Digital camera data - Chiswick High Road - March 2022 to September 2022
Request ID: FOI-1589-2223 Date published: 18 October 2022
You asked
Further to previous FOI requests (most recently FOI-2735-2122), please could you provide the data from the digital cameras on Chiswick High Road captured between 01-03-2022 and 30-09-2022.
The data should include all countline IDs previously supplied (where possible), as well as any new countline IDs added since the previous FOI request (noted above) was made.
For each countline ID, please provide:
(a) the location of the countline
(b) the location of the camera monitoring the countline
(c) the direction of travel being monitored (eastbound, westbound, or both)
(d) the mode of travel for which the countline is optimised (vehicles, cycles, or pedestrians)
Please could you also provide the following additional information in order to assist with the interpretation of the data:
(i) details of any known camera outages / missing or dubious data
(ii) specify which countline IDs are used / considered authoritative by TfL when collating cycle counts for Chiswick High Road. If cycle counts are derived from multiple countline IDs, please supply a worked example of any calculations used.
(iii) specify which countline ID is best used to represent flow of each mode in any situation where 2 or more countline IDs monitor the same approximate location (eg countline IDs 22096 and 22081 at the junction with Turnham Green Terrace).
We answered
TfL Ref: FOI-1589-2223
Thank you for your request received by Transport for London (TfL) on 3rd October 2022 asking for digital camera data from Chiswick High Road. Your request has been considered in accordance with the requirements of the Freedom of Information Act and our information access policy.
Specifically you asked:
“Further to previous FOI requests (most recently FOI-2735-2122), please could you provide the data from the digital cameras on Chiswick High Road captured between 01-03-2022 and 30-09-2022.
The data should include all countline IDs previously supplied (where possible), as well as any new countline IDs added since the previous FOI request (noted above) was made.
For each countline ID, please provide: (a) the location of the countline (b) the location of the camera monitoring the countline (c) the direction of travel being monitored (eastbound, westbound, or both) (d) the mode of travel for which the countline is optimised (vehicles, cycles, or pedestrians)
Please could you also provide the following additional information in order to assist with the interpretation of the data:
(i) details of any known camera outages / missing or dubious data
(ii) specify which countline IDs are used / considered authoritative by TfL when collating cycle counts for Chiswick High Road. If cycle counts are derived from multiple countline IDs, please supply a worked example of any calculations used.
(iii) specify which countline ID is best used to represent flow of each mode in any situation where 2 or more countline IDs monitor the same approximate location (eg countline IDs 22096 and 22081 at the junction with Turnham Green Terrace).”
I can confirm that we hold some of the information you require, which is provided in the attached folder. This contains the data, where held, from 01/03/22 - 30/09/22 for all of the count-lines previously supplied. The exceptions to this are:
Sensor 66 which has been offline since December 2021 due to large scale roadworks/redesign of the junction. Works are now complete in the area but we are awaiting power to be reconnected to the sensor
Sensor 64 which has been offline since 13th September 2022 as the lamp column has been removed and repositioned
Sensor 97 - the road has been redesigned and a dedicated cycle lane put in. Therefore we have provided data from the old count-line (22509) from 01/03/22 – 30/6/22 and from then onwards provided the data from the two new count-lines which have been added. These are 43032 in the road and 43031 in the new cycle lane.
The spreadsheet labelled “Chiswick High Road count-line info provides the answers to questions a, c, and d.
Question b) asks “specify which count-line IDs are used / considered authoritative by TfL when collating cycle counts for Chiswick High Road. If cycle counts are derived from multiple count-line IDs, please supply a worked example of any calculations used”.
The following count-lines are currently used to monitor the scheme as cycle numbers at specific point locations.
Scheme
Count-line
Sensor
Name
Site name in monitoring dashboard
C9 - Chiswick & Kew
22096
62
S62_ChiswickHighRd_cycleln_tfl002
Chiswick High Rd CL
C9 - Hammersmith
43031
97
S97_KingSt_cyclelane_tfl002
King St – CL and CW
C9 - Hammersmith
43032
97
S97_KingSt_road_tfl002
King St – CL and CW
C9 - Hammersmith
22149
68
S68_HammersmithRd_cycleln_eastbound_tfl002
Hammersmith Rd – Cycle Lane EB
C9 - Hammersmith
22201
68
S68_HammersmithRd_cycleln_westbound_tfl002
Hammersmith Rd – Cycle Lane WB
C9 - Hammersmith
22148
68
S68_HammersmithRd_tfl002
Hammersmith Rd – Main CW
The correct methodology for monitoring the success of the scheme as a whole along the corridor, or along any stretch of road is to measure cycle demand as the total number of cycle kilometres (kms) travelled by all of the cyclists traversing the route.
This diagram illustrates how this would be done in principle for Chiswick High Road Eastbound over 24 hours.
Note, this is achieved by allocating each point location which has a camera and direction to a fixed length of Chiswick High Road and assuming that a cyclist counted at each camera location completes the journey over the section of the road to which the camera is allocated. This prevents overcounting when cyclists complete journeys across multiple camera locations. .
It is important to note that cycle demand is never measured by adding together cycle counts from different point based cycle monitoring locations, and TfL never quotes numbers of cyclists using its infrastructure other than at point locations or when crossing a screen-line. The above methodology is also true for counts of general traffic. The correct unit of demand on the network is always cycle-kms as one cyclist in a trip can do 1 km or several kms, so adding numbers of cyclists together over a length of the network does not make sense.
TfL has not yet assigned such a demand metric to Chiswick High Road as the scheme is still being re-designed and TfL it is currently still developing a full stratified sampling framework for cycle monitoring in London, for where it has cameras such as the ones used to monitor this specific scheme. This methodology will aim to mirror our current strategic cycle monitoring strategy, which uses annual manual counts of cycles at over 1,400 count points across all of London, to identify the total annual cycle demand by road type in cycle kms.
In lieu of this methodology not yet being in place, the current scheme on Chiswick High Road is assessed by treating each camera in the scheme monitoring table above as a sampling point.
The scheme is then assessed by measuring the growth in sample of cyclists across the pooled set of cameras in the monitoring table at the start of the scheme, versus the most recent pooled sample, aiming to use comparative sample months to take into account seasonality in cycling. So to replicate the above example looking at changes in cycling Eastbound on Chiswick High Road we would use the following formula.
We then report the success of the scheme in terms of the percentage change in the sample of cyclists as measured by these cameras.
Please note that cycling on a corridor or area basis is never reported as a count of cyclists. It can only be expressed as either a percentage change in sample of cyclists or more accurately as the change of cycle demand observed in cycle kms.
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
