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FightBack Forums _ Technical Discussion of Enforcement Devices _ Red light camera trigger sensors

Posted by: Baaartz Sun, 25 Oct 2020 - 14:57
Post #1594520

Hi, just a quick question, does anyone know where the sensors that trigger the red light camera are based?

I have had a pretty awkward situation on the a41 in cricklewood when I was driving my tipper, the lights were green I have approached them with caution however when my cab unit went through on green the lights have turned to amber, I was loaded so I had to slow down drastically to turn right on that junction, I'm pretty sure my back wheels cleared the white stop line as soon as the lights have turned to red.

Now is there also any grace period until the camera goes active to allow for situations such as these?

Is there also anything I could do to get this NIP revoked if it has arrived?
I'm pretty sure anyone that drives anything with a wagon had a similar situation, sometimes they're unavoidable as you cant simply speed up like you would in a car with a loaded lorry.

I have had attached a picture with a red line roughly stating where my back wheels were when the light has turned red, I just want to know if there is still a chance of me receiving the nip or was I already past the sensors which trigger the camera?



Any help and advice is welcome,
Regards.


 

Posted by: 666 Sun, 25 Oct 2020 - 15:24
Post #1594525

Someone more knowlegable will confirm the location of the sensors.

What strikes me from the photos is that at least part of your vehicle must still have been behind the line - the position of the wheels is irrelevant.

Posted by: Baaartz Sun, 25 Oct 2020 - 15:47
Post #1594531

QUOTE (666 @ Sun, 25 Oct 2020 - 15:24) *
Someone more knowlegable will confirm the location of the sensors.

What strikes me from the photos is that at least part of your vehicle must still have been behind the line - the position of the wheels is irrelevant.


I always thought it's the wheels that trigger the sensors? Might have been wrong.

Posted by: 666 Sun, 25 Oct 2020 - 15:54
Post #1594534

QUOTE (Baaartz @ Sun, 25 Oct 2020 - 15:47) *
QUOTE (666 @ Sun, 25 Oct 2020 - 15:24) *
Someone more knowlegable will confirm the location of the sensors.

What strikes me from the photos is that at least part of your vehicle must still have been behind the line - the position of the wheels is irrelevant.


I always thought it's the wheels that trigger the sensors? Might have been wrong.

Those days are gone. Inductive loops detect metal objects.

Posted by: Baaartz Sun, 25 Oct 2020 - 17:11
Post #1594542

QUOTE (666 @ Sun, 25 Oct 2020 - 15:54) *
QUOTE (Baaartz @ Sun, 25 Oct 2020 - 15:47) *
QUOTE (666 @ Sun, 25 Oct 2020 - 15:24) *
Someone more knowlegable will confirm the location of the sensors.

What strikes me from the photos is that at least part of your vehicle must still have been behind the line - the position of the wheels is irrelevant.


I always thought it's the wheels that trigger the sensors? Might have been wrong.

Those days are gone. Inductive loops detect metal objects.


Right either way if my vehicle was across the line and one of the sensors triggers it would only result in 1 picture being taken and not 2 which means no fine to my understanding?

Posted by: Jlc Sun, 25 Oct 2020 - 19:31
Post #1594564

If the loop detects a vehicle moving then 2 shots are taken in quick succession to prove the vehicle was moving.

If the camera unit see a long vehicle then they may not issue a ticket - but in law an offence occurs if any part of the vehicle moves over the stop line when red is illuminated.

Posted by: baroudeur Mon, 26 Oct 2020 - 13:49
Post #1594695

The camera takes two photos. The first of whatever crosses the sensor at the stop line when the light turns red and the second at a sensor at a predetermined distance past the stop line. These will show if the vehicle was moving by virtue of the times on the photos and may also be used to indicate the speed of the vehicle for speeding offences.

Posted by: TryOut Wed, 18 Nov 2020 - 09:36
Post #1600327

QUOTE (Baaartz @ Sun, 25 Oct 2020 - 17:11) *
QUOTE (666 @ Sun, 25 Oct 2020 - 15:54) *
QUOTE (Baaartz @ Sun, 25 Oct 2020 - 15:47) *
QUOTE (666 @ Sun, 25 Oct 2020 - 15:24) *
Someone more knowlegable will confirm the location of the sensors.

What strikes me from the photos is that at least part of your vehicle must still have been behind the line - the position of the wheels is irrelevant.


I always thought it's the wheels that trigger the sensors? Might have been wrong.

Those days are gone. Inductive loops detect metal objects.


Right either way if my vehicle was across the line and one of the sensors triggers it would only result in 1 picture being taken and not 2 which means no fine to my understanding?

There is a sensor before the line and a second sensor after the line. The camera is connected to the relevant light display. The camera will measure the light sequence and look for a 3 second amber then a red light. The camera will only arm if the amber and red sequence is correct and the green light is extinguished. It will then look for the red delay setting, can be anything from 0 seconds upwards, typically 1 second but no delay is OK too. After the correct light sequence and delay period the system will arm for red light enforcement.

Once armed the system will then look for vehicles passing over the first and then the second sensor. If it sees a vehicle passing over sensor 1 and then 2, it takes a photograph immediately, thus showing an image of the vehicle in a position that has the stop line under part of the vehicle. A second image is then taken some time afterwards to show the vehicle was continually driven past the stop line position. The images are arranged to show the relevant traffic light in them.

If there is a long vehicle the driver may be in a position that is past a position where the traffic light can be seen when the arming sequence is in progress, i.e. an amber light or the light is red and in the red delay period. This means it may be possible that the driver didn't see the red light that is at the stop line. The arming sequence can complete when the driver of the long vehicle is in the junction. If the vehicle is long enough and is continually driven forwards the camera will trigger and take 2 pictures with the long trailer passing over the stop line. Same for buses.

The resulting record could be ambiguous as far as the driver view of the relevant signal lamp is concerned so is normally rejected.


The driver does however need to arrange to stop or prepare to stop at the amber signal so an intention not to stop at amber is usually the case when the long vehicle is part way through the junction. It is also the case that the driver will be able to see the repeater traffic signal at the far side of the junction so does have all of the information needed not to continue driving through a red light.

Perhaps drivers of long and heavy vehicles should take extra care not to continue to drive through a junction that is displaying an amber light for 3 seconds and a red light for probably 1 second, and fail to stop. At 30 mph the amber gives 40 m warning, almost 1/2 a football pitch, to stop. If you are still driving your long vehicle through a junction and the camera has armed I would say the wrong decision has been made by the driver, although it is not likely a prosecution will follow from an automatic camera record. If, as you say you "...proceeded with caution..." you would not have driven your tipper truck through the junction at all, the sequence of operation and the camera triggering shows your likely intent at the time I fear.

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