White Horse Alliance - A350 Westbury Bypass Campaign

Inquiry day: 3

Inquiry date: 19 June 2008

Inquiry index


Original document(PDF): Day_2_3_Helps.pdf

Then ........

4.478 COBA but have feeling that this is a part of ANDREW NICOLSON’s! Included here in case it is useful to you. Here goes :

AN: Journey times in para. 2.12. Variations in journey times – high journey time of 21.30s. – is this the average figure, single figure or maximum duration? NH: Single figure journey times surveys taken in June 2007 – that was maximum.

AN: SATURN modelling: Is Saturn capable of modelling journey time reliability in terms of journey time variation in journey times? NH: Have provided journey time reliability information as ? sheet to support the summary table, produced this month, WHA 108 day to day variation? NH: The assessment undertaken was in this evidence for the reliability of time which is presented as ? sheet to support DfT specific system. Work undertaken showed that the reliability improvement is.

AN: Thank you – this is the evidence you have? ................. NH: 19% reduction in stress.

DfT take as ?frequency? evidence – this shows it improves journey times and that work is done in COBA.

AN: 3.30 Middle validation. 3.11 twice, clearly it is important a practical model validated Government Guidance. You tell us you did at 3.90, you conducted fresh traffic surveys, interviews and counts – was that the basis of validation? NH the additional roadside interviews. The validation was done with roadside interview surveys in 2005 for data for the model, not for validating model.

AN: Count and journey time, is this in 3.11, automatic count data. Paragraph 3.13 – 87% of 7/700 were modelled close enough to forecast these were minor roads. NH: standard had to meet was 85% and was made in excess of that - 87%.

AN: Next figure – 82% - 2,700. These within the 85% - but it was 82%. This is outside 85% or closer wasn’t it? NH: Contradiction there, but outside the 85%.

AN: 15% or more error in validation of model for 2007. Do you expect the model and its fluctuations to get more accurate in future years, or will it diverse more from actual flows? NH: When you have a basic model and add it to future years, you are adding traffic growth and scheme. You are not trying to improve model then, you want to relicate it and present the future situation. With the proposed scheme you may actually be getting a more robust model as having new link, such as proposed bypass, it is more .......... to predict with certainty that scheme than the old road.

AN: Whether model is likely to get closer to reality than further from it, not talking about reality to model. NH: Easier to predict characteristics and flow on proposed scheme than the other, less junctions for future year. It is possible we have a more robust model for that length and as traffic .......to that link, it will be more robust.

AN: What should next question be? COBA benefits mainly dependent on traffic flows and journey time saving. Journey time savings? NH: It does depend on traffic flows and the network is integral part of model.

AN: How important to COBA is accurate traffic modelling? NH: When you are contemplating a traffic model drawing to represent present situation, as much as possibly accurate, it is model, so trying to get close to reality and so create a robust situation.

AN: Is the traffic forecasting a main input into the COBA? NH: Yes

AN: In evidence and County’s evidence, I was looking for any mention of induced traffic and could not find anything? NH: In Rebuttal evidence I am saying the work I have undertaken does not suggest there will be induced traffic. Initial evidence, fixed trip matrix, so does not include induced traffic. Only take sensitivity work to assess whether there would be induced traffic.

AN: Government work Roads & Bridges asks for it to be done? NH: Only if the level of induced traffic preliminary assessment undertaken a sensitivity test.

AN: Why not in the Council’s evidence? NH: Ongoing work. Undertaking further work on behalf of DfT – ensure DfT are content when assessing Business Case, so that they will accept the Model as robust.

AN: Have you not done any of this when Environmental Statement was produced? NH: Tests were undertaken but demand modelling tests.

AN: Demand modelling sensitivity? NH: Not for Environmental Assessment stage.

AN: I have exhibited a model, you have dealt with it in Rebuttal? NH: It is what it seems to be, a Report by Mouchel Parkman on variable demand preliminary assessment Westbury started 12 September 2007.

AN: Address it in Rebuttal? Seem to accept it was done for or by Council for scheme. Should the Inquiry rely on this document that I have exhibited as the County’s Preliminary Assessment Variable Demand? NH: At date of Report, that was the extent of work at September 2007.

AN: Another more recent report? NH: Because work is still ongoing, no report on sensitivity tests. These are sensitivity tests which if they meet criteriaq for DfT will mean that the modelling work will be valid, not a replacement for work which

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