You're entirely right that we shouldn't rely on sensory input from our ears to drive or cycle. However, the fact of the matter is that many people use their hearing to supplement their other senses.
When I worked with deaf people as relay operator, a question asked by a coworker during our orientation session on deaf culture was 'How do deaf people drive if they can't hear sirens from emergency vehicles?' The answer is that they rely on their other input to and have learned to compensate for their lack of hearing. In effect they may be aware of these possibilities and check their rearviews more frequently to account for not being able to depend on auditory updates.
If all vehicles were completely silent, it would remove the benefit those of us with hearing gain from the additional input, even though this input isn't strictly speaking necessary. We could and would adapt, sure, but I think that additional factor when cycling does help in some situations. I can see engines making some noise to be advantageous, even if it only makes the difference of one fatality a year, because there is very little drawback.
When I worked with deaf people as relay operator, a question asked by a coworker during our orientation session on deaf culture was 'How do deaf people drive if they can't hear sirens from emergency vehicles?' The answer is that they rely on their other input to and have learned to compensate for their lack of hearing. In effect they may be aware of these possibilities and check their rearviews more frequently to account for not being able to depend on auditory updates.
If all vehicles were completely silent, it would remove the benefit those of us with hearing gain from the additional input, even though this input isn't strictly speaking necessary. We could and would adapt, sure, but I think that additional factor when cycling does help in some situations. I can see engines making some noise to be advantageous, even if it only makes the difference of one fatality a year, because there is very little drawback.