It still must be safe on the sidewalks, since the overwhelming
majority of bike users in America just ride on them.

=v= Not in New York City. N.Y.C. is the most carfree city on
the continent, and an excellent place to ride a bike. Part of
the reason is that the pace of ground transportation is set by
pedestrians and motorists are for the most part resigned to
their fate, and even impatient clueless out-of-town motorists
usually have nowhere to go at the speed they're accustomed to.
The city also has an extensive greenway system.

=v= There are some bicyclists on sidewalks -- mostly delivery
vehicles -- but for the most part it makes no sense and the
density of pedestrians prevents it.
_Jym_