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  1. #1
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    Default Margin of Error as a Defense to Speeding

    My question involves traffic court in the State of: CA

    Hello

    On March 17th I was stopped in San Francisco on Highway 1 doing 61 mph in a 45 mph zone and was given a ticket for CVC 22350 - Unsafe Speed. I understand from the Bail and Penalties schedule that there are higher penalties for being 16 mph over v 15 mph over the speed limit.

    My question is: Can I contest this on the basis of the fact that there is always some margin of error (2-4 mph for Radar/ Lidar depending on stationary or moving) and so I am being given a higher penalty (16-25 MPH) even though I may well have been guilty of a lesser offence (1-15 MPH)?

    Thanks

  2. #2
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    Default Re: Cvc 22350 16-25 mph v 1-15 mph

    Quote Quoting barrabing
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    My question involves traffic court in the State of: CA

    Hello

    On March 17th I was stopped in San Francisco on Highway 1 doing 61 mph in a 45 mph zone and was given a ticket for CVC 22350 - Unsafe Speed. I understand from the Bail and Penalties schedule that there are higher penalties for being 16 mph over v 15 mph over the speed limit.

    My question is: Can I contest this on the basis of the fact that there is always some margin of error (2-4 mph for Radar/ Lidar depending on stationary or moving) and so I am being given a higher penalty (16-25 MPH) even though I may well have been guilty of a lesser offence (1-15 MPH)?

    Thanks
    You can but it isn't likely to work... Because if the margin of error is 2 to 4, it actually would be +/-2 to +/- 4 which means your speed was anywhere between:

    (61 + 4) and (61 - 4) =

    65 and 57

    Which means that there was a 50% probability that your speed was above 15mph in excess and 50% that it was below 15mph in excess.

    And 50% isn't enough for "beyond a reasonable doubt"... (The burden of proof standard for criminal matters).

    In fact, it isn't good for preponderance of the evidence either (The burden of proof standard for civil matters)... For that, its got to be at 51% or more!

    Now... If the officer did in fact use Radar/LIDAR to measure your speed, the question becomes: why would you only shoot for a fine reduction when there is a chance, slight as it maybe, that you might have an valid argument to have the entire case dismissed. That, of course won't come at a cheap price... You will have to invest quite a bit of time and effort to get through the process, however, the probability of such a result should become clear much sooner than later.

    Start by contacting your local CALTRANS office and request the most recent copy of the Engineering and Traffic survey for the segment of HWY 1 you were allegedly speeding on, and when you get that, upload it to photoshop.com or imageshack.com... etc, post links to it here in this thread.... And someone will review it and guide you from there...

  3. #3
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    Mar 2012
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    Default Re: Cvc 22350 16-25 mph v 1-15 mph

    Thanks for your response. I have already placed a request with CalTrans and will upload the survey information here when I get it.

    I was reviewing the citation again (uploaded here) and while the box for Radar/ Lidar Unit/ Patrol No. is checked, it doesn't explicitly mention how the speed was measured. Do you know how I can get this information? Would this be a part of requesting discovery?

    The reason why I was unsure about contesting the ticket and pleading "not guilty" is that I have read on this forum that if I lose my case I may not have the option of going for traffic school. Since this is my first ticket I thought traffic school may be better to avoid the ticket from getting onto my record.

    Thanks

  4. #4
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    Default Re: Cvc 22350 16-25 mph v 1-15 mph

    Quote Quoting barrabing
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    Do you know how I can get this information? Would this be a part of requesting discovery?
    Oh, I thought that was already given.... Not an issue though. and yes, you obtain that via discovery. keep in mind if the officer paced your speed, then the survey will do you no good simply because speed trap laws do not apply for a pace, only when Radar or Lidar is used!


    Quote Quoting barrabing
    View Post
    The reason why I was unsure about contesting the ticket and pleading "not guilty" is that I have read on this forum that if I lose my case I may not have the option of going for traffic school. Since this is my first ticket I thought traffic school may be better to avoid the ticket from getting onto my record.
    Might be a good idea... but you better make an educated decision than one you might second guess later.... get the survey, evaluate your case and if it is iffy, certainly traffic school should still be an option!

  5. #5
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    Default Re: Cvc 22350 16-25 mph v 1-15 mph

    Thanks That Guy

    I received the Engineering and Traffic Survey information from CalTrans and have uploaded it here. The relevant portion - Section D. From Lake Street to the Route 101 Junction (PM 5.88.7,07) starts on the second half of 5. I was driving Southbound on Highway 1 and was stopped a little before Lake Street.

