RichardA35 wrote: ↑Sat Apr 13, 2019 18:06Ruperts Trooper wrote: ↑Sat Apr 13, 2019 17:47RichardA35 wrote: ↑Sat Apr 13, 2019 17:27Yes this is done when appraising schemes. Of course the "Do Nothing" scenario might have a worse outcome (think longer queues of slower moving traffic on all approaches) or the scheme would not go ahead.
Perhaps I should have underlined the "unneccessary" - the difference between full-time lights and peak-only lights.
As has been emphasised here many times previously, once you have optimised the geometry for signals and the queuing capacity at the stop line, this would the become a less safe geometry for vehicles to run at speed without signals.
So the argument moves on from reducing congestion and environmental emissions, to one of traffic management.
Why bother implementing a scheme if it only brings negative outcomes?? It would be better not to spend the money at all, seriously.
Nearly every controlled, signalised junction I’ve had the misfortune to encounter has at least some congestion attributable to the cycle of lights, and naturally sluggish traffic after moving off.
Sometimes the green cycle is so short, as the queue moves off so slowly that only half of it manages to move away from the roundabout.
Looking at the examples from Preston there, that was obviously designed as an urban link road, whether as 50, 60 or NSL. It was also designed to be free-flowing with roundabouts. It at least one of the shots, the roundabout was replaced with a signalised T-junction.
I just cannot comprehend why, when all it will do is add to queueing, stationary traffic, and more vehicle emissions, and added CO
2 from the lights themselves.