At the end of any restriction, a circle with diagonal bar — reminiscent of the National Speed Limit sign — had the meaning "road clear".
The MS4 is the latest idea in motorway signalling and is capable of some impressive things, but what's truly remarkable is that the innovation that it represents is mainly in optics and illumination. The Highways Agency's Interim Advice Note 109/08 on its use states that "advances have been made in Light Emitting Diode technology that enables a wider viewing angle and a higher resolution display with two colours" — and that's all that has really improved since the earlier models.
What hasn't changed much in the preceding forty years is the type or concept of the signal itself, something that the Ministry of Transport refined to an incredible standard in a few short years in the 1960s.
Picture credits
- Photograph of Piccadilly Circus adapted from an original by Colin Pyle and used under this Creative Commons licence.
