The government specifically refused to do such a thing, knowing that it would lead to a mass cacophony of random noises. In the proposed rule, all vehicles of the same year, make, and model must sound the same with no provisions for customization.
Ugh. It has to be a pleasant sound that does not make young people or people with good hearing go deaf or get damaged hearing. We are not in the Rock Music age any more, so it is not expected that everyone will have hearing damage already. No need to make more handicapped people. If it is not a safe pleasant sound, guaranteed it will be disconnected and the cure will be worse than the disease. I could see people who get damaged hearing from the sound of it driving very fast through crowded pedestrian areas just so their ears don't hurt. I really hope the government has people smart enough to realize that when picking a sound, rather than Hollywood-style focus-grouping it.
There's a regular horn, but also a "cricket" button to notify pedestrians and cyclists in low-speed zones.
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Edit: you can hear it from a pedestrian POV in this video (at 4:04):
No. Just no. A cricket sounds like a cricket. It won't help people because they'll think it's a small insect, like a cricket, rather than a big dangerous car. The focus groups got it wrong. The focus groups were probably packed with urban people who have never seen a tree, or at least never anything but a stupid dead Maple tree. It has to sound like a man made object worthy of hurting you, but not sound ominous, just big. Something man-made sounding and big but pleasant and not ear-damaging (even for those with good hearing). (btw, those gentlemen looked pleasant looking in the second video
)
Over this side of the pond (maybe over your way too?) the larger construction sites only allow heavy vehicles that have reversing sounders which produce white-noise, because pedestrians poorly estimated the location of vehicles using the older beep-beep type warnings. For years I thought the white-noise vehicles had reversed into something and had broken their sounders!
This does solve a problem. The reason that focus groups picked the ear-damaging beeps is that the deaf people on the focus groups could barely hear them, so they were able to locate them, while younger people who still have good hearing would hear the ear damaging beeps bouncing around from literally all directions and be accosted by the injurious nature of them, so they would basically recoil in horror, and eventually use ear plugs and ignore them since they are meaningless and constant (any normal construction site has about 500 vehicles making the noise whenever they back up, so it didn't mean a thing). I like the white noise idea in concept, but they still got it wrong: on a construction site, many pieces of equipment would both sound like and drown out any white noise. I can consider a construction site simply an extreme version of a busy urban area. Something besides soft white noise and harsh damaging beeps has to be picked; something melodic, orderly, yet identifiable and clearly audible while not being overly loud. A lower pitched noise would be a good start.
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Ok, so let me think. What sounds like a big man made object capable of stampeding you? First of all, I can think of an animal that is similar: an elephant. Even a large cat. Or a bear. So, if we take the trumpet of an elephant, the roar of a cat, or the growl of a bear, and mix them all together, and then try to find some man made noises that can adjust that, such as some music that is not clanging metal, nor high pitched beeps, nor anything ear damaging, and then sort of put a little art into it that is not insulting or noise polluting, then it would be a good foundation for a noise that makes sense.
Maybe a
tuba? Essentially a quieter version of a fog horn from a distance. The tuba doesn't have the metal clanging problem. Since it's a tuba, a nice three note piece could be made that changes in tempo, melody and pitch according to speed, direction of turn, and acceleration (or deceleration). Matching which thing to which thing could be focus grouped, but not by a bunch of stupid people.
I propose starting with pitch for speed (higher pitch for higher speed, but all very low pitches both in upper and lower bounds of the sound speed range), tempo for acceleration (more tempo for more acceleration, less tempo for less acceleration), and the melody could start and end with the same note (3 notes) for straight, end with a slighty higher note for right turn, and end with a slightly lower note for left turn, and the pitch difference of the first to last note can be the angle of turn (more difference equals more angle of turn). The middle note could be in pitch roughly equal to the necessary stopping distance of the vehicle: higher for longer stopping distance, lower for shorter stopping distance; this would be a measure of reaction danger. The sound would be three notes, then a pause of two notes, so 5 beats per measure. This would allow both the ascertaining of which notes are first, middle, and last, to be able to guage direction and stopping distance, while allowing the ability to match one measure with the next measure so that the mind could track a single vehicle (I've heard notices that are either too frequent or too infrequent and fail on those marks). No note should ever exceed Middle C on a piano (
261.626 Hertz) (and thus that would define the upper bound of the ranges), nor the decibels that would ever hurt any human ear. It should literally be a
tuba sound that uses no metal sounds. Any blind person would instantly find this an easy regimen to learn and understand with pretty clear understanding.
Oh, and before the bean counters get to it and say "the speaker that makes a tuba sound is too expensive because it has to be too large", then I answer by saying, then disconnect the speaker and throw it in the garbage, because
WE DON'T NEED ANY STINKING NOISES TO BEGIN WITH!!! So, if there's ever going to be any noise, the bean counters can get over it and put a proper system in, or else it will be bypassed and they might as well save the money and have no noise system.