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GPS Used As Defence In Radar Speeding Case
James Thigpen writes "There is an article over at Ars Technica about an accused speeder contesting his speeding ticket based on his car's built-in GPS system's records. According to the article his car says he was going slower than the radar gun clocked him at. Contesting a ticket based on GPS data has never before been tested in court."
Plus it would be cool to have onboard footage of your driving for analysis and review.
If this ends up being a valid way to argue against getting a speeding ticket, the next step I see will be people speeding like hell, and then hacking their car's GPS records to show they were going at the speed limit.
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This time, it is the lack of privacy that helps the little guy. Oh, the irony.
But will he be able to produce the source code for the GPS when the police request it to check its accuracy?
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Closed Source -> Charges Dismissed?
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GPS data was actually used recently in taiwan to prove a man's innocence. A truck driver A went into an accident with a motorcyclist B. A stayed and helped B up, and even paid cash. B said he's fine, so A drove off, only later to recevie a notice that B has filed a hit and run case against him. The court found A not guilty since the gps data showed that A stayed at the site for more than 15 mins.
The pretty large difference between his 'radar' speed, and his 'gps'(actual) speed was pretty large. IMHO this sets brings into question just about every speeding ticket ever given by radar gun.....
lets say that the gun is wrong 1% of the time, which in the case of a cop handing out tickets by hand is okay (imho) because there is human intervention, he (or she) can look at the thing, bang it on his hand a little, and shake the error off as a fluke.
The speed cameras on the 101 in scottsdale, arizona issue about 250 tickets daily. Thats 2.5 tickets daily that the gun gets wrong (the 1% figure was pulled from my ass, but I'm using it as an example). With THIS there is no human intervention at all (other than a pissed off commuter)..
grr...not sure where i'm going with this, I just REALLY hate it that humans are being taken out of (at least that little part) of the legal system. I don't want my fate decided by a computer!
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When we were on vacation in CA, we were stopped for speeding on highway 299 and had the GPS running. I told it to stop tracking the rest of the trip so I can get the data later. When I looked at it, it was dead on what the officer clocked us at so I think this person has a good case.
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From my understanding, and the contention of the officer, the GPS logs average speed. Which means that during a short period of time, the defendant could have greatly exceeded the speed limit (and was clocked by the officer at that time), while the average speed was far lower than that. In which case, both the cop and the defendant are correct, and the cop is till valid in giving the ticket...
On my system the GPS application stores its logs in a textfile which I can easily edit. It would be trivial for me to doctor the text file to contest any speeding ticket. I'm not sure that this is a good form of evidence.
I used the GPS defense when pulled over.
.75 mph.
In San Antonio, TX I was pulled over for doing 76 in a 75 zone. I successfully argued that the GPS was more accurate than the RADAR, when I said that it used "government satellite signals."
In fact, most police radar units are +/- 3mph. A consumer GPS speed indicator is typically accurate to within
When working in ship navigation systems (Laser Plot), I was involved in dumping track information from a ship to show that it was not in an area when a boating accident occurred.
The hacking issue is correct, one can always hack the data. The Cop can lie about the reading on the radar unit too. If it gets to 'real court' you have the standard issues of scientific reliability (Daubert test) and the authenticity of the data. In the late 90s, there was a case (in Georgia, I think) where a speeding conviction was thrown out because there was no reliability of the laser speed testing introduced.
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It's actually supposed to be pretty easy for the defense to win a speeding ticket case. This is true regardless of whether you were actually speeding, GPS data, or any other evidence you present.
The cops have to prove their case. This means showing up to court with the proper evidence. The evidence has to be maintained and presented in a condition where it is admissible. Very often, one or more of these things do not happen and the defense wins by default.
Everyone should always take their speeding tickets to court. Speed limit laws need to be made unprofitable for the government and then maybe we can get our freedom back on the roads.
Eaton VORAD units, which are a phased-array anti-collision radar for trucks, have been used to provide evidence in favor of the truck driver. The VORAD units track individual car-sized targets, and provide range, range rate, and azimuth. Range and range rate are quite good; azimuth isn't that accurate. The control unit keeps track of recent events ten minutes before a collision, and also has speed info available. The latest versions can interface with GPS and other vehicle systems. This allows detailed accident reconstruction.
