If you just want the answer, the most widely accepted plural form of bus is buses in all varieties of English, but busses is acknowledged as an acceptable variant by most American dictionaries.
For the verb form, spellings with double s (bussed, busses, etc.) is usual, but the spelling with a single s (busing) is usual when talking about the practice of sending schoolchildren, according to their race, to distant schools in order to manipulate the racial make-up of the population of schools throughout the district. Derived forms of the verb meaning to clear tables almost always have a double s in practice, but American dictionaries typically list the spelling with a single s first.
One day, as I was browsing through my local library, I found an interesting book called The Plural of Bus is Buses, Isn't it? by Michael Paul. The front cover had a picture of a billboard advertising something or another and had the phrase "Busses Welcome". Throughout the whole book, the author made fun of signs of others' use of the English language.
The book was interesting not because I was in agreement with the author but because of my opposition to the author's belief. "Buses?" I thought, "if that were a word, it would be pronounced like fuses and be the plural of buse. The plural of bus is busses." At this point, I (who deem myself the standard of English) became enranged about this one particular word, and started getting upset whenever I saw the word buses.
Until, one day, when I was reading my son one of the stories of the Railway Series by Rev. Awdry (one of the originals, not one of the new politically correct ones that refer to the Fat Director/Controller as "Sir Topham Hat"). There I read all about Bertie the 'Bus.
I had forgotten that the word bus was merely a curtailment of omnibus. Now, I would easily see the plural of omnibus would be omnibuses (since the last syllable of omnibus is not accented). So likewise, anybody who used the term 'bus as a contraction for omnibus would obviously make the plural 'buses.
I began to be more sympathetic towards those who used buses.
However, I would still contend that bus is a distinct word, although historically related to omnibus. Therefore it deserves a plural formed on its own: busses seems to be the best term.
These days I do not get angry when I see the spelling buses. I just figure that those guys are really intending 'buses, but they're one of the many folks nowadays who don't use apostrophes traditionally.
Linguistic concerns
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