While reading a recent discussion about the existence of car horns, I started to wonder if there were any safety mandates in the US about how sound-proof a car could be (against outside noise). Is there a maximum percent, or maximum # of decibels, or something similar? The purpose would be so that the driver could hear things like other car’s horns, trains, those warning strips on shoulders, etc.
I recall a commercial for, I think, Lexus in the '90s that had a bunch of percussionists playing pieces of car doors. The other makes of cars sounded tinny, but the piece from the Lexus sounded very muted. I recall thinking that this might not be all that safe, even then, but what do I know?
Car manufactuers, even Lexus, dream about making their cars soundproof. There are no regulations because the technology doesn’t exist. And most likely will not be an issue as long as we use glass for windows. Although I do recall hearing that they can treat the glass with a laminate to reduce road noise as well. Perhaps someone will develope an active noise cancelation technology in the future that makes a totally quite interior possible, but that is just a dream also
You can"t hear sirens and horns when the stereo is making you go deaf anyway. . .
There are road noise limits in the other direction. Though they aren’t enforced much on the street, they are at the manufacturing level. A new car can’t seem too loud to a pedestrian. You might remember sporty models with scoops on the hoods. Because the whawnk of an open scoop would have been too loud, plugs were riveted into the scoop.