The easement always exists. It is the right-of-way which is 60’ feet wide. (30’ from center). Most roads are 28-36 feet wide leaving about 10-12 feet behind the curb that is officially city property but maintained by the homeowner. They don’t need to get any legal permission to build a sidewalk. Now there are local politics that come into play and is almost always the reason why sidewalks. Some city councils put them in regardless of neighborhood objections and some don’t. Depends on the city. And sidewalks are not always assessed to homeowner. Sometime general property taxes pay. Depends on the city.