Traffic data shows effects of traffic restrictions in south Chiswick 

Image: Fox in the street; photograph Jon Perry

Counting cars again

Guest blog by Michael Robinson

In a Chiswick Calendar article back in February I analysed the impact of measures to restrict traffic in the South Chiswick area. Hounslow has since carried out additional traffic surveys so more analysis is now possible.

Unfortunately in May 2021, 20 traffic counters in the South Chiswick area were vandalised over a single night, impacting on the completeness of the data. While some blamed fox cubs, a more generally accepted explanation is that it was deliberate sabotage. Some locations were not affected by the vandalism and some additional surveys were done in June.

Hounslow has not yet provided data for Hartington Road. After the original vandalism, additional survey equipment on Hartington Road was replaced, vandalised yet again, then replaced once more. It isn’t therefore possible to comment upon the effectiveness of those measures, but one can assume that data for Hartington Road will be made available at some point.

The Bigger Picture

Since the start of the pandemic, the Department for Transport has been doing daily traffic surveys at hundreds of locations throughout Great Britain to understand the impact of the pandemic upon people’s journeys. The DfT figures don’t say what may be happening on an individual road but provide an indication of traffic on the overall road network.

A graph of traffic levels is shown below, where 100% represents the level of traffic before the start of the lockdown in March 2020. The Chiswick traffic survey dates are shown on the graph. National traffic was at or above 95% of pre-pandemic levels during all surveys.

Image above: DfT Daily Vehicle Traffic as a % of pre-COVID with S Chiswick Traffic Survey Dates

Harvard Hill

Access to the A4 has been closed at Harvard Hill. This measure reduced northbound traffic from an average of 1,400 vehicles per weekday in 2019 to about 50 in the September 2020 survey and there were only an average of 13 vehicles per day in the latest survey. It isn’t possible to say if these vehicles were illegally accessing the A4 or were simply driven over the counter then reversed or driven back again.

Image above: Traffic survey results in the Harvard Hill area. Arrows point to the locations of traffic counters.

Southbound traffic from the A4 into Harvard Hill has remained steady at about 300 vehicles per weekday.

Traffic on almost all other roads in the area has also reduced. The only exception is Elmwood Road which has seen an increase of about 280 eastbound vehicles over a 12 hour period from 7.00 am to 7.00 pm on a weekday. However care needs to be taken with this estimate as there is only a single day of traffic data for Elmwood Road before the Harvard Hill restrictions were implemented so this figure is unlikely to represent accurate average traffic.

Analysis: Overall the measures for Harvard Hill seem to have been very successful at reducing traffic through the area with minimal disadvantages from displaced traffic.

My view: One could therefore conclude that The Harvard Hill measures should be made permanent.

Staveley Road

September 2019 and September 2020 surveys of Staveley Road between Burlington Lane and Fitzroy Crescent showed traffic of about 5,200 vehicles per weekday.

Following the implementation of the Staveley Road barrier in September 2020, traffic reduced by about 4,500 vehicles to 700 per day in October 2020. The latest survey in May 2021 showed just over 600 vehicles per day.

However the October 2020 survey only covered roads around the Staveley Road barrier. The latest surveys cover other roads in the area so it is possible to see the impact of the measures elsewhere.

Image above: Traffic survey results in the Staveley Road area. Arrows point to the locations of traffic counters. Arrows point to the locations of traffic counters. Staveley Road (Burlington – Fitzroy) means the traffic counter was on Staveley Road between Burlington Road and Fitzroy Crescent. The same convention applies to other location names.

The greatest effect has been on Burlington Lane west of Staveley Road. In the September 2019 and September 2020 surveys this had about 2,500 vehicles a day. In the June 2021 survey, this had increased by about 4,100 vehicles to 6,600 vehicles a day. Data from Hartington Road isn’t available to say how much of this displaced traffic comes from the measures on Hartington Road or from Staveley Road.

Displaced traffic now travelling via Burlington Lane to Sutton Court Road has produced an increase of about 2,600 daily vehicles on Sutton Court Road south of Staveley Road from about 7,900 to 10,600 vehicles per day. However traffic on Sutton Court Road north of Staveley Road shows a decrease of about 1,100 vehicles from about 11,700 to 10,600 vehicles per day.

