Request ID: FOI-1224-2324 Date published: 08 August 2023
You asked
Follow-up to FOI-0917-2324: Thank you so much for your kind help. The hourly data is indeed helpful for my safety research. I will draft my first version soon and will update the progress and acknowledge the TFL's kind support.
Meanwhile, can I kindly ask for a more comprehensive dataset regarding all the boroughs of London, including the city of London, from 1st January 2019 to 1st January 2023? I will use this dataset to further measure the traffic exposure and the context of ' safety in numbers'. I believe this will be a good foundation to provide more nuanced suggestions for the transport plan.
It would be kind to have your further help.
We answered
TfL Ref: FOI-1224-2324
Thank you for your further request received by Transport for London (TfL) on 17th July 2023 asking for traffic count data.
Your request has been considered in accordance with the requirements of the Freedom of Information Act and our information access policy.
Specifically you asked:
“Can I kindly ask for a more comprehensive dataset regarding all the boroughs of London, including the city of London, from 1st January 2019 to 1st January 2023? I will use this dataset to further measure the traffic exposure and the context of ' safety in numbers'. I believe this will be a good foundation to provide more nuanced suggestions for the transport plan.
I can confirm that we hold the information you require.
You will shortly receive a separate email (please wait an hour or so) that will provide a link to the requested data (please check your junk / spam folder if you do not receive it directly in your inbox).
This link provides hourly data from the set of 296 automatic traffic counters (ATCs) which have been in continuous operation form 1st January 2019 to 1st January 2023 inclusive. Also included is a metadata file that provides references for location, and details of the Borough in which the asset is found, and the road type where the asset is located - for example, on the TLRN (Transport for London Road Network) or the BPRN, (Borough Principal Road Network).
ATC’s are magnetic loops in the road that count all motorised vehicle movements that pass over the loop. These assets are not able to distinguish the mode or vehicle type. Some ATC’s in this table are at similar grid references and are directional.
The flow monitoring strategy that has determined the deployment of these assets dates back to the year 2000. These assets were originally deployed to provide a statistically representative flow count at the level of central, inner and outer London and also at the point location at which the asset was installed. The number of assets needed to provide accurate flow estimations by type of road, corridor, by Borough or any other geography are many more hundreds than were originally installed.
Over time TfL added more assets to the TLRN, such that by division of the TLRN into 80 flow monitoring sections there were sufficient assets on the TLRN to provide an accurate estimation of vehicle kilometres across its 580km. Note this is length of 580km represents only circa 4% of London’s roads. We estimate that despite fitting these extra ATCs we have only 95% accuracy of flow measurement over 56% of the length of the TLRN. However, in the round there are sufficient ATCs to provide a globally accurate estimation of the volume of traffic on this 4% of London’s roads, noting however, these are the strategic set of roads and they carry about one-third of London’s traffic.
On the remaining 96% of London’s roads (outside of the TLRN) there are insufficient ATCs to accurately estimate the vehicle demand in vehicle kilometres with any reasonable level of accuracy. The following caveats therefore apply to this data set.
Any ATC on a road in London outside of the TLRN (96% by length of all London’s roads), the data at any ATC site s only representative of the counts and traffic flow at the exact location of the ATC asset.
Data from these ATCs should not beaggregated within a Borough or across multiple roads, or corridors outside of the TLRN, with a view that this forms an accurate assessment of the traffic volumes (total vehicle kms) across a larger area of London. To accurately assess total traffic volumes on the 96% by length of roads outside the TLRN it would require many thousands (at least multiple hundreds) more traffic counters than are available in this data set. An accurate assessment of traffic volumes requires very specific placement of traffic monitoring assets stratified across many different types of roads, to be able to provide this type of accurate traffic flow estimation. This data set does not meet these essential requirements..
This data set outside of the TLRN should not be used in calculations to estimate road safety exposure rates from casualty data. There is insufficient data in this data set to provide robust and accurate road safety exposure rates.
This data should not be used to calculate volumes of traffic levels in individual Boroughs or to compare traffic levels between Boroughs. There are insufficient ATCs in this data set to provide robust representative traffic volume estimates within Boroughs or between Boroughs.
This data should not be used to normalise general traffic journey times, or any calculations that are used to evaluate the impact of delay or congestion across the London road network. There is insufficient data in this data set for it to be representative of flows on the London road network to do this.
The Department of Transport provides an annual survey of London’s roads, using over 3,600 count points and this data series is converted to an annual average daily flow. It is a data set designed to provide a statistically robust estimation of the total vehicle volume across London’s roads, it has the added benefit of being available by mode, and it will support many of the calculations, that this ATC data set is not suitable for. It is important that you use the data in a way that is statistically valid for your purposes, and often the DfT data will be more appropriate to use than the data supplied in this ATC data set. This data set can be accessed at this link. https://roadtraffic.dft.gov.uk/regions/6
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,
David Wells FOI Case Officer FOI Case Management Team General Counsel Transport for London
