罗斯 is right. In British English, the phrase is 'public transport', while US English speakers say 'public transportation' or 'public transit'. In general, the British English convention is used in the UK, Ireland, Australia, NZ and SA, while the US version is usually confined to North America.

in British English (and I think in American English as well) "public transportation" sounds very odd. It makes perfect grammatical sense, but to the native speaker "public transport" sounds much more normal.

Hi Rook, I may be wrong but I believe it is an Amercian / European English difference. In my Irish / European English 'transportation' sounds very unusual but I believe in American English 'transportation' is more usual.