This was sent to me a while back:
We are aware of the impact that the temporary configuration of the signals are having on the traffic and have been raising these concerns with the contractor who is responsible for temporary works and have asked them to address the problems, this has been raised at all levels from site up to Director level.The signals that are operating at the moment at Gipsy lane are on a temporary configuration and are operating under lane restriction constraints so will be far less efficient than the permanent signal arrangement, however I believe that further adjustments can be made in the short term to alleviate some of the traffic congestion.
The new signals at Gipsy Lane were part of the original design prepared in 2003. The signals, although introduce a break in the flow of the main traffic, will manage the flows much better as traffic flows increase. As the scheme has been design to cater for traffic growth for the next 20-30 years a roundabout would not cope with the predicated traffic growth, certainly not the size of the old roundabout, to stand a chance of coping it would have to be something akin to Junction 10 roundabout of the M1 which there is simply not enough room to accommodate at this junction.
The signals will be operated by a MOVA system which is effectively an intelligent vehicle actuation system, which can learn and record traffic flows and adjust itself to cater for the greatest demand at different times of the day, which you would expect to be the A1081 from the M1 towards Hitchin in the morning and the opposite in the evening, therefore greatest green time should be given to the highest demand but still allow green time to the side road.
Once the MOVA system is activated and all lanes are operating I am sure you will see a dramatic improvement. As for the roundabout v signals debate this would only ever be realised in the longer term but as signals have replaced the small roundabout we will not have a direct comparison to make.
I trust that this helps you understand some of the issue relating to the evolution of this junction.'