Warning signal detection and the acoustic environment of the motorcyclist.

A two-part study was undertaken to investigate warning signal detection by motorcyclists. First the acoustic environment was established for both the helmeted and bareheaded rider between speeds of 0 and 100 mph. For the helmeted rider it was found that below 20 mph vehicle noise was dominant and between 20 and 40 mph there was a variable contribution from both vehicle and wind noise. At 40 mph wind noise became the dominant sound source and increased linearly with the log10 of speed from 90 dB(A) to reach 112 dB(A) at 100 mph. Sound levels were consistently 18 dB(A) greater for the bareheaded rider once above 10 mph, and followed a similar pattern. Recordings of these sounds were sampled into an Amiga computer. Suitable sound combinations were played back at levels appropriate to speed to recreate the rider's acoustic environment at differing speeds. The minimum detection level (MDL) of four traffic warning signals was then measured in 19 normal hearing subjects for three test conditions: no helmet, helmet and helmet with earplugs. The MDL for all warning signals was lowest with a crash helmet in place for sound levels equivalent to speeds of 30 mph or less. The addition of earplugs led to significant reductions in MDLs at sound levels equivalent to speeds of 40 mph, or greater. Signal detection was poorest at all speeds greater than 0 mph, when bareheaded. We would conclude that earplugs are not required for motorcyclists in the urban environment.(ABSTRACT TRUNCATED AT 250 WORDS)