I think the UK and Ireland seems to be unique in our love for single door buses. In every other country buses have at least two doors. Even in small minor towns and on quiet rural routes the buses have at least two doors. In fact some parts of Mainland Europe even two door buses are rare with almost all buses having three or more doors.
What has shocked me is that in some Mainland European countries even their breadvans have two doors! Mercedes Benz Sprinter breadvans are made as two door buses which is absolutely crazy! Whilst we might be obsessed with single door buses i think this is an example of the Europeans being obsessed with multiple door buses as a breadvan does not required more than one door! It takes up so much seating space on such a small vehicle!
Some examples of these here:
Over in Mainland Europe many rigid buses can have as many as four doors and many bendy buses can have as many as five doors!
Some examples of these here:
Four door rigid buses:
Five door bendy buses:
So even four door rigid buses and five door bendy buses are common in certain parts!
Even over in, New Zealand, Australia, Canada, USA, all of their buses have two doors. I can not think of anywhere in those countries that operate one door buses.
Even in Singapore and Hong Kong and Macau (which have similar buses to the UK) they use all two door buses. You will find no single door buses there.
Malta was originally all single door buses until just over ten years ago when the bus network was modernised and newer buses were bought in.
Then of course there was the crazy situation with the bendy buses in Malta where they operated as single door buses for their first couple of months. This was because the drivers had previously only driven single door buses so were refusing to operate the middle and rear doors. They were citing safety concerns over using multiple doors but some say that it was really just an opportunity to get a pay rise. Arriva tried covering up the dispute by telling passengers the middle and rear doors were locked out of use to prevent fare evasion. After a couple months the unions negotiated a pay rise and the drivers finally started operating the middle and rear doors. It was almost like a bus version of our DOO disputes. But those first couple months were a nightmare with extremely long dwell times on bendy buses (which were used on the vast majority of routes) as everyone had to board and alight through the front door only with the middle and rear doors remaining shut.
Arriva ended up loosing the contract and the bendy buses are gone. Nowadays all buses in Malta have two doors. But there have been some single door buses imported from the UK used for brief periods. But i think these are all gone now.
Cyprus has also previously used some single door buses imported from the UK for brief periods. But i think these are all gone now.
I think the only other place to use full sized proper buses that are single door is probably South Africa which still uses single door buses in most of their cities. Even in all the major cities in South Africa like Cape Town and Johannesburg and Pretoria etc they use almost all single door buses. Even the new modern low floor electric buses they have ordered are still single door. So this might be the only other place.
Also in most third world countries around Africa and Asia and Central America and South America they use some single door buses but most of these are breadvans rather than proper buses.
Russia and the ex USSR countries have their Marshrutka buses but these are the equivalent of our breadvans too rather than proper buses.
The UK and Ireland love doing things differently when it comes to buses. We are the only place that loves using single door buses. We are the only place that loves using double deckers. We are the only place that hates using bendy buses.
So i think the UK and Ireland and South Africa are the only three countries using single door full sized proper buses on city bus routes. Other than the UK and Ireland and South Africa everywhere else puts at least two doors on their buses.