When you are riding your bike on a roadway, you are
riding parallel to other traffic, conforming to rules of the road that
provide for the smooth movement of traffic and the management of
conflicts. You are moving in a position that other roadway users
expect to find a vehicle.
When you are riding on a sidewalk, you frequently are
also riding in a roadway. This occurs every time you cross an
intersecting street or driveway, where you will be travelling perpendicular
(!) to the traffic on that roadway. If you are riding at pedestrian
speeds, you have plenty of time to spot approaching vehicles and yield if
necessary. But at cycling speeds that you would use if you actually
want to get somewhere, you often will “appear” in these
intersections as if by magic (that is what the driver that hits you will
tell the officer).
Roger Pierce