Conclusions
Conclusions
Our conclusions about the traffic modelling
Looking over the all the different tests and measures outlined above this traffic model fails on every one of them. If fails to meet the required standard for either calibration or validation. And even when the criteria are extended, the equivalent of lowering the pass mark, it still fails all the calibration standards, and just manages to scrape a pass for validation over one time period. However, it is important to note that the required standard (not the relaxed or lowered one) is required for a very good reason – it is the way in which high standards in traffic modelling are maintained. This model does not meet them.
At the level of individual count points or route journeys the results are erratic and appear to defy any logic or grounding in the real world. There are large errors
both overstating and understating that which is being measured and these appear across the model – especially at the local area of the Putney Link Road scheme. There is simply no consistency
to the patterning of the results. Some of them could almost be random.
Taking these two levels together the traffic forecasts produced by the model are unlikely to be robust and must be viewed with great caution. The failure of the model to meet the required standards is almost certainly the reason why the results and the traffic claims for the Putney Link Road scheme do not appear to make sense. This can be seen in the conclusions of the councils own analysis where the link function only works one way, and it produces longer journey times when it does function that way, with all the benefits of the scheme being created by local non-through traffic. Similarly, the claims for this road in terms of impact on traffic don’t make sense to those familiar with local traffic, the routes it takes, and the times and places where congestion is worst.
This is why we have severe doubts about the adequacy of the traffic modelling for this link road, and why we have little confidence in the claims about the impact it will make. This modelling cannot forecast with any degree of accuracy how this road will function in the wider road network and the difference it will make. We have our views, based on our experience of the local road system and how it works. The council only
has the traffic modelling, and appears to accept it without question. To proceed blindly with a plan for a road costing in excess of £5 million which could have hugely negative consequence for many different groups appears to us as highly irresponsible and bordering on the reckless.
