Patent US 5,223,907

A guard rail detecting device mounted on a motor vehicle has: two image sensors spaced vertically to sense a scene in front of the motor vehicle; a window setting device for setting a plurality of windows on the display screen at predetermined positions; a distance calculating device for calculating the distances from the vehicle to the parts of the guard rail which are held as images in the windows; and a device for calculating the curvature of the guard rail from the distances thus calculated.