some quarters of the industry to call for a clearer differentiation between advanced driver assistance systems and fully autonomous cars. Thatcham Research, the UK automotive insurance industry’s research organisation which also carries out the Euro NCAP crash tests on new models, believes this has led to a degree of public confusion about ADAS, and it is concerned that some drivers believe their new cars have autonomous capability when that is not the case. [*citation http://news.thatcham.org/pressreleases/carmaker-use-of-the-word-autonomous-a-danger-to-uk-roads-2537576]
In the United States, the Insurance Industry for Highway Safety (IIHS) has echoed Thatcham’s concerns. In a report assessing the various ADAS functions of a number of current production models, IIHS chief research officer David Zuby said: “Designers are struggling with trade-offs inherent in automated assistance. If they limit functionality to keep drivers engaged, they risk a backlash that the systems are too rudimentary. If the systems seem too capable, then drivers may not give them the attention required to use them safely.” [*citation: www.iihs.org/iihs/news/desktopnews/evaluating-autonomy-iihs-examines-driver-assistance-features-in-road-track-tests]
It’s important, then, that consumer awareness of the benefits of ADAS increases in order to accelerate the uptake of what are for now, in many cases, only optional safety systems. But it is equally important that the message about what ADAS can’t do, as well as what it can, is put across clearly and not lost among marketing claims. There is an obvious pathway leading from today’s ongoing ADAS developments to the fully autonomous cars of tomorrow, but as far as ADAS is concerned for the time being, the operative word here is ‘assistance’: in all cases, at all times and no matter what the level of assistance, the driver remains not only in overall control but also responsible for what the vehicle does.
The future of ADAS
ADAS technology is advancing at an almost unprecedented rate. Speaking in 2016, chairman and CEO of General Motors Mary Barras wrote: “The auto industry will change more in the next 5 to 10 years than it has in the past 50.” [*Citation www.forbes.com/sites/joannmuller/2016/01/18/davos-2016-gm-boss-sees-a-revolution-in-personal-mobility/#230e04c746bf]. While Barras was also referring to the electrification of vehicles, at the heart of her statement was the drive towards creating safer cars, and safer roads, through ADAS and self-driving technology.
As Barras noted, the next step-change for the advancement of ADAS technologies will be the advent of the so-called connected car, made possible by the widespread adoption of vehicle-to-vehicle (V2V), vehicle-to-infrastructure (V2I) and vehicle-to-everything (V2X) communications. Current ADAS functions are limited by what the vehicle’s own sensors can detect, which today extends to a useful forward range of around 250 metres. V2V communication has the potential to expand on that exponentially by allowing appropriately equipped vehicles to communicate with each other directly and share information on relative speeds, positions, directions of travel and even control inputs, such as sudden braking, accelerations or changes in direction. By fusing this data with the vehicle’s own sensor inputs it will become possible to create a much wider and more detailed picture of the surrounding area and provide earlier and more accurate warnings, or even corrective actions, to avoid collisions.
As an extension of V2V, V2I will provide vehicles with information from the road network’s infrastructure, such as traffic lights and signals, variable speed limits and congestion information. Such information is expected to not only improve safety but also reduce congestion by enabling a freer flow of traffic, and it is also recognised as a key driver towards full autonomy. V2X, meanwhile, adds data streams from beyond the immediate road network, including cloud-stored information, meteorological updates and possibly cyclists, pedestrians and other vulnerable road users (VRUs).
However, in order for the connected car to be realised, a consensus still needs to be reached on which communication system the industry will adopt in order to enable V2V, V2I or V2X. Originally it looked like a standardised system called dedicated short-range communications (DRSC) would win favour. Operating in a 75 MHz-wide band around 5.9 GHz, DRSC would allow V2V communication and and a V2I interface via dedicated roadside beacons (although it’s unclear who would pay for, operate and maintain them). In the United States the frequency was allocated for transport system use as long ago as 1999, then it received approval for the same use in Europe in 2008. Since then much work has been carried out by developers and manufacturers to ensure DRSC’s robustness and reliability for V2V and V2I communication.
In the meantime, V2V’s rollout has been clouded by the arrival of an alternative system with greater potential benefits. C-V2X (‘C’ standing for ‘cellular) was conceived using the LTE 4G mobile phone network. LTE not only allows direct device-to-device communication (i.e. not via the mobile phone network’s communication infrastructure) but it can also, importantly for V2V and V2I, broadcast from one device to multiple recipients. C-V2X also opens up the possibility of incorporating pedestrians and cyclist data in the V2X loop via smartphone integration, thus enhancing VRU safety. It should be noted that in terms of both hardware and infrastructure, C-V2X’s LTE technology has no compatibility with DRSC – the two systems are, in effect, mutually exclusive.
