With the trailer I'm stuck on trails-no cars. I do have to watch out for other people though-don't ride down the middle of the trail and look behind me as well as in front before I pass. With or without music. I have not been listening to music with my kiddo because I want to stay tuned to his needs and joy.
Still, I can hear just fine over JB's songs.

When I'm on the road no music but for the constant drone of cars, punctuated by the sharp notes of honking and tire squeals.

I wouldn't want music in town but I think it'd be fine on country roads-if some guy's going to hit you while passing there really isn't going to be any way you'd know it until you were being hit and even if he had, say, a sudden tire blowout (this happened to a cyclist a few years ago around here), and swerved into you there would be no time to react and move out of the way. When I was hit by a truck coming out of a side street I was not wearing earbuds and was aware of the truck who was stopped at a stop sign. He hit the gas when I was directly in front of him and there was nothing I could do to get out of the way even though I heard the engine rev a second before I was hit. All IMO, of course.