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."

Re:Video Evidence

[Albert Sandberg]

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.

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[account_deleted]

Comment removed based on user account deletion

Brings accuracy into question

[blhack]

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!

Re:This could only be the first step

[kc5goi]

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

[j00r0m4nc3r]

That's exactly why this should not be allowed. Or I could hack my speedometer to always read 25 and keep a video camera in the car. "See, I was only going 25!" People are asshats and will do anything to get out of speeding tickets.

What I don't understand is how this kid is explaining the discrepancy between his GPS and the radar gun? The radar says he was going 62, but he claims he was going 45? How would that happen? That's a big difference when you consider the accuracy of radar guns. I'm not saying they're infallible but they definitely have a proven track record compared to GPS.

Re:admissible?

[larry bagina]

chain of custody is important for proving guilt (beyond a reasonable doubt). Exculpatory evidence doesn't need such high standards (it just needs to give a judge or jury doubt).

At least in theory. Traffic court judges exist mainly to uphold a cop's decision.

Re:Video Evidence

[ls -la]

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.

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

[jordan314]

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.

many units clock max speed

[jpellino]

Many clock max speed. On long hiway trips in unknown areas I keep my eTrex Legend on trip computer with max as a field just in case. I figure a couple dozen DoD satellites might hold sway over a lone radar gun.

Speeding cases are easy to win

[Kohath]

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.

Re:Video Evidence

[zippthorne]

Problem is, in an age where insurance is a requirement people think that lowering insurance rates is an appropriate goal for public policy. Drag racing, even by yourself on a deserted road, is risky behavior, which raises risk for insurance companies and therefore their rates as well. They're not just going to absorb that loss.

Re:Video Evidence

[caluml]

I'm no expert - hell, I'm not even American, so not really sure what the 5th amendment actually states - but I think "not saying something" is different to "destroying stuff that can prove your guilt".
Like I say though, IANAL. Or AA.

Re:Speeding cases are easy to win

[Kohath]

The kid should have his license revoked.

Really? For going 62 in a 45? What about 61 or 60 or 59? What should happen to him if he was going 65? The death penalty? Just wondering.

What the hell does this mean? You want no speed limits?

Do you think you're everyone's Mom? Do we all need your advice on how fast we should go on each stretch of road in every weather and traffic condition at every time of the day? Do we need your wisdom so much that you should be able to use armed troops to force it on us -- threatening us with imprisonment or worse if we don't obey you? (Because otherwise someone might go 62 in a 45! Gasp!!!)

Stop trying to control everyone. We don't need your help. No one wants to get in a car crash. We are all competent adults and must be assumed to know how to drive. We can judge speed, traffic, weather, road conditions and available light to choose our own speed.

For any Mom, there comes a time when you have to let your children go. You've been a good Mom, but we're all grown up now. Thanks for trying to protect us, Mom, but now we need to be free to live our own lives and make our own mistakes.

Re:Video Evidence

[Thyrteen]

Sure, it's messed up, but do you realize that in many, many countries, having interaction with the law is much worse than the US? We may still have fundamental rights violations here by officers, but south american / mexican / other countries have much worse things to fear from authorities. My point is, it's been wrong for a long time :)

Re:First Post?

[wtansill]

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.

Re:This could only be the first step

[hummassa]

I don't know how things are where you live, but down here, public employees in police or fiscalization jobs have public faith, that is, what they say is always truth except where proven false. Also, there are harder penalties for falsifying information given in public faith than for the (otherwise simple) perjury.

Instantaneous velocity

[hummassa]

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.

Re:Instantaneous velocity

[Paul Jakma]

No, my friend, you are wrong.

Don't be so sure. ;)

Instantaneous velocity is the limit of the average velocity where the time of averaging tends to zero.

Yes, that's obvious. You'll note my original post mentions "You can /approach/ t=0," - you can take that as a not-so-subtle clue that, yes, I have in fact done at least secondary school (== high school in USA?) mathematics (and indeed, more).

You're unfortunately missing the words "approximated by", in between "is" and "the limit". Interestingly, given your post, you obviously are quite aware that physical measurements approximate the real-world. However, you seem to think, fallaciously, that your math provides infinitely precise truth.

