Well it could do with buffering lights going into the roundabout then, so that a pressure sensor under the coming from east lane sets off a red light on the north queue every now and again.
The round about below has such a system, where the north eastern lane can often have way too much traffic to allow others through. So it has a light dependent upon traffic volume.
http://maps.google.com/maps?q=whitfo...15000&t=h&z=19
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