The House always wins

Even though GPS speedometers are clearly more accurate than those inside the car, the police aren’t going to accept GSP records as evidence in speeding cases.

Typically, [inbuilt car] speedometers would give a faster reading so drivers were travelling slower than what was shown.

Many comments touched on the accuracy of GPS devices when it came to reading speed.

But yesterday a national police headquarters spokesperson said GPS devices were not a certified method of tracking speed.

“Given that a GPS is not accepted as a reliable means for proving a driver’s speed, police do not accept this as an excuse for speeding.

“GPS systems used for speed or locations can only be an indicator, not a source of absolute true information due to signal loss through buildings, terrain or weather conditions,” the spokesperson said.

Police detection devices, such as speed cameras and speed guns, were checked annually for accuracy, and were calibrated to strict international standards.

GPS devices were not set to the same standards and were unlikely to be recognised as a reliable way to gauge speed in the future.

Yesterday, a Timaru driver said he had recently received a speeding ticket in the mail alleging he was travelling 5kmh over the limit on King St.

He called the Police Infringement Bureau claiming his GPS device showed he was sticking to the speed limit, but his fine was not revoked.

The police accepted speedometers “are designed to over-read”. “This provides an in-built level of tolerance in the driver’s favour,” the spokesperson said.

So, reading between the lines, if your GPS says you’re going 100 km/h, and the police ticket you at 107 km/h, you don’t have a leg to stand on, because your car speedometer would have read at least 110 km/h, and had you used that, you would have known you were speeding.

As far as I can see, the message now is:   There will be no speed limit tolerance applied.  101 km/h will get you a ticket.  On top of that, if you use your GPS to gauge your speed, you are more likely to stray over the limit because you will be closer to the 100 km/h limit then you would be if you used your in-car speedometer that has been built to lie to you.

End result?   To make sure you aren’t ticketed, you better not exceed 90 km/h on your GPS either.   Or 95, if you’re the devil may care type.

Hands up those of you that think this is starting to get ridiculous?


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  • Yeahright

    What about people towing a trailer, going 80km in holiday traffic IS going to wind a few people up, and this in turn will make them do crazy things…..we wait and see!!

    • Bob D

      It was never about safety, it’s all about the Police justifying their existence – and of course the money they bring it for Government.

  • rantykiwi
  • ozbob68

    Now here is an interesting question; when my self-driving car (with GPS) exceeds the speed limit, who is responsible and gets the ticket? The car was not under my control, do I have to sue the manufacturer for selling me a faulty product?

  • Winston Smith

    I remember in the 70s attending court and the previous defendent had
    been booked for 61 in a 60 zone. The magistrate told the booking
    enthusiast to wake up to himself and dismissed the case.
    What would happen today?

    • dgrogan

      I bet that Cop didn’t do it again though. Wouldn’t take long for the Cops to learn to use a certain amount of discretion.

      • Bob D

        But they will do it again – that’s the whole point of this discussion. The Police have announced that doing 1km/h over the limit (using equipment that doesn’t even have that precision) will result in a ticket.

        • dgrogan

          But from the very example you have used, the Cops will quickly find out that a zero tolerance approach will not be workable. A few people will get nabbed in the interim, but as we say, they’ve been warned.

          • Bob D

            Except they will have sewn up the legal arguments, making it very difficult to win the court cases without expensive lawyers. Most people won’t bother, they’ll just pay up. Many more millions for the consolidated fund.

            A friend of mine once went to court to try to argue about the calibration certificate, etc. The judge just talked over him and effectively told him to shut up and pay.

          • Mark

            crown law works for the police & govt paid for by the Taxpayer,the rod is of our own making.

          • Bob D

            Herein lies the solution – the Police don’t care, but the politicians do.

            Note that all this is happening within months of the election. Would they have tried this in July this year, even though it’s much more dangerous when it’s wet and dark on the roads? Of course not.

        • One way to turn the table on Plod and register your protest is to call #555 as a “genuinely concerned citizen” whose speedo is reading 50km but is worried that the police car in front who is going faster must have a faulty speedo and surely they would want to know this …..

