By Dr Kalvis M. Jansons

The LTI 20-20 is a laser speed gun in common use by the police throughout the UK. It works by sending a stream of short infrared pulses from the gun to the target, and measuring the return times to determine distance. The rate of change of this distance is then interpreted as speed. Since not all parts of the target vehicle will be at the same distance, small movements of the gun can lead to erroneous speed measurements, as the rate of change of distance measurements is not entirely due to the motion of the vehicle. This is called the slip effect, and has been the subject of many reports, many of which feature Dr Michael Clark. The manufacturer and UK distributor of the LTI 20-20 boldly claim that the closed-source error trapping software will trap slip and other errors, provided the LTI 20-20 is correctly used by a trained police officer. However, Dr Clark’s observations make this claim look somewhat suspect, and the closed-source nature of the code means that professional scientists like myself cannot check the algorithms used. Furthermore, many scientists with whom I have discussed the LTI 20-20 agree with Dr Clark that the design concept of this device is fundamentally flawed.

Based on the LTI 20-20 UtralLyte 100 user manual, the acquisition time is less than 0.4 seconds, the range is 23 to 610 metres, and it can determine speeds from 0 to 299 mph with error less than 1 mph. It can measure the distance of the target within 0.1 metres and the beam divergence is 3 milliradians.

Many speed convictions are obtained by police officers not following the LTI 20-20 instruction manual. To avoid slip errors, the LTI 20-20 manual says that the target should be the number plate as this will be a good reflector of the infrared pulses and has the correct orientation. However, the LTI 20-20 is also used on approaching motorcycles, which do not have front number plates.

There are many other issues with its use on motorcycles that concern me. Motorcycles are generally much more irregular in shape than other vehicles, particularly from the front, and even more so if they are without fairing. The scope for slip in motorcycle speed measurements seems intuitively to be much greater than that for cars, but I am unaware of any research which quantifies this effect. In fact, I am unaware of any research that determines the rate of false positive errors for different vehicle classes. Furthermore, these rates of false positive errors should be determined for different distances and speeds, and the data made available to the public for use in court.

The manufacturer of the LTI 20-20 produced a report on the concerns of Dr Clark entitled:

Review, Analysis and Criticism of the Report by Michael A.G. Clark, Ph.D.: “Technical note: Unreliability of Laser Speed Meters” (Issue 1, Copyright 2005) prepared by Daniel Y. Gezari, Ph.D. and Chevy Chase, MD

This report is, in my opinion, a very unprofessional and unscientific attack on Dr Clark, and is filled with unsupported assumptions regarding the LTI 20-20, and what could be expected of a police officer using the LTI 20-20. It contains no new science to address Dr Clark’s concerns, and suggests that Dr Clark does not know how to do science, but that the author of the report does. If the report had attempted to address the issues in a more professional manner, I would have taken those points one by one and replied to them here. However, this report is not a useful basis for discussion.

Having read the report I was left wondering about the scientific background of the author. Most of the research of Dr Gezari is not, in fact, in a field directly applicable to the theory behind the LTI 20-20. However, some of his recent papers are, at least, concerned with laser measurements of the Earth-Moon distance. In his article “Lunar Laser Ranging Test of the Invariance of c”, he believes he has found “a first-order violation of local Lorentz invariance; the speed of light seems to depend on the motion of the observer after all, as in classical wave theory, which implies that a preferred reference frame exists for the propagation of light.” Any scientist reading this would have alarm bells ringing and maybe they would be hearing the music of “The Twilight Zone”. Roughly speaking, based on a very simple but erroneous calculation, Dr Gezari believed that he had overturned most of modern physics from Maxwell, Einstein, Hawking, etc. Most of us would probably think hard before publishing such a paper, and most likely assume that there was an error of some kind. What was his error? He forgot to correctly take account of the motion of the Earth and the Moon.

It is clearly true, as pointed out by Dr Gezari, that the working of the LTI 20-20 does not depend on special relativity, but it is noteworthy how Dr Gezari appears to deal with obvious errors in his scientific work. He seems to totally ignore them, and assume everyone else is wrong!

