Question about Police Lidar Standard Deviations

[Hacp]

I was charged for speeding today but I was beyond a reasonable doubt not speeding. I think the Lidar equipment may have been in error. I'll have to defend myself in court.

I looked online for Standard Deviations, Accuracies, and distribution curves for Lidar devices and I can't seem to find any. Anyone know of a paper/standard that establishes this? I can't believe companies don't publish this information. It is important!

 

[Captante]

What exactly leads you to believe you are not guilty "beyond reasonable doubt"?

Not saying it isn't possible you were not speeding ... just wondering what your plan is beyond the stated. I can tell you from experience that trying to prove the device they used to clock you was defective isn't likely to work.


Edit: I've contested every ticket I've gotten and only one time was I found not guilty. (due to the officer not showing up twice) Having said that, just about every other time I've been able to get the charge reduced to a "no-points" violation just by being polite. This might be a more realistic goal then trying to prove the cop wrong.

 

[Humpy]

Not sure if this is from TV or real life but I thought you can request a record of any required calibration of the device and if not provided there is the possibility of the ticket being dismissed?

 

[Hacp]

What exactly leads you to believe you are not guilty "beyond reasonable doubt"?

Not saying it isn't possible you were not speeding ... just wondering what your plan is beyond the stated. I can tell you from experience that trying to prove the device they used to clock you was defective isn't likely to work.

Thanks for the response. I won't attempt to prove that the device was defective. A device can be working perfectly with no operator error and ideal conditions, and still return a reading that is wrong!

I just need the data above to prove my point. With this data, I can point out that if an officer takes X measurements in a year, he will have Y false positives. I have more but that's the beginning.

 

[Hacp]

Edit: I've contested every ticket I've gotten and only one time was I found not guilty. (due to the officer not showing up twice) Having said that, just about every other time I've been able to get the charge reduced to a "no-points" violation just by being polite. This might be a more realistic goal then trying to prove the cop wrong.

Thanks for the reply. I am not trying to prove the cop is wrong. I am not trying to prove that the device is faulty. I will not be rude. Instead I intend to convince the magistrate or judge that there is reasonable doubt that I was speeding.

 

[Captante]

Not sure if this is from TV or real life but I thought you can request a record of any required calibration of the device and if not provided there is the possibility of the ticket being dismissed?

That was the case with old-school radar guns but I don't think LIDAR requires calibration in the same sense.

 

[Fanatical Meat]

Just file for a court date and watch it get dismissed. I did it three times, twice I showed up and they had no idea why I was there, cases dismissed the final time I was told my record was clean enough and it was dropped before I even said anything.

 

[brianmanahan]

for some reason, i thought this was going to be an anarchist420 thread

 

[Humpy]

Just file for a court date and watch it get dismissed. I did it three times, twice I showed up and they had no idea why I was there, cases dismissed the final time I was told my record was clean enough and it was dropped before I even said anything.

LOL, Canada. Must be nice!

 

[Fanatical Meat]

LOL, Canada. Must be nice!

Oops I'm on a mobile and I didn't see that

 

[Humpy]

Oops I'm on a mobile and I didn't see that

Damn it! No. I was making a crappy joke about how you must live in Canada if you had your tickets dismissed so easily. :\

 

[Fanatical Meat]

Damn it! No. I was making a crappy joke about how you must live in Canada if you had your tickets dismissed so easily. :\

Nope, Commonwealth of Massachusetts

The first two were in my early 20s the final one I was around 32.

 

[Paladin3]

The OP is confusing the term "beyond a reasonable doubt" with "beyond all possible doubt." Even if the speed guns were found to return an inaccurate result 1% of the time, and I doubt it is anywhere close to that level of inaccuracy, that would mean 99% of the time they get it right and they likely got it right in your case. Combined with the officer's testimony that the gun performed correctly, you won't get this thrown out just because there is a tiny, tiny chance the reading was inaccurate. And by inaccurate, do you mean they are occasionally off by 1-2MPH? 5MPH? Maybe you were actually going 5MPH faster than the ticket and you got lucky.

