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.

How are the phases of traffic lights controlled anyway? Is there a program
inside them written in some standard programming language, and someone has
put the IF statement in the wrong place? I would have guessed that the
danger of conflicting greens would have prevented the control sequence from
being written in a standard language and that something much less flexible
would have been used, which would have prevented the error I see at this
junction.