Funny, as a pedestrian, I daily observe that any sidewalk a bicyclist is capable of riding on will be entered by a bike, with resulting risk of injury or death

Funny, as a pedestrian, I daily observe that any sidewalk a bicyclist is capable of riding on will be entered by a bike, with resulting risk of injury or death to pedestrians. I have indeed daydreamed about ways to introduce barriers to prevent bicyclists from riding on sidewalks, but without success. Any ideas?