Traffic Lights on the Motorway? - 'Ramp Metering'

摘要

Having been asked recently 'Why are there traffic lights on the motorway?' and, in reply, offering the explanation that 'ramp metering' has been installed on a limited number of motorway slip roads to reduce congestion through managing traffic flows onto the main carriageway the understandable response was, 'Well that makes sense doesn't it?' But where did the idea come from?