An adaptive cruise control system 1 for a vehicle 3, is capable of operating in at least two modes, a Cruise mode in which the speed of the vehicle 3 is controlled to maintain a set speed, and a Follow mode in which the speed of the vehicle 3 is controlled to maintain a set distance from the preceding target vehicle 5. The system 1 includes means 7 to switch from Cruise mode to Follow mode if a target vehicle 5 is detected within a predetermined distance 9 of the vehicle 3, and a driver display interface 11 for displaying the mode of operation of the adaptive cruise control system 1. A change anticipation system 13 detects when the system operation is about to change mode from Cruise to Follow and causes the display interface 11 to display to the driver that the mode change is about to occur, prior to the system change to allow the driver to take avoiding action.