  • Watcher

    It is ridiculous and I can see the courts becoming overwhelmed with trivial fine appeals.
    Good job.

    • Mark

      The simple way to fix this is to dispute every ticket you receive,in court if it gets that far. The latest campaign has increased my speed up to 9k over,simply put I’ve had a gutsful. I’m sick & tired off being stopped at “random” I have not had a speeding ticket of any kind in at least 10 years & I don’t drink & drive. How about I be allowed to go about my lawful business!

      • Bob D

        There’s the problem – they have had no revenue from you for over ten years now. They can do better to meet their targets, and so they will.

        • Mark

          “There’s no way to rule innocent men. The only power any
          government has is the power to crack down on criminals. Well, when there
          aren’t enough criminals, one makes them. One declares so many things to
          be a crime that it becomes impossible for men to live without breaking

          Ayn Rand

          • She was pretty focussed on trains too. Maybe that’s where Loopy Len gets it from ….

  • Bob D

    The Police will never allow any kind of defence that might block the flow of revenue.

    • Ross

      Ironically they don’t see the revenue. But I’m sure they get a pat on the back by their bosses for issuing another ticket “to keep the road toll down”.

      • They use the money raised – which is handed to Government – to argue fheir budget requirements. “See, Minister, we spend so much of our budget on road policing that we need more money so we can think about policing some real crime ….”

        That’s how they benefit from the revenue they raise. Indirect but very much related.
        Can you really believe that Plod would devote so much resource and effort if it wasn’t in his best interest?

        • david

          I don’t know the current situation but only a few years ago we had a Land Transport Safety Authority and they contracted (ie paid out of the money they collected from you and me in license fees and fuel levies) the Police to provide road safety enforcement. The role of the LTSA has been taken over by the NZ Transport Authority, but I think the same arrangement may apply. That would be one of the reasons why police are wasting their time pinging motorists travelling at 101 km/h instead of chasing burglars rapists and child molesters. Part of the contract with LTSA was a specification of outcomes. The number of tickets issued would be one measure of the effectiveness of the police enforcement effort so achievement of targets would be very important to the police.

  • dgrogan

    Not me. If you exceed the speed limit you are open to getting nabbed. End of. There are no excuses IMO.

    • david

      IMO if the state imposes penalties for failing to comply with a totally arbitrary regulation it should be challenged. By saying in the past that they will allow a latitude of 10km/h or 4km/h the police are showing that they have the ability to exercise discretion. I would accept an arbitrary limit if the police exercised discretion in a sensible way – for example not ticketing someone for travelling at a higher speed if it was obviously safe to do so. Unfortunately that doesn’t seem to be how they work.

      • They used to work like that. Back in the old days when we had, and would show, respect for cops. Anyone remember those days,

  • richard.b

    Are car makers already using GPS to detimine the speed of the car? If it is a much more accurate way of calculating speed it can’t be far off.
    That could be interesting.

    • rantykiwi

      Mazda certainly aren’t – the speedo in MrsRanty’s new car reads 6kph lower than the inbuilt GPS at 100kph.

      • By agreement with requests from most law enforcement authorities, most car manufactures deliberately cause their instruments to read higher than the true speed, i.e. as a GPS would calculate.

        • PhantomsDoc

          I believe it is worst with US vehicles. From memory, by law over there all vehicles must be manufactured to read under the speed limit no matter what after-market rim/tyre combination is installed onto a vehicle. If someone puts huge tyres on and the speed reads low and they get a ticket I believe they have grounds to sue the vehicle manufacturer. Hence the always reading low on the speedo.

  • JJ

    and that is why I have a radar detector in both of my vehicles

    • Whitey

      Time I invested in one myself.

  • sheppy

    What a load of total nonsense. GPS is a computer based calculation, it needs no calibration and is only out when it doesn’t have a proper fix.


    “How does a GPS device calculate speed?

    Using GPS, a device is able to calculate a lot of information about a moving object. Using even basic time and location data, a GPS unit can quickly calculate the relative speed of the object, based on how much distance it covered in a given time.

