Here is the ordinance for sidewalk in Sioux City. Proably typical of other communities.
Section 10.52.050 Riding on sidewalks.
1. A person shall not ride a bicycle upon a sidewalk within a business zone or a school zone.
2. A person shall not ride a bicycle upon a sidewalk located on any bridge and shall not ride on the sidewalk approaches to bridges within a distance of twenty feet (20') from either end of the bridge sidewalk.
3. The Chief of Police is authorized to erect signs on any sidewalk or roadway prohibiting the riding of bicycles thereon by any person. Said restrictions, if any, are in addition to the absolute restrictions in 1 and 2 above.
4. Whenever any person is riding a bicycle upon a sidewalk, such person shall yield the right-of-way to any pedestrian and shall give audible signal before overtaking and passing such pedestrian. (Ord. 88/T-6735)
I understand & agree with not riding in a business zone, but not a school zone. In a way I think this discourages people from riding to school, whether it is an elementary school or a college.
The bridge one does not make sense either, especially on the Floyd viaduct. It is part of the established bike trail route. There is a sign that says bicycle traffic yield to pedestrians on each end of the bridge. I think this overrides the ordinance.
3 & 4 are pretty self explanatory.
A largest part of the problem with riding on sidewalks is the severe lack of curb cuts or smoothe tranistions where the sidewalks cross intersect with roadways.