Southwark’s traffic counts
The Council has given us a lot of pretty bar charts intended to show ”traffic down, cycling up” in the Dulwich area. But do they give us the full picture?
At our meeting with Cllr McAsh in June, we said that there was a lot of data missing from the Dulwich Streetspace Data Dashboard, and followed this up with an email on 16 August 2023 (reproduced below) explaining why. Now that Cllr McAsh has responded, our concerns are:
1. No more data
Cllr McAsh’s response on 24 August 2023 shows that the Council wants to stop publishing data on the the Dulwich LTNs.
Cllr McAsh’s argument is that data isn’t produced in the same way for other Southwark schemes, for example in Walworth, and that Dulwich up until now has had special treatment. He says, “I am not convinced that this prioritisation should continue now that the schemes are permanent.”
Stopping the publication of data at this stage makes no sense whatsoever. The Dulwich LTNs were introduced in June 2020 as emergency measures during Covid, were altered in November 2020, and were changed again in December 2021. No traffic count data has been published at all since September 2022, and traffic is only now reaching pre-Covid levels. So what we have in September 2023, three years after the LTNs were introduced, is a confused and incomplete history of traffic counts that cannot possibly show whether or not the Dulwich LTNs are achieving the Council’s Streets for People aims.
2. Huge inequalities
The traffic count data that exists (see the Dulwich Streetspace Data Dashboard) shows huge inequalities between different roads in the Dulwich area.
For example, the first table shows traffic up by 12% on East Dulwich Grove – a significant increase given the numbers of vehicles already travelling on this road (a road with a large number of schools and a health centre).
Although Lordship Lane North is shown as a black line (apparently because there is no baseline data), later tables show that weekday peaks here far exceed – by a long way – any other road.
If the Council is genuinely interested in whether the Dulwich LTNs have displaced traffic from some roads to others, these figures must surely cause considerable concern.
3. Misrepresentation
Data presentation on the Dulwich Streetspace Data Dashboard presents an incomplete picture. Problems include unidentified baselines, no adjustments for school holidays, roadworks or temporary road closures, annual averages compared with monthly or weekly figures, data missing for key roads like Dulwich Common, and cycling figures only for roads closed 24/7 (see our email below).
Essentially, what we have here are pretty bar charts intended to show “traffic down, cycling up” even if it’s taken quite a lot of data manipulation to get there.
If road closures are genuinely about “streets for people” rather than “streets for some very privileged people”, should the Council not be basing policy on data, rather than manipulating data to support policy?
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Email from One Dulwich to Cllr James McAsh in response to his query about data
Wednesday 16 August 2023
Dear James,
Thank you for your email asking for more detail on what data we think is missing.
Looking at the Dulwich Streetspace Data Dashboard, the omission that stands out most clearly is from your own ward, Goose Green. Lordship Lane North is a black line in the first chart (nan% i.e. not a number). We have to assume that this is because there are no baselines, either ‘pre-Covid levels’ (whatever they may be) or ‘September 2021’. However, the tables that follow establish that Lordship Lane North has very high volumes of traffic at peak hours (for example, a weekday peak in February 2022, between 3pm and 6pm, of 4,728 vehicles), suggesting levels of traffic much higher than the comparison baselines given for other roads. Given the importance of establishing if the Dulwich LTNs have displaced traffic from some roads to others, the omission of this particular road in your ward from the Dashboard needs urgent investigation.
Similarly, the omission of air quality data is striking – and we know you will agree, as cabinet member for clean air, that we need to look at whether the Dulwich LTNs have delivered improvements to all streets or just to a few. The most recent Southwark air quality data shows that NO2 levels have increased year-on-year in the Dulwich area from 2020 - 2023, and we know you will want to analyse why this is. It may be of particular interest to you, as councillor for Goose Green, that one of the Council’s monitors in your own ward – on East Dulwich Grove, close to the junction with Lordship Lane – shows a particularly sharp increase in NO2 levels between 2022 and 2023, giving this site readings similar to those on the South Circular.
More generally, with regard to traffic data from ATC counts:
1. No data has been published since September 2022.
2. Baseline data is not disclosed – for example, the date used for ‘pre-COVID’ and why it was chosen.
3. The crucial issue of whether congestion and pollution have got better or worse on local roads at key times of day is hidden or unavailable because:
a) In the first table, the figures are based on monthly averages (with, as the opening caveat makes clear, no corrections or adjustments for school holidays, lockdowns, roadworks, etc – even though school term times, for example, have a significant impact on traffic patterns and volumes in the Dulwich area)
b) In the interactive bar charts showing weekday am and pm, the comparisons between traffic counts on selected roads in September 2022, and traffic counts on these roads ‘pre-COVID’ and ‘September 2021’, are invalid because the hours of the timed restrictions in the local area changed between November 2020 and December 2021. Please see Note 1 below. In other words, these charts are not comparing like with like.
c) There is no graph comparing weekday am or pm peaks on different roads. This is key to understanding how the LTNs have affected the whole area
d) Weekday averages and vehicle volume figures are based on five-day averages, but these dates are not identified
e) The ‘pre-Covid’ and ‘September 2021’ lines are all straight, suggesting that these are annual averages being compared to monthly or weekly figures, which is clearly unhelpful.
4. With regard to cycling and walking, only figures for Calton Avenue and Melbourne Grove (both closed by 24/7 traffic filters) have been published. Unless figures are gathered for all roads there is no way of knowing whether cycling and walking overall, across the Dulwich area, have increased.
5. Data is missing for Dulwich Common, a key Dulwich LTN boundary road (monitored by Southwark in 2016 and 2017, so a baseline exists).
6. Data is based on ATCs which cannot measure traffic travelling under 10km/hr, so do not record stationary traffic (in other words, heavy congestion).
7. It is not clear why the Dashboard has surveyed only selected sites from the Southwark Highways map. If it has inadvertently focused on counters where rush-hour traffic is usually so heavy that it is slow or stationary, the under-reporting of traffic volumes will be significant.
Rather than publishing charts that deliver an incomplete or flawed analysis, it would be helpful if the Council made all raw data available in an accessible format for public review – i.e. every data point recorded by all ATC, Vivacity and NO2 diffusion tubes within the Dulwich LTNs and on surrounding roads up to the present day.
In addition, in order to draw conclusions about whether the Dulwich LTNs have made any positive difference to CO2 emissions, air quality, safety, health, or active travel, it would be helpful to compare pre- and post-LTN data relating to:
the number of miles driven by local residents and businesses – the DfT claims this has not been done nationally, but perhaps Southwark has carried out its own studies?
car ownership within and outside the Dulwich LTNs;
walking and cycling on boundary roads, particularly those with schools, nurseries and health centres (for example, East Dulwich Grove, Lordship Lane, Croxted Road);
road safety (all road-users, including pedestrians and cyclists);
impact on the travel needs of those with disabilities, including Blue Badge holders;
impact on health professionals – for example, first responders, and GPs, community nurses, midwives, and social care workers visiting housebound patients;
impact on local shops and businesses;
impact on bus journey times (crucial to the Dulwich area, where PTAL scores are low).
Thank you.
We look forward to hearing from you.
Best wishes
One Dulwich
Note 1
In June 2020, the Council closed the Dulwich Village junction to all motor vehicles 24/7. In November 2020, the Council introduced traffic restrictions on some roads from 8 – 10am and 3 – 6pm. In December 2021, these hours were reduced to 8 – 9am and 3 – 4.30pm, with additional 24/7 closures on Derwent Grove, Elsie Road and Tintagel Crescent at their junction with Grove Vale, and on Melbourne Grove South at its junction with East Dulwich Grove.