SIR - From your column On This Day I learned that it was decided in September, 1929, that traffic lights would be green for "go" and red for "stop". It seems simple enough, but 77 years later some people still don't seem to have grasped it. Given this level of mental incapacity, it is no wonder that we have problems with metrication.

L Hobsbaum, Willow Crescent, Wrose