snagitseven

There is nothing in the manual's 6 pages of the ACC section stating the system will disable if no vehicles are detected after any time period. (It does mention that ice, snow, dirt, insects, etc. can prevent ACC from working properly).

ACC only senses moving vehicles that are being followed. The system will not react to stationary objects not previously followed or any other object, person or animal in or adjacent to the lane of travel such as guard rails, signs, stationary vehicles, poles, trees, etc.. Also, anything crossing in front of the direction of travel, i.e. vehicles, pedestrians, animals or oncoming traffic will not be detected. The ACC is designed to only register a followed moving vehicle and Braking Guard will activate on the tracked vehicle if that vehicle subsequently stops. It will NOT stop the car if an already stopped vehicle or any other stationary object is encountered.
It's all comprehensively described in the manual.