Analysis of Railroad Horn Detectability

The Acoustics Facility of the Volpe National Transportation Systems Center (part of the Research and Special Programs Administration of the U.S. Department of Transportation), in support of the Federal Railroad Administration, is conducting safety research to evaluate the effectiveness of various methods of reducing the number of accidents and resulting casualties at highway-railroad grade crossings. As part of this research, the effort reported here evaluates the probability of detecting railroad horn systems used as audible warning for motorists at highway-railroad grade crossings. To evaluate the detection probability, three sets of acoustic data were collected: (a) acoustic characteristics of railroad horns, including sound level and directivity; (b) insertion loss of motor vehicles; and (c) baseline interior noise levels of motor vehicles. These data were used to determine the warning-signal-level-to-interior-noise-level ratio inside the motor vehicle at the minimum distance that would give the motorist sufficient time to react and avoid a collision. Signal detection theory, which incorporates the motorist’s prior expectations of encountering a train, is then applied to estimate the probability of detecting three currently used railroad horn systems at active and passive grade crossings.