From my reviews of safe bicycle riding, the sidewalk is less safe than the street. Marcus_Ti points out the key reason. It turns out that the highest accident in our town is a sidewalk. The town, which is slow to encourage bicycling on a wide basis, did create a bike lane on a sidewalk next to one of our small town, busy street. The result was the highest accident rate in the city. It crosses busy shopping driveways. Motorists do not look along the sidewalk and consequently accidents occur.