Dramatic drops in traffic in south Chiswick after introduction of Low Traffic Neighbourhood schemes

Image above: Library picture of a traffic jam

Traffic schemes were introduced in south Chiswick during 2020 to try and stop commuters cutting through a residential area to shave a couple of minutes off their journey time.

The Streetspace schemes were introduced in the area south of the A4 which includes Grove Park and Strand on the Green, to try and dissuade drivers cutting off the corner on their way from the A316 to the A4 to avoid Hogarth roundabout.

Have the schemes caused annoyance to some of the local residents? Yes they certainly have. Will they be ripped out as a result of London taxi drivers’ court action against a Streetspace scheme in east London? Possibly.  But have they worked?

It’s now possible to do a comparison of traffic levels before the pandemic and during it, and to see what effect the various Streetspace schemes in south Chiswick have had on the number of cars driving through. The drop in the number of vehicles is dramatic.

At Harvard Hill, where the road was blocked on one side to prevent vehicles driving on to the A4, there were over 1100 vehicles fewer per day than in 2019.

In Staveley Rd, where a barrier was introduced to filter the traffic so that vehicles could no longer drive along the whole length of the road, there were more than 3700 fewer vehicles per day to the east of the filter and over 2800 vehicles fewer to the west of it.

Michael Robinson, engineer, local resident and data geek, has been crunching the numbers.

Counting Cars

If you were out and about in Chiswick in September and October of last year, you may have seen black tubes stretched across the surface of many roads. These were Automatic Traffic Counters installed by Hounslow to measure traffic volumes and speeds at over 50 locations around Chiswick. The source data is available upon request from the Hounslow traffic department so I asked for it and crunched the numbers, focusing on Chiswick south of the A4. I already had September 2019 traffic survey data for this area from a previous request, so was able to carry out comparisons with the most recent data.

Overall the survey data for the South Chiswick area provided 1.8 million vehicle readings.

September 2020 traffic levels almost back to pre-pandemic numbers

Although traffic levels have been affected by the pandemic, the data shows that by September 2020 the amount of traffic travelling through south Chiswick was back to almost pre-pandemic levels.

In September 2020, there were no traffic restrictions on Hartington Road, Thames Road or Sutton Court Road.  September 2020 traffic volumes on these roads as a percentage of traffic in September 2019 (pre-Covid, that is, offering a “normal” baseline) ranged from 83% for Thames Road, 93% for Hartington Road and 99% for Sutton Court Road. The data therefore shows that by September 2020 traffic was almost back to pre-pandemic levels.

Image above: Comparison of mean daily weekday traffic between surveys in September 2019 and 2020.  Sutton Court Road (Lawford – Staveley) refers to the survey done on Sutton Court Road between Lawford Rd and Staveley Rd.

Harvard Hill

Harvard Hill was a well-known rat-run for drivers heading through Grove Park from the A316 to the A4. Accessing the A4 at Harvard Hill bypassed Hogarth roundabout and the traffic lights at the A4 / Sutton Court Road junction.

The traffic survey from September 2019 measured an average of around 1200 vehicles accessing the A4 from Harvard Hill between 7.00am and 7.00pm on weekdays. This survey also included Automated Number Plate Recognition (ANPR) and this showed that about 80% of these vehicles had come from the A316 and were therefore using the route as a cut-through. In other words, 80% of these 1,200 vehicles were non-residents rat-running.

Image above: Road blocked at Harvard Hill to prevent exit from south Chiswick northward onto A4

In July 2020, measures were installed to block northbound access from Harvard Hill to the A4. Southbound access to Harvard Hill from the A4 remains possible.

The September 2020 survey showed northbound traffic had fallen to around 40 vehicles between 7.00am and 7.00pm on weekdays, that is, over 1100 fewer daily vehicles than 2019. The data does not show if any of these 40 continued to illegally access the A4, as the counter is in the middle of the street (so drivers realising there was no access to the A4 may have U turned and gone back the way they came).

Image above: Comparison of mean hourly weekday traffic between surveys in September 2019 and 2020 on Harvard Hill.