It's most useful where an accident resulted when someone drove in front of a truck. The VORAD record shows not just what the VORAD-equipped vehicle was doing, but what the other vehicles were doing.
In most jurisdictions, such traffic cases are considered civil and the standards for evidence are different than those of criminal cases or what you may see on 'Law & Order'. The judge is free to weight the officers evidence more highly than yours and presume it to be correct unless you can show overwhelmingly that it is not. Sort of like being guilty until proven innocent.
Furthermore, courts have quite a bit of latitude to allow or deny the admissibility of data as evidence. For example: Radar is quite accurate (it reads the speed of an object quite close to its actual speed) but not very selective (it might be reading the speed of something else, or interpret some RF noise as speed). Take the boilerplate testimony that an officer reads about 'calibrating the gun with a tuning fork' and all the b.s. about standards traceability. None of this is necessary, as the most common source of errors are due to poor selectivity. But it sure sounds great in court.
In fact, calibrating a radar gun with a tuning fork is a good demonstration of its susceptibility to AM noise. An ideal radar gun should only measure frequency shift due to the Doppler effect and reject the sort of modulation that a tuning fork creates. After all, the instantaneous velocity of its tines is dependant on its amplitude and the average velocity is zero (unless you throw it). But no court would hear such an argument, as it would undermine their entire traffic enforcement/revenue collection program. And, as a civil case, they are not required to consider it.
Have gnu, will travel.
GPS units compute your speed by computing the difference between your current position and your previous position divided by the time between samples. There's no other way to do it. Doppler is not involved.
The time between samples is what's important here. If it's only a few seconds then there's a good case for innocence. If on the other hand it's 30 seconds or a minute, the cop with the radar gun wins. BTW, it is the radar gun that uses doppler to measure speed.
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SMDs measure your speed based on the reflection of light waves traveling straight lines through short distances through clear air. GPS measure your speed by calculating the difference between points derived as the average of the intersection of between 3 and 12 paraboloids determined by light waves traveling through the atmosphere, weather, and possibly reflecting off of buildings, trees, hills, and the ground divided by the update interval.
Like it or not, the radar gun is a more accurate speed measuring device than a GPS.
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So should I get some sort of prize for my Highlander that can go 352 MPH, based on my Garmin 350 "trip max" history?
I personally don't remember driving 352 MPH, even when driving up I15 to Vegas, but then again, maybe my wife did it when I wasn't in the car with her... yeah that must be it.
This issue is a bit more complicated than you think.
You see, Instantaneous velocity is the limit of the average velocity where the time of averaging tends to zero.
In other words, the value of f'(t0), where the position x is x = f(t) at a given time t0.
Or in other words, angle of the tangent of the curve x = f(t) in the given time t0.
Now, if your argument is that "a GPS device cannot give the measure of the instantaneous velocity because it does not sample fast enough to get a really good approximation of the curve x = f(t) and hence, the value of f'(t0)", then you could be right because 1Hz is not really a high sampling rate. But you could have said so
The (analog) speedometer in most cars measure speed by measuring the RPMS of the gear box and multiplying by gear ratios and tire size: they normally do that with a continuous measuring (springs and coils), and what they measure is a good approximation of the instantaneous velocity of the vehicle. A good analog speedometer is somewhat reliable, especially if the scale is correct(*)
(*) their scale is not linear like you see in a normal car: but exponential, so it should be like: and this is why they have a "sweet calibration spot" (normally near the top of the dial; have you already thought about why they make 1.2l-engine cars with 220 km/h marking in the speedometer [a speed they usually don't achieve even in freefall
DISCLAIMER: I was a software developer for a road engineering company for one and a half year.
It's better to be the foot on the boot than the face on the pavement. ~~ tkx Kadin2048
Cameras and speed displays don't have radars in them.
They use induction loops buried below the road, and work exactly the same way you do - compare times at positions A and B.
