Originally Posted by UniChris

I don't think anyone is expecting that a bike route alone be built, but rather that the non-motor-vehicle route sometimes would be best separated into mandatory pedestrian and cycling routes.

Of course non-compliance is an issue - occasionally by cyclists (though not as much as on routes that have no cycling alternative), much more by pedestrians.

Some examples from NYC:

Ocean Parkway path has a fence down the middle, massive non-compliance by baby carriage pushing grandmothers

Williamsburg Bridge - bikes on one side pedestrians on the other with all the car lanes in between, again reported pedestrian non-compliance

Brooklyn and Queensboro bridges - in the process of having a drastically separate vehicle lane turned into a bike lane to replace a previous shared one (which in the Brooklyn case had a paint divider). We can guess from the Williamsburg bridge example how that will go...

My favorite example though is in Battery Park where they just made the bike-only lane too darn pretty. It's this sinuous pair of directionally split single-file paths through a flower garden, and people just can't resist taking an evening stroll there, and not on the no-bikes-allowed sidewalk 30 feet away. They should have left it harsh and utilitarian to be the key connector that it is, and maybe planted the garden with its paths a bit to the east for the evening stroller crowd.