Analysis: This indicates an overall reduction of traffic from the A316 to the A4 through Grove Park, but a main route has changed from Staveley Road to Burlington Lane. The barrier at Staveley therefore hasn’t been sufficient to deter drivers (or SatNavs) from using the route via Burlington Lane instead. There is a difference of only 0.2 miles between the length of the two routes.

My view: It is difficult to see how the current measures can be considered sufficient given the small overall reduction in traffic and the significant displacement to another road. One would hope that Hounslow is considering options for further changes.

Thames Road

Thames Road has a ‘No Entry for Motor Vehicles Except for Access’ restriction which means there is a penalty if a person drives a vehicle through the designated area without stopping to access a location. This restriction is enforced by the time taken between two cameras.

The contravention occurs if there is no stopping during access and the time taken is used to infer that the vehicle didn’t stop. The time is, in effect, circumstantial evidence rather than direct evidence of the access contravention. Hounslow is apparently the first local authority in the UK to trial this method of restricting through traffic. It was implemented on Green Dragon Lane in Brentford before Thames Road.

Image above: ‘No Entry Motor Vehicles Except for Access’ signs on Green Dragon Lane, Brentford and Strand on the Green

Thames Road surveys showed reduction in traffic (7.00 am to 7.00 pm) from 2,900 vehicles in September 2019 to 2,500 vehicles in September 2020 to 1,900 vehicles in June 2021. The ‘except for access’ restrictions were implemented in December 2020 but I believe this has not yet been enforced by cameras.

Image above: Traffic survey results in Thames Road

Analysis: Automatic Number Plate Recognition (ANPR) data from 2019 indicated that about 70% of vehicles were driving along Thames Rd in under 5 minutes. If the measures were effective stopping all through traffic, this would mean about 900 local journeys compared to the 1,900 vehicles actually measured, however with a single counter location it isn’t possible to determine the number of vehicles making through and local access journeys.

My view: The Thames Road results do not yet conclusively prove any significant benefit or disadvantage.

Summary

Overall, there is a mixed bag of results. There appears to have been a modest reduction of around 10% overall traffic through the area between September 2020 and May/June 2021. The Harvard Hill measures are successful, Staveley Road measures work for that street but not for other streets, and the jury is still out if the measures using ANPR cameras are effective.

It will be difficult to justify why ANPR cameras should be deployed in more locations unless there is good evidence that they have been effective where they have been deployed already.

ANPR camera enforcement relies on ‘No Motor Vehicles’ signage with exemptions but a recent survey found that 50% of drivers don’t know what this sign means and almost one third thought that it meant ‘only cars and motorcycles allowed’.

The objective of low traffic neighbourhood funding is to enable more walking and cycling by reducing traffic. Calls for restrictions on traffic entering an area but with no change to how residents themselves drive are unlikely to be funded.

Technical note

There is a vast amount of traffic data available and I will be happy to try and answer any questions arising from this article. Please email Chiswick Calendar at info@thechiswickcalendar.co.uk

Survey dates were 22 September 2019 to 5 October 2019, 14-20 September 2020, 12-18 October 2020 for the Staveley Road area, 22-30 May 2021 and 25 June 2021 to 3 July 2021.

The September 2019 ANPR survey only counted traffic between 7.00 am and 7.00 pm. The Automatic Traffic Counters count traffic 24 hours a day but the graphs on maps for Harvard Hill, Staveley Road and Thames Road only show traffic counts between 7.00 am to 7.00 pm to provide a like for like comparison between surveys.

Two wheeled vehicles are excluded from numbers. Traffic counters cannot distinguish between push bikes and powered two wheeled vehicles.

Source traffic data from Hounslow traffic department was provided in 163 Excel files with data contained in 1450 sheets within the files. Data was extracted, reformatted and analysed with code written using python and pandas data analysis libraries. Graphs created using seaborn and matplotlib software libraries.

Michael Robinson is a Chartered Engineer, Chiswick resident, data geek and a member of London Cycling Campaign. He receives no payment for being anything other than an engineer. 

Read more stories on The Chiswick Calendar

See also: South Chiswick residents’ groups join forces to call for traffic scheme changes

See also: Lies, damned lies and statistics … and the cycle lane

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