Dodgyscope question...
Discussion
scuffham said:
can anybody remeber what the rules are for the dodgyscope in terms of 'shooting' accross a dual caridgeway?
TT LTI manual states:
TT said:
Line Of Sight
While setting up it is important that a position be chosen which has a clear view to the section of the road that will be targetted. It is important that no trees, telephone poles, buildings, etc. are situated between the instrument and the section of the road that will be targetted.
Line Of Sight
An important requirement of the laser speed detector that must be adhered to at all times is that the operator must have a clear line of sight to the target vehicle. It is important that nothing intersects the laser beam as it travels between the instrument and the target. If at anytime an object does intersect the beam while a velocity merasurement is being taken the instrument will display an error message.
The result stated from the latter isn't necessarily true; the software for teh LTI version can discard up to 5 dodgy samples from the measurement set (~40) and still display a speed reading. However, it won't suffer from slip error in these instances because the rate of change of the laser flight times will be wildly discontinuous; hence the unit will either display the target's true speed or 'E03'.
However
Make dammed sure the unit was aligned correctly at the start and end of the session; a beam swept along a section of amrco or road is a different matter entirely.........
scuffham said:This is because of the cosine effect, where the measured speed will be less than the true vehicle speed, this differential increasing with the applied angle (of measurement from the direction of the vehicle).
I seem to remeber something about having to be within 14' of the carridgeway?
TT manual said:The maximum operating angle is recommended to be 10 degrees (but there's no defined upper limit).
To minimise the effect on the laser the angle should be kept small by setting up the laser as close to the road as possible witout creating safety risks. The laser should be targeted down the road at sufficient ranges so as not to create an angular effect
This extract is based upon the ACPO guidelines:
TT manual said:
When operating handheld devices from the roadside the operator should be within 10 feet of the edge of the carriageway and beyond the minimum operating range, i.e. 50 feet.
However, the wording is 'should be' not 'must be' so I don't think you can rely upon that as a defence. Don't forget, the further away from the carriageway the operator is, the lesser the measured speed will be (it's in your favour).
smeggy said:
This extract is based upon the ACPO guidelines: TT manual said:
When operating handheld devices from the roadside the operator should be within 10 feet of the edge of the carriageway and beyond the minimum operating range, i.e. 50 feet.
However, the wording is 'should be' not 'must be' so I don't think you can rely upon that as a defence. Don't forget, the further away from the carriageway the operator is, the lesser the measured speed will be (it's in your favour).
Interesting perspective. But I don't agree. The point of the guidelines is that they are intended to be followed. I don't think the wording 'must' would be appropriate in the context of guidelines.
I see working more than 10ft from the edge of the carriageway to be a material defect in the evidence because it represents a failure to operate in accordance with the guidelines.
safespeed said:Then we will continue to disagree
Interesting perspective. But I don't agree. The point of the guidelines is that they are intended to be followed. I don't think the wording 'must' would be appropriate in the context of guidelines.
The guidelines contain the words ‘should/should not’ and ‘must/must not’, even within the Lidar section. It is of course good practice to follow the ‘should/should not’s, but I really think these advisory terms cannot be relied upon given the technical nature of our legal system. Scuffham,
I just found this in the ACPO code of conduct:
When operating hand-held devices from an overbridge:
ACPO said:
In respect of minimum range, the operator must carry out a height check from the level of operation to the road surface directly below then multiply this by a factor of ten. This figure becomes the minimum distance for operation.
OK, I can understand when it's from above (as in bridge) but in the case of being parked on the side of a dual carridgeway with a dividing green area bwteen the caridgeways.
the road in question is on a slow curve and also on a gradient, so if you can imagine going up hill and gently left, the van is parked on the left with the back facing towards you as you come round the curve.
this I can see being just fine and dandy for catching people going up towards the van, but the other side of the road is not only >60 feet away from the van at it's closest point, but also does not follow the same curve the 'up' lanes do (the island in the centre of the road at one point is over 200 feet wide, and also at a different hight - the two were built at different times).
Thus if you are going to target cars on the way down, then you have to look probably 20+ degrees to the left of where the van is, and the are not only going away from you, but also down from you.
I will get a pic of where I am on about if I can.
the road in question is on a slow curve and also on a gradient, so if you can imagine going up hill and gently left, the van is parked on the left with the back facing towards you as you come round the curve.
this I can see being just fine and dandy for catching people going up towards the van, but the other side of the road is not only >60 feet away from the van at it's closest point, but also does not follow the same curve the 'up' lanes do (the island in the centre of the road at one point is over 200 feet wide, and also at a different hight - the two were built at different times).
Thus if you are going to target cars on the way down, then you have to look probably 20+ degrees to the left of where the van is, and the are not only going away from you, but also down from you.
I will get a pic of where I am on about if I can.
scuffham said:
this I can see being just fine and dandy for catching people going up towards the van, but the other side of the road is not only >60 feet away from the van at it's closest point, but also does not follow the same curve the 'up' lanes do
Aha, now I understand where you’re coming from (sorry, I was a bit slow on the uptake).
I’m very sure that UK operators do not factor in the angle of measurement into the speed measurement to compensate for the cosine effect.
The manual does not eliminate cross carriageway measurements, but it does give recommendations and imposes limitations of acceptability.
TT manual said:
Setting up to minimise the angular or cosine effect
……………
To minimise the angular effect on the laser the angle should be kept small by setting up the laser as close to the road as possible without creating safety risks. The laser should be targeted down the road at sufficient ranges so as not to create an angular effect.
TT goes on to show a table for setup characteristics showing the limit of acceptability (‘acceptability’ being questionable for legal acceptance considering additional error is in the motorists favour).