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

But you're still not an engineer, obviously. If you were you'd know:

a) In the real-world, we can't measure things to perfect accuracy. All measurements have error. Further, the current scientific consensus around quantum theory suggests that this error is in fact *fundamental* to the universe (rather than any limitation in our tools) - we live in a probabilistic universe.

b) Mathematics is a means of modeling, at least how engineers use it.

You can make a graph of how an x kg body accelerates due to the gravity of the earth. You might be really clever and account for the following (or more):

- air pressure
- altitude
- the lunar cycle

In the real-world: if you drop that body from a decent height, the spot you draw on the ground, which your maths say will be the impact point, will often be wrong (and I'll let us assume a windless earth..). Because your mathematical model is just that, a *model* - very useful, but it can't (yet - probably never) model the chaos of the real-world.

I.e. your math be able to say "at this point in time, we can approximate the speed as X, for a delta-t that's so tiny, we can consider it as zero", but it's still a model, an approximate one (and yes, it's very useful..). In reality however, there is still no such thing as instantaneous speed.

The real-world is chaotic, both inherent in the systems found there, and in how we can measure them. They do not quite conform to the nice, precise graph on your screen, no matter how clever your math. It's extremely important, as an engineer dealing with physical systems at least, to know to model and then account for error.

Re:Video Evidence

[Anonymous Coward]

"speeding is dangerous" is a rather general and over broad statement. If speed limits were 55 and you were going 70, you would say its "dangerous", but if on the same road, the limit was raised to 70 and you went 70, it would suddenly stop being dangerous since you aren't speeding?

AFAIK, speed related crashes are not the biggest threats on the road, its people with poor driving habits and reckless behavior. A cop munching on doughnuts and sipping coffee with his dash-mounted radar waiting for it to beep is, imho, a poor way to enforce safety on the roads. They only do this because speed enforcement is more profitable than actual enforcement of more important public safety issues.

Re:Video Evidence

[G-funk]

Speeding is not dangerous. Driving too fast for your abilities / your car / the road is dangerous, but saying speeding is dangerous is disengenious. That implies that the speed limit has anything to do with safety, which is rediculous. If I drive 80km/hr down a certain patch of road, and one day the speed limit is lowered, I'm not driving any less safely than I was beforehand.

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

Re:Your Mileage May Vary

[PPH]

When starting and ending a shift, the officer verifies the displayed speed with the fork and makes note of it. Your allowed to call that evidence and it will be granted providing the judge doesn't feel your just wasting his time. The operator is not a radar technician, he has no control over what the radar displays period.

Its semantics, but I'll admit that you are correct. The officer verifies the unit's calibration.

No court hear such arguments as yours because there are so many BS excuses the judge has heard them already. It's ancient proven technology. That's as lame as trying to tell the judge that because the cop got your speed while aiming his radar down from an overpass that it's inaccurate. Well, due to cosine error, your correct.. but also means you were going faster than you were ticked for, the judge also knows that as well.

We have a couple of radar speed signs in our neighborhood (the "Your speed is XXX" kind). They work well if there is only one vehicle in their field of view. More than one vehicle and they either display bizzare numbers (flipping back and forth between an actual speed and some odd value) or nothing at all. Interestingly enough, these units are capable of discriminating between approaching and departing vehicles, something most police radar does not do. This indicates that they have some rather sophisticated DSP software inside. And yet they still don't work very well.

Police radar suffers from similar problems. A skilled and trained operator can reject bad readings if they watch the display and/or listen to the audio tones. But the fact remains that there radar units do generate a lot of garbage readings. Some officers do take care in making readings, others don't. Can you question the officer's technique? Generally no, unless you have some hard evidence. Without such evidence, your testimony is written off as a 'BS excuse'.

Re:Certainly does

[juhaz]

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.

Re:Video Evidence

[erroneus]

And it doesn't mean we shouldn't always push for something better either. Even if what we have is "the best there is," we should STILL strive for something better or some improvement at all times.

Re:Video Evidence

[KingSkippus]

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

[cbiltcliffe]

What does not wearing a seatbelt and getting thrown from a vehicle after hitting black ice have to do with speeding?