Running on a sidewalk is terribly unpleasant, and has its own dangers. Sidewalks tend to be uneven, among other tripping hazards. And there is limited reaction

Running on a sidewalk is terribly unpleasant, and has its own dangers. Sidewalks tend to be uneven, among other tripping hazards. And there is limited reaction time to anticipate motorists who speed out of driveways, bowling past the sidewalk but braking before they enter the street.