The Cooperative Adaptive Cruise Control (CACC) is an extension to the

adaptive cruise control Adaptive cruise control (ACC) is an available cruise control advanced driver-assistance 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 un ...

(ACC) concept using

Vehicle-to-Everything Vehicle-to-everything (V2X) is communication between a vehicle and any entity that may affect, or may be affected by, the vehicle. It is a vehicular communication system that incorporates other more specific types of communication as V2I (vehicle ...

(V2X) communication. CACC realises longitudinal automated vehicle control. In addition to the feedback loop used in the

ACC ACC most often refers to: *Atlantic Coast Conference, an NCAA Division I collegiate athletic conference located in the US *American College of Cardiology, A US-based nonprofit medical association that bestows credentials upon cardiovascular speci ...

, which uses

Radar Radar is a detection system that uses radio waves to determine the distance ('' ranging''), angle, and radial velocity of objects relative to the site. It can be used to detect aircraft, ships, spacecraft, guided missiles, motor vehicles, w ...

, Camera and/or

LIDAR Lidar (, also LIDAR, or LiDAR; sometimes LADAR) is a method for determining ranges (variable distance) by targeting an object or a surface with a laser and measuring the time for the reflected light to return to the receiver. It can also be ...

measurements to derive the range to the vehicle in front, the preceding vehicle's acceleration is used in a feed-forward loop. The preceding vehicle's acceleration is obtained from the Cooperative Awareness Messages (alternatively BSM in the US) it transmits using ETSI ITS-G5,

DSRC Dedicated short-range communications (DSRC) are one-way or two-way short-range to medium-range wireless communication channels specifically designed for automotive use and a corresponding set of protocols and standards. History In October 1999, ...

WAVE In physics, mathematics, and related fields, a wave is a propagating dynamic disturbance (change from equilibrium) of one or more quantities. Waves can be periodic, in which case those quantities oscillate repeatedly about an equilibrium (r ...

technology (both based on IEEE 802.11p) or LTE-V2X PC5 interface as part of the

C-V2X Vehicular-to-Everything (V2X) communication is important in enabling safe, dependable, and efficient transportation services, which can be implied in both the near- and long-term and can meet the requirements of today and tomorrow. Cellular V2X (C- ...

technology (specified by 3GPP). Generally, these messages are transmitted several times per second by future vehicles equipped with ITS capabilities.

Benefits over ACC

ACC systems, like human drivers, may not exhibit

string stability String or strings may refer to: *String (structure), a long flexible structure made from threads twisted together, which is used to tie, bind, or hang other objects Arts, entertainment, and media Films * ''Strings'' (1991 film), a Canadian anim ...

. This means that oscillations which are introduced into a traffic flow – by braking and accelerating vehicles – may be amplified in the upstream direction. This leads to so-called phantom traffic jams (in the best case) or head-tail collisions (in the worst case). It has been shown that ACC systems designed to maintain a fixed following ''distance'' will not be string stable. ACC systems designed to maintain a fixed following ''time'' may or may not be string stable. CACC addresses this problem, and in either case may improve stability, by reducing the delay of the response to the preceding vehicle. In human drivers this delay depends on reaction time and actions such as moving the foot from throttle to brake pedal. In ACC this delay is reduced, but there still is a large phase delay because of the estimation algorithm needed to translate the discrete range measurements (supplied by radar or lidar) to a metric of change in range over time (i.e. acceleration and deceleration of the lead vehicle). CACC utilizes vehicle-to-vehicle communications so that the vehicle has information not just on the vehicle immediately in front (through sensors), but also on a leading vehicle or vehicles further in front, through vehicle-to-vehicle communications of key parameters such as position, velocity, acceleration.

Implementations

The Dutch Connect&Drive project implemented CACC in seven Toyota Prius vehicles in 2009–2010. This project used a communication stack based on the reference architecture of the Car-2-Car Communication Consortium, using IEEE 802.11a hardware at the physical layer. The Grand Cooperative Driving Challenge (GCDC) in 2011 was an international challenge for teams from universities and industry to participate with a vehicle which could cooperatively drive several defined traffic scenarios. CACC was a large part of the challenge. The communication stack was based on CALM FAST, using (by that time commercially available) IEEE 802.11p hardware in the 5.9 GHz range. The criteria on CACC performance included low platoon length, fast traveling time, platoon merging behaviour, and damping behaviour in strong acceleration and deceleration situations.

References

{{Reflist Vehicle safety technologies