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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.
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.
>In San Antonio, TX I was pulled over for doing 76 in a 75 zone.
For what, Driving While Black?
Yup. On most people's home projects list that's the one right after "Get microwave to stop blinking 12:00."
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
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.