Relationship Between Train Horn Sound Levels Tested at 25 m and Sound Levels Experienced at Distance by Track Workers

The factors that affect sound propagation and audibility of train horns were investigated. Sound levels from a static horn above a test track decayed by 6 dB per doubling of distance up to about 30 or 50 m. At greater distances the level decayed by approximately 12 dB per doubling of distance—significantly higher than would be expected from spherical spreading. The effective range of a horn was found to depend on its height—at 400 m, the sound level from a horn 2.5 m above the ground was about 10 dB higher than one at 0.5 m, despite levels at 25 m being the same. At two mainline sites, the mean attenuation rates beyond 90 m were around 9 and 11 dB per doubling of distance respectively. At the second site, horn sound levels were highly correlated with distance. At the first site, horn levels were poorly correlated, suggesting variability in propagation or source sound levels.