A few points I go by. Buses are to move people around small areas and metro/subway stops. Metros are to move people between districts. My bus routes are relatively small and I try to limit them to 6 stops. By making them small you reduce the down time for people who want to travel in the opposite direction (e.g your route travels clockwise but their destination is counterclockwise of the bus stop). My developed 'inner city' is pretty grid like, so I have a north and south metro line that feeds my downtown commercial and office area then continues on to my industrial. My bus lines only feed the metro stations and don't take people downtown. So far I can keep about 40% trips saved. Another tip if you have long blocks --- break them up with pedestrian paths. Cims will walk all the way around the block but a single pedestrian path will cut down travel quite a bit.