It is estimated that up to 9.3 million people may be impacted by locomotive horn noise and up to 4.6 million of those may be severely impacted.1 In 2009, there were over 1,900 incidents, over 700 injuries, and over 240 fatalities at highway-rail grade crossings.2 Approximately 4,000 times per year, a train and highway vehicle collide at one of over 262,000 public and private highway-rail grade crossings in the United States. Compared to a collision between two highway vehicles, a collision with a train is eleven times more likely to result in a fatality, and five and a half times more likely to result in a disabling injury. Approximately half of all collisions occur at grade crossings that are not fully equipped with warning devices. Some of the drivers involved in these collisions may have been unaware of the approaching train.3 The National Academy of Engineering Committee on Technology for a Quieter America has indicated that the public would benefit if a train horn was more directional and has recommended that research and development be undertaken to better understand the effects on safety, with benefits to the public.4
As a part of an ongoing Federal Railroad Administration (FRA)-sponsored research and development effort, the authors have developed an Acoustical Warning Device (AWD) prototype with an overall goal of maximizing safety at a grade crossing and minimizing environmental noise pollution (at the wayside and in the cabin of a locomotive in reducing railroad worker occupational hazard noise exposure). An initial prototype was created that consisted of one acoustical element. An advanced prototype is currently being developed with three acoustical elements to provide variable directivity and steering capabilities through beamforming. A digitized horn signal has been created based on characteristics from an analog air-pressure locomotive horn. The initial AWD prototype has been analyzed for detectability and noise impact area and the directivity pattern of its sound emissions have been tested. The expected performance of the advanced three-unit prototype has been evaluated based on the test results of the initial prototype and acoustic simulation modeling.
During development of the initial AW D prototype, spectrograms, polar directivity plots, frequency response plots, 1/3-octave band plots, and LAeq measurements of the AWD propagation were analyzed to ensure proper functionality of the AWD, in accordance with FRA and QinetiQ North America’s (QNA) specifications. Based on acoustic simulation modeling, the advanced AWD prototype is expected to generate sound up to 110 dBA at 100 feet forward of the locomotive. The AWD prototype is expected to improve detectability and reduced environmental noise exposure to the community and locomotive cabin.