Request ID: FOI-1205-2122 Date published: 24 September 2021
You asked
The Steer report analysing Streetspace (LTNs and C9T) in Chiswick seems to have forgotten to assess the impact of these traffic changes on traffic on the residential A4 in Chiswick.
Could you please provide us with monthly traffic data for the A4 from Jan 2018 to Sep 2021, separated by Eastbound and Westbound, to cover the stretches:
-Hammersmith Rdbt to Hogarth Rdbt
-Hogarth Rdbt to Sutton Ct Rd traffic lights
-Sutton Ct Rd traffic lights to Chiswick Rdbt
Is this measured at the traffic lights?
And can you please clarify how does TfL account for traffic increase so high that causes standstill / stop-start traffic - do you count by hours of gridlock, or how does this high traffic appear on statistics?
We answered
TfL Ref: FOI-1205-2122
Thank you for your request received by Transport for London (TfL) on 5 September 2021.
Your request has been considered in accordance with the requirements of the Freedom of Information Act and our information access policy. I can confirm that we hold some of the information you require. You asked:
Could you please provide us with monthly traffic data for the A4 from Jan 2018 to Sep 2021, separated by Eastbound and Westbound, to cover the stretches: -Hammersmith Rdbt to Hogarth Rdbt -Hogarth Rdbt to Sutton Ct Rd traffic lights -Sutton Ct Rd traffic lights to Chiswick Rdbt Is this measured at the traffic lights?
And can you please clarify how does TfL account for traffic increase so high that causes standstill / stop-start traffic - do you count by hours of gridlock, or how does this high traffic appear on statistics? If it is constant gridlock so that not as many vehicles get through, the statistics may not show high number of vehicles.
The attached spreadsheet provides data for the A4 at two locations by direction where we have automatic traffic counters closest to the locations you have requested. A map in the spreadsheet shows the locations of our automatic traffic counters on this part of the A4.
The data provided shows that traffic levels on the A4 corridor as a whole are lower now in 2021 than their baseline of 2019/20 as shown in the chart below, taken from our traffic flow monitoring dashboard. Traffic volumes on the A4 have not increased. Currently, traffic volumes are 10% less in operational hours (7am to 7pm) than for their equivalent days in 2019.
Operational hours (7am to 7pm).
We measure the impact of changes in road capacity or changes in traffic volumes affected by the implementation of a Streetspace scheme such as the one at Chiswick by monitoring bus journey and general traffic journey times relative to their baseline in 2019/20.
The latest information for the A4 corridor for the most recent 4 weeks that measure the change in delay (excess travel time in minutes per kilometre) on the A4 relative to the same weeks in 2019, show that overall over operational hours (7am to 7pm) traffic delay relative to the same weeks in 2019 is down 2.5%. We do however see an increase in delay in the Inter-peak 10am to 4pm. This is related to changes in travel patterns that have become established on the network post the pandemic.
Change in delay on the A4 for the period Sunday 22 August to Saturday 18th September relative to their equivalent weeks in 2019 (baseline year).
12 Hour
AM Peak
Inter Peak
PM Peak
A4 Inbound
-8.2%
-9.2%
4.5%
-24.5%
A4 Outbound
3.2%
-0.2%
16.2%
-9.4%
A4 Overall
-2.5%
-5.9%
10.4%
-15.6%
Where a deviation away from the normal variance in journey times seen in the baseline year is detected for example in bus journey times, we will look to mitigate any adverse impacts, particularly those seen during the build and establishment of the scheme.
If this is not the information you are looking for, or if you are unable to access it for any reason, please do not hesitate to contact me.
Please see the attached information sheet for details of your right to appeal as well as information on copyright and what to do if you would like to re-use any of the information we have disclosed.
Yours sincerely
Eva Hextall FOI Case Management Team General Counsel Transport for London
