Nissan and the Public Work Research Institute of the Ministry of Construction are developing an Automated Highway System. We are investigating a longitudinal control system in AHS. In this paper, a vehicle control method using two actuators an engine and a brake, is described. Experimental and simulated results are shown. A Platoon driving control method using road-to-vehicle and vehicle-to-vehicle communication is described. And the influence of the communication on the control performance is shown by experiments and simulation. The effects of the communication device and control device mentioned above are verified by experimental results in an AHS field test conducted in September 1996 on a dosed highway. 5 refs., 8 figs.