AHS (Advanced Cruise-Assist Highway Systems) provide drivers with information, warnings, and operational support to eliminate 1) delays in recognition, 2) errors in judgment, and 3) errors in operation, which are the three major causes of accidents. The systems consist of 1) roadside sensors, which detect obstacles such as standing vehicles, slow vehicles, and rear-end congestion, and transmit the information to vehicles, and 2) on-vehicle systems that transmit the information to drivers by voice and head-up displays (images projected on the front glass) depending on the speed of the vehicle. AHS effectively prevent accidents through cooperation between the roadside and in-vehicle units and providing information to drivers in real time.