I've been creating routable Garmin maps since 2012, first generating a .mp file and then using mkgmap to produce a Garmin IMG file. Last year I noticed that the routing had changed, directing me along short-cut paths which were supposed to be blocked for the chosen "Activity". This week I delved into that problem and found that setting the the .mp "RouteParam" "denied_bicycle" flag to 1 now does not have that effect - bicycles are always routed just as automobiles are. FYI I tested all the "RouteParam" "denied" flags and could not find any which could deny bikes but not deny autos, or vice versa.
I could not find any mention of this change on the forums except for popj noting that "GPSMAP 66, Edge: Bicycle routing uses highways" in the recent topic "Garmin .img maps" (I know that most people do not make routable maps.) So I wanted to note here that this routing change seems general since it occurs on my GPSMAP 64 as well as my 66. Hopefully it is a bug that Garmin will later correct.
Any additional info that others have would be appreciated. The loss of the additional "Cycling" routing option, leaving only "Automobile" and "Pedestrian" options, has affected both how I make and how I use my maps. [Background: my maps are hiking maps and previously I could control routing over roads, official trails, and use trails - but now in order to preserve ability to route or not-route along use trails I cannot discriminate between roads or trails in the routing.]
Jack
PS: forgot to mention that the "denied_pedestrian" RouteParam now does not block the "Pedestrian" activity!
PPS: later found that the expected behavior works for my 66 only when I also select the "Minimize Time" option - for "Minimize Distance" it routes along "denied" paths. A still trying to figure out how the "Minimize Time" and "Minimize Distance" choices affects things.