I've been in Japan for the summer and noticed that the announcement for the closing doors (in the Kansai area, at least) on trains is always 扉が閉まります. However, the equivalent announcement on buses appears to be a toss-up between 扉が閉まります and ドアが閉まります.
Is there an accepted distinction between 扉 and ドア? jisho.org gives ドア as a Western-style door and 扉 as a (generic) door. Are there any other distinguishing nuances?
I always think of 扉 as sliding doors (as also usual in trains and buses), and of ドア as a door with hinges (or some other more modern/Western construction, like elevator doors).
See 類語例解辞典《小学館1994,2003》
① 「扉」は、[蝶番]{ちょうつがい}などを軸に回転するようにして開閉する機構のものも左右に開閉するものもいう。
(「扉」 is used for both doors with hinges and sliding doors)
③「ドア」、主に[蝶番]{ちょうつがい}で開閉する機構で洋風のものをいうが、「自動ドア」の場合は、左右に開閉する機構であるのが普通。又、「ドア」は、出入り口以外には使わない。
(「ドア」: mainly for doors with hinges; except for automatic doors, here it is common for sliding doors as well; only used for entrances/exits)
I suppose, when thinking of a western-style door, one associates it with ドア first, as it has got the more specific term ドア. Thus, 扉 is associated especially with sliding doors, in contrast to ドア. But as a general term, 扉 may refer to other kinds of doors, as evidenced by the [広辞苑]{こうじえん} definition [開]{ひら}き[戸]{ど}の[戸]{と}, and 扉 comes from [戸片]{とひら}.
ドア is about equivalent to 戸, and (usually) has just one pane.
扉 is (usually) two panes.
But, I think they can be used interchangeably.
Thinking longer about it, I am now more fond of the explanation that a 扉 opens from the middle (with two moving parts) and a ドア opens from one side only.
Expressions like 心の扉, 夢の扉 and a picture search seem to corroborate this hypothesis.
This also would explain why trains (with two doors sliding open from the middle) and buses (with two doors swinging out from the middle) use 扉, but a bus with a single sliding door might still use ドア.
Sliding doors in a 和室 have their own names anyway (襖, 障子).
I'm japanese. Most japanese don't consciously use these words properly in daily coversation. And I don't, either.
When you are in a tram they will almost always say ドア.
In an elevator --> ドア / 扉
In a bus --> ドア / 扉
For a wardrobe / closet --> 扉
Or maybe 「未来への扉」
The difference may be that people pass through ドア but they don't pass through 扉
This page had some interesting comments, especially this one:
扉は日本式の戸だと思います。 ドアは外来語なので、西洋式の戸だと思います。 戸（出入口や門に使う板などの総称） 今はあまり使い分けがはっきりしてませんね。 日本人は無意識に使い分けていると思うので、違いを発見したらご報告しますね
Which would mean that 扉 was used for Japanese-style sliding doors, whilst ドア was used for western-style hinged doors. But nowadays the distinction has become blurred, with people using the term they feel is appropriate or which they are more used to.
