Hi all,
we had some discussions on the weirdness of Garmin's routing algorithm in the past.

In August 2014, I described an example, and popej could give a good explanation:
https://www.mkgmap.org.uk/pipermail/mkgmap-dev/2014q3/thread.html#21825

Beyond that, "newer" Garmin outdoor devices (ehm, my Oregon is from 2013) have "activity routing" which causes odd artifacts even when you think that you do not use it: it may send a car to a cycleway parallel to a primary road. or a bicycle onto a motorway. Hence the trick by ligfietser to use non-routable lines for non-cyclable ways is important. Perhaps you can find the messages some where on the forum https://forum.openstreetmap.org/

Regards,
Bernhard

Am 07.06.2022 um 16:16 schrieb lig fietser:

Harri,

Thats why I use on my Openfietsmap not routable lines for highways with bicycle=no.

I misuse the avoidance of toll roads to force the routing to take cycle routes only.

In my scripts I retag all highways that are not part of a cycle route relation with toll=yes,

and all cycle routes with toll=no

I also "upgrade" cycleways and lower classified roads, but this comes indeed with a penalty of

slow or even impossible route calculations.