Keywords: train horn, directivity, level crossing, safety, audibility, detectability, environmental noise exposure, occupational noise exposure.

Locomotive horns sounded at level crossings can cause significant noise impact to neighbouring communities. The use of locomotive horns provides audibility of approaching trains to minimize the risk of incidents, accidents and injuries. A directive train horn has the potential to focus audible warning signals to desired locations including pedestrians and motorists at highway-rail level crossings while minimizing noise to the surrounding community and employees in the locomotive cab.

As a part of an on-going U.S. Federal Railroad Administration (FRA)-sponsored research and development effort, the authors have examined the feasibility of and recommended an acoustical specification for a directive on-board locomotive horn that would improve the detectability of the warning signal for motorists at critical positions along the crossing road while reducing the area of environmental noise impact. Near the beginning of most sounding events (400 m from the level crossing) the directive horn reduces noise exposure because a narrow beam of sound can be generated and focused at the crossing. As the train approaches the crossing, the beam width must become wider.

It has been found that detectability could be improved and noise impact area reduced by 20 to 40%, but the directive horn must have a directivity pattern that dynamically changes as a function of train position relative to the crossing. While reducing environmental noise exposure, the directive horn can also improve detectability. The variably-directive horn is audible to a motorist inside an automobile with the windows closed at the critical position along the road for a longer distance/duration (measured in regard to the location of the train throughout the sounding event) than a typical standard horn. A standard horn is audible for the entire sounding event, 425 m, and noticeable for 290 m. In comparison, the variably-directive horn also is audible for the entire sounding event, 425 m, noticeable for 348 m and reaches a 95% likelihood of noticeability for 117 m. The directive horn defined in this study also could provide substantial reduction of in-cab noise levels if the device can be mounted forward of the cab.

The directive horn requires a control system with information on the train position relative to the crossing. A directive horn should be able to change orientation and generate different directivity patterns for different crossing road speed limits and track and road geometries to maximize performance. Specific crossing information such as crossing road speed limit, crossing road skew angle and track curvature could be accessed based on a positive train control system or radio-frequency identification tags on signs near the crossings.

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