Non-social obstacles.

Just before I took this photo someone who was busy on his smartphone ran right into the fence. I LOL'd.

There are also non-social obstacles, mostly the physical obstacles such as signs (construction, advertisements, etc), tables from a restaurant, dog poo, vomit and discarded items (clothing, furniture, etc.).

This adds to the complexity when compounded by social objects (see below). What is the best route between the static non-social obstacle and the moving and/or non-moving social obstacles? Planning (looking) ahead say in 3 obstacles ahead can provide the time to figure out the best tactic.