In the UK the speed camers are checked by hand (or at least are ment to). They do this by taking 2 photos from the camera at a set time interval. On the road by the camera there is meant to be a lot of little white marks which are big enough to see in the camera and are spaced at
Though i know this system is sometimes ignored by police int he uk
Also in the UK (at least n.ireland) the police are meant to run a test car though speed traps a few times documenting it and keeping a tape etc.. If they fail to produce a copy of the documentation on this to you at the scene if you ask for it then they dont have a case if oyu push it to court.
Another thought about safty on the road is around where i live they have started putting in speed bumps everywhere. Which is meant to slow the traffic down to improve safty. Slow it donw it does. It also annoys the crap out of people driving over bumps all the time and it makes the safty problem worse. Since all the traffic is now slower no gaps form in it so people can no longer cross the road when its busy whichout taking higher risks which is exactly the opposite they were traying to prevent.
Its amazing what the UK goverment can come up with.
It's probably far too late to get a mod up on this, but I thought I'd add it to the knowledge base of the Internet in case somebody decides to Google it one day.
Simply put: This is not going to work.
The system is rigged against fighting speeding tickets. Even if you've got the money to pay for evidence collection, expert witnesses, and everything else -- BEFORE your trial -- you'll still lose. The justice system will protect the police from having even one ticket investigated, because it calls into question other tickets the officer may have written using the same or similar equipment; a very large expense. It just won't happen.
Here's a TRUE story, as related to me by my friend who drives commercial truck:
My friend was pulled over by a police officer for "speeding" and given a ticket for 75 in a 65. Only one small problem here: The area in Ohio where he received the ticket was absolutely flat, and his truck is GOVERNED at 68. Exceeding 68 miles per hour on a flat road is literally IMPOSSIBLE for his truck, so says the manufacturer of the engine and the manufacturer of the vehicle. Understandably, my friend was very upset at receiving such an obviously bogus ticket, and decided to fight it.
Nice thing for my friend, engines in big trucks have computers to track fuel usage, speed, etc. over time. Getting the data from the engine is a matter of taking it to the service center, hooking up a computer, and getting a printout. He obtained this printout and showed it to me; it's so simple my grandmother could easily see his truck hadn't gone over 68 at any point during the data recording. The dates were clearly marked; it showed on the day in question, the truck did not go anywhere near 75.
Armed with this and people willing to testify that the truck's governor was functional and the printout was accurate, he attempted to fight the ticket. He was informed that he would have to pay all of the trial costs up front ($10,000) before the trial began, and even if he won, he wouldn't be able to get reimbursed for this expense. So basically, it came down to a choice: Swallow pride and pay the $350 ticket, or pay $10,000 to prove he was in the right and get the ticket voided on the basis of the evidence.
Sadly, but wisely, my friend opted for the former. Proving his case was not worth the extra $9650 it would cost to do so.
Take note: Traffic court is rigged against regular people. If the highwaymen in blue try to rob you, just give up the money; losing your time, energy, and sanity over government sponsored theft will just victimize you more.
I work for the radar company that made the radar gun the cop used. I don't have all the information about what happened, but I have a hard time believing the GPS is more accurate.
Radar guns are certified regularly, which is most often a pretty simple accuracy test (but very well could have been a full diagnostic), so it's doubtful the radar gun was malfunctioning (iirc, those guns have an internal lockout in case of malfunction).
Also, remember that we're talking basically the speed of light here, with some minor latency for the unit to process the Doppler shift. Radar's pretty much instaneous, within miliseconds, at least.
Now, that's not to say that the officer didn't make an error. Radar's not an exact tool--b/c the beam is so wide, you can pick up a lot of things and an untrained officer can get some misleading speeds.
At the same time, remember that most traffic officers do this all day, at least five days a week. They make mistakes just like anybody else, but they're rare. And for that matter, officers are trained to use the radar as a confirmation of their own judgement of how fast the vehicle's moving. And since they're doing it all day long every day, they can tell you within a mph or two how fast a car is going just by looking at it.
Again, I'm not pretending to have all the information, but if it came down to trusting GPS or trusting the radar, I'd trust the radar. It's just a simpler tool, with less hoops to jump through (and fewer things to go wrong).
Disclaimer: I'm in marketing for Decatur Electronics. But for what it's worth, I use Linux on my machine at home, hehehe.