On Apr 3, 8:06 pm, Tristan Miller
wrote:
Greetings.

What is the purpose of the "open" buttons on the doors of the London
Underground carriages? On every Underground train I've used, the doors
open automatically at every station. Is/was there a time or place where
they don't open automatically and the buttons must be used?

Here is a question you can ask fellow-travellers.
On either side of the inside of doors on a Northern Line train there
are two vertical yellow bars.
( You can see them in this picture http://tinyurl.com/5uws7q). These
slightly slanting yellow bars are the same as any other yellow bars,
vertical or horizontal, in the carriage, EXCEPT that there is a black
bit of plastic about 6 inches from the top. The question is: What is
that piece of black plastic there for?