But even LTE 4G is bordering on redundancy as the next-generation 5G network looms, with selected area coverage expected from 2019 prior to a more widespread rollout. 5G is set to offer all of LTE 4G’s benefits but with significantly lower latency – as low as 1 ms compared with 30-100 ms for LTE 4G – along with a data rate of up to 20 Gbps. Such is 5G’s appeal that an increasing number of technology companies, telecommunications firms and car manufacturers have been showing their support for it, not least by joining the 5G Automotive Association (5GAA) that was formed late in 2016. 5GAA membership continues to grow and now includes Audi, BMW Daimler, Ford, Honda, Jaguar Land Rover and Volkswagen, along with AT&T, Bosch, Samsung, Telefonica, LG, Intel and Huawei.
Connected ADAS undoubtedly opens up a new world of opportunity in enhancing road safety and paves the way for full autonomy, but until a technology pathway is agreed upon, its widespread adoption remains some way off.
Current ADAS combines a number of technologies in order to operate. In essence each system comprises at least one sensor to monitor given parameters and relay when necessary information which is then processed and analysed before, if required, sending a command either to give a sensory alert to the driver or to intervene or assist with the control of the vehicle, by braking or steering, for example. With some systems, and under some conditions, a combination of some or all of the above may occur.
Driver alerts may consist of nothing more than a flashing light – a stability or traction control system’s intervention can be so subtle that the driver might be unaware it’s doing anything at all without a tell-tale blinking light on the instrument panel. Other alerts are necessarily more overt: a parking sensor’s increasingly urgent chimes are today familiar to many drivers, while a forward collision warning system often combines escalating warning chimes with an illuminated dashboard alert and a haptic alert through the steering wheel.
Haptic alerts – vibrations through the steering wheel and/or seat – are also a common feature of lane departure warning systems. When the lane departure warning function is expanded to lane keeping assist, the system can intervene in the control of the car to move the vehicle back towards the centre of its intended lane. The automotive industry’s recent wholesale switch to electric power assisted steering (EPAS), which was adopted largely for fuel efficiency reasons, has equipped many cars with hardware that is ideally suited for ADAS functions that intervene with autonomous steering inputs. Self-parking functions and the latest traffic jam assist features that can control the vehicle for limited periods in slow-moving traffic have also been enabled by the advent of EPAS.
Autonomous braking interventions are facilitated by components that heralded the arrival of ADAS in the first place: the ABS control module and pump. Today’s stability control, autonomous emergency braking, adaptive cruise control and traffic jam assist functions, among others, make use of developments of ABS hardware that allow for precisely controlled braking interventions when required.
If necessary, engine output is controlled or modulated by one or more means. In the case of traction control and electronic stability control systems, which often require a relatively subtle limiting of torque, it can be done by suppressing the ignition spark or restricting the fuel flow via the fuel injection system. On later vehicles with electronically controlled ‘drive-by-wire’ throttles, torque can be modulated via the throttle control unit.
Cruise control and active cruise both require full control of the throttle mechanism, either via an actuator on the throttle cable itself or, again on later vehicles, through the drive-by-wire throttle control unit.
Sensor technology is a key driver of ADAS development. ADAS and autonomous driving functions feed off a continuous stream of information about the environment surrounding the vehicle, and it’s the sensors’ job to provide that.
The sensor is required to detect not only everything the driver can see but also that which the driver can’t – or hasn’t noticed. There are a number of different kinds of sensor already in use, each with their own advantages and disadvantages in terms of capability, cost and packaging, and it is increasingly the case that more than one type of sensor is used for each ADAS function. Each type of sensor has acknowledged strengths and weaknesses, so by combining different technologies it’s possible to refine the ADAS functions. This fusion of sensor technology is rapidly becoming the norm – the task then is to process the influx of data from multiple sources both accurately and quickly.
Another factor to consider is the robustness and durability of the sensors. While some sensors can be inside the vehicle’s cabin, many require mounting externally towards the vehicle’s extremes, in vulnerable areas such as the corners of bumpers and behind the grille, and these can be hostile environments for high-tech equipment.The automotive insurance and repair industry has also raised concerns about the issue of expensive sensor replacement or recalibration if the vehicle is involved in an accident.
The growing uptake of ADAS and the ongoing development of autonomous vehicles is driving the advance of sensor technology at an accelerated rate. In terms of object detection and classification, many systems already in use are still operating at a relatively basic level and there is a long way to go before ADAS functionality can make the jump to fully autonomous applications. Current systems can, for example, struggle to identify pedestrians beyond a very specific form. They may fail to recognise a person wearing clothing that significantly alters their outline, if they are carrying a large object or if they are below a certain height. As the technology develops, however, these limitations will inevitably be addressed.
