These are really unfriendly for hard of hearing people. They're too quiet, so I wouldn't be able to hear one.<br><br>The noise also blends into the background, especially on a busy street. It's not going to be easy to hear.,(reply>), @Face palm Na, not completely right. It is easier for our brains to locate sources of high frequencies because of the small wavelenght. <br>Our brain uses 3 systems: 1. interaural time difference, 2. interaural level difference, 3. spectrum analysis (because highest frequencies are even filtered out on their way around the head). And especially the second one doesn't work if the wavelenght of the sound is longer than the diameter of your head because the wave bends around.<br>So to put in in order:<br>1. white noise -&gt;best to locate<br>2. high frequency<br>3. low frequency (some low bass tones are nearly impossible to locate because their wavelenght is meters long) lambda = c/f <br>e.g. 340m*s/50s=6.8m. That is one long wave.,(reply>), @Nathan Gamble it's not that it's easier to hear the sound, but it's much much faster and easier for people to locate it. A single tone will only have a single simple wavelength to the sound, this is a problem because the brain uses the difference in time between the two ears receiving it in judging the direction. The problem with a repeating pattern is that it's easy for the pattern to be mis-read, to trick you into thinking it's coming from a completely different direction. This is only an issue with higher pitched noises, because they have very quick repeated waves. White noise is probably preferred over a low pitched beeping and so was chosen.,(reply>), @Face palm Of course the science has been done and shown that it's easier to hear white noise than a high-pitched beep, but has it actually been tested in a busy environment where other things are making noise?,(reply>), @Captain Quirk You are wrong. It's wide bandwidth noise, meaning multiple wavelengths. Multiple different chances for your ears to pick up a frequency or two for the "hard of hearing" The purpose for this isn't so it's safer for the streets because it will not make any difference there, a backing up truck is already so far out of the ordinary people will be abruptly aware of it in a normal street side situation. Science isn't just a bunch of people smoking blunts and throwing around ideas, it's hypothesis proven by evidence taken as fact. Your opinion of it is probably intuitive, but that's all that it is. Opinion.,(reply>), @Squant : But it <b><i>does</i></b> blend in.  That's the problem.  It's white noise -- the most bland, ordinary, unobtrusive, "background" kind of noise there is.  It literally sounds like air escaping, which is a perfectly normal thing to hear on a construction site.   And construction sites are noisy -- a warning signal or alarm needs to have a shrill sound that cuts through that noise -- like....oh, I don't know....maybe a high-pitched beep or something. <br><br>So in other words, the brilliant minds that came up with this harebrained idea took the best solution, cast it aside, and replaced it with the worst solution.