6.08 seconds = $165.50

August 3, 2007 2:44 PM

Does anyone have any data for human error while operating a timing device? Litigeous details and much

I was stopped for speeding, I decided to contest and the trial date is rapidly approaching. The officer used a device/technique known as a tracker to clock my speed. To the best of my understanding (feel free to enlighten me if I am incorrect) a tracker uses 4 measurements to calculate speed: start time, end time, start distance, and end distance.

What happens is the officer driving behind you starts his timer when you pass some landmark and stops it when you pass another landmark. He then starts it again when he passes the first landmark and stops it when he passes the second.

My obvious rebuttal is that even a small discrepency could be huge multiplied across the four especially since I was only timed for 6 seconds in a 50 mph zone, but i have not been able to find any good data on human error as it relates to timing things. I am thinking a nice 1 standard deviation would be a good assumption to go with, but my google fu has failed me.

This is in PA if that makes any difference. Also, has anyone had any experience asking the judge to reimburse them for time off from work upon winning in traffic court. It seems like I should be compensated considering there are an infinite number of things I would rather be doing.

Thank you all for your help!

posted by jmugrapler to Law & Government (31 answers total)

At what speed were you allegedly driving?
At what speed were you actually driving?
posted by demiurge at 2:51 PM on August 3, 2007

50 mph is about 73 feet per second. You were probably doing over 80 feet per second, or you wouldn't have been cited.

Now just intuitively thinking about it: your task is to press a button as your car passes a post. Do you honestly believe it's possible to create an error of more than 1 carlength (10 ft) in either direction? I don't. I think it'd be tough to convince anyone that it was.

So over those 6 seconds, you traveled somewhere between 420 and 480 feet. A potential error range of 10 feet on each end, in opposing directions (the most favorable for you), means an error of roughly 2.5% in the calculation. That's a difference of roughly 1.5 mph. That means that unless you were cited for 1 mph over the limit, you were speeding.

You have no way of making an argument with regard to standard deviations because you have no way of measuring the cop in a series of trials to determine his true precision. Such an argument would also be undermined by the fact that he ran a 'calibrating' or control trial on his own car at the same time as he ran you: such a trial would be likely to include the same error as you're trying to attribute to him, and likely his figures already corrected for any such error.
posted by ikkyu2 at 2:54 PM on August 3, 2007

Ikkyu2,

I do not need to measure the cop in a series of trials to determine his true precission. That burden falls to the officer or his respective police department.

Is it possible he was inaccurate? Yes
It is the prosecutions responsibility to show that he/she is accurate.

Also, not to be rude, but please answer the question. I am looking for data on timing accuracy.

Demlurge, Allegedly going 69 actually going just under 60 (I beleive). Ticketed in a 50 zone, but it had just dropped (within a quarter mile) from 60.
posted by jmugrapler at 3:10 PM on August 3, 2007

Adding to what has already been said, in most places, the squad car speedometer is calibrated and considered a viable means of issuing a ticket. He was following you, and was probably well aware of what your speed was when he decided to use the other method to confirm.
posted by quin at 3:11 PM on August 3, 2007

In defense of my position (feel like i am in court already), I find it hard to beleive that the officer was able to maintain a consistent following distance all the while making 4 measurements?

All this helps though, as I am sure I will get the same skepticism from the judge / officer.
posted by jmugrapler at 3:17 PM on August 3, 2007

That burden falls to the officer or his respective police department.

OK, but you're going to have a hard time using those results to bolster your case when you appear in court.

Good luck to you.
posted by ikkyu2 at 3:21 PM on August 3, 2007

I love a good "YOU CAN'T HANDLE THE TRUTH!" courtroom heroism fantasy. But most times I've gone to court for alleged speeding, the cop never showed, and I either got off with nothing, or got to go to a driving class so my insurance didn't go up.

So for your sake, I hope the cop does show up and you can blow his mind with math!
posted by M.C. Lo-Carb! at 3:22 PM on August 3, 2007

actually going just under 60 (I beleive). Ticketed in a 50 zone

Also, if I can give you some free advice: Don't take the above quote into your court date for speeding. It's an admission of guilt.
posted by ikkyu2 at 3:26 PM on August 3, 2007

For what it's worth, my dad used to be a big fan of these scientific defenses for speeding tickets when he was driving all over the state (CA) for work. There was one time that he created and had printed all of these maps of the freeway and diagrams illustrating how the officer's line of sight precluding him from measuring how fast my dad was driving and so on. When the court day came, my dad went through his spiel and made his case. When the officer was asked what happened, he lied and my dad had to pay the ticket.
posted by rhizome at 3:28 PM on August 3, 2007

I was thinking a little more about this, and I seem to recall from my cog psych classes that the average human can discriminate the timing of an event into a 40 ms wide timeslice; that is, the error is on average no more than 20 ms. That translates to about 15 feet of possible error at these speeds: slightly less than a carlength in either direction.
posted by ikkyu2 at 3:31 PM on August 3, 2007

M.C. Lo-Carb- I would blow just about anything to get out of this ticket. JK.