Traffic also decreased in Burnaby Gardens, Fauconberg Road, Gordon Road and St Mary’s Grove. Grove Park Terrace was unchanged but there was an increase of about 200 vehicles daily eastbound on Elmwood Road over the 12-hour period.  There may have been ‘double counting’ of vehicles that went all the way to Harvard Hill only to find there was no access to the A4 and then turned to find an alternative route.

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

Changes to roads take time to bed in, GPS maps to be updated and drivers to get used to alternative routes. No access to the A4 at Harvard Hill was periodically enforced by a mobile camera car after the filter was put in. A fixed enforcement camera was installed in October 2020, so the September 2020 data does not show driver behaviour with continual enforcement.

Anecdotal reports from residents confirm that few vehicles now illegally access the A4. Reports of kids skateboarding in the streets are also a ‘canary’ indicator of a low traffic neighbourhood.

Image above: Barrier on Staveley Rd creating a filter. Whichever way you drive along it, you are forced to turn left. Staveley Rd looking westbound towards the junction with Park Road.

Staveley Road

Staveley Road was another high traffic rat-run between the A316 and A4. The September 2019 survey showed an average of around 5500 vehicles each weekday, 90% of which were through traffic.

In September 2020 a diagonal filter was installed that prevents east-west journeys in both directions along Staveley Road and north-south journeys in both directions along Park Road.  Left turns are possible from Staveley Road onto Park Road and right turns from Park Road onto Staveley Road.

Hounslow carried out a further traffic survey in October 2020 after the Staveley Road measures were implemented. Not all the same locations were surveyed in September 2019, September 2020 and October 2020 so an exact ‘like for like’ comparison for every location isn’t possible. The map shows changes in weekday traffic between 7.00am and 7.00pm.

Image above: Traffic survey results in the Staveley Road area.  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 the other location names.

Similar to other roads in the area, Staveley Road traffic had risen back to pre-pandemic levels by September 2020.

Following the installation of the filter, Staveley Road traffic dropped by over 3700 vehicles daily east of the filter and by over 2800 vehicles west of the filter.

The filter also prevented right turns for westbound traffic on Staveley Road onto Park Road. This route was a secondary rat-run for traffic heading from the A316 to the A4 using Eastbourne Road, Milnthorpe Road or Park Road to avoid the lights at Sutton Court Road. Traffic on this section of Park Road north of Staveley Road was also almost back to pre-pandemic levels by September 2020. After the filter was installed there was a reduction in traffic of about 500 daily vehicles 7.00am to 7.00pm weekdays.

The October 2020 survey shows there are between around 300 to 600 vehicles 7.00am to 7.00pm weekdays on each road leading to the Staveley Road filter with Staveley Road east and west of the filter and Park Road north of Staveley Road; all show substantial reductions in traffic. Unfortunately, there is no survey data for Park Road south of Staveley Road prior to the filter being installed

Lawford Road shows an increase of about 90 vehicles over the 12-hour survey period. The survey data does not reveal how many of the westbound drivers on Lawford Road didn’t see or just ignored the banned right turn from Park Road onto Lawford Road.

Next steps

At time of writing, 8 February 2021, more measures are due to be implemented using ANPR cameras to restrict westbound traffic on Hartington Road and through traffic along Thames Road. In addition, there will be School Streets schemes that will have timed access restrictions around Grove Park Primary and Chiswick schools. I assume that Hounslow will be doing more traffic surveys to assess the effectiveness of these measures and the longer-term impact of the physical filters.  So, there will be more opportunities for even more data crunching!

Summary

The data clearly show that by September 2020, traffic had almost returned to pre-pandemic levels.

The physical filters at Harvard Hill and Staveley Road were highly effective in reducing numbers of motor vehicles on these roads which had been previously blighted by traffic driving through the area.

Technical Details

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 and 12-18 October 2020 for the Staveley Road area.

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

Source traffic data from Hounslow traffic department was provided in 142 Excel files with data contained in 1267 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: Future of Streetspace schemes in doubt

See also: Mayor of London acted ‘unlawfully’ in Streetspace scheme

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