Maps: visual clue for forbidden roads and take bicycle=no into account
Some roads are forbidden for bicycles. On highways this is obvious but when smaller roads are forbidden it is not. Therefore, I suggest to visually distinct forbidden roads from roads where you are allowed to cycle. You could do this by crossing them out.
Forbidden roads can be detected by the bicycle=no flag. The route builder should take this flag into account! Currently it seems it only does not route on motorways (highway=motorway).