Sidewalks often intersect car trajectories, either due to driveways or street crossings. Pedestrians are relatively easy for drivers to see because they move s

Sidewalks often intersect car trajectories, either due to driveways or street crossings. Pedestrians are relatively easy for drivers to see because they move slowly. Bicycles on the other hand can be moving quite quickly and often believe (often correctly) that they have the right of way. Combine that with poor visibility, typical lack of bicycle lights/reflectors/etc, and unpredictable behavior, and you have a recipe for disaster.