Current ADAS sensor technology can be divided into four main categories, which we’ll look at in a bit more detail.
Perhaps the best-recognised of all the technologies currently adopted for ADAS sensors is radar. Radar – an acronym for radio detection and ranging – is a well-established technology that detects objects by measuring the time it takes for transmitted radio waves to reflect back off any objects in their path. Radar was first developed for concurrently by several nations for military use in the lead-up to the Second World War, but today it has many applications on land, in the sea, in the air and in space. Radar has been in use in automotive systems for some years now so the hardware is well developed and relatively affordable, making it attractive to car manufacturers.
For ADAS applications radar can be divided into three categories: short-range radar (SRR), mid-range radar (MMR) and long-range radar (LRR). SRR systems traditionally used microwaves in the region of 24 GHz but there has been an industry shift towards 77 Ghz due to, among other things, the 24 GHz frequency’s limited bandwidth and changing regulatory requirements. SRRs have a useful range of around 10 metres but up to 30 metres, making them suitable for blind spot detection, lane-change assist, park assist and cross-traffic monitoring systems.
MRR and LRR ADAS functions already use the 77 GHz frequency, which offers higher resolution (relaively speaking) and greater accuracy for speed and distance measurements. MRR operates between 30 metres and 80 metres, while LRR systems have a range extending up to 200 metres in some cases, making them suitable for systems such as adaptive cruise control, forward collision warning and automatic emergency braking. One of LRR’s disadvantages is that it’s measurement angel decreases with range, so some functions, such as adaptive cruise control, combine inputs from both SRR and LRR sensors.
Aside from it being a proven technology, radar’s other key advantages for ADAS use are its ability to function effectively in poor weather, such as rain, snow and fog, and at night. It’s limitations, however, are equally well acknowledged by the industry, namely that radar does’t offer sufficient resolution to identify what an object is, only to say that it’s there. It also has a limited field of view in automotive applications, so a number of sensors are required on the vehicle in order to to provide appropriate coverage. Additionally, SRR using the 24 GHz frequency struggles to differentiate between multiple targets.
Ultrasonic sensors use reflected sound waves to calculate the distance to objects. Of all the ADAS sensor technologies ultrasonics are the oldest and most well-established – bats have been using it for around 50 million years – and ultrasound systems generally have an enormous range of applications in both industry, scientific research and medicine.
Ultrasonic sensors, also known as ultrasonic transducers, have a relatively short effective operating range – around 2 metres – so they are typically used in low-speed systems. Their use in parking sensors has been widespread for some time, but they have also found a place in more complex ADAS functions such as park assist, self-parking and some blind-spot monitoring applications. Ultrasonic sensors are cost-effective and relatively robust and reliable, plus they are unaffected by night time or other challenging light conditions, such as bright, low sunlight.
Given the limited range of established ultrasonic sensors, however, some manufacturers are abandoning them in favour of short-range radar. This is particularly the case with the latest rear cross-traffic/pedestrian alert systems that combine existing parking sensor technology with additional blind-spot detection, although recent developments in ultrasonic technology have seen the ranges of some sensors extend to 8-10 metres or so, making them suitable for such applications.
Lidar (a contraction of ‘laser’ and ‘radar’, or an acronym for, variously, ‘light detection and ranging’ or ‘laser imaging, detection and ranging’ – take your pick) works on essentially the same principle as radar but swaps electromagnetic waves for lasers to generate a high-resolution 3D image of the surrounding environment. Lidar was first developed in the 1960s for meteorological, surveying and mapping use but has more recently been adopted for ADAS and autonomous vehicle development applications. Broadly speaking the automotive industry – with the exception of Tesla – is hedging its bets that Lidar is the best solution for ADAS and autonomous applications.
There are two basic types of Lidar but both adopt the same fundamental principle of measuring reflected laser light. In the first instance, a pulsed laser is emitted onto a rotating mirror which radiates the laser beam in multiple directions. These systems are extremely effective, with a range of 300 metres or more and, if roof-mounted, offer a clear, 360° field of view. Their size, however, prohibits their use for ADAS functions on production vehicles and they are also expensive. A more compact and ADAS-friendly variation of the same theme uses a microelectromechanical systems (MEMS) technology-based rotating mirror to radiate the laser beam.
The second type is known as solid-state Lidar, of which a couple of variations are being developed. One fires a single laser through an optical phased array in order to direct the beam in multiple directions, while the other, so-called flash Lidar, uses a single pulse, or flash, of laser to create its image.
Each of the two main systems has its advantages and disadvantages. Solid-state Lidar is preferable for automotive use not least for being more robust – but in each case the emitted laser is reflected back off any objects within range and is received by a highly sensitive photodetector, after which the information is converted into a 3D model of the immediate environment.
