In 2007, when a combination of 40+C heat and an extra arse grown due to the Brooks saddle I had on my Birdy, I hopped on a bus from Linz to Mauthausen in Austria. I folded the Birdy, but didn't need to, as there were bike spaces at the front of the bus.
Talking of which, when we travelled back on the train to Passau, there was a whole carriage devoted to cyclists. One side was taken up by bike hanging racks, the other side by fold-down seating. There was also plenty of space for panniers, etc. I paid 25 Euros for a 3-hour journey. I thought this was each, but it turned out to be the fare for the three of us and three bikes. All in all, a 3-hour journey.