To summarise, it shows that the ‘range to the target vehicle’ has to be at least 10 times greater than the ‘setup distance from the roadway’ to yield an acceptable reading, thus giving a maximum error coefficient of 0.995 (or a maximum measurement error of -0.5%) (this can be deduced via Pythagoras theorem).
Does ‘roadway’ mean a single lane for a given road, or just the road itself? (the former would be technically correct in our scenario)
The manual does not mention bends in the road, but it does imply this effect when describing the cosine effect. I reckon applying compensation for bendy roads might be too much for operators to handle, but again this is in the motorists favour so I guess TT left this out for reasons of simplicity.
Richard C said:
Tut tut Paul - even you are falling into the lying CPS' trap of referring to the ACPO Code of Practice in this way ! 
Hi Richard.
That's probably my fault; however, this is how the TT manual refers to them so I did the same.
BTW, I emailed you a couple of times, did you receive them?
I've started a separate thread regarding these ‘guidelines’:
www.pistonheads.com/gassing/topic.asp?t=237496&f=10&h=0
www.pistonheads.com/gassing/topic.asp?t=237496&f=10&h=0
Hi Scuffham,
Can I ask if that is the exact view from the laser to your car?
If it is, I am guessing that the angle of incidence in that situation would be quite high. The laser is designed to be used on the front of a vehicle, and the guidance with regard to the angels involved are there to make sure that this happens.
The angle on your case may be something like 30-40 degrees on some parts of the road. In Dr Mike Clark's experiments on TV, one of the factors which he increased in order to induce an error was the angle of incidence between the laser and vehicle, thus giving the beam more chance to slip down the side of the lorry.
Secondly, there looks like there is a road sign obstructing the view.
Whether either of these factors have made a difference to the reading is one question. The other question, is if these factors can be used in your defence.
Can I ask if that is the exact view from the laser to your car?
If it is, I am guessing that the angle of incidence in that situation would be quite high. The laser is designed to be used on the front of a vehicle, and the guidance with regard to the angels involved are there to make sure that this happens.
The angle on your case may be something like 30-40 degrees on some parts of the road. In Dr Mike Clark's experiments on TV, one of the factors which he increased in order to induce an error was the angle of incidence between the laser and vehicle, thus giving the beam more chance to slip down the side of the lorry.
Secondly, there looks like there is a road sign obstructing the view.
Whether either of these factors have made a difference to the reading is one question. The other question, is if these factors can be used in your defence.
bluepolarbear said:
I’m very sure that UK operators do not factor in the angle of measurement into the speed measurement to compensate for the cosine effect.
I would agree with you but this is because it is always in the favour of the motorists (eg it reduces measured speed)
Not sure if we got our crossed wires here. To clarify: the uncompensated cosine effect is always in favour of the motorist (speed measurement is less than true speed); compensating for this effect would reduce this error to zero (and beyond if not applied correctly - in favour of the scammer)
Hi, I am joing this debate a bit late but I have been persuing this isue through another board.
The home office scientific development bureau who gave type approval insist that the type approval is subject to ACPO code of practice being followed.
This is also confirmed by a letter I got from home office minister Paul Goggins
Home office minister Paul Goggins wrote
"Requirements for The day to day operation of enforcement devices have been laid down in the publication “Roads Policing Enforcement Technology Code of Practice(p67)” issued by ACPO. A copy is on their website: www.acpo.police.uk under policies.
Section 14.4 of the code of practice requires the operator to act within 10 feet of the carriage way and at a range exceeding 50 feet. It says it is important that the beam is held steady on the target area to avoid any slip factor."
I interpret this to mean that the ACPO guide lines must be followed in day to day operation. Other parts of the letter state that HOSDB only tested under these conditions to give the device its type approval.
I know of at least three cases in court at the moment with opposite c/way detection.
I interpret "the carraigeway" to be "the carriageway" you are driving on. not the lane you are driving in.
I Don't want to go in to a Nick Freeman impression but this is how the equipment was type approved and the code of practice laid down, The government minister is relying on these procedures being followed. There must have been a good reason for these rules being published.
Rules are rules, guidelines are guidelines, code of practice are rules and type approval is dependant on rules being followed.
shout mode: ACPO IS A CODE OF PRACTICE NOT A GUIDELINE!!!!!!!!! :end shout mode:
>> Edited by tony13579 on Thursday 26th January 19:39
The home office scientific development bureau who gave type approval insist that the type approval is subject to ACPO code of practice being followed.
This is also confirmed by a letter I got from home office minister Paul Goggins
Home office minister Paul Goggins wrote
"Requirements for The day to day operation of enforcement devices have been laid down in the publication “Roads Policing Enforcement Technology Code of Practice(p67)” issued by ACPO. A copy is on their website: www.acpo.police.uk under policies.
Section 14.4 of the code of practice requires the operator to act within 10 feet of the carriage way and at a range exceeding 50 feet. It says it is important that the beam is held steady on the target area to avoid any slip factor."
I interpret this to mean that the ACPO guide lines must be followed in day to day operation. Other parts of the letter state that HOSDB only tested under these conditions to give the device its type approval.
I know of at least three cases in court at the moment with opposite c/way detection.
I interpret "the carraigeway" to be "the carriageway" you are driving on. not the lane you are driving in.
I Don't want to go in to a Nick Freeman impression but this is how the equipment was type approved and the code of practice laid down, The government minister is relying on these procedures being followed. There must have been a good reason for these rules being published.
Rules are rules, guidelines are guidelines, code of practice are rules and type approval is dependant on rules being followed.
shout mode: ACPO IS A CODE OF PRACTICE NOT A GUIDELINE!!!!!!!!! :end shout mode:
>> Edited by tony13579 on Thursday 26th January 19:39
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