Many serious runners think the asphalt of a street is easier on the joints than the concrete of a sidewalk. When I was a runner, I didn't run long enough distances for it to make a difference. Running was painful on my joints either way!

Anyway, running can be safer than biking. A runner can legally run on the left side of the street and have a shot at jumping out of the way of an oncoming car. That's not an option while riding a bike. A biker can have a rear view mirror while biking on the right side of the street, but still the visibility would not be nearly as good as a runner who's facing traffic. Also, a runner can still wear the reflective gear that lights up the runner like a Christmas tree.