It's more likely your speedometer, your recollection of how fast you were going, or both, are incorrect. Has your speedo EVER been calibrated? Do you have any training or special equipment for determining the speed of moving vehicles? The cop has all that and does this for a living. You are just trying to get out of a ticket. Whom do you thing the judge will believe?

 

[DrPizza]

Thanks for the reply. I am not trying to prove the cop is wrong. I am not trying to prove that the device is faulty. I will not be rude. Instead I intend to convince the magistrate or judge that there is reasonable doubt that I was speeding.

Think about what you're saying though. You seem to be saying, "I want to produce a piece of evidence that effectively brings reasonable doubt to every speeding ticket, based on LIDAR, ever given." That's not happening.

 

[Hacp]

Think about what you're saying though. You seem to be saying, "I want to produce a piece of evidence that effectively brings reasonable doubt to every speeding ticket, based on LIDAR, ever given." That's not happening.

This is one piece of the puzzle, not the whole puzzle.

 

[Paladin3]

This is one piece of the puzzle, not the whole puzzle.

Just promise that you will come back and tell us how much the judge eventually makes you pay.

 

[Eli]

What are the details here? Why do you say you weren't speeding? How fast were you going, and how fast is the posted limit?

I've always wondered what I would do if I was accused of speeding and I knew for a fact I was not. I always imagined this happening due to human error.. zapping a car and then pulling another car over, both cars being the same color, or something...

 

[Hacp]

The OP is confusing the term "beyond a reasonable doubt" with "beyond all possible doubt." Even if the speed guns were found to return an inaccurate result 1% of the time, and I doubt it is anywhere close to that level of inaccuracy, that would mean 99% of the time they get it right and they likely got it right in your case.

This is actually not true. Let's say a police officer measures 100 cars going at exactly the speed limit and the measuring device had a 1% chance of showing a speed 10mph above the speed limit. In this case, the officer will end up ticketing a guy who was actually going AT the speed limit with an inaccurate reading. 100% of the drivers who are ticketed in this case are victims of the reading.

This is the same effect plaguing psychology. Over half of psychology papers are not reproducible even though their results are accurate at 95% confidence intervals.
http://www.nature.com/news/over-half-of-psychology-studies-fail-reproducibility-test-1.18248

I have yet to have someone assist with providing me this information. I did find a consumer grade device with some info. Assuming a normal distribution (the best I have to work with since they don't tell distribution!), there is a .03% chance on each reading that the measurement will be 12+ MPH greater than the actual speed of the car. To put it in other words, if I took 300 readings, most likely I will measure one guy going 12MPH faster than he actually was.

 

[Fanatical Meat]

This is one piece of the puzzle, not the whole puzzle.

Honestly just show up, dress professionally, be respectful and it will get dismissed. I'm assuming your driving record is reasonably clean. No matter what you think of the Judge has heard it 10,000 times. In my state you are usually in a room with one judge, one or two assistants to keep everything organized and a guy from the district representing the state who honestly gives no f's about each case. The room will have 20-60 pending cases all sitting there. They will want to clear them as fast as possible. Most will be dismissed immediately due to someone being a driver and it puts their job in jeopardy or some paperwork not filled out correctly or simply because the person had no previous offenses. Some will take more time but there will be no Perry Mason moments because there is no time for that.

 

[Imp]

Wasn't there a story recently about cops not calibrating their LiDAR units? Or was it radar? I be too lazy to look them up.

I've used LIDAR for traffic studies before... hate those pieces of shit. So many times I couldn't register a reading while trying to blast the license plate. And one of them ran off a car battery I had to hump through rough terrain.

 

[Paladin3]

This is actually not true. Let's say a police officer measures 100 cars going at exactly the speed limit and the measuring device had a 1% chance of showing a speed 10mph above the speed limit. In this case, the officer will end up ticketing a guy who was actually going AT the speed limit with an inaccurate reading. 100% of the drivers who are ticketed in this case are victims of the reading.

