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."

Video Evidence

[ZERO1ZERO (948669)]

I've often thought it would be a good idea to have a constant video recording your driving, like the police camera setups. This could help clear up who to beleive at the scene of accidents, because of the video.

Plus it would be cool to have onboard footage of your driving for analysis and review.

Re:Video Evidence

[Albert Sandberg (315235)]

If you dragrace with yourself and yourself alone one a lone road in the middle of nowhere, does it really matter? I would not like to have the authorities to have a closer look at my driving. I hate the speed cameras they tend to set up everywhere on the road, but in front of schools for instance (where they'd really matter), I'm yet to spot one.

Re:Video Evidence

[billcopc (196330)]

Yep, police work is only performed where it matter$, aka speed traps and deliberately low limits. Saving lives is not a profitable business, which is why no matter what you do (or don't do), if a cop shows up, you get a fine.

In my opinion, if they're not enforcing speed limits in the few areas where they are actually beneficial, then we should abolish that system entirely as it is working for no one. I pay taxes like (most) everyone else, if that money isn't enough to afford proper police without the need for profiteering practices, then raise my goddamned taxes and destroy those stupid radar guns. Maybe then people will start respecting these so-called peace keepers again.

Something is very very wrong with the world when honest law-abiding citizens live in fear and/or contempt of the law.

Re:Video Evidence

[KingSkippus (799657)]

Actually, some college students at Georgia State University tried an experiment [google.com] in which they blocked off all lanes on Interstate 285 going 55 miles per hour, the speed limit. Keep in mind that most people drive 65 to 70 on that road.

As a result, the people behind them got very angry and began active extremely dangerously. One van even had an accident when he passed them on the right shoulder and clipped a car that was parked in the emergency lane.

There is nothing inherently dangerous about going faster than the speed limit. Sometimes, when it's raining and there is low visibility, driving the speed limit is unsafe. Other times, when there is low traffic volume, high visibility, and the roads are dry, it's perfectly safe to go 10 to 15 miles per hour above the limit. The law doesn't take that into account, though, and as a result, the speed limit is set arbitrarily low on almost every road.

Re:Video Evidence

[dangitman (862676)]

Speed limits are arbitrary, and (specifically on the highways between Brisbane and Melbourne) designed to make money, not save lives.

There's a simple solution to that - if you don't exceed the speed limit, they won't make any money from the cameras. So, if they are about making money, then they would be removed once they stopped being profitable. Unfortunately, it seems highly unlikely to get the majority of people to obey the road rules for even one day or one week - so it looks like the cameras are here to stay. I still think it would be a hilarous protest, though - everybody obey the law today, and screw the police and government. It would be an act of civil obedience.

Re:Video Evidence

[drsmithy (35869)]

I don't think so.

Kind of right. What they actually do is reduce the tolerance levels. This happened in Victoria (Australian state - probably has some of the most brutally enforced speeding laws *in the world* - unsurprisingly its roads aren't meaningfully safer), where you will be booked for driving as little as 3km/h over the posted limit (how this lines up with speedometers only having to be accurate within 10% hasn't been tested in court yet AFAIK).

So whereas you use to be able to do 120km/h in a 110 zone without too much to worry about, now you'll get pinged for 114km/h. No-one without an agenda seriously thinks a ~3.6% speed differential has any meaningful impact on road safety.

Police and politicians have to get places by car, too.

Poor examples. Police can (and do) break the speed limit at will with little fear of either detection or punishment. Politicians are typically being driven, for short distances, and only in urban traffic.

Generally I think the speed limits are pretty reasonable. It's just that drivers can't stand any form of restriction, and always want to go faster.

Also untrue. Research has demonstrated that in typical conditions - especially high speed roads like motorways - drivers choose the safest speed for the conditions. People actually interested in road safety know this as the 85th percentile. It's what the posted limit on a road *should* be set at for "maximum safety" (but usually isn't).

For a concrete example, there is a major highway north of Brisbane, Queensland (2 lanes each way, divided, limited access). Some years ago the speed limit was *raised* from 100 to 110km/h (amidst the typical outcries from ignorant fools about how the roads would be awash with blood). Not only does the road remain as safe as it was, but average traffic speed actually *dropped* by about 3km/h.

Seriously, if people can't follow a simple speed limit, why should they be entrusted with more liberty on the road? If people would obey them and drive like sane people, then they could be allowed to drive faster. You have to earn responsibility.

Because following a badly set speed limit - *especially* on higher speed roads like motorways - actually *increases* risk. *DRIVERS* have to earn trust ? What a joke. Maybe if the government was more interested in saving lives than making money - and demonstrated it - we'd be able to trust them with things like speed limits.

Very, *very* few governments have shown any real interest in improving road safety. Why would they ? Doing so would be expensive (both in monetary and political terms) and it's trivial (and cheap) with a good advertising campaign to demonise things like speeding (despite it being a relatively insignificant factor in overall road safety) so they have someone to pin all the "carnage" on.

