"Basil Jet" wrote in message
...

Late at night, the traffic lights on Finchley Road at the junction
of West Heath Avenue often go red for a couple of seconds before
reverting to green. This is far too short for another traffic or
pedestrian phase to have occurred in between. It seems that sensors
facing into the side roads detect that there is no traffic there and
that this causes the green phase for the side roads to be skipped,
but unfortunately the other lights have flipped to red before this
decision is made. Surely this must be a mistake rather than design.

It is quite common for lights to run though a short cycle when they
have not been triggered for some time. I presume the controller is
running some sort of error check sequence.

If it's common, where else does it happen? There is a pedestrian crossing in
Harrow which has phantom pedestrian phases, but apart from that, I've never
noticed it elsewhere.