In my opinion, based on the report itself, and what I now know about the work of Dr Gezari, this report has no credibility, and almost no content. Furthermore, I also find it disturbing that Dr Gezari has served as an expert witness in a dozen court cases involving laser traffic speed measurements, and his report is used in UK courts.

Assuming that Dr Clark’s observations are correct, and they should be independently checked, I believe that the approval of the LTI 20-20 for use in the UK was initially a cock-up but the defence of it risks degenerating into a conspiracy. So much time and money has been invested in the use of the LTI 20-20 in the UK that in the short-term it is easier for all involved with its use to defend it rather than to review it properly in an open and scientific manner, and the report of Dr Gezari is just one part of this tangled web.

The fixed penalty fine system does not help either. Many people who know they have been wrongly charged for speeding using the LTI 20-20 will just pay up and take the points on their licence as the penalties can be so much larger if you go to court and fail to win your case. Most cases are won on the basis of incorrect use of the LTI 20-20, rather than on its flawed design concept and the erroneous false positive results that are likely to follow. A device like this should have never been approved without much more thorough testing with the results of those tests published in full and posted on the web for all to see.

Dr Clark appears to have demonstrated that the LTI 20-20 can be unreliable, so the use of the LTI 20-20, and similar devices based on laser distance measurements, needs to be urgently and thoroughly reviewed. Remember, that an erroneous speed measurement by such a device can put you in prison, or get you banned from driving, and several people have been clocked by the LTI 20-20 at speeds beyond the capability of their vehicles according to the vehicle manufacturers.

Many of the documents on which this comment is based can be found here:

http://www.benslow.org.uk/Speeding/index.html

You stated; ‘Yes in the UK the software is modified but only to ignore readings obtained below a short distance so the courtroom trick of panning the device doesnt work any more as the UK has smaller courtrooms.’

What exactly does this mean, what ‘courtroom trick’? Perhaps some specific distances too?

You also mention ‘…with magistrates choosing to accept the operators manual as part of the law when it suits and other times citing it as merely an operators manual and not law.’

Which specific legislation do you refer to in relation to the subject under discussion?

In the end the CPS moved the court on the day without telling me (as I was now respresenting myself) I guess in the hope of a conviction in my absence (sneaky and not becoming of the state imo) but I was on the ball and travelled from Kings Lynn to Swaffham where the case was held. I was not allowed to use any of the evidence I had compiled in my case as this would have blown this open globally as nearly all laser speed devices are made by a couple of US companies. The implication would cause problem for Insurance Companies and refunds of premiums and would also cause an admin headache for the refunding of fines and points here and elsewhere.

In the patent the manufacturers clearly state the devices are capable of getting speed readings from stationary objects, like armco barriers, vegetation and buildings.

Becuase the device is incapable of determining where the reflection has come from it, its incapable of determing the speed so an algorithm exists which takes the most consistent readings and uses that for speed but there is no way of telling where the device has got the reading from and its not enough to just have the device pointed in the general direction of the target vehicle especialy if the device operator is on the end of the road and you are travelling in the carriageway furthest away from the device operator.

The avg. length of a car in the 0.3 secs the device takes to send out the burst of (laser) light equates to + or – 30mph. Secondly if the device is used on the roadside then the speed readings will more likely get a reading from the side of the car or the surrounding environment like Armco Crash barriers or concrete central reservation barriers.

Theres two areas of doubt with these devices. Firstly there is nothing in the software for it to work out whether the reflection came from a car or its surrounding.
The device wont be accurate at all if the operator has to move the device to track the vehicle aka slip effect. These operators are not military trained long range snipers you know who undertake months and years of training in this art so it goes without saying there will be movement and panning errors. The most blatent errors cant be handled by the software on the device but these have to be very blatent.

Yes in the UK the software is modified but only to ignore readings obtained below a short distance so the courtroom trick of panning the device doesnt work any more as the UK has smaller courtrooms.

Finally if the state has nothing to hide then their reluctance to hand over their devices for independant inspection and analysis is a massive indicator that they are hiding. The already hide behind the acpo guidlines with magistrates choosing to accept the operators manual as part of the law when it suits and other times citing it as merely an operators manual and not law. The UK law is purposely grey here.

