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I was curious so I tested the 'on ramp' strategy that seems to be in place on UK motorways at rush hour - namely that they are traffic light controlled, but tha
by herghost 7y ago
I was curious so I tested the 'on ramp' strategy that seems to be in place on UK motorways at rush hour - namely that they are traffic light controlled, but that they always seem to be Green for ~3 cars, Red for ~6 cars.
Always seemed really pointless.
Turns out that was the only way I could get traffic going again on the curved road with the on-ramp (even though I could only control the main traffic, not actually the on-ramp). Even dropping the speed limit had no effect on clearing the congestion at the junction.
- takk309 7y agoIn the US we call this ramp metering. It is usually a dynamic system that monitors the upstream traffic density and only allows as many vehicles as can be added to reach a maximum density. We usually allow only 1 car per green signal. There have been some attempts to use them on roundabouts too.
- Sohcahtoa82 7y agoIn all the traffic light controlled on-ramps I've seen in the USA, the lights specifically only allow 1 car per green (and they have signs indicating such). They make a lot of sense. Traffic entering an on-ramp will usually come in bursts from traffic light. A burst of cars will have a much harder time merging with traffic than a trickle. So rather than creating, for example, a group of 20 cars every 60 seconds trying to merge at once, the on-ramp traffic light throttles that to 1 car every 3 seconds. Total throughput is the same, but the effect on existing highway traffic is significantly reduced.