There shouldn't be a lot of sooty exhaust. Well, there doesn't have to be. San Francisco's run diesel-electric hybrids for about fifteen years now and Califor

There shouldn't be a lot of sooty exhaust. Well, there doesn't have to be. San Francisco's run diesel-electric hybrids for about fifteen years now and California is far more stringent about diesel emissions than most of the rest of the country. So, sure, it's entirely believable that you're seeing buses belch smoke but it's also mandatory. Unleaded gasoline will leave a nasty residue on your exhaust but that's about as bad as it (should) get. Alcohol and gas will burn cleaner but come with their own drawbacks. Trolley buses, of course, don't have tailpipe emissions but not everyone is willing to put up with the overhead infrastructure. And hey, battery EV buses are starting to become a thing too (e.g. SF is trialing ones from a few different manufacturers).