Anyway anyone can contact me for more info it will help blow the massive global coverup on these devices although it appears US law maybe a little more honest than UK law.

The device cant detect if you created the reflection As also mentioned on here I think, you have also noticed that beam divergence is greater than stated.

http://www.motorcyclenews.com/MCN/News/newsresults/mcn/2007/February/week-06-feb5-feb11/feb0707camerabossadmitsflaw/?R=EPI-72976&content-block=1

http://www.motorcyclenews.com/MCN/News/newsresults/mcn/2007/February/week-06-feb5-feb11/feb0707camerabossadmitsflaw/?R=EPI-72976&content-block=1

http://www.teletrafficuk.com/downloads.htm

As I said earlier, I have attended many speeding cases in court, but have yet to see anything that unequivocally challenges the robustness and accuracy of the LTI speedscope in the eyes of those who matter on the day. Whilst Clark/Lee may have sprinkled the seeds of doubt with their research, this is nowhere near enough to halt the system as it stands or whatever continent or country it operates in.

This may be of interest to you if you haven’t already seen it, you may find something of value hidden away whilst at the same time increasing your knowledge base;

Youhttp://www.motorcyclenews.com/MCN/News/newsresults/mcn/2007/February/week-06-feb5-feb11/feb0707camerabossadmitsflaw/?R=EPI-72976&content-block=1r Comments

Good luck.

Speaking of sources, I had to work with what I had. LTI wouldn’t provide me with any thing technical and even tried charging me for the manual. The police department refused to hand over any documentation. The court did not provide me with any of the evidence that was used to prosecute me until yesterday when they showed me case logs of checking in/out the lidar gun and trainer certifications. All of this was what led to the original order of disclosure of source code in which even the Judge refused to compel the State to comply with her order. Although the source code alone is not enough to determine an accurate defense, it is the cornerstone.

I appreciate your comment on the divergence but at the same time the size of the beam is what is addressed under Florida law. The issue is that Florida law states the beam must not exceed the thresholds specified by the manufacturer. The discrepancy here is not whether the beam is collecting data but rather if the size meets or exceeds what is disclosed by the manufacturer. The moment the beam extends outside this allotted parameter, it violates the requirements governing the use by a State agency.

I agree with your last statement. Becoming reliant on information that I can not back up by expert witnesses did leave me wide open for prosecutors. This does not negate the facts that some LTI 20-20 devices, regardless of codebases, do or previously had flaws causing or enabling invalid speed calculations. This brings home the necessity for transparency within the brains behind the device. Without out, its nothing more than fancy physics assumed to be accurate, protected from being proven otherwise, and relied on by U.S. judicial systems to railroad citizens while violating their civil rights.

-Michael

Obviously, not your preferred outcome.

Having faced people in court, many who have sourced the cornerstones of their defence from the internet, without question, the biggest drawback with this, is that it is more often that not, completely flawed. It is usually out of date, or simply based upon misguided gossip.

With this in mind, I did at least attempt to get you to identify which LTI model detected your speed, quoting Mr Lee’s hopelessly outdated report will always fall short of what is required and can only really be supplied by an expert witness who is up to speed with current models and software versions.

One thing that potentially let your defence down (although I doubt anyone in court would have been aware), is the issue of beam divergence.

Although the beam does indeed diverge conically, it isn’t all active. If you can picture the metering pattern of a modern camera, the LTI’s laser is very similar in that it has stripes that focus the sent and received data. We have gone from three vertical stripes within the cone, to two horizontal and back to three again over the course of three different LTI models. Although the beam does indeed extend beyond the published 30cm at 100m, the published 30cm refers only to the active portion, the bit that extends further/wider plays no part whatsoever in the collection of data. So even if the edges of the laser contact another vehicle, a wall or whatever you like, only the area within the metering stripes are the bits that do the work.

I strongly recommend you don’t get too reliant on antiquated information that you cannot corroborate. Unless you can cite definitive tests using the Ultralyte model and loaded software version, then no-one will take you seriously regardless of what you personally believe about codebases.

Hope this helps clarify such an important issue.