I always find these cases strange given that in court you can overturn a speeding ticket if the police officer can't provide a certificate of calibration for his speed trap device.
To apply the law equally, the driver can't provide a certificate of calibration for his GPS device so legally he's unable to prove that his GPS is giving an accurate speed measurement.
The law is not applied equally in court. By design, defense faces a much lower bar than prosecution. It is perfectly reasonable to require certified calibration to determine guilt, but accept data from an uncalibrated consumer device to overturn a ticket.
(As an aside, I don't think GPS would require any calibration anyway. If I understand it correctly, it'll pretty much either work or not work, with the accuracy of the output determined largely by atmospheric conditions and satellite geometry. The worry here would be deliberate tampering rather than calibration.)
There are other factors that can affect the accuracy of GPS; for example, receivers tend to be significantly less accurate in a CBD with lots of tall buildings. I've also seen receivers with an error before, eg. one that consistently reported itself as being 150m south of where it really was.
But I agree that by far the more significant problem would be deliberate alterations to the data. It doesn't seem like it would be particularly hard to do so...
the main reason why you'd be able to overturn a speeding ticket in the first scenario you mentioned, is because the burden is on law enforcement to prove you are breaking the law. It's one of the last few bastions where the intangible burden of proof remains high and squarely placed on law enforcement.
In civil cases, it's not actually all that high. "Preponderence of the evidence" roughly means "it is more likely than not" the case that you are guilty of the alleged offense. "Beyond a reasonable doubt" only comes into play for criminal offenses.
Minor traffic offenses are civil, not criminal, so the much lower preponderence standard applies.
I always find these cases strange given that in court you can overturn a speeding ticket if the police officer can't provide a certificate of calibration for his speed trap device.
To apply the law equally, the driver can't provide a certificate of calibration for his GPS device so legally he's unable to prove that his GPS is giving an accurate speed measurement.
The law is not applied equally in court. By design, defense faces a much lower bar than prosecution. It is perfectly reasonable to require certified calibration to determine guilt, but accept data from an uncalibrated consumer device to overturn a ticket.
(As an aside, I don't think GPS would require any calibration anyway. If I understand it correctly, it'll pretty much either work or not work, with the accuracy of the output determined largely by atmospheric conditions and satellite geometry. The worry here would be deliberate tampering rather than calibration.)
There are other factors that can affect the accuracy of GPS; for example, receivers tend to be significantly less accurate in a CBD with lots of tall buildings. I've also seen receivers with an error before, eg. one that consistently reported itself as being 150m south of where it really was.
But I agree that by far the more significant problem would be deliberate alterations to the data. It doesn't seem like it would be particularly hard to do so...
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the main reason why you'd be able to overturn a speeding ticket in the first scenario you mentioned, is because the burden is on law enforcement to prove you are breaking the law. It's one of the last few bastions where the intangible burden of proof remains high and squarely placed on law enforcement.
In civil cases, it's not actually all that high. "Preponderence of the evidence" roughly means "it is more likely than not" the case that you are guilty of the alleged offense. "Beyond a reasonable doubt" only comes into play for criminal offenses.
Minor traffic offenses are civil, not criminal, so the much lower preponderence standard applies.
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