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, and living organisms have found many ways to extract directional information from sound."
(ECE Department, University of California - Davis)
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
"The average person facing a 21 mph wind experiences wind noise at an intensity of 92 dB."
(Experiments on the Noise Heard by Human Beings when Exposed to Atmospheric Winds, NTNU, Trondheim, Norway)
"Innovative safety technologies will continue to play an important role in the way
cyclists interact in traffic... particularly as vehicles become quieter." (Safety Science 2018)
Wind Noise Masking the Sound of Approaching Vehicles
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.
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.
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)
Sight ))) Sound ((( Safety
SPEECH INTERFERENCE LEVEL (SIL)
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.
"Cycling safety improvements have an aggregate elasticity value that is greater than one.
This means that safety improvements attract proportionately more people to bicycling
(i.e. a 10% increase in safety results in a greater than 10% increase in bicycling)."
Noland R., Perceived Risk and Modal Choice. Dept. of Economics, University of California, Irvine, CA