Sidewalks are important. Besides being (obviously?) part of the transportation system (because the purpose of a transportation system is to move people and goods from point A to point B, NOT to move your private motor vehicle from point A to point B), we can put trees in them, manage water and pollution in them, move water/electricity/gas/communications under them and over them, conduct business and engage in social interactions in them. In engineering lingo, they are part of the “public right of way” along with the street. This is why most U.S. cities recognize that they are a critical part of the urban public infrastructure…wait, what? They don’t? They pretend they are private property and put the onus on private property owners to keep them in a state that provides all these public amenities. The article I link to here compares sidewalk policy in U.S. cities and concludes that some are better than others.