I’ve become concerned about how Highways England (HE) seem to have collected much of their data for the A27 bypass proposals so I worked through the argument in the A27 Chichester Bypass Local Model Validation Report and my comments are linked to sections in that document.
‘HE aims to remove conflict and congestion at the bypass junctions and improve access to Chichester, the Bournes, the Manhood and the wider Bognor Regis area, enabling other local transport improvements to be implemented.’(1.3.1) So, for those backing the Northern Route, there’s no commitment to trunk road traffic bypassing Chichester except to ‘understand the impact of identified options to relieve the congetion on A27 Chichester bypass’ (1.4.3) –‘congetion’ is but one example of a rushed production. The ‘study area’ is widely defined (2.5.2) but detailed treatment is largely restricted to Chichester itself (see 3.4.1 & Fig. 3.1 Link Counts by Data source). and only1/7 routes recruited for measuring Journey Times actually travelled along the bypass and three of the others crossed the railway without any reference to the potential effects of that holdup (see Fig. 3-4 & Appendix G).
However, be aware of shortcomings in the actual collection of the data. For a start Traffic Flow Peak Periods for weekdays were defined as 08:00 – 09:00 and 17:00 – 18:00 (2.8.2). From lengthy experience I know the MoT years ago used 07:00 – 09: and 17:00- 19:00 for that observation and, even then, virtual gridlock can develop beyond those limits. Video recordings of defined Traffic Turning Counts were virtually restricted to a single day (12 June 2014) (3.4.1). Also note this ryder: ‘To avoid any anomalies, data of holiday periods was removed’ apart from Tuesdays & Thursdays (1 – 20 July) as ‘Mondays and Fridays are considered less typical weekdays’ (3.6.4). Did HE appreciate how holiday grossly distorts traffic problems here? Data on trips was ‘based solely on mobile phone data’ on six days in July and ‘the dates used were before the school holiday period, and did not coincide with major Goodwood events which could have distorted travel patterns’ (3.71) Note HE admit ‘mobile phone data under represented short distance trips’ (9.10.3) so how much data did that distort? Anybody reading this document might question the soundness of any decision made on such evidence.
I thought the national purpose of this scheme was to eradicate a weak spot in a major trunk road system. The overall verdict the report declares is that it provides ‘confidence to estimate a robust set of future traffic flows for proposed schemes to upgrade that bypass’ (10.2.1). I beg to disagree.