Re:Video Evidence

[liquidpele (663430)]

It would have to be hidden. A lot of cops will make you turn off any recording equipment they see as soon as they start talking to you - and if you don't comply many of them will just arrest you for BS charges. Not saying ALL cops, but I've read articles where already asshole cops went berserk over recording equipment and the person not dropping their pants and bending over to their demands.

Re:Video Evidence

[ls -la (937805)]

I'm pretty sure that's not what the OP is advocating. If you set up a camera in your car, YOU control it and all the tapes. If you do something illegal or that you don't want taped, you can either turn the camera off beforehand or destroy the tape after. The only place the government comes into this is if you turn the tapes over to the government/court to prove your innocence.

Open source GPS?

[KillerCow (213458)]

But will he be able to produce the source code for the GPS when the police request it to check its accuracy?

Breathalyzer Source Code Revealed [slashdot.org]
Closed Source -> Charges Dismissed? [slashdot.org]

used in Taiwan

[xldyniac (1180595)]

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.

Brings accuracy into question

[blhack (921171)]

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!

Speed = Distance / Time

[imstanny (722685)]

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...

Re:Speed = Distance / Time

[ls -la (937805)]

Two things:

1. What is the time the GPS device averages over? On the devices I've seen it updates about every second. Unless you have a REALLY nice car you're not going to go from 65 to 90 and back down for long enough to average 65 over that kind of time.

2. At least one state (MA) and perhaps others have laws that require your AVERAGE speed over some distance (I believe MA is 1/4 mi) to be over the limit for a speeding ticket.

Instantaneous velocity

[hummassa (157160)]

No, my friend, you are wrong.
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:

0 .... 20 .... 40 .... 60 .... 80 .... 100

but exponential, so it should be like:

0 . 20 .. 40 .... 60 ........ 80 .............. 100

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 :-)] ?? ) -- in my GM Celta, the sweet spot is at 100 km/h [~60mph], so speeds lower than 100 km/h are usually reading HIGHER than real and speeds higher than 100km/h are usually reading LOWER than real. The speed limit in our highways is 110km/h.

DISCLAIMER: I was a software developer for a road engineering company for one and a half year.

What's to prevent me from doctoring the GPS log?

[jordan314 (1052648)]

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 have used this

[www.sorehands.com (142825)]

I used the GPS defense when pulled over.

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 .75 mph.

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.

Re:I have used this

[by Anonymous Coward]

>In San Antonio, TX I was pulled over for doing 76 in a 75 zone.

For what, Driving While Black?

Speeding cases are easy to win

[Kohath (38547)]

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.

VORAD units have been used this way

[Animats (122034)]

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. [etrucker.com] 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. [etrucker.com] The VORAD record shows not just what the VORAD-equipped vehicle was doing, but what the other vehicles were doing.

Your Mileage May Vary

[PPH (736903)]

Don't depend on GPS (or any other) evidence being allowed into court that contradicts the officer's testimony. Some courts may allow GPS data, others may not.

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.

Not Going To Work

[by Anonymous Coward]

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...

[crazybilly (947714)]

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 [decaturradar.com]. But for what it's worth, I use Linux on my machine at home, hehehe.

Re:This could only be the first step

[kc5goi (772773)]

I have heard stories of people trying to submit GPS data logs in the past to prove they were not speeding. The judges would not accept the data because it could be considered suspect, particularly if you presented it on a USB dongle since the data is beyond easy to modify. Radar does have its issues, specifically if you are in a group of cars (have you ever been blamed for speeding when the car beside you was passing you). Unless you can provide data in a method that is deemed "un-crackable", I doubt it would be allowed. I could easily re-run the route that I was on when I got stopped, take the track log and modify the time stamps (if they are present and that depends on the GPS data stream you selected). You would want the time stamps to be there to compare against the time the police officer stated on the ticket. I have to take this jab at the judicial system though, despite the fact the the citations say you are not pleading guilt or innocence at the time of the infraction, you are pretty much labelled guilty, the police never lie in the courts point of view and if you claim you are innocent, you get treated as if you were guilty anyway. The only way I can see to defend yourself is to have the same set up in your car as the police do and have it display speed on the recording. Then again we saw recently what happened someone who tried that in Missouri.

Re:This could only be the first step

[Paradise Pete (33184)]

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.

Yup. On most people's home projects list that's the one right after "Get microwave to stop blinking 12:00."

Re:First Post?

[wtansill (576643)]

I don't get why this is tagged as privacy.

Think about it. This guy is using his GPS data to contest a ticket. Next up, the government subpoena's your car's GPS and/or engine computer info to prove (or snoop on) your whereabouts last Friday night, or to send you tickets based on the readout of your computer (once the wireless interrogation system gets worked out). Do you really want to be under observation at all times and everywhere, regardless of what you may or, most likely, may not have done? I do not.