If you (society, per laws made by our elected representatives) let people walk along interstate highways, you'll have teenagers dribbling basketballs while they walk, occasionally losing control of said balls and letting them bounce out into traffic. You'll have little toddlers walking with their parents. People will bring their pets, and not always on a leash ( EJR and Phaed wouldn't want those statist leash laws either). Pets will dash out into traffic. On a regular street this would just mean the animal becomes roadkill. But on the interstate highway with people going 80 miles an hour, tailgating each other like they do all the time in Atlanta, this would mean a multi car high speed rack with rollovers and fires and big loss of life.