Ikkyu2, thanks, apparently i will need the luck, but I would definately not be foolish enough to repeat that in court.
posted by jmugrapler at 3:33 PM on August 3, 2007

You will need something more precise than just random human error while operating a timing device as the difference between an average error rate and the error rate of someone presumably trained to professionally make these measurements is going to differ, and I'm guess by a wide margin. Unless you where varying your speed it wouldn't be terribly hard to maintain a constant following distance and simply pushing two different buttons (on/off) twice would be a piece of cake.

there is some more relevant information over here and here.

Google polive timing error rate may get you some place.
posted by edgeways at 3:33 PM on August 3, 2007

er police
posted by edgeways at 3:34 PM on August 3, 2007

Ikkyu2, use 69 MPH instead of and you get 20 feet on each measurement. This brings me down to 59 MPH.
posted by jmugrapler at 3:36 PM on August 3, 2007

According to the NIST guidelines for stopwatch usage, reaction time for stopwatch use was usually around 100 ms, with the maximum discrepancy at 700 ms.

So, let's be uncharitable and say that the measurement was off by 700ms. Then say you were really going 60mps (88 fps).
He recorded you traveling 69mph so he thought you did 606 feet in 6 seconds. If he was off 700ms on the measurement, then he really should have recorded you going 606 feet in 6.7 seconds, which is only 59 miles per hour.
posted by demiurge at 3:37 PM on August 3, 2007

Or 61 miles per hour, double check my math.
posted by demiurge at 3:40 PM on August 3, 2007

Excellent guys, now we are getting somewhere. However, demlurge, Remember to apply your error to all calculations, remember i am going to assume worst case scenario for my benefit.

I can handle an argument from the officer regarding this, i just want some data to back me up.

Thanks all!
posted by jmugrapler at 3:42 PM on August 3, 2007

i commend you for trying to fight, but i am not sure it will work. you will show so fancy math and logic to prove that it would be difficult for an officer to calculate such results. then the officer will say that he was trained to do this at some police academy. it is difficult, that is why they are trained.

and i don't think you will have much luck asking for your lost wages for appearing in court. that is essentially like asking the other side to pay for your court costs, which is only generally given when the other side has misbehaved in some way. you would have to show that the officer gave you the ticket in bad faith. and the judge will likely assume that the officer was acting in good faith, especially if he was trained in this procedure, which he almost certainly was.

perhaps you should look into how officers are taught to do this technique. either way, good luck.
posted by Flood at 3:44 PM on August 3, 2007

One of the troubles with demiurge's idea is that there are two button-pushes per test, one at the start and one at the end. If the first click was off by 100ms due to reaction time, the second click will be too, and the differences will cancel out.
posted by ikkyu2 at 3:54 PM on August 3, 2007

Also don't forget that you have a large incentive to lie, while the officer only has a small one.
posted by smackfu at 4:15 PM on August 3, 2007

ikkyu, that isn't necessarily the case.

I've worked as a timer and automatic timer for some 20+ years (track and field). Generally, it was observed that humans are approximately +-.2 sec off of the actual time. It doesn't balance itself. And some people are wildly off in one race, and then much less so in another.

We'd always compare hand times to the automatic times (for every heat of every race.) People are uniformly inconsistent along these lines.
posted by filmgeek at 4:17 PM on August 3, 2007

Here's an abstract of a paper published in Human Factors, about estimating the motion of vehicles in traffic. It was the best I could do in a quick search--if nothing else, it might give you some good keywords and subject headings for further research.

At the risk of sounding pessimistic: it won't be a jury trial. If it comes down to your word against the officer's, the judge is probably going to believe the officer. As observed above, you have more incentive to lie than s/he does. And it sounds like lying is what you plan to do. You admit above that you were speeding. When the judge asks how fast you were going, what do you plan to say? In my experience, you're better off being humble and deferential and hoping that they lower the penalty a little. 69 in a 50, in PA? Ouch.
posted by box at 6:22 PM on August 3, 2007

Or, if you absolutely must beat the thing, retain a lawyer who handles a lot of these kinds of cases.
posted by box at 6:41 PM on August 3, 2007

IANAL, but I don't think the judge can't ask him how fast he was going unless he consents to be a witness, and he need not incriminate himself.

Typical approaches I've seen for contesting as as said:
1. show up
2. be polite
3. doubt everything

(eg, Can the officer identify the driver of the vehicle? Was the driver of the vehicle the same as the person identified on the license? Don't let the officer use notes - he shouldn't present evidence/exhibits without your consent)

As far as measurement/procedure error, you could try to argue parallax - from his point of view, he couldn't possibly have done the timing the same for his vehicle and yours because his point of view was so different, but if you do the numbers, you'll find that it won't matter enough. I think you'd have better luck making sure that the officer dotted all his i's and crossed all his t's on the ticket.
posted by plinth at 7:12 PM on August 3, 2007

OP won't be asked how fast he was going unless he takes the stand in his own defense.

If he doesn't, he won't be able to cast enough doubt on the officer to get out of the ticket.

