Nevermind safety and all that .........
Check into LEGALITY. In some states and provinces it is ILLEGAL to ride your bicycle with headphones. No, you may never get caught. Maybe the police really don't care and will never enforce that law. But one day ....... maybe they will.
And .... when you're parents taught you to ride a bicycle back when you were 5 or 6 years old, didn't they tell you about listening to hear the traffic, and about being able to locate where the traffic is by sound, and about being able to tell how fast the traffic is moving by sound and all those things? Or have you just recently learned how to ride a bicycle?