On Wednesday we ran our latest meetup ahead of our next hack day on the 20th October. During this session, we had an update from the council on the scope of the ANPR survey and then had a discussion about how to use the data to create some impact. Here’s an overview of what we learned and discussed.

Air quality survey

The presentation from Robin Spalding of the B&NES air quality team gave us some useful background on the ANPR survey which forms the bulk of the new data released for this event. We’ve published Robin’s slides online so you review the facts and figures provided.

The key points were that:

  • B&NES have been legally directed to produce a clean air plan that will achieve compliance with EU air quality regulations as soon as possible, and by 2021 at the latest
  • The directive was issued as a result of poor air quality on London Road which was flagged by DEFRA forecasts and modelling. It was only recently flagged because of changes to the DEFRA pollution and air quality model which mean that local conditions now breach expected limits
  • The EU limits will still need to be respected following Brexit as they have already been transcribed into UK law
  • It is the NO2 readings which are the cause for concern. Other air quality measurements, e.g. of particulate matter (PM10) are not currently an issue, but this might change as air quality regulations change
  • Our knowledge of traffic in B&NES is limited. We only have national data from the Department for Transport which gives annual average traffic volumes for cars. This isn’t detailed enough for accurate assessments
  • B&NES decided to run a data collection exercise to give more information about traffic. This survey ran for two weeks in October-November last year
  • The survey involved installing ANPR cameras at some specific sites around the city: entrances and exists to the car parks, sites around the city centre and then on key roads on the outskirts of the city
  • ANPR cameras read number places from vehicles that pass by the camera. The number plates can then be used to identify the make, model, age and other attributes of the car. This information has been anonymised and released for the hack day. You can get a sense of the information available from this demo application
  • The data is being used to assess plans for a clean air zone in the city. When introduced cars which don’t comply with emission standards will be charged a fee for driving through the zone
  • A consultation on the zone is expected to start this month. A full business case for the zone will be discussed at the December B&NES cabinet. If approved it’s likely to come into effect in late 2020


During the discussion we covered a range of different questions and issues, not all of which could be accurately assessed with the newly available data. Topics included:

  • exploring how different types of vehicle contribute to air quality at different locations and times of the day (“source apportionment”). The council and the consultants who have analysed the data have explored this but only at a high level
  • looking at popularity of car parks and the volume of traffic that might be circulating between car parks due to people trying to find parking spaces. This contributes to congestion and poorer air quality in the city centre
  • comparison of bus and other vehicle journey times across locations
  • considering possible sites for electronic vehicle charging points. This is a topic that the council are interested in as investing in new infrastructure may be part of the clean air plan. However more information would be needed to assess this, e.g. information on power supplies in specific locations
  • identifying risks for the clean air zone creating “rat runs” in side streets with motorists avoiding zones, and impacts this might have on local communities
  • thinking through the ability of different groups impacted by the clean air zone to charge
  • identifying personas in the data, e.g. motorists that drive into the city for the day, but don’t park in a car park; motorists that only drive around the city centre; through traffic, etc. helping people see themselves in the day might help encourage shifts to different modes of transport
  • calculating costs for residents of the clean air zone, e.g. would it be cheaper to get a new car, switch to bulk transport, etc
  • helping people understand their personal contributions to air quality, e.g. asking people to give details of their typical commute or vehicle usage patterns and indicating the impact they have

Broadly the debate ended up with two clear themes:

  • Myth busting: there is a perception that transport and air quality issues in Bath are caused by through traffic (e.g. goods vehicles), coaches or school traffic. Plans for, e.g. a by-pass and park and ride infrastructure are often tied to these perceptions. What can this new, more detailed data tell us about traffic in Bath? Can we make it clearer to everyone?
  • Behaviour change: it’s likely that for significant progress to be made on air quality then we will all need to think through how we use vehicles around the city. What can be done to encourage behaviour change? Could we highlight the impact that we individually have on local air quality and provide tools to help us make better choices? Are there insights that could help to improve policy making that will encourage behaviour change?

We’ll be digging into these topics further at our next meeting on Weds night. You’re welcome to come and join the conversation and the hack day next weekend.

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