• As long as you look behind yourself frequently you will be fine.

    Your ears are very fallible, sound reflects, some vehicles are silent (as are bikes). So hearing can't be relied upon.

    Your eyes can tell you the proximity, speed and size of a vehicle behind you, which your ears can not do.

    Rely on your eyes and not your ears, but try to have music playing at a volume that does not exclude the background noise.

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