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Heavy Vehicle Forward Collision Warning System (FCW or CWS)
Collision warning systems transmit and receive radar signals using a forward-facing, front-end mounted radar antenna. The system uses data from the antenna to determine the distance and relative speed between the host vehicle and objects in front. It can then provide audible and visual alerts on a display unit to warn the driver of potentially dangerous situations when other vehicles are within predefined distances or closing times. This gives the driver more time to react and, hopefully, avoid a rear-end collision through avoidance maneuvers. Current agency research is underway to evaluate safety benefits and user acceptance of collision warning systems.

Heavy Vehicle Adaptive Cruise Control (ACC)
ACC utilizes conventional cruise control (CCC) and forward-facing radar from a collision warning system in a combined function. With the system operational and no target in the host vehicle’s lane within range of the radar, the system operates like CCC by maintaining a speed set by the driver. If the radar detects a vehicle ahead of and in the same lane as the host vehicle, ACC will maintain a pre-set minimum following interval between the lead vehicle and the host vehicle. The system maintains the following interval set by the driver by adjusting vehicle speed via the engine control module and/or ECBS, thereby helping the driver avoid a situation that could lead to a collision. The primary goal of agency research involving ACC systems is to evaluate its effectiveness in preventing and reducing the severity of collisions.

U.S. Department of Transportation National Highway Traffic Safety Administration
1200 New Jersey Avenue, SE
Washington, DC 20590
1-800-424-9153 (TTY)