Systems designed to prevent vehicle collisions by using sensors, imaging, and real-time processing to detect potential conflicts and to suggest or perform actions to change the trajectories of the vehicles involved. Different technologies are used for different vehicle types. For aircraft, traffic/airborne collision avoidance systems (TCAS/ACAS) are based on the use of radar and aircraft transponders, and typically instruct the pilots on the most appropriate action to take. For shipping, the automatic identification system (AIS) uses marine radar and satellite tracking, along with a VHF transceiver on board each ship. For cars, systems are being developed using lidar, all-weather radar, and cameras linked to image processing systems, with a focus on forward collision detection and automatic braking.