    GPS devices are positional speedometers, based on how far the device has moved since the last measurement. The algorithm also uses the doppler shift in the pseudo range signals from the satellites. It should also be noted that the speed reading is normalized, and is not an instant speed.

    Speeds are updated at short intervals to maintain accuracy at all times. It uses frequent calculations to determine the vehicle’s speed. For example, using a standard movement per time calculation, if you have covered 80 feet in one second, the GPS device works out and converts that to MPH, which in this case is 55MPH.

    Why does GPS speed differ from the vehicle’s own speedometer?

    GPS speed calculations are more accurate than a vehicle’s speedometer since it is not affected by the same inaccuracies, including the vehicle’s wheel size or drive ratios. It is dependent however on GPS satellite signal quality but with the use of moving average calculations any errors are minimal.

    Vehicle speedometers also require calibration to maintain perfect accuracy as general wear and tear, changing wheel sizes, and the manufacturers own ‘erring on the side of caution’ and setting the speedometer to read higher than the actual speed, all contribute to inaccuracies.”

    Generally most manufacturers claim a 0.1MPH tolerance with speed readings, however will go as far to say a 0.5MPH inaccuracy is possible, to make allowances for any satellite signal variations beyond their control.”

    • Rightsideofthebed

      Just one wee problem with GPS speed readings – they are only accurate on a perfectly straight, flat piece of road. Any bend or gradient will mean your vehicle has travelled further that the point a to point b speed measure of the GPS, which will mean it ‘under reporting’ your speed.

      At the end of the day a speed limit is just that – a limit, not a target.

      As an aside, if everyone is so good at checking their GPS to know their speed all the time, why can’t they use that same scan process to look at their speedo.

      For all the conspiracy theorists out there, it isn’t actually about revenue. The decision was made operationally by Police, who don’t get any money from it. The government, who does get the money, wasn’t consulted about the decision.

      • PhantomsDoc

        Wrong, GPS calculations include height and change of direction. GPS’s are able to give you altitude, after all, they are a triangulation device requiring 3 satellites for an accurate position. This means they can calculate latitude, longitude and height. Around New Zealand you can often have up to 7 satellites available for positioning.

        I was using a Honeywell DVR recording platform about 10 years ago. These are the in-car units you see in the US cop shows that show alight on, braking and speed etc as well as the camera footage. They were/are also used in all the yellow school buses in the US.

        The speed on these units is done by GPS and has a guaranteed speed accuracy of 0.25mph for police evidential purposes.

        I don’t know what the police use here in NZ.

        • Rightsideofthebed

          I realise that GPS can triangulate exact position, including altitude.
          My question is – do the on-dash ones use altitude as part of their calculations, or straight line distance between 2 triangulations from the satellites – assuming that commercial GPS is using 3 satellites, not 2 as they often used to, with the consequent loss of accuracy.

          • If they can see 4 satellite they will computer altitude into their speed normalisations. 5 + satellites will simply increase the accuracy.
            WhenPlod tells you that GPS results are not accurate, beware. Plod has his own reasons. And they involve cashflow!

          • PhantomsDoc

            I expect they would use altitude, after all, it would be easier for them to calculate that because, if they didn’t, their location accuracy would keep changing if they didn’t include height.

            Putting it simply, they are always calculating on the 3 axis’s, otherwise, as you change height location accuracy would change.
            If they are doing this then it would be easier to calculate distance between these 2 points rather than trying to flatten their data out onto a flat plane (to then calculate the distance between to point on that plane).

            Why would you do that when you already have the 3 dimension points plotted and only need to calculate the distance between these points?

  • JJ

    If the Police believe that the 4kph tolerance was working so well, why is the road toll way higher than last year already. Doesn’t quite make sense does it.

    • InnerCityDweller

      That’s why it now needs to be dropped to 1kph…

      • JJ

        obviously you drive and live in the city where you might be able to go over the speed limit after hours on the motorway. Try living rurally where the majority of roads i drive on are rural 100kph full of farm machinery & tourists driving dangerously. Yet Police continue to sit at the end of passing lanes pinging people for a few k over the speed limit and ignoring everything else. Easy money isn’t it

        • They certainly run a very efficient revenue stream in the Waikato.Very little real crime is allowed to distract their officers from their primary focus – fines.
          And to hell with the loss of public respect.

