I have noticed that carpoollanes avoidance blocks all roads with access=no or motorcar=no tags in the car and bicycle profiles :confused:
So in the default mkgmap settings this means that cycleways are avoided even in the bicycle profile (default tags are access=no & bicycle=yes). A solution is to use other profiles where carpoollanes avoidance can be switched off or where carpoollanes are ignored (dirt bikes?).