I wish people (including motorcyclists, yeesh they play them loud) wouldn't play music on speakers. Cars included if I can hear it.
I do enjoy listening to stuff myself, audiobooks and podcasts, spoken word stuff, through a single earbud in the right ear. It does not impair my ability to hear traffic in any way, I have tested this - I can hear cars just as far away with or without the earbud in.
As far as I know, NO state in the US forbids wearing a SINGLE earpiece while riding a bicycle or driving.
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Work: the 8 hours that separates bike rides.