You cannot ride your bicycle on a sidewalk in Wisconsin unless permitted by "local authorities." This means a bicyclist must look to his or her City/Town/Village ordinances to determine whether or not sidewalk bicycle riding is permitted. While it is highly unlikely that a bicyclist riding in a reasonable manner on the sidewalk would ever get cited by the police, it is highly likely that if there is a collision, the insurance company and defense attorney for the non-bicyclist will argue that because the bicyclist should not have been riding on the sidewalk in the first place, the bicyclist is 100% at fault no matter what happened.
See Wis. Stat. 346.94 (1) holding in part, "The operator of a vehicle shall not drive upon any sidewalk area except at a permanent or temporarily established driveway unless permitted to do so by the local authorities."
In Madison for example, the City allows bicycles upon sidewalks under certain circumstances:
12.76 (1) No person shall ride a bicycle on the sidewalk where a building abuts the sidewalk. Bicycle riding on sidewalks is permitted, except as prohibited in this subsection and otherwise regulated in this chapter.
In Milwaukee for example, the City allows bicycles upon sidewalks under certain circumstances:
102-14. Bicycle Riding Permitted on Certain Sidewalks. The commissioner of public works is authorized to mark by appropriate marks and signs that the riding of bicycles by all age groups is permitted on the sidewalk or sidewalk areas of specific portions of highways. Specific locations of bicycle routes may also be found in the common council proceedings, the official record on file in the city clerk's office, and the code on file in the legislative reference bureau.
5 IMPORTANT THINGS TO KEEP IN MIND IF RIDING A BICYCLE UPON A SIDEWALK:
1. When local authorities permit bicycles on the sidewalk, every person operating a bicycle upon a sidewalk must yield the right-of-way to any pedestrian and shall exercise due care and give an audible signal when passing a bicycle or electric personal assistive mobility device rider or a pedestrian proceeding in the same direction.
2. Riding on the sidewalk may increase your chance of collision with a motor vehicle. This is because many drivers pull out onto the sidewalk area when leaving a driveway area. Drivers also tend to look for things that are a personal danger to them (like other cars) and neglect to look for bicylists.
3. Cars turning right at an intersection with a green light may not look behind them and will not see a bicyclist coming from behind them on the sidewalk. Cars turning left from opposite a bicyclist usually look at the oncoming lane of traffic and not the sidewalk-therefore cars will often not see a bicyclist approaching from the sidewalk. The car will turn left in front of the biker.
4. If riding the opposite direction of traffic on a sidewalk be especially careful as drivers pulling out of a gas station driveway and turning right onto a roadway will tend to only look to their left before pulling out. In this circumstance, the driver will not see a bicyclist approaching from his or her right.
5. There is a danger of collision with other bicylists. For example, along PD in Madison, the sidewalk crosses the Badger State Trail bike path. Bicyclists on the Badger State Trail heading north will usually not stop their bikes before they get to the sidewalk because they are primarily concerned with motor vehicles on PD.
More information regarding riding a bicycle on a sidewalk and safety tips from TransMadison and Griessmeyer Law Bicycle Injury Lawyer.