Sound and Safety
"The car that will kill you is the one you don't see."
"A major study by the League of American Bicyclists finds that the most likely type of fatal bicycle crash is 'motorist overtaking bicycle' - i.e. being struck from behind - accounting for forty percent of cyclist fatalities.”
"It has been said that 'the purpose of the ears is to point the eyes.'
While the ability of the auditory system to localize sound sources is just one component of our perceptual systems, it has high survival value." (ECE Department, University of California - Davis)
"I turn my head about 20-30° to reduce wind noise when talking or listening to someone when I ride.
However, this probably isn't a good idea for long conversations or watching where you're going."
(comment from a major cycling forum)
At moderate cycling speeds (~15 mph to ~20 mph), Wind Noise can easily exceed 85 dB
Wind Noise alters the threshold of hearing, masks, and impacts the perception of sounds
The Wind Noise Spectrum is predominantly low frequency - similar to road and traffic noise
When localizing a sound source, we are best at estimating direction, next best at estimating elevation, and worst at estimating distance. The difficulty of making auditory judgments of distance to a sound source in an open space has been recognized for many years. The combination of loudness, knowledge of the source, and previous sound presentation experience, provide useful information for judging the distance and speed of approaching vehicles.
Visual localization is not always possible in low or reduced light situations, or when the sound source cannot be seen.
Visual / Auditory Localization
Front / Back
Auditory Distance Error
The charts below demonstrate that even at low cycling speeds, wind noise will mask the sound of an oncoming automobile, and at moderate cycling speeds, wind noise will mask the sound of a heavy truck.
Wind Induced Noise
CE Road Test Data (~10 to ~25 mph)
>5,000 calibrated / accumulated data points
(perceived Ear-Wind Noise can vary from recorded
- and perceived Wind Noise varies from person to person)
Wind Induced Noise Spectrum (20 to 20k Hz)
Smoothed Fast Fourier Transform (FFT)
CE Road Test Data (~5 to ~25 mph)
(amplitude variation averaged
- hertz distribution similar
across wind speeds)
Drivers Cone of Vision
Driving speed has a dramatic effect on the driver’s 'cone of vision'. As speed increases, peripheral vision decreases.
At higher speeds, drivers tend to be more focused on where they are going - and less aware of cyclists in the periphery.
Hearing approaching vehicles sooner gives you an opportunity to prepare to be passed safely.
Speech Interference Level
Excessive wind noise interferes with speech which can cause annoyance and irritation. When verbal communications are difficult, the likelihood of miscommunications when cycling increases. A-weighted sound level is the simplest method used to predict speech intelligibility. It is a plot to specify talked-to-listener distance for just-reliable communications. It is common for a person to raise his voice when the background noise is high. Typically, a person raises the voice by 3 ~ 6 [dB] for every 10 [dB] increase in background noise level above 50 dBA.
Sight ))) Sound ((( Safety