The city of Bath is among a number of cities in the UK tasked with reducing Nitrogen Oxide (NOx) emissions. NOx pollution is thought to contribute to poor health and the government has required clean air plans from the relevant local authorities to be in place before 2021. I had no idea that this would result in my statistical expertise being needed to answer a political row over the BathBreathes2021 plans to charge cars driving into Bath and you can read my report to see what my answer was!
BathBreathes2021
In 2018, Bath & North East Somerset (B&NES) council announced their proposals for dealing with NOx emissions within the city of Bath. A website BathBreathes2021 was set up to provide the public with all the necessary information but the element that immediately caused controversy was B&NES’ proposal to implement a Class D charging scheme for certain vehicles driving into the Bath Clean Air Zone (CAZ). The government gave local authorities 4 options to choose from should they decide to charge vehicles which were:-
- Class A – charge Buses, Coaches & Taxis
- Class B – charge Buses, Coaches, Taxis & HGVs
- Class C – charge Buses, Coaches, Taxis, HGVs & LGVs
- Class D – charge Buses, Coaches, Taxis, HGVs, LGVs & Cars
It should be noted that environmentally friendly vehicles of all types are exempt from charges since the purpose of the charging scheme is to encourage the vehicle owners to switch to lower emission vehicles. Still a number of private car owners would have been affected so it is no wonder that a political row began on the council. At the time, B&NES was run by the Conservatives with the Liberal Democrats providing the main opposition.
How I got involved
B&NES had made their proposal based on Air Quality Modelling (AQM) undertaken by a specialist company. The AQM had compared the expected outcome in 2021 if no action was taken with the expected outcome in 2021 if either of the 4 options (A, B, C, D) were implemented. From this analysis B&NES drew the following conclusion:
“Our preferred option to achieve these improvements is a Class D Clean Air Zone (CAZ). This would mean charging drivers of all higher emission vehicles – including cars – to drive in the city centre from late 2020. Lower emission vehicles would not pay the charge.
We also looked at other options, including not charging higher emission cars, but extensive analysis has shown that none of these options would enable us to meet the required reduction of NO2 in the time allowed.”
A group of Conservative councillors had looked at the various scenarios produced by the AQM and they did not agree that a Class D CAZ was the only solution. They decided to approach me to provide an independent assessment of the publicly available information and I agreed to provide an expert opinion. Since this would involve assessing data produced by a forecasting model, and forecasting inevitably requires statistical modelling and interpretation, the councillors correctly identified that the expert had to be a professional statistician i.e. someone like me!
A report by an Independent Statistician
I wrote my report in December 2018 and this was submitted to the public consultation that B&NES were undertaking at the time. As this was a public document, there is no issue with me making it available here. Please click on the title below to read it in full (10 pages in total)
Bath CAZ Options – A Statistical Opinion of Likely Impacts
The layout of this report is similar to many other reports I have written as an expert witness. The five section headings are:-
- Why I was asked to write this report – A brief description of the background to the issue and the question(s) that I was asked to provide an expert opinion on. This section also lists my credentials as to why I am qualified to offer an expert opinion.
- Documents reviewed during the writing of this report – I consider it extremely important for the reader to be aware of what data and information I used to form my opinion and equally what data and information I did not use. In this instance, the number of documents on the BathBreathes2021 site was considerable but in the end I decided I could form an opinion with just 6 documents.
- My assessment of the Class C & D CAZ options – the councillors who engaged me were happy to support a Class C CAZ but felt the evidence did not justify a class D CAZ. In this section, I commented on the available information for these two schemes as provided by the relevant AQMs.
- My Conclusions – I concluded that the councillors were right i.e. B&NES could not claim that only a class D scheme could meet government targets by 2021. It was clear to me from the available AQMs that a class C scheme could also meet government targets.
- Declarations of Interest – Since this was a public document that I had been paid to produce, I felt it was important to state all possible conflicts of interest though in the event, there were no conflicts at all. I also listed the professional standards which I am required to follow as an Independent Statistician.
I hope you find this report of interest and it gives you a good idea of the kind of report you would receive from me should you engage me as an expert witness in your case. If you would like to contact me for an initial discussion, you can find my contact details here.
What happened next in Bath?
In March 2019, B&NES changed their mind and conceded that a Class C CAZ was feasible for Bath. The council is currently preparing its final business case to be submitted to the government and if it is accepted, the scheme would commence in November 2020. One point to bear in mind is that in May 2019, the Liberal Democrats won outright control of the council for the first time ever. Prior to the election, they had expressed support for the Class D option so it is still possible that the final business case will be for a Class D zone. Should they make such a decision, I will happily state in public that they cannot use the available air quality modelling data made public to state that a class D will be better than a class C. There might be financial or political grounds for favouring a class D scheme over a class C but they cannot claim environmental grounds since the AQM data clearly states there is almost no difference in their impacts.
Update 12th August 2019 – The Lib Dem council has indeed announced a review of the Class C proposal! See this article from my local paper Bath Chronicle. Let’s see if I need to get involved in local politics!