This is the same effect plaguing psychology. Over half of psychology papers are not reproducible even though their results are accurate at 95% confidence intervals.
http://www.nature.com/news/over-half-of-psychology-studies-fail-reproducibility-test-1.18248

I have yet to have someone assist with providing me this information. I did find a consumer grade device with some info. Assuming a normal distribution (the best I have to work with since they don't tell distribution!), there is a .03% chance on each reading that the measurement will be 12+ MPH greater than the actual speed of the car. To put it in other words, if I took 300 readings, most likely I will measure one guy going 12MPH faster than he actually was.

You assume way too much. If the gun has a margin of error (which so far you've found no proof of) it's not always going to be over reporting speeds. It could just as likely under report speeds. And exactly how can you prove YOU were the one who got the very unlikely bad reading?

Stop doing wacky math and think for a second. The cop is going to say "I observed a car traveling at a high rate of speed in accordance with my training. I verified that speed with my Lidar unit +/- 2mph. Gave chase and ticketed the individual for speed violation."

Your response of "nuh-uh, bad gun" isn't going to work. Again, just promise you will come back and tell us how much the judge makes you pay.

 

[Toastedlightly]

http://www.nhtsa.gov/staticfiles/nti/pdf/809811-LIDARSpeedMeasuringDevice.pdf

Seems to be +1/-2 mph

 

[Hacp]

What are the details here? Why do you say you weren't speeding? How fast were you going, and how fast is the posted limit?

I've always wondered what I would do if I was accused of speeding and I knew for a fact I was not. I always imagined this happening due to human error.. zapping a car and then pulling another car over, both cars being the same color, or something...

Thanks. If you have further details please provide it.

I was clocked going 73mph on a 55mph speed limit. I was not looking at the speedometer at the time so I don't know my actual speed. I was following the car ahead of me and cars usually go at the speed limit on this piece of the highway since police are always there!

I try to keep below 65mph all the time for fuel efficiency reasons. In this section of the road I keep AT the speed limit so 55mph. 73 mph is far too high.

My strategy is simple. First I will establish that I am an excellent driver with no previous violations. Next I will establish that I had no inventive or motive to speed, there's actually a disincentive for speeding (gas mileage)!

I will then show evidence that I was averaging far below the speed limit based on the time I left work, average time it takes to go from my chair to my car, and time it takes for my car to leave work and arrive at the spot I was LIDAR'd. I will provide written evidence form my boss on the time I left work since he was there the exact moment I left my chair. I will use google maps to show how I was averaging below the speed limit.

Finally I will bring up the LIDAR confidence interval defense. Because I had no incentive to speed, because I am a safe drive, and because of the possibility of false positives in LIDAR, there is reasonable doubt that I was going above the speed limit.

 

[Paladin3]

Thanks. If you have further details please provide it.

I was clocked going 73mph on a 55mph speed limit. I was not looking at the speedometer at the time so I don't know my actual speed. I was following the car ahead of me and cars usually go at the speed limit on this piece of the highway since police are always there!

I try to keep below 65mph all the time for fuel efficiency reasons. In this section of the road I keep AT the speed limit so 55mph. 73 mph is far too high.

My strategy is simple. First I will establish that I am an excellent driver with no previous violations. Next I will establish that I had no inventive or motive to speed, there's actually a disincentive for speeding (gas mileage)!

I will then show evidence that I was averaging far below the speed limit based on the time I left work, average time it takes to go from my chair to my car, and time it takes for my car to leave work and arrive at the spot I was LIDAR'd. I will provide written evidence form my boss on the time I left work since he was there the exact moment I left my chair. I will use google maps to show how I was averaging below the speed limit.

Finally I will bring up the LIDAR confidence interval defense. Because I had no incentive to speed, because I am a safe drive, and because of the possibility of false positives in LIDAR, there is reasonable doubt that I was going above the speed limit.

If the judge rewards you for that defense he doesn't deserve to be a judge.

 

[Hacp]

http://www.nhtsa.gov/staticfiles/nti/pdf/809811-LIDARSpeedMeasuringDevice.pdf

Seems to be +1/-2 mph

Doesn't say that's a standard deviation.