"While on the DLR it came to a sudden halt for five minutes. the conductor looked perplexed, then picked up the speaker phone, apologised for the delay and said it was due to signal failure. I asked how he knew the stoppage was due to those old enemies of the train timetable. He said: "I don't know why we stopped, but if in doubt, we are told to blame a delay on a signal failure".
So now you know why there are so many "signal failures".
See the links to the right on Protest to let them have your own stories about commuting in London.