Nicked by scamera on other side of wide dual carriageway?
Discussion
The other day on the way home I noticed (too late to react for various reasons) plod parked up in a layby on the other side of a dual carriageway paying me an unhealthy interest. No sign of pursuit at the time so I thought nothing of it until a NIP landed on my doormat this morning. The NIP states that it's supported by photo/video evidence. Given that the dual carriageway in question has a wide grass central reservation this means any speed measurement must have taken place across 4 lanes of tarmac and a central reservation approx 2 lanes wide - I thought speed measuring equipment was only certified to be used at an angle that was almost "head on" to your direction of travel but in this case must have been used at a much greater angle - does any one know whether this is indeed the case?
does not necessarily matter if they are pointing across the road, roads are rarely straight, curve to the left and you can actually be pointing directly at someone on the other side of the road, on a very wide road, this curve only needs to be very slight
even if the road is straight, your windscreen has a fairly low visible angle, particularly to the right, so if you can see him out the windscreen and not out the side window, you're well with the kind of angle they could get you in.
even if the road is straight, your windscreen has a fairly low visible angle, particularly to the right, so if you can see him out the windscreen and not out the side window, you're well with the kind of angle they could get you in.
agtlaw said:
Google ACPO RPET. See cosine effect.
...and you are sure to find that a measurement taken at an angle with a radar or laser will reduce the speed reading so you will have been driving faster than the speed indicated.Of course the police may have used a VASCAR type device that has no such error.
If you fish for long enough you may eventually have a long list of items that you can confuse a court with.
Thanks for the advice. I realise that the angle to the camera means I would have been travelling more slowly than my recorded speed, I was more interested to know whether I could (successfully) contest the offence on the basis that they can't provide an ACCURATE speed due to the cosine issue and/ or their equipment was operating outside it's certified envelope.
emmaT2014 said:
...and you are sure to find that a measurement taken at an angle with a radar or laser will reduce the speed reading so you will have been driving faster than the speed indicated.
Of course the police may have used a VASCAR type device that has no such error.
If you fish for long enough you may eventually have a long list of items that you can confuse a court with.
By Vascar, I assume you mean the good old fashioned tape measure, stopwatch and mark I right thumb ? Of course the police may have used a VASCAR type device that has no such error.
If you fish for long enough you may eventually have a long list of items that you can confuse a court with.
Unfortunatly the mark 1 right thumb on a stopwatch is uncannily accurate in my experience from taking lap times on a pit wall and comparing later with the race cars data logger whose times are triggered by a transponder.
More often than not over say a 70 second lap, a difference of less than a tenth is not unusual. Plod will be timing you over, say 15 secs I imagine, so less room for error. Well unless he just presses the timer a bit early, just to be sure.
More often than not over say a 70 second lap, a difference of less than a tenth is not unusual. Plod will be timing you over, say 15 secs I imagine, so less room for error. Well unless he just presses the timer a bit early, just to be sure.
I looked into this a few years ago and really don't think there is any mileage in it. The guidelines state that the operator should be within a certain distance from your trajectory (10% of the range from memory - so if you are 400m away, they can be 40m from your trajectory). There is also a separates guideline that they should be within 10 metres of the carriageway. But they are only GUIDELINES. In my case, the van was up a side road and the offset was about 16%.
According to some, more relevant when measuring your speed at an angle to the vehicle is the risk of a "slip error". Again I don't think you'd get very far with this.
FYI, here's the pic from my incident. As you can see, the side of the car is clearly visible. Using known dimensions such as the wheelbase of the car I was able to calculate the offset of the camera. It was an interesting exercise but luckily I got offered a course anyway:
According to some, more relevant when measuring your speed at an angle to the vehicle is the risk of a "slip error". Again I don't think you'd get very far with this.
FYI, here's the pic from my incident. As you can see, the side of the car is clearly visible. Using known dimensions such as the wheelbase of the car I was able to calculate the offset of the camera. It was an interesting exercise but luckily I got offered a course anyway:
Edited by Pappagallo on Thursday 9th October 15:07
BBC said:
The slip effect
If the laser doesn't focus on the same area you can get the slip.
As the gun calculates speed by measuring the changing distance to a car, if the beam of the gun is moved along the car while taking a reading, this could affect the results.
As Dr Clark explains; "This instrument doesn't know if it [the speed gun] is moving. So it started measuring a little bit further away down the vehicle, now it's a bit closer so it thinks there's a speed reading".
He then pans the speed camera down the side of a stationary car and clocks it doing 4mph.