It is the detail and resolution of that 3D model that give Lidar the potential to be such a powerful tool. With the appropriate analytical algorithms, a Lidar system has the ability to detect objects, differentiate between them and accurately track them, all in high-resolution 3D. Lidar also works well in rain and snow, although it can be adversely affected by fog, and its function is unaffected at night.
Historically Lidar has been prohibitively expensive for use in production automotive applications but it is slowly becoming more common in ADAS development as the technology is refined and costs come down. Prototype fully autonomous cars have already made use of the bulky roof-mounted Lidar systems to good effect, but such a set-up is impractical and prohibitively expensive for commercial ADAS applications. For the time being the Lidar systems that are compact enough – and affordable enough – to be packaged out of sight on production vehicles have a relatively limited range measured in the tens of metres rather than hundreds and are therefore only effective at lower speeds.
Camera-based solutions have gained traction as the ADAS developer’s sensor technology of choice. They have their limitations – namely their susceptibility to compromised performance in poor weather and low or challenging light conditions – but the technology, while relatively new compared with, say, radar or ultrasonic sensors, is already capable and versatile. Unlike the other sensors here, cameras are the only ones able to identify colour and contrast information, which makes them ideally suited to capturing road sign and road marking information, and they also offer the resolution to classify objects such as pedestrians, cyclists and motorcyclists. Cameras are also extremely cost-effective, which makes them particularly attractive to volume-selling vehicle manufacturers. Due to the limitations of the technology, the data from cameras sensors is increasingly being combined with radar to provide a more robust and reliable data stream across a wider variety of conditions.
Cameras are used in both monocular and, increasingly, binocular ADAS applications. Forward-facing monocular camera systems feature in medium- to long-range functions
such as lane-keeping assistance, cross-traffic alert and traffic sign recognition systems. Rear-facing cameras have enjoyed widespread adoption primarily as a reversing aid for the driver. A mirror-image view of the area behind the car is displayed on a dashboard-mounted screen, in some cases augmented with positional graphics relative to steering wheel movement to provide parking guidance.
Forward-facing Binocular or stereo cameras are a more recent development. A pair of cameras is able to present an essentially 3D image that provides the information necessary to calculate complex depth information such as the distance to a moving object, making them suitable for active cruise control and forward collision warning applications.
Another branch of camera technology that has established a foothold in ADAS development is thermal imaging. Instead of using visible light, or what little of it that might be available, thermal imaging cameras are ideally suited to detecting humans and animals, particularly in conditions of poor visibility or at night, or simply in an otherwise busy and cluttered driving environment. Again, the technology is well-established and widely in use across the automotive industry, first appearing as passive night vision assist systems on premium-brand models around 10 years ago.
Thermal imaging cameras have a range of up to 300 metres or so and are unaffected by fog, dust, glare from low sun and, of course, complete darkness, and they have a valuable role to play in the ADAS developers arsenal of sensor technologies.
Advanced driver assistance systems on the road
As we have already seen, some ADAS functions are already commonplace on the roads, with many other systems available either as cost options or as standard on more expensive luxury models – an exclusivity that will inevitably change in the foreseeable future.
Many systems share common sensory inputs with each other. By adopting the methodology of lateral thinking so prevalent in ADAS development, manufacturers have been combining existing and new functions to create marketing-friendly ADAS packages, in many cases with some apparent degree of autonomy. Take Tesla’s Autopilot, Nissan’s ProPilot and Volvo Pilot Assist, for example. Each bundles functions including active cruise control, lane keeping assist and blind spot detection to offer Level 2 autonomy under specified conditions. The 2018 Audi A8’s Traffic Jam Pilot function is said to offer Level 3 autonomy, although regulatory issues have so far meant that the system will only be available to buyers in certain regions.
Broadly speaking today’s ADAS can be divided into two camps, although there are inevitable crossovers. First we’ll look at the systems that assist with the the control of the car while it is being driven, either through warnings and alerts or by actively intervening in some way. Secondly, we’ll look at the ‘comfort and convenience’ features that make control of the vehicle easier by reducing distractions to the driver, although some of these systems integrate with those in the first group to provide broader functions.
Anti-lock braking system
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, 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. [*Citation https://one.nhtsa.gov/Research/Light-Vehicle-Antilock-Brake-Systems-(ABS)-Research-Program]
Even so, ABS wasn’t mandated in the United States until 2013, and then in conjunction with electronic stability control (ESC).
Electronic stability control
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.
Traction control system
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.
Cruise control and active cruise control
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 (see below) to offer Level 2 autonomy or beyond.
Forward collision warning and autonomous emergency braking
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 Volswagen’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.
Blind spot monitoring/lane change assist
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.
Lane departure warning/lane keeping assist
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 intially 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.
Parking sensors/parking assist systems
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 apooraching 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.
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