Originally Posted by AndrewP
The speed difference between a ped and cyclist does matter, because motorists only scan the sidewalk for a distance 6 ft away from the path of the car before they cross the sidewalk. Riding on the sidewalk also places cyclists closer to visual obstructions, which delays the point where they can be noticed.
While riding on a sidewalk is not the best idea... the idea that you can only see 6 feet is rather unusual. I find I can usually see to about 1/2 up a block when I am driving. Now perhaps I would not see a cyclists approaching at 20MPH... but rarely do cyclists on sidewalks do 20MPH. Most of the contra-flow sidewalk cyclists I see around here are kids moving at about 8-12MPH or less. The adult contra flow sidewalk cyclists are moving at about the same speeds and are larger, thus easier to see.
Perhaps motorists need to learn to look both ways at sidewalks. And look twice... instead of that blink-glance that usually passes for "Gee, I looked." (and is too often followed by "I just didn't see... " )