The U.S. Federal Highway Administration has released a fact sheet that evaluates how Cooperative Adaptive Cruise Control enables vehicles to adjust their speed to the preceding vehicle in their lane by using sensors and vehicle-to-vehicle communication.

Using a combination of sensors and vehicle-to-vehicle communication, cooperative adaptive cruise control (CACC) takes cruise control to the next level, enabling vehicles to adjust their speed to the preceding vehicle in their lane. The CACC system can also respond more quickly to speed changes by the preceding vehicle and other vehicles farther ahead that are beyond the line  of sight. These advancements improve the stability of traffic flow, increase  driver confidence, and make shorter vehicle-following distances possible. Ultimately this results in better use of  a highway’s effective capacity and greater fuel efficiency. Overcoming the key remaining technical challenges to implementing CACC is the goal of the Exploratory Advanced Research (EAR) Program project “Using Cooperative ACC to Form High-Performance Vehicle Streams.”  The California Partners for Advanced Transportation Technology (PATH) Program at the University of California, Berkeley (UC Berkeley), is conducting  this research, which is funded by the Federal Highway Administration (FHWA). The Technical University of Delft in the Netherlands is PATH’s research partner.

Advancing the State-of-the-Art The sensor-based adaptive cruise control (ACC) currently in use has significant performance limitations. These include a long delay in responding to motion changes by the preceding vehicle and a minimum time gap of 1 second in following the preceding vehicle, which is long enough to encourage other vehicles to cut into the traffic stream. This EAR project will enable CACC to overcome these limitations and provide significantly better performance for drivers. CACC enables vehicles to follow each other more closely and accurately than does conventional ACC, thus improving traffic flow and allowing drivers to safely use their cruise control at shorter gap settings. These shorter gaps can make it possible to almost double the capacity of a highway lane. CACC also helps drivers to feel more confident using cruise control, as the system activates braking action faster than a driver can react to brake lights on the preceding vehicle.

Researchers will also fill the gaps in knowledge and performance that need to be bridged before field operational tests of CACC can begin, which will be needed to enable commercialization of the technology. Knowledge gaps include defining the maneuvers that vehicles have to perform to join and leave a CACC “platoon” or stream of vehicles under different conditions and demonstrating how vehicle-to-vehicle message sets can be adjusted to support CACC operations. These sets allow vehicles to send wireless messages to other vehicles about such data as speed, location, and application  of brakes.