Abstract
An investigation was conducted to determine the audibility of locomotive horns and, in particular, the effect of masking when other sources of sound may be present. The investigation was triggered by an accident in which two workers were struck by a moving train. The workers were engaged in routine maintenance work at the time. Tests were conducted with a stationary locomotive as well as one in motion (pass-by tests). The overall sound levels and the frequency spectra of the locomotive horn were measured. During the final pass-by test, a portable hand grinder was in operation. The combined sound level was measured, and the subjective response of persons assembled in the vicinity of the test site was sought regarding the audibility of the locomotive horn above the sound of the grinder. The sound level of the horn of a stationary locomotive, which was about 103 dBA at a distance of 50 m (164 ft) from the microphone location, attenuated at a rate of 7.25 dB per doubling of distance up to the final measurement distance of 800 m (2625 ft). During the pass-by tests, the sound level measured approximately 92 dBA at 50 m (164 ft). Most of the acoustical energy of the horn was concentrated in the range of frequencies from 400 to 1000 Hz. The sound level from the portable hand grinder varied from 96 to 100 dBA at a distance of 30 cm (12 in.) from its motor. Its attenuation rate was 6 dB per doubling of distance. The subjective test revealed that the sound of the grinder motor could mask the horn effectively. The length of warning time depends on the speed of the locomotive. At a speed of 64 km/hr (40 mph), the people grouped around the grinder motor would have had no more than a 10-sec warning. The effects of such environmental factors as air absorption, variation in temperature and pressure, wind and temperature gradients, and ground effect are also discussed.