"This is of course very relevant. If a policeman is pointing at a vehicle going by and he moves it across [the vehicle] then he will get an increased, or indeed a decreased, speed reading."
Dr Clark says that all laser speed guns suffers from the same problem so we thought we would give it a go on a wall with one of the latest guns used by the police: an LTI 20.20.
speed camera showing a reading of 58mph
We clocked a stationary wall at 58mph - now that's motoring
By aiming at the wall and pulling the trigger whilst panning with the device we managed to get a reading of 58mph from the stationary wall - enough to get three points and a fine in urban areas.
Dr Clark has only been demonstrating the speed guns on stationary cars to us, but he says the problems could be worse in real-life situations;
"Because the car itself is moving they have to hold it very very closely on the same point on the vehicle otherwise they will get an erroneous speed reading."
In theory, this means that when doing a speed check, if the operator lets the measuring laser move across the side of a car during the speed check, then the length of the car could be added to the distance the machine uses to calculate the car's speed.
Laser guns typically take their series of measurements in about a third of a second. If a slip effect adds an extra couple of metres onto the distance you travel in a third of a second it can increase the speed registered by anything from an extra one to 30 mph.
http://www.bbc.co.uk/insideout/southwest/series7/speed-cameras.shtmlIf the laser doesn't focus on the same area you can get the slip.
As the gun calculates speed by measuring the changing distance to a car, if the beam of the gun is moved along the car while taking a reading, this could affect the results.
As Dr Clark explains; "This instrument doesn't know if it [the speed gun] is moving. So it started measuring a little bit further away down the vehicle, now it's a bit closer so it thinks there's a speed reading".
He then pans the speed camera down the side of a stationary car and clocks it doing 4mph.
"This is of course very relevant. If a policeman is pointing at a vehicle going by and he moves it across [the vehicle] then he will get an increased, or indeed a decreased, speed reading."
Dr Clark says that all laser speed guns suffers from the same problem so we thought we would give it a go on a wall with one of the latest guns used by the police: an LTI 20.20.
speed camera showing a reading of 58mph
We clocked a stationary wall at 58mph - now that's motoring
By aiming at the wall and pulling the trigger whilst panning with the device we managed to get a reading of 58mph from the stationary wall - enough to get three points and a fine in urban areas.
Dr Clark has only been demonstrating the speed guns on stationary cars to us, but he says the problems could be worse in real-life situations;
"Because the car itself is moving they have to hold it very very closely on the same point on the vehicle otherwise they will get an erroneous speed reading."
In theory, this means that when doing a speed check, if the operator lets the measuring laser move across the side of a car during the speed check, then the length of the car could be added to the distance the machine uses to calculate the car's speed.
Laser guns typically take their series of measurements in about a third of a second. If a slip effect adds an extra couple of metres onto the distance you travel in a third of a second it can increase the speed registered by anything from an extra one to 30 mph.
vee5 said:
Thanks for the advice. I realise that the angle to the camera means I would have been travelling more slowly than my recorded speed, I was more interested to know whether I could (successfully) contest the offence on the basis that they can't provide an ACCURATE speed due to the cosine issue and/ or their equipment was operating outside it's certified envelope.
You'd need to find out which speed meter was used and the measured distances.The LTI20.20 UK manual says this:
"A good rule of thumb is not to exceed 1 metre off the road for every 10 metres shooting down range to the targets. If you want to target vehicles 150 metres down the road, for example, set up no more than 15 metres off the road."
The cosine issue appears to be a red herring. If your defence is that you were going faster than the speed alleged then you need your head examining.
This motorcyclist was on the opposite carriageway, over the central reservation barrier.
http://www.safespeed.org.uk/forum/viewtopic.php?f=...
http://www.pistonheads.com/gassing/topic.asp?h=14&...
I'd forgotten the space docking information
He was done after a retrial. Did that points swapping police couple in Portishead face a retrial?
http://www.safespeed.org.uk/forum/viewtopic.php?f=...
http://www.pistonheads.com/gassing/topic.asp?h=14&...
I'd forgotten the space docking information
He was done after a retrial. Did that points swapping police couple in Portishead face a retrial?
Pappagallo said:
Feel free to correct if I am wrong but if what I have been told is correct, I am lead believe this is the same Dr who is slowly being discredited as an expert witness by many constabularies around the UK. The device he was using to demonstrate this theory was a overseas Specification Laser rather than type approved version being used by UK forces.Forums | Speed, Plod & the Law | Top of Page | What's New | My Stuff