From the math I've seen, bicycling is 1 order of magnitude lower CO2 emission than driving. Here is one source https://ecf.com/news-and-events/news/how-much-co2-does-cycli...

I was surprised it wasn't a bigger difference myself.

It also appears buses are in the 1 order of magnitude range: http://www.dnrec.delaware.gov/dwhs/info/Pages/OzonePublicTra..., https://www.citylab.com/transportation/2012/11/can-we-please...