A dual operational mode vehicle detection and collision avoidance apparatus is disclosed characterized by use of a single active or passive acoustic ranging device mounted for azimuth directional movement relative the vehicle to automatically detect the presence and direction of objects in the vicinity of the vehicle. Signals generated by the ranging device are time processed along with azimuth directional signals to generate an output utilized to provide both an audio and visual display of distance and direction of the detected object from the vehicle. In a first operational mode, i.e. a surveillance mode, the acoustic ranging device is sequentially positioned in a left, center and right azimuth directional position to selectively indicate the presence of objects in the individual azimuth direction. In a second operational mode, i.e. a lane change mode, the acoustic ranging device is driven to either a left or right azimuth directional position in response to actuation of the vehicle's turn indicator lever to continuously detect the presence of objects in the adjacent lane of a roadway.