Request ID: FOI-0305-2122 Date published: 01 June 2021
You asked
Dear Transport for London,
I am interested in the traffic lights at the junction of Highgate Hill, Dartmouth Park Hill and Horney Lane at the boundary of N19 and N6. There are several times of day (and not only in rush hour) when there are long queues of traffic heading south, down Highgate Hill, and no queues for traffic heading in other directions. Tests have shown that air pollution in the area is at its worst on the stretch of road north of these lights, where the queuing is most common.
Can you please supply the information that allows us to understand why the queues are virtually always in the one direction? To what extent can the light sequencing be adjusted manually or be left to an automated system, and how does any automation work?
Do you have data for length of the green light phase in each direction and traffic flows on the three roads mentioned? If so, please provide it for a period of 12 months?
We answered
TfL Ref 0305-2021/22
Thank you for your request received by Transport for London (TfL) on 12 May 2021 asking for information about traffic light phasing on Highgate Hill.
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 the information you require. You asked:
I am interested in the traffic lights at the junction of Highgate Hill, Dartmouth Park Hill and Horney Lane at the boundary of N19 and N6. There are several times of day (and not only in rush hour) when there are long queues of traffic heading south, down Highgate Hill, and no queues for traffic heading in other directions. Tests have shown that air pollution in the area is at its worst on the stretch of road north of these lights, where the queuing is most common.
Can you please supply the information that allows us to understand why the queues are virtually always in the one direction? To what extent can the light sequencing be adjusted manually or be left to an automated system, and how does any automation work?
Do you have data for length of the green light phase in each direction and traffic flows on the three roads mentioned? If so, please provide it for a period of 12 months?
The junction you have asked about has four signal stages which run in each signal cycle, which are as follows:
Stage 1: Highgate Hill, both directions
Stage 2: Pedestrians
Stage 3: Hornsey Lane
Stage 4: Dartmouth Park Hill
Within each cycle (the time it takes for all stages to operate once in turn) we not only provide green time to vehicular traffic and pedestrians, but also allow safety critical timings that ensure conflicting movements can safely be separated.
The junction is controlled by an automated signal system called SCOOT, which uses detectors in the road to measure how much traffic is on each approach, and adjusts the signal timings in real time to satisfy that flow. We influence this optimisation in various ways, such as setting the importance of particular approaches to ensure they are prioritised accordingly. All stages except for stage 1 are demand dependent, which means they will only appear in the cycle if there is a pedestrian who pushes the button or a vehicle is detected as waiting. This is intended to give as much extra green time to Highgate Hill as possible, however our system shows that there is demand for the other stages in the vast majority of cycles, so this extra green time is very rare.
Please find attached data from the SCOOT system for vehicle flow and green times on the approaches mentioned, separated into AM, off peak and PM periods over the last 12 months. Please note that the flows are not verified traffic counts. This 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. Please only use this flow data 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.
We have also scheduled a full timing review of this junction for this financial year, during which we will fully review the SCOOT setup and ensure the junction is operating as efficiently as possible.
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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.
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Yours sincerely
Sara Thomas
FOI Case Management Team
General Counsel
Transport for London
