I was waiting at Snaresbrook last week for rather longer than expected and was surprised by the operation of the signalling system.
The only visible signals are a three-aspect "starter" at each end of the platforms. These show red when a train has just passed (as we would expect, of course), but then change to a white light in the middle aspect (where I would expect to see yellow). Then, after an extended period (a few minutes) that eventually changes to green.
I think (although I am not certain) that the signal at the south end of the station (westbound line, towards central London) "reverted" at one time from green to white. Is that normal or possible?
There did not appear to be any trip-cocks (or train stops) associated with either signal.
Can the Underground experts enlighten me, please?