Bus drivers are pretty kind to cyclists around here, but I meet up with one at the start of a very narrow steep hill, with the exhast at ground level. If I see a bus coming, Ill stop and let it pass, then wait a minute to let the exhasut gas blow away.
The technology for clean buses is out there, why does no-one use it. High exhaust pipes is such an obvious solution, and using liquified natural gas would be clean and cheap. So may drivers ridicule busses, becuase they produce so much exhast, like there is no way to reduce it.

The best draft I ever had was a high-sided electric mild delivery vehicle.