Scoot data and traffic light green phasing data for Highgate Hill
Request ID: FOI-0433-2122 Date published: 11 June 2021
You asked
F/O from 0305-2122
Thank you for the reply. Alas I do not understand what the numbers mean.
If there is a 30 in a cell (for example one date, peak a.m., in phase 1) what does that mean? If it means the average number of vehicles that pass through each green phase during those hours, I will need the actual number passing at each green phase. (Just supply a week of data to keep the file small enough to be manageable.)
Please can you supply the weekend data too.
Can you please explain how you can "fully review the SCOOT setup and ensure the junction is operating as efficiently as possible" when in your own words "the flows are not verified traffic counts"? Where are the scoot detectors? And what other data might you use?
We answered
TfL Ref 0305-21/22 and 0433-21/22
Thank you for your further email as below asking for clarification on the information about traffic light phasing on Highgate Hill that we provided to you in our reply to your FOI request. I apologise if the data was not fully explained in my reply.
You asked:
If there is a 30 in a cell (for example one date, peak a.m., in phase 1) what does that mean? If it means the average number of vehicles that pass through each green phase during those hours, I will need the actual number passing at each green phase. (Just supply a week of data to keep the file small enough to be manageable.)
Please can you supply the weekend data too.
Can you please explain how you can "fully review the SCOOT setup and ensure the junction is operating as efficiently as possible" when in your own words "the flows are not verified traffic counts"? Where are the scoot detectors? And what other data might you use?
The four different sheets contained in the zip file called ‘Highgate Hill SCOOT Detector Flows’ show the average vehicle flow for each of the roads leading to the junction; so for example, sheet "Highgate Hill SB" in cell D2 indicates there were 282 vehicles flowing over the detector per hour for each hour in the AM peak period on 20 May 2020.
The three different sheets contained in the zip file called ‘Highgate Hill green time’ FOI show the time each stage is at green so for example sheet "AM Peak (0700 - 1000) green time shows cell 2E as stage 1 receiving 29 seconds of green time and so on.
This is not 100% accurate as the flows are not verified traffic counts. This is because the flow data has come from the SCOOT detectors which calculate an approximate number of vehicles based on how long the detector is occupied. They are therefore at risk of inaccuracies during busy times when static vehicles queuing over the detectors increase this occupancy measurement so this flow data should only be used as an indicative guide. There are also some dates that do not have SCOOT detector flow available, which is a result of intermittent faults with the detection equipment. The pedestrian green time is always fixed at 6 seconds which is the time when the green figure is shown and does not include the additional blackout period when pedestrian can continue to cross safely.
Please find attached the weekend data provided on the same basis as above.
Can you please explain how you can “fully review the SCOOT setup and ensure the junction is operating as efficiently as possible” when in your own words “the flows are not verified traffic counts”?
The flows calculated by the detectors allow the SCOOT system to understand the volumes of traffic on each approach to the junction. The system uses the volume of traffic to calculate a degree of saturation, which is a percentage representing the capacity (green time) used out of the capacity available in each signal stage. It also calculates congestion based on how long the detector is occupied by stationary traffic. The system therefore does not need to know precise vehicle numbers, as it bases these calculations on the footprints of traffic going over the detectors.
As part of our review we will ensure that the degree of saturation is being calculated correctly. There are parameters in the SCOOT system that we can change to help it understand how quickly the traffic is able to pass through the junction. On top of this we will also be reviewing the cycle time to ensure that there are appropriate green times available to each movement, without causing excessive delay to other approaches. We will also review the bus priority technology which looks to give more green time to buses when they are detected, to ensure this is working well without adverse impacts on the junction’s capacity.
Where are the scoot detectors?
The Site Layout Drawing is attached.
And what other data might you use?
We are able to provide the degree of saturation and congestion data that is calculated by the SCOOT system if this is of interest.
Below are the staging diagram below shows the stages so 1, 2, 3 and 4: We have not provided the timings for the stage 2 pedestrians as it runs the same time each duration - fixed at six seconds.
This shows the locations of the SCOOT detectors:
This is a more zoomed in plan but only shows SD2 (SCOOT Detector)
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Yours sincerely
Sara Thomas FOI Case Management Team General Counsel Transport for London
