Traffic congestion and accidents can be dangerous to other road users, for example people riding bicycles or walking, especially in an old town built when automobiles were few. Some 20th century towns are designed for automobiles as the main transport. This can cause other problems, such as even more pollution and traffic, as few, if any, people walk. Communities are divided and separated by big roads. Pedestrians are in danger where there are too few foot bridges, small road bridges or other special crossings.