        • InnerCityDweller

          Sorry, bad attempt at being sarcastic. I totally agree with you. Yes, I am an inner city dweller, but they do let me out every now and like you I guess, I am totally peeved off every time I see the cops sitting there after you passed the guy who was doing not even 90 but then speeds up the moment the passing lane opens up. Thank god I won’t be travelling this Xmas

          • JJ

            thats ok just annoys me police only focus on speed. I have been first on the scene at 1 fatal & 3 very serious accidents in the past 5 years not far from my house, not one of them was due to speeding. (drunk driving, attempted suicide, domestic dispute) Every time the Police first on the scene have run around like headless chooks not knowing what to do & chaos has ensued. Very dissapointing.

    • But they will tell you it would have been much worse if they hadn’t been enforcing the lower limits. Plod will defend his revenue raising against anything!

  • Whitey

    Just remember folks, it’s not about revenue gathering at all. No way. Definitely not.

  • cows4me

    Imagine the consternation if the public decide to keep to the speed limit. These extortion artists would be spinning like tops. Next years speed limit would have to drop, all for our good of course. But it’s the politicians that should be getting hounded, they sit there smugly as the the cops take the heat. It’s the politicians that call the shots and it’s the politicians that should be held to account. Yes this is revenue gathering and it says more about a increasingly greedy government that is trying desperately to balance the books. Think it’s bad now you wait for another couple of months when Mr English realises he’s about eight billion short. Speed fines will simply be the entrees.

    • Mark

      My point would be that road users have been keeping on task. The road tolls have been falling for many years. Drink driving is not the problem it once was,if in fact it ever was, Dept of Pre-crimes,no longer self funding?
      All of the recent law changes are related to being able to levy fines rather than the complicated business of going to court & proving offenses. For example use of phones while driving,which is no more a distraction than a myriad of other distractions. An offense already covered under “Careless use of a motor vehicle”,but of course proving that involves actual police work,much better to just institute an instant fine.
      Asset forfeiture laws,majority juries,crime by association,just laziness.
      The Police cannot work without community backing,due to the law of unintended consequences this is being lost to them.Respect cuts both ways,now they only receive the co-operation they are able to compel

      • cows4me

        Dead right Mark. I have more to say on the respect police are losing in the country, re stock rustling, in backchat . The police and the politicians really need to get their acts together, things aren’t good.

        • Hard1

          It must be extremely depressing signing up for the action-packed Police job that only helps the communities and protects honest citizens, only to find yourself alone in a parallel universe cruising highways with the sole purpose of making people poorer and angry. Think of the downflow when ticketed people get home, snap at the spouse and the kids, get a bit of acid reflux when laying down to sleep.

  • Justsayn

    He is, perhaps on purpose, confusing two different types of “error”.

    A deliberate “error” is incorporated into your speedo so that it displays a higher speed than you are doing. On my car it displays about 114 when I’m actually doing 108. The size of that error will differ from car to car. There may also be a non-deliberate measurement error in any speed reading device – be it a speedo, a GPS, a speed laser – whatever.

    Despite what he says, the fact remains that by checking your speed with something like a GPS (especially if you do it over a km or two when on your cruise control) is far more accurate than your speedo as it removed the deliberate error.

    But if the Cop says I clocked you at 101 and you’re now going to die, it won’t help you to say I looked at my X, my Y, or my Z… you’re caught.

    • Bob D

      I worked briefly for a fleet tracking company. In the UK, they were able to go to court and prove using their GPS data that a customer’s truck had not in fact broken the speed limit.

      Fat chance with these clowns.

  • those new speed cameras they invested in for xmas are going to be a real money spinner this year

  • Greg M

    Take every speeding ticket to court, every time, no exceptions. If the powers that be are going to be arbitrary and unreasonable, then so will I.

  • Halcyon

    Why not just cruise along at 95kph on the speedo. You can always make up the lost drinking time later.

