On Dec 5, 11:13 pm, Barry Salter wrote:
Can anyone tell me if this is in use? How does it work? Are there
others? Etc..

The short answer is that it's a SPAD (Signal Passed At Danger) Indicator.

snip Barry's explanation

There are others dotted around the country. I know of some at
Reading. They tend to appear in busy/cluttered areas where risk of
over run is higher (or at least, the consequences could be worse).

PhilD

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