How do sequential traffic lights stay green along a through route?

I seem to recall Reading, Berks, more than 50 years ago, having traffic lights whereby if you travelled below 30mph along the main through route, and the lights were green, then the remaining lights stayed green. Some kind of linkage, I imagine.

Asked on 4 May 2012 by KA, Norwich

Answered by Honest John
That's how Euston and Marylebone Roads used to be before they messed up the sequence to create congestion that they could then use to support the Congestion Charge. Back in the 1970s I've driven all the way from Tottenham Court Road to Edgware Road non-stop.
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