  • Yeahright

    If I get a ticket for do 101, I might as well do 120! This might have a reverse effort.

  • Bunter

    Ever noticed how many unregistered or unwarranted vehicles that are on the road (mainly you see them when they are parked) oh but hang on this is only road safety, my mistake!! The police probably look at them and say to themselves can’t afford rego and warrant probably can’t afford fine.

  • redherring2

    I am still calling their bluff. They keep sending the messages out (and this is just another one) – in the hope that 99.9% will conservatively drive @ 100 or below anyway (on their speedo). It worked overnight last summer.

  • Bombastic

    I have a classic car with a speedo on MPH, I’m not sure how I will spot 0.6 MPH over 62. A protractor and calculator perhaps, that’ll make driving interesting as multi-tasking challenges this bloke at the best of times.

    • Hard1

      The real challenge will be staying cool when the bastridge behind you is tailgating and becoming obnoxious.

    • burns_well_eh

      When we switched to metric measurements you could get a handy set of stickers to put on your speedo to show when the needle had reached 50kph, 80kph etc. You must have them in a drawer somewhere…

  • Teletubby

    Ironically GPS is accepted by LTNZ for the purpose of calculating distances for road user charges and off road miles for refunds. There are two crucial differences to bear in mind between these “commercial grade” GPS units and the one in your car. Firstly the commercial one can, to keep it simple, “see” more satellites and therefore provide greater accuracy, secondly they upload telemetry data in real time so the details are actually recorded on the tracking companies servers and can be reproduced if necessary, e.g in court. The GPS providers in NZ that are authorised for road user charges had to undergo a very rigorous accuracy audit before their authorisation was granted so there data can be accepted as having a very high level of reliability. As for the one in your car the only evidence you can produce is your word.

  • Skydog

    Who cares what the Police think. It’s the Court who would decide if the GPS evidence is admissible. If you truly believe your GPS unit, defend the ticket and see what the Judge thinks.

    • You won’t win. But you will have the satisfaction of tying up some police prosecutor’s time in court, and perhaps, by forcing the issuing office to appear as well, by impacting on their revenue raising core competency.

  • When someone gets pinged for exceeding the speed limit and can prove, in Court, that it was safer than conforming to the law, we might get some sunlight on this stupidity. We all know that passing is safer when the speed limit is exceeded, safely. Plod knows that too. But Plod on the road who needs Joe Public’s respect and support has had his discretion taken off him by those who polish seats in Wellington.

    Ask yourselves this. Has you respect for the Police uniform:
    (1) increased, (2) decreased, (3) stayed the same
    over the last 5 years?

    • Bartman

      2! Not just speeding, but the steady decay of respect due to old cases where Police determination to pin the tail on a crim to build a career outweighed the need for justice. Many cases now, the list is growing and the Police hierarchy do the service no favours by bluntly refusing the condemn their own when it’s clear as day they should. Shame.

  • Dave

    An employee got off a ticket previously as our business car he was driving had GPS tracking. A staff member was clocked at 117 in a 100 km/h section of road, he always maintained he was being overtaken at the time. We had the GPS provider save a report stating at that time there was no way the vehicle was speeding, and was in fact (cant recall exact speed) under the limit of 100 Km/H. It went to court, the judge deciding to discharge without conviction as for approx 5 mins before and after the alledged offence, our employee was just under the speed limit, having set cruise control. They also worked out the radar van was almost a KM from where they said it was on their submissions. Small win for the innocent guy!

  • Allan

    Id like to know what the repeatability and uncertainty of measurement values are for the police radar guns is. I work with scientific equipment that spits out values for whatever we are measuring at the time (spectrometers and you can measure the same sample ten times and get a range of answers that theoretically should be close to each other. the police radar gun even though its calibrated would show the same repeatability problem that any other instrument has, and that speed that they ping you for should have a +/- value associated with it – so at a bare minimum the minimum tolerance they have may well be incorrectly measured and be below (or above) what they write on the ticket.

  • Slijmbal

    Allan hits the issue on the head

    we also get to ask what happens with hand held guns as it’s not hard to add a km or 2 when they trigger the gun – it is not a fixed mounting …..