    Is there anything here that you think is worth contesting?

    Thanks!

  6. #6

    Default Re: Cvc 22350 16-25 mph v 1-15 mph

    The raw data sheet is required (People v Ellis).

    Thatguy and Quirky, is there an argument under People v Goulet ("Obviously the collective judgment of the presumed reasonable and prudent majority of drivers does not support the speed limit based on readily apparent conditions.) since the average speed (46.3 and 46.7) is also over the speed limit, thereby making the average driver a criminal? Does it matter that they simply rounded down given this ETS was done in 2008?

  7. #7
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    Feb 2010
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    Default Re: Margin of Error as a Defense to Speeding

    Quote Quoting barrabing
    View Post
    My question involves traffic court in the State of: CA

    My question is: Can I contest this on the basis of the fact that there is always some margin of error (2-4 mph for Radar/ Lidar depending on stationary or moving) and so I am being given a higher penalty (16-25 MPH) even though I may well have been guilty of a lesser offence (1-15 MPH)?

    Thanks
    Well if the error is +/- 1 then his reading actually has a +/- error of 1 (duh) & I think this does establish more than reasonable doubt of being 16 over ... it a certainty that 15 over is the highest value he can testify to in reality.

  8. #8
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    Default Re: Cvc 22350 16-25 mph v 1-15 mph

    I know you didn't ask for my opinion, but I hope you don't mind.

    Quote Quoting California student
    View Post
    Does it matter that they simply rounded down given this ETS was done in 2008?
    If the survey was done in 2008, then the 2006 CA-MUTCD would apply. It requires that, "When a speed limit is to be posted, it should be established at the nearest 10 km/h or 5 mph increment of the 85th-percentile speed of free-flowing traffic." (CA-MUTCD sec 2B.13, p. 2B-7). So, if the speed was 49 mph, the limit should be 50, unless the survey indicates that conditions justify a 5mph reduction in the speed.

    Quote Quoting California student
    View Post
    Is there an argument under People v Goulet ("Obviously the collective judgment of the presumed reasonable and prudent majority of drivers does not support the speed limit based on readily apparent conditions.) since the average speed (46.3 and 46.7) is also over the speed limit, thereby making the average driver a criminal?
    It certainly doesn't hurt. I used the CA-MUTCD's guidance in addition to Goulet in my trial and was able to convince the judge that the speed limit had been set too low. TG was skeptical that the accident rate in survey was actually affected by the 10mph reduction that had been applied to my street. However, the judge was swayed by the fact that, "studies show that establishing a speed limit at less than the 85th percentile (Critical Speed) generally results in an increase in collision rates." Just goes to show that you never know.

    From a statistics and engineering standpoint, the average speed isn't very useful without the raw data from the speed survey sheet. The CA-MUTCD rule for establishing speeds at the 85% percentile assumes a standard normal distribution. In a normal distribution, both the median and the mean are the same. A standard normal distribution looks like this:



    In this picture, mu is the average (and median), and sigma is the standard deviation. In a standard normal distribution, 85% of the sample falls between -3 sigma and 1 sigma. This means that the remaining 15%, who are the violators, are between 1 and 3 standard deviations from the mean. So, if you had no raw data, you could suggest that 65% of all drivers are within a standard deviation of the average speed -- assuming a standard normal distribution. Unfortunately, without the raw data sheet you're also unable to calculate the standard deviation. However, if you know both the 85% percentile speed and the average, you can guess that the standard deviation is approximately 4, since the 85% speed is 49 and the average speed 46. This would mean that the -1 sigma would be 42, which is below the speed limit. So, without the raw data we're still not able to calculate exactly what percentage of drivers in the survey were made violators by the posted limit. Parenthetically, this also makes for interesting analysis when the data in the speed survey is bimodal, or otherwise appears not to conform to the normal distribution. Unfortunately, the CA-MUTCD offers no guidance for speed surveys that don't come out as normal.

  9. #9

    Default Re: Cvc 22350 16-25 mph v 1-15 mph

    I should have picked up that what was meant was the median, but assuming a roughly normal distribution then there normally isn't any meaningful difference between the two. Additionally, when the ETS requires measurement of the average but not the median, I don't want to be the one arguing why the average is the wrong metric the calculate.

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