I bet the earplug stuff is buried in general vehicle regulations, if there is any specific language.
(Like stuff prohibiting headphones on drivers...even though I see it often. Not just one earphone/headphone....)
I wonder how many states changed laws to allow use of cellphone headsets?
If you're on a Goldwing, or big touring bike, how loud do you have to crank up the stereo to be able to hear it over the road noise, and can you still hear an ambulance coming up behind you?
I don't crank the stereo up in the pickup much, and it isn't real loud anyway, but the newer cars are pretty quiet with the windows up and it's difficult to hear emergency vehicles coming at you.
And then we have the megawatt morons 'boom....boom...booming' down the road, annoying everbody.