  • Champagneshane

    There is an unforeseem fishook here. Whoever checks the rolling circumference of their tyres when they get new ones ??.. No one….. So if your spanking new Firerock whiz bang super radials are 5 or 10 cm longer in rolling circumference, and believe me it happens, then the moment you drive off the tyre court you speedo is going to lie to you……the wrong way
    You speedo is only as good as the RPM of your wheels across the ground. So if the wheel is longer when flattened out then you’re moving faster across the ground, and Constable Plod is going to empty your wallet

    • Dumrse

      So, you know that the minute you drive off the forecourt so your problem is…..

      • Champagneshane

        I dont have a problem. I perhaps know it when I drive off the tyre court but most others don’t

  • TonyM

    Ok maybe someone can answer this…

    Surely the police radar needs to know how fast the vehicle it is mounted in is travelling. How is this done?

    • Hard1

      If God created the world, and the only constant is change, what did the world look like when God created it ?
      The radar beam on the police microwave unit can be foiled by mounting a shop door sensor pointing forward through your grille. More modern laser units measure the reflected distance.

  • TonyM
  • Bartman

    Hand is waving all over the place! I’m regularly getting tickets for 3, 6, and most recently 9kph, over the 50kph limit. Just travelling with the general traffic flow on main roads in Chch city. Revenue collecting, pure and simple, as those speeds are hardly an affront to road health & safety.

  • Dumrse

    I guess when pulled over don’t engage in conversation. Say nothing except confirm ” number rank and name” or whatever it is you must state. Then appear in court. As others have said they will soon be snowed under. That said, ignoring instant fines will see you at the debt collector in a heart beat. I-Plod is on a wining streak.

  • Jonathan P

    I’m all for safer roads and a reduced tolerance but 1 km/h is far to low.
    It takes a mere “blip” of the throttle at 100 km/h to get to and or past 100 km/h.

  • stanace

    can I post this stuff

  • stanace

    Sorry I am not used to posting although i read the site every day. Here is my take on all this, Mr. Grumpy is my nickname.
    Firstly it is many years ago when the police had to go to a party that was getting out of hand. They threw bottles at the police called them pigs and F words, and when it went to Court the judge more or less said it was OK to shout this sort of stuff at the Police as it was common language.
    This really P me off, I thought the judiciary needed to support Law and Order.
    I have never been happy that this still continues to this day.
    Now regarding the result from last year, hypothetically, if the road toll had gone up, should we have put the speeding limit back up to reduce the death toll?
    I know this is only hypothetical, but where is the proof of cause and effect?

  • who’stoblame

    Don’t start me. Buy a quality radar detector and drive at your own speed limit. Current limits are totally inadequate. Quality driver training is what is required. If anyone has travelled SH 16 from Hellensville to Wellsford and observed all those stupid speed recommendation signs you will know what I’m talking about. Especially at night time those signs are a total hazard and WILL cause accidents. Just one example.

  • friardo

    I’ve pretty much decided to go at 95 not because of the fines, more because of the demerit points than anything else. It’s just an arbitrary figure but it so happens that my cars speedo says 100 when in fact I’m doing 95. So far I have noticed that people don’t come howling to my bumper rearing to pass, they settle in behind at 95. In fact driving at a speed well away from the limit is in fact far less stressful. I do find I have to leave a few minutes earlier… so what. Try it, it’s no so bad. I think most of the opposition is academic nonsense about rights and justice, revenue gathering and tying up the courts.

    I suppose with the state of our highways (few median barriers etc) there has to some speed limit, they’re hardly autobahns are they? Any limit is arbitrary so avoid the grief.

    • TreeCrusher

      It’s people like you that annoy the hell out of me. So arrogant to think that you’ve decided therefore stuff anyone else. And 95 is such a pain the neck speed to choose as it makes passing more difficult. Police are ultimately enabling people like you with this sort of clap trap, when in reality our roads and cars have never been safer. Speeds should be going up, not down.

      Just do the bloody speed limit!

      • Nige.

        I’m sure he will move to the left to allow you to pass.