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Camberwell Green 20mph Camera Question
ConfusedDaze
post Wed, 21 Aug 2019 - 11:49
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Hi Guys,

Here's a question.

If someone was at the traffic light line on their motorbike and sped up past 20 to say 28(ish) mph before he got to the end of the dotted lines on the ground, would that trigger the camera.

So for the camera in question where the blue van is;

https://www.google.com/maps/@51.4787904,-0....6384!8i8192

If you were going from 0mph to 28 before the end of the dotted lines would that trigger the camera?

Also do the Metropolitan Polce/Greater London area offer 20mph courses?

Thanks!


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post Wed, 21 Aug 2019 - 11:49
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TryOut
post Wed, 21 Aug 2019 - 12:36
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The speed is measured where the blue van is. You can see the sub-surface sensors on the road.

A vehicle passing between those black tar-filled lines has the time it arrives at the sensors measured, the distance is known so a speed can be calculated. Before and past the lines no speed is measured by the camera other than a secondary check speed from 2 photographs. If the speed is not above a set threshold speed from the sensors no secondary check images are taken.

If you mean the dotted lines that form the crossing then you may well have your speed recorded in the circumstances you describe. If you mean the secondary check marks then probably not.

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ConfusedDaze
post Wed, 21 Aug 2019 - 16:07
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So;

Attached Image


If the bike was where the red box is and stationary waiting at a red light and then when the light went green accelerated up to just under 30mph possibly by the time it got to the end of the white lines, the 20mph trigger of the camera wouldn't deploy as the bike would have had to go over those black sensors at 20 when it was stationary?

Thanks


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cp8759
post Wed, 21 Aug 2019 - 16:26
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Trigger point should be at least 24mph.


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Fredd
post Wed, 21 Aug 2019 - 17:40
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From those images I reckon you'd need to accelerate at an average of about 0.53g to hit 24mph by the last line. From a standing start, with reaction time, maybe wheel spin, and a very non-linear torque curve, I think you'd be lucky to find many bikes that could achieve that. And that's without any of the issues around where the camera would trigger and the need for a secondary check when you've already left the check lines. I stand to be corrected, of course. smile.gif


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cp8759
post Thu, 22 Aug 2019 - 15:17
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QUOTE (Fredd @ Wed, 21 Aug 2019 - 18:40) *
From those images I reckon you'd need to accelerate at an average of about 0.53g to hit 24mph by the last line.

I think you'd need your average speed between the lines to be 24 mph, so even if the rear wheel were to pass the last line at 25 or 26 mph, it's highly unlikely that the average speed as measured between the two lines would be measured at 24+


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Fredd
post Thu, 22 Aug 2019 - 16:13
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Yes I know, but I assumed the OP's question was related to the (virtually) instantaneous primary speed measurement, not the average speed presumably inferred using the lines as a secondary check.


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cp8759
post Thu, 22 Aug 2019 - 16:25
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What virtually instantaneous check? My understanding is that the primary measurement is taken from the two lines of senors buried in the road, and the secondary check is the two photos taken 0.5 seconds apart in combination with the dragon teeth?


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Fredd
post Thu, 22 Aug 2019 - 16:32
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And how long do you imagine it takes to cross those two lines of sensors?


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cp8759
post Thu, 22 Aug 2019 - 18:21
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QUOTE (Fredd @ Thu, 22 Aug 2019 - 17:32) *
And how long do you imagine it takes to cross those two lines of sensors?

The question isn't how long it takes, but whether you can accelerate at such a rate that the average speed of the vehicle exceeds 24 mph while the rear wheel moved between the two lines. From your previous response we seem to be in agreement that this is possible but unlikely.


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ConfusedDaze
post Fri, 23 Aug 2019 - 20:01
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Are we talking about the black lines in the road under the blue van as the motorbike was sat stationary on those black lines at a red light.

The light went green, the bike then would have accelerated to a speedo indicated 28mph-ish (so 25/26) by one point near or after the end of the white road markings.

The bike in question can apparently do 0-60 in 3.1 seconds but I'd guess this start was nowhere near that at all!


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TryOut
post Sat, 24 Aug 2019 - 09:02
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QUOTE (ConfusedDaze @ Fri, 23 Aug 2019 - 21:01) *
Are we talking about the black lines in the road under the blue van as the motorbike was sat stationary on those black lines at a red light.

The light went green, the bike then would have accelerated to a speedo indicated 28mph-ish (so 25/26) by one point near or after the end of the white road markings.

The bike in question can apparently do 0-60 in 3.1 seconds but I'd guess this start was nowhere near that at all!

The black lines are the speed detectors. As the bike is not moving there will be nothing to detect. As the bike moves off an acceleration is detected, no speed will be shown for the acceleration from 0mph to a higher speed than 0mph.
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ConfusedDaze
post Sat, 24 Aug 2019 - 12:24
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QUOTE (TryOut @ Sat, 24 Aug 2019 - 10:02) *
QUOTE (ConfusedDaze @ Fri, 23 Aug 2019 - 21:01) *
Are we talking about the black lines in the road under the blue van as the motorbike was sat stationary on those black lines at a red light.

The light went green, the bike then would have accelerated to a speedo indicated 28mph-ish (so 25/26) by one point near or after the end of the white road markings.

The bike in question can apparently do 0-60 in 3.1 seconds but I'd guess this start was nowhere near that at all!

The black lines are the speed detectors. As the bike is not moving there will be nothing to detect. As the bike moves off an acceleration is detected, no speed will be shown for the acceleration from 0mph to a higher speed than 0mph.


So basically there's zero chance of it having detected in those circumstances?


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TryOut
post Sat, 24 Aug 2019 - 15:17
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QUOTE (ConfusedDaze @ Sat, 24 Aug 2019 - 13:24) *
QUOTE (TryOut @ Sat, 24 Aug 2019 - 10:02) *
QUOTE (ConfusedDaze @ Fri, 23 Aug 2019 - 21:01) *
Are we talking about the black lines in the road under the blue van as the motorbike was sat stationary on those black lines at a red light.

The light went green, the bike then would have accelerated to a speedo indicated 28mph-ish (so 25/26) by one point near or after the end of the white road markings.

The bike in question can apparently do 0-60 in 3.1 seconds but I'd guess this start was nowhere near that at all!

The black lines are the speed detectors. As the bike is not moving there will be nothing to detect. As the bike moves off an acceleration is detected, no speed will be shown for the acceleration from 0mph to a higher speed than 0mph.


So basically there's zero chance of it having detected in those circumstances?

Basically or exactly, whichever you prefer.
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ConfusedDaze
post Sat, 24 Aug 2019 - 23:01
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Lol got it thanks :-)


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