Bike lanes. Pure and simple... on my commute, there is one particular area where the motor traffic backs up for up to a good half hour to do about one mile up a pretty steep hill. (it is unbelievable that people would actually wait this long to go this "shortcut"). The reality is that the only other routes tend to back up also, so folks take this route thinking it is a viable alternative, but there is no escape outlet once you have gone this way... so the queue can become quite unmanageable.
There is a bike lane on the road, and taking the bike lane allows a cyclist to pass all this traffic... with only one intersection (that leads to an apartment complex). I do it at about 8MPH and just zoom past all the motorists sitting right there.
I don't think this is a case of vehicular verses non vehicular, but it sure is a case of "the skinny vehicle" beating the heck out of "the big fat cages."
Other areas that I ride that are non-vehicular involve sidewalks... and slow recreation rides with my wife.
Frankly I really like going fast, and that to me involves cleats and funky pedals... so I really don't like anything that puts me into pedestrian mode... thus I tend to ride vc style, just to get to smooth pavement.
I do however on rare occasion make a quick run to the local stores on my beach cruising fat tire bike... and I use any surface I can ride on with that thing... sidewalks, dirt tracks, alleys, median centers, lawns... If I can roll across it... it is fair game.