A collision avoidance system adapted for use with a vehicle, and a method of modifying a first warning assessment algorithm of the system to reduce false alerts caused by overpasses, and maintain sufficient warning distances are presented, wherein the system includes at least one sensor operable to detect an object location, a locator device operable to determine the current position coordinates of the vehicle, a map database presenting a plurality of overpass locations ahead of the vehicle, and an electronic control unit operable to execute a second algorithm, if the detected object location generally matches an overpass location, and in a preferred embodiment, a third algorithm, if the detected location does not match an overpass location, such that the third algorithm is executable over a shorter period than the second, and the second algorithm is executable over a shorter period than the first.