Privately operated public transport (e.g. jitneys and ferries) frequently are when positioned at a premium, as Waymo is.
The driverless cars can also, well, drive themselves to a cleaning center during the night-time when it won't affect the income generation.
Another interesting possible feature is to redesign cars to be more easily cleanable. Driverless cars can dispense with the central console, steering wheel and pedals, with simple hard plastic covered in detachable covering. Even the seats can be made detachable.
In New York right now. Subway stations are dinghy. But the cars themselves are fine. Hop on the Metro-North or LIRR and they're on par with European cleanliness standards. (If not behavioural.)
European trains are far cleaner.
They can. My local state operated ferry plays an announcement on every ride that if you harass the staff, they will issue a no trespass order banning you from the service for 60 days. Violating the order is criminal tresspassing.
Of course, enforcement isn't easy, and confronting passengers to issue the orders isn't easy, and both can contribute to confusion and delay. It's a little easier to do on a ferry vs a bus because there's more staff.
If you're looking for easy clean surfaces, you could go for police car backseats. Not very comfortable from the looks of them, but very amenable to cleaning.
I might believe that for ferries, they have personnel for that.
Our local bus drivers were told that fentanyl fumes are not harmful, and that asking the state to do anything about junkies smoking _on_ _the_ _bus_ is systemic racism or something.