A study of sound level of train horns measured inside selected vehicle types

The audibility of a locomotive horn inside five vehicle types was investigated. A-weighted and octave-band sound level measurements of a recorded train horn were taken both inside and outside each selected vehicle in order to determine vehicle shell attenuation values. These values were subtracted from train horn levels as measured 350 and 500 feet from the front of the locomotive to predict warning signal level inside each vehicle. Sound level measurements were then taken of the internal noise level of each vehicle while moving 30 mph with the air conditioner/heater; (a) off; (b) at medium setting; and (c) at high setting. Thus, six simulated conditions were considered for each vehicle.

A predicted signal-to-noise ratio of horn signal level and vehicular interior noise was determined for each simulated condition. The criterion, for audibility was a +9 dBA signal-to-noise ratio or a +9 dB signal-to-noise ratio for at least two octave-bands.

In four of the six conditions considered in this study, locomotive horn signals did not penetrate vehicles with sufficient intensity to warn a motorist. For one of the five vehicles used in this study, the audibility criterion was not met for any condition. Specifically, the audibility criterion was not met when the vehicle air conditioner/ heater was set on high and when the simulated critical stopping distance required for the vehicle was 500 feet from the locomotive. Further, none of the sound measures taken in the luxury vehicle (Cadillac DeVille) met the audibility criterion.