This paper is concerned with safety in (cooperative) adaptive cruise control systems. In these systems, the speed of the cars is maintained automatically, based on the preferred speed of the driver and the speed of the preceding car. Technologies that are used in these systems, such as radar and radio communication, introduce many factors of uncertainty in the system. In this paper, we present models for different adaptive cruise control strategies, in which this uncertainty is explicitly modelled. By simulating emergency braking situations under these uncertain circumstances, we find the minimal safe time headway for these strategies.