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Speed log

Discussion in 'Gen II Prius Technical Discussion' started by SoILL_Prius, Oct 1, 2011.

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  1. SoILL_Prius

    SoILL_Prius New Member

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    Yesterday, I got pulled over by the police for allegedly going 50 MPH in a 30 MPH zone. I vehemently deny those allegations and plan on fighting the ticket in court, since the officer who was running radar was not the same one who pulled me over. Be that as it may, it got me thinking about the ability to hack into the ECU and extract a log of my speed during the time that I was clocked, and whether or not the Prius Gen II (2008 Touring) kept such data in the ECU. Anyone out there know? It would be solid evidence to substantiate my case. Thank you.
  2. uart

    uart Senior Member

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    30 MPH and 50 MPH is a fairly big discrepancy. What speed do you think you were doing?
  3. firepa63

    firepa63 Former Prius Owner

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    The Prius doesn't log your speed.
  4. dhanson865

    dhanson865 Expert and Devil's advocate

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    What size tires are on your Prius? Revs per mile will tell us how far off your speedometer was (within a MPH or two).
  5. firepa63

    firepa63 Former Prius Owner

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    Regardless of the tire size, the speedometer can't be off by 20 MPH...
  6. dhanson865

    dhanson865 Expert and Devil's advocate

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    True but maybe the OP has non stock rims or an odd brand/model tire and doesn't realize how far off the speedometer can be.

    On top of that the radar gun can be inaccurate. But if the OP doesn't know he is driving over the limit when he really is it doesn't do him much good to fight the radar possibility if he was truly speeding.

    I could imagine a poor tire choice being 6% off at 60 MPH and even more at low speeds. The radar gun being innacurate as well wouldn't matter if he was doing 33 in a 30 as long as they didn't tack "reckless driving" or some other addon charge it doesn't matter if he is 2 MPH over or 20 MPH over the charge is still speeding.

    So my question to the OP is what size rims, what year Prius, what brand of tire, what model of tire, what PSI are they loaded at? Until you can confidently do the math and say you weren't speeding at all...
  7. David Beale

    David Beale Senior Member

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    Well, some miss-information here.
    The Prius DOES log speed along with several other measurements. But there is ONLY a short time period of data saved (a few seconds) and can be read out if the car is not operated again until readout. It IS NOT saved if the battery is disconnected. Which is what just about every firefighter does when coming upon a wrecked car (to prevent a short from starting a fire). So the bottom line is it was useful when investigating the "unintended acceleration" nonsense, but not so much in an accident, and certainly not useful in this case.

    The Lawyers among you may weep now. ;)
  8. archae86

    archae86 Member

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    GPS crumb-trails

    Had the vehicle in question been equipped with and operating any of the more usual sorts of aftermarket GPS units, the track log data (aka crumb trail when displayed) might very well have provided some useful speed information for this incident. For my Garmin 855, uploading the tracklog to BaseCamp lets one see logged points with time stamps, and as points on a map. Speed is calculated between each pair of points. When satellites are good and other problems not present these are actually quite good during even pretty short cruise conditions, even though I think they use position difference vs. elapsed time calculation, without use of the Doppler that helps real-time speed display accuracy.

    Does the OEM GPS system installed on a higher-upgrade Prius retain a track log? Does anyone know a means to export the data or to access it in-situ?
  9. The Electric Me

    The Electric Me Go Speed Go!

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    Is it worth the fight?

    I don't know your personal driving history or record, or insurance rates. But I noticed you didn't answer the question, " How fast do you think you were going?".

    Might be worth the time and trouble to fight it. Sometimes it works out to the advantage of the accused. But often it's pretty automatic, and the judges are just going to side with the law officer and the technology.

    Unless this infraction was going to put my driving record and thus my insurance rates over the top? and unless I felt I was TOTALLY guiltless, IE: Not speeding at all...I think I would just pay the fine.
  10. JimN

    JimN Let the games begin!

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    In NJ it is 4 points & a fine. IMO it is always worth fighting. A lawyer should be able to plead this down. The cop isn't going to have any hard evidence. The judge will listen to the cop then listen to you then side with the cop. Don't expect a fair trail. Municipal Court exists for revenue enhancement.
  11. The Electric Me

    The Electric Me Go Speed Go!

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    Yeah, but you're illuminating exactly why I ask if it's worth fighting. You really want to go to the trouble of hiring a lawyer? And you are exactly right, a judge will listen to the cop, listen to you, then side with the cop.

    Sometimes just paying the fine and moving on with your life is the best answer.
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