Adaptive cruise control


Adaptive cruise control is an available cruise control system for road vehicles that automatically adjusts the vehicle speed to maintain a safe distance from vehicles ahead. As of 2019, it is also called by 20 unique names that describe that basic functionality. This is also known as Dynamic cruise control.
Control is based on sensor information from sensors. Such systems may use a radar or laser sensor or a camera setup allowing the vehicle to brake when it detects the car is approaching another vehicle ahead, then accelerate when traffic allows it to.
ACC technology is widely regarded as a key component of future generations of intelligent cars. They impact driver safety and convenience as well as increasing road capacity by maintaining optimal separation between vehicles and reducing driver errors. Vehicles with autonomous cruise control are considered a Level 1 autonomous car, as defined by SAE International. When combined with another driver assist feature such as lane centering, the vehicle is considered a Level 2 autonomous car.
Adaptive cruise control does not provide full autonomy: the system only provides some help to the driver, but does not drive the car by itself.

History

-based systems do not detect and track vehicles in adverse weather conditions nor do they reliably track dirty vehicles. Laser-based sensors must be exposed, the sensor is typically found in the lower grille, offset to one side.
Radar-based sensors can be hidden behind plastic fascias; however, the fascias may look different from a vehicle without the feature. For example, Mercedes-Benz packages the radar behind the upper grille in the center and behind a solid plastic panel that has painted slats to simulate the look of the rest of the grille.
Single radar systems are the most common. Systems involving multiple sensors use either two similar hardware sensors like the 2010 Audi A8 or the 2010 Volkswagen Touareg, or one central long range radar coupled with two short radar sensors placed on the corners of the vehicle like the BMW 5 and 6 series.
A more recent development is the binocular computer vision system, such as that introduced to the US market in model year 2013 by Subaru. These systems have front-facing video cameras mounted on either side of the rear view mirror and use digital processing to extract depth information from the parallax between the two cameras' views.

Assisting systems

Radar-based ACC is often sold together with a precrash system, which warns the driver and/or provides brake support if there is a high risk of a collision. Also in certain cars it is incorporated with a lane maintaining system which provides a power steering assist to reduce steering input burden on corners when the cruise control system is activated.

Multi-sensor systems

Systems with multiple sensors can practice sensor fusion to integrate the data from to improve safety and/or driving experience. GPS data can inform the system of geographic features such as a freeway offramp. A camera system could notice driver behavior such as brake lights and/or a turn signal. This could allow a following car to interpret a turn signal by an exit as not requiring the following car to slow down, as the leading car will exit. Multi-sensor systems could also take note of traffic signs/signals and not, e.g., violate a red light while following a vehicle that crossed before the signal changed.

Predictive systems

Predictive systems modify vehicle speed based on predictions of other vehicles' behavior. Such systems can make earlier, more moderate adjustments to the predicted behavior, improving safety and passenger comfort. One example is to predict the likelihood of a vehicle in a neighbouring lane moving in front of the controlled vehicle. One system predicts a lane change up to five seconds before it occurs.

Vehicle models supporting adaptive cruise control

The three main categories of ACC are:
In 1999, Mercedes introduced Distronic, the first radar-assisted adaptive system, on the Mercedes-Benz S-Class and the CL-Class. Distronic adjusts the vehicle speed automatically to the car in front in order to always maintain a safe distance to other cars on the road.
In 2005, Mercedes refined the system making the Mercedes-Benz S-Class the first car to receive the upgraded system. Distronic Plus could now completely halt the car if necessary on most sedans. In an episode of Top Gear, Jeremy Clarkson demonstrated the effectiveness of the system by coming to a complete halt from motorway speeds to a round-about and getting out, without touching the pedals.
In 2016, Mercedes introduced Active Brake Assist 4, the first emergency braking assistant with pedestrian recognition.
One crash caused by Distronic Plus dates to 2005, when German news magazine "Stern" was testing Mercedes' original Distronic system. During the test, the system did not always manage to brake in time. Ulrich Mellinghoff, then Head of Safety, NVH, and Testing at the Mercedes-Benz Technology Centre, stated that some tests failed because the vehicle was tested in a metallic hall, which caused problems with radar. Later iterations received an upgraded radar and other sensors, which are not disrupted by a metallic environment. In 2008, Mercedes conducted a study comparing the crash rates of Distronic Plus vehicles and vehicles without it, and concluded that those equipped with Distronic Plus have an around 20% lower crash rate.