Cooperative Adaptive Cruise Control

The Cooperative Adaptive Cruise Control (CACC) is an extension to the adaptive cruise control concept.CACC realises longitudinal automated vehicle control.In addition to the feedback loop used in the ACC, which uses Radar or LIDAR 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 or DSRC / WAVE technology (both based on IEEE 802.11p). Generally, these messages are transmitted several times per second by future vehicles equipped with ITS capabilities. The Cooperative Adaptive Cruise Control (CACC) is an extension to the adaptive cruise control concept.CACC realises longitudinal automated vehicle control.In addition to the feedback loop used in the ACC, which uses Radar or LIDAR 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 or DSRC / WAVE technology (both based on IEEE 802.11p). Generally, these messages are transmitted several times per second by future vehicles equipped with ITS capabilities. ACC systems, like human drivers, may not exhibit string stability. 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.