> The ideal size for a bus goes down No, it doesn't, because if you have lots of small buses then high-traffic areas will get clogged with lots of little buses

> The ideal size for a bus goes down No, it doesn't, because if you have lots of small buses then high-traffic areas will get clogged with lots of little buses loading and unloading and just physically taking up space in bus lanes. If anything, you generally want _bigger_ buses; most large cities size buses as big as the road infra will take (with the exception that a lot of cities won't consider double-deckers even where they'd make sense, due to lack of familiarity). Now, some of that is drivers, but some of it is just capacity. (Or sometimes slightly bigger than the road infrastructure will take. About once a decade, Dublin Bus tries articulated buses, which then get stuck on roundabouts, reminding Dublin Bus why it doesn't have articulated buses.) The mass difference between a big bus and a small bus also isn't generally _that_ huge. A smallish single-decker is about 10 tonnes, these days a big double-decker is only about 12.