Also, OP, keep in mind that it's not you vs. the cop, it's you vs. the prosecutor, who will be calling the cop as a witness, and I agree that the judge is not going to be all that impressed with your fancy (hypothetical) maths.

Especially if you flounder on how fast you were going. Which means you're either going to have to lie (which seems somewhat hypocritical) or admit guilt.

You were speeding. Pay your ticket, go to defensive driving, and move on with your life. You're not being persecuted. You just got caught doing something you probably do all the time anyhow.

If you don't like getting speeding tickets, do the speed limit.
posted by toomuchpete at 7:58 PM on August 3, 2007

toomuchpete, there will not be a prosecutor, typically just the police officer here in PA. Both parties are sworn in and you go from there.

I have no problem saying I wasn't speeding, because I do not beleive that I was. It was an unmarked transition between 60 and 50 MPH. Saying I wasn't speeding is no more or less dishonest, though, this is not the subject of the question. Also, thank you for implying that i break the law all the time, making unnecessary and unfounded assumptions is probably something you do all the time.

I am sure that I am not being persecuted, however, I like money and will do what I can to keep my money out of undeserving hands.
posted by jmugrapler at 8:15 PM on August 3, 2007

Also, has anyone had any experience asking the judge to reimburse them for time off from work upon winning in traffic court.

This would have to be dealt with in a separate civil suit -- you vs. the police officer and/or the police department -- but you have no leg to stand on provided there is no extenuating evidence of gross negligence or some other criminal wrongdoing. There is no "damage" involved with a lawfully issued court order to appear, no matter how it puts you out personally.

Keep in mind that traffic court judges get their rocks off from dealing with people that think they're Perry Mason and wave their little papers about reaction times and feet per second mathematics. It's their entertainment and their daily bread. When they play golf with their buddies, you're the guy they're joking about with hale and hearty cries of can-you-believe-this-shit. It's your name they're invoking ("Mugrapler!") when they try to ruin each other's putts with well-timed jokes and banter.

"Mugrapler!"
"Stop saying his name -- I almost spilled my gin-and-tonic that time!"
"I can't stop! He had ... he brought in a ... Mugrapler! He brought in a thing he printed off the Internet about track-and-field timing! Bwah-hah-hah! Oh Jesus, make it stop. Mugrapler! OK, OK. Whew. All right, calm down. OK. 180 yards, dog-leg right. I think I'll use the five iron. Now, don't you go saying Mugrapler on my back-swing now!
posted by Cool Papa Bell at 9:26 PM on August 3, 2007

You said up above that you know that you were speeding. By how much, whether it was intentional or not, and for what distance isn't really that important.
Since you are an impeccable driver and have never ever sped before, nor have you ever failed to completely stop at or before the white line of an intersection, nor failed to signal when changing lanes, parallel parking or pulling out of a driveway, this will be the one and only time you will ever get cited for any vehicle code moving violation.
Save your time and frustration and some taxpayers money and just pay the fine and never think of it again.


If it was truely an unmarked transition, go to the area, take plenty of pictures proving such and present them in court.
If the signs have 'magically' appeared, contact the local D.O.T. office responsible for that section of road and get a copy of the work order showing that the signage was installed after you were issued a citation.
posted by whoda at 9:38 PM on August 3, 2007

Step one: Stop snapping at people who are trying to help you out. It's not helping.

That being said, all of this Feet Per Second mathematics and margin of error business will get you exactly nowhere in traffic court. You are questioning the ticketing officer's credibility as someone who is trained to do this. Neither the ticketing officer nor the judge will like this. I have a number of friends who have fought tickets trying to cite human or technical error, and none who have ever "won," bar the ticketing officer just not showing up.

I do have a friend that has won in traffic court, though. He did exactly what whoda described: he took his digital camera, and took photographs from the last marked speed limit sign to where he was pulled over, showing that the speed transition was, in fact, unmarked.
posted by The Esteemed Doctor Bunsen Honeydew at 11:28 PM on August 3, 2007

I've been to traffic court just enough times to have an idea how well your aggressive Chewbacca defense is going to work.

Your odds with the lottery are better.

Basically whenever you contest, you make everyone in the courtroom spend more time on you, and even if you get one charge dismissed you may get hit with the maximum fine on another, just so you don't try it again.

As Honeydew points out, the major factor in outcomes is whether the cop shows up. Another might be if your lawyer knows the prosecutor.

Otherwise, good luck.
posted by dhartung at 12:34 AM on August 4, 2007

"actually going just under 60 (I beleive). Ticketed in a 50 zone"

"I have no problem saying I wasn't speeding, because I do not beleive that I was."

Step #1 for court: get your stories straight.

As someone who has tried a few traffic court cases in my day... unless you do as Whoda says, you will lose.

You will not impress anyone but yourself with your assumptions about a trained officer's accuracy or your snazzy maths.

You will rest your case thinking you really showed that asshole cop, and then the judge will tell you how he doesn't believe a word of your "maybe I wasn't speeding" line, pronounce you guilty, and levy your fine.

Focus on the unmarked change in speed limit. If it was marked, you screwed up and got caught.
posted by toomuchpete at 8:40 PM on August 4, 2007