Do any of you use routes which are not strictly speaking official routes of any kind (road/sidewalk/bike path).

I think on every commuting route I have made use of tracks, trails and shortcuts which are not marked on any map.

Judging by the number of tyre tracks, I am not the only one using these routes.

Michael, interesting.

I cannot say I do use "grey routes," since I have
so many established routes that serve me well.

Yet I do remember searching for a particular shortcut through a park where there were no routes
shown on the map. Some trails led me into the woods and around a lake, behind some houses, but the only cut-through would have been through someone's yard. Other times I have looked for cut-throughs but failed because creeks/ravines severed the possible routes.

I ride my mountain bike on nasty days and for sure 'create' routes; I love playing in the mud on my way to work. My favorite is across an earthen dam at a nearby park, mostly to scatter the geese.

Bike paths often end in a manner that invites use of "grey" routes, such as at intersections of 5 streets with busy motor traffic.

One of my routes has a bike path that ends at a grass field with 200 yds to a road on which to continue my ride.

On one route home I take 50 yds against the traffic to save doing a left turn at a nasty high traffic intersection, and also save a bit of travel distance.

On the way in to work I have to do a left turn at traffic lights off a divided road with 3 lanes in each direction. When the lights are red as I approach, I cross to the sidewalk on the opposite side, while the cars are stopped at the lights. I have never encountered pedestrians there.

Where I live, there is a major train line for commutes and I can bike by a few of the stations (or take a path at the golf course) to get under the highway that is next to the train tracks. I don't think any of those paths are actually on maps.