This report summarizes the research and development of a variable directivity Acoustic Warning Device (AWD) used as a locomotive horn. A Global Positioning System (GPS) was developed to control an arrangement of directional loudspeakers. Loudspeakers are arranged on the locomotive so that sound is directed forward when the horn is initially sounded 1/4 mile from a grade crossing. Other loudspeakers are sounded approaching a crossing to direct sound more to the wayside. This approach reduces wayside noise and maintains horn detectability. The work took place at the Transportation Technology Center (TTC) with wayside sound levels comparing well to predicted patterns.