While running on the sidewalk offers some serious safety features, like no cars, Cool Running has ranked it as the worst surface for running. Rock-hard concrete is hard on your joints since it provides zero shock absorption. Ideally, we should all run on grass or dirt trails, which are more gentle on our joints. If you're an urban runner, finding these surfaces for your regular runs can be a challenge. Asphalt is considerably more forgiving than concrete, which is why running in the street is preferable over the sidewalk. Remember if you run in the road to go against traffic, so you can see oncoming cars. I suggest mixing up your surfaces and searching for tracks in your area for at least one run a week. Tracks are great for interval practice too. Where do you usually run?