Imperial College Clarification Letter
24 Feb 2023
SEJ letter seeking clarification around a number of points in the recent study assessing Canonbury East, Clerkenwell Green and St Peter’s LTNs. https://www.sciencedirect.com/science/article/pii/S1361920922003625
Dr Audrey de Nazelle
Faculty of Natural Sciences
Centre for Environmental Policy
Imperial College
Dear Dr de Nazelle,
Open Letter
We are writing to seek clarification around a number of points in the recent study assessing Canonbury East, Clerkenwell Green and St Peter’s LTNs.
https://www.sciencedirect.com/science/article/pii/S1361920922003625
We have several questions about the study:
· Can you tell us why these three Islington LTNs were chosen?
· Why was there no mention of the other LTNs that were in the same area and put in at the same time? Does this not invalidate the report’s definition of control sites?
· Data was provided by Islington Council - a council which previously admitted to get some of its data wrong. Which data was used in the study?
· Can you say why ‘boundary areas’ were assessed rather than specific roads, as was done in the consultant reports commissioned by Islington?
· Previous counts from all councils, including Islington, showed significant traffic increases on some boundary roads (see Appendix 1). Was this assessed in the study?
· What assessment was made of displaced traffic beyond the ‘boundary areas’? Did you do any analysis as to whether the council monitoring covered likely alternative displacement routes? From a traffic map it seems several key roads were not monitored.
· The ATC analysis software in some boroughs was found to have had a default setting to include low speed (below 10kmph) traffic in 2020 – i.e. during the 'before' counts, but the default was changed by the vendor in an update in 2021 to exclude low speed traffic (i.e. for 'after' counts). Do you know whether low speed traffic was included or excluded for each data point?
· In addition to this, how did the report account for the reduced accuracy of low speed traffic where that traffic was included, where congestion increased on boundary roads at peak times?
· Councils have also said they used 'fill in' data where ATCs failed to collect data on some days - was this data included or excluded?
· We saw no raw data in the report, only summaries. Can you disclose key raw data - like traffic flow numbers & not just percentages?
· We also have questions about the location of the comparative sites used. It seems that some of Boundary Sites and External Control Sites were also boundary roads for other LTNs and some were located within other LTNs. We outline the sites we are concerned about below.
Where traffic measurements were taken:
Boundary Sites
Junction Canonbury Road/Halton Rd: also boundary road for St Mary’s Church LTN
Essex Rd: Also boundary road for Canonbury West LTN
External Control Sites
Highbury Grove: boundary road for Highbury LTN
Holloway Road: boundary road for Highbury LTN
Where air pollution measurements were taken:
Boundary Site
Arran Walk: within Canonbury West LTN
External Control Site
Just south of Penton Rise: within Amwell LTN
Highbury Fields: within Highbury LTN
Highbury Grove: boundary road for Highbury LTN
Holloway Road: boundary road for Highbury LTN
We look forward to your response.
Happy to discuss in person.
Many thanks.
Yours sincerely,
Clair Battaglino
Katharina Herrmann
Stella Sawyer
John Stewart
Directors SEJ (Social & Environmental Justice)
https://socialenvironmentaljustice.co.uk/
Appendix One:
Below is a summary the traffic data collected by Islington Council. It seems to show a different picture from the Imperial Study.
Highbury LTN
Internal roads (roads inside the LTN):
67% reduction
Boundary roads:
Hornsey Road -28%,
Highbury Grove by -10%,
Seven Sisters Road +7%,
St Paul’s Road +15%,
Blackstock Road (north) +65%
Blackstock Road (south) +17%.
Interim data for Holloway Road was found to be of unacceptably poor quality to use for analysis,
Anwell LTN
Internal roads:
44%. Reduction
Boundary roads:
Amwell Street -2%,
Claremont Square +4%
Rosebery Avenue +3%
Pentonville Road -3%
Farringdon Road + 36%
Traffic on roads beyond the trial boundary
‘could be influenced by factors beyond the Amwell trial’.
Local roads 14% reduction
Main roads 27% increase
Canonbury East LTN
Internal roads
78% reduction
Boundary roads
New North Road +7%
Balls Pond Road +7%
Essex Road +5% and -3% (two different locations),
Southgate Road -13% and -49% (two different locations)
Baring Street -8%
Canonbury West LTN
Internal roads
46% reduction
Boundary roads
Essex Road -9%
St Paul’s Road +15%
Canonbury Road -42%
Clerkenwell LTN
Internal roads
34% reduction
Boundary roads
St John Street +38%
Skinner Street +22%
St Peters LTN
Internal roads
22% reduction
Boundary roads
New North Road – 11%
Essex Road +3%
City Road -21% (on a very small sample)
St Marys LTN
No info on council site
