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Accuracy of GPS Speed indicators
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arthurking83
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Joined: Nov 27, 2005
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PostPosted: Sun Nov 27, 2005 10:42 am    Post subject: Reply with quote

Howdy folks!
Here in Aus, we have overhead speed indicators on some of our freeways/motorways.
The speedo on my vehicle, indicates 3km/h LESS! than the actual speed, and therefore has caused me some grief in the past!!

The MeridianGPSr speed indicator is absolutely spot on :D
At every speed trap on our freeways, it has indicated the exact figure that the speed trap has.

I now use the GPSr as my speedo, despite the fact that I drive @ 3kmh less than the speed limit for a given road.

So the 3% accuracy figure qutoted elsewhere would seem about correct.

cheers.
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bazza_c
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PostPosted: Wed Dec 21, 2005 2:15 am    Post subject: Reply with quote

My work Van speedo shows 34mph at a GPS 30mph, and 76mph at a GPS 70 mph.
However, I am told Police guidelines are to nick people that do 10% over the speed limit + 2 mph.
Anything under that is allegedly unlikely to be pursued!
Therefore 30mph +10% = 33mph + 2mph = 35mph.

I reckon 34mph to be below the 'nickable 10% + 2mph.

In my van a true GPS 34mph shows up as 38mph on the speedo. Similarly at 70mph, I should be able to travel at a true 78mph without worrying about blue flashing lights. A true 78mph as indicated by the GPS comes up as 85mph on my Van's speedo. So far I have stuck rigidly to this formula and have not been nicked for speeding ever since.
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Robin2
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PostPosted: Fri Dec 23, 2005 3:34 pm    Post subject: Reply with quote

You're correct that the ACPO guideline for prosecution is 10% +2 mph, but it is not mandatory and there are some areas where there is a zero tolerance policy applied, ie prosecution at 31 mph. 34 mph is OK if you know the local policy, but if you are driving in a strange area you might be unlucky!
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Strawbs
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PostPosted: Thu Jan 12, 2006 5:55 pm    Post subject: Reply with quote

I stand with the "10% +2mph" brigade for the UK! The law written is that way to factor in tyre wear! Plod allows 2mph because even their properly calibrated speedos will be off a little when their tyres are past their best.
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neil01
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PostPosted: Sat Jan 14, 2006 1:29 am    Post subject: Reply with quote

bazza_c wrote:
My work Van speedo shows 34mph at a GPS 30mph, and 76mph at a GPS 70 mph.
However, I am told Police guidelines are to nick people that do 10% over the speed limit + 2 mph.
Anything under that is allegedly unlikely to be pursued!
Therefore 30mph +10% = 33mph + 2mph = 35mph.

I reckon 34mph to be below the 'nickable 10% + 2mph.

In my van a true GPS 34mph shows up as 38mph on the speedo. Similarly at 70mph, I should be able to travel at a true 78mph without worrying about blue flashing lights. A true 78mph as indicated by the GPS comes up as 85mph on my Van's speedo. So far I have stuck rigidly to this formula and have not been nicked for speeding ever since.


While I thought that what you say is true, a work collegue claimed that he was prosecuted for doing 71mph in a 70mph area - this is less than 2%! I do not know the exact circumstances.
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adam808
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PostPosted: Fri Mar 31, 2006 7:21 pm    Post subject: Reply with quote

Hi ya,

wanna stick my beak in here !!

car manufacturers are obligated to deliberately make their speedos OVER read.

USUALLY by 10%

this is for ALL the reasons you've all said (to account for different wheel/tyre packages, to account for inaccuracies in calibration etc)

it also covers their ass so too speak...

imagine u had aserious accident, your were speeding but you've proved the speedo said you weren't.

now the car oem is liable for the accident

for your claim
the other party's claim
oh also to recall every single world wide model of that vehicle...

sod that they say, lets just make the speedo over read :D

cheers
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adam808
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PostPosted: Fri Mar 31, 2006 7:28 pm    Post subject: Reply with quote

neil01 wrote:
bazza_c wrote:
My work Van speedo shows 34mph at a GPS 30mph, and 76mph at a GPS 70 mph.
However, I am told Police guidelines are to nick people that do 10% over the speed limit + 2 mph.
Anything under that is allegedly unlikely to be pursued!
Therefore 30mph +10% = 33mph + 2mph = 35mph.

I reckon 34mph to be below the 'nickable 10% + 2mph.

In my van a true GPS 34mph shows up as 38mph on the speedo. Similarly at 70mph, I should be able to travel at a true 78mph without worrying about blue flashing lights. A true 78mph as indicated by the GPS comes up as 85mph on my Van's speedo. So far I have stuck rigidly to this formula and have not been nicked for speeding ever since.


While I thought that what you say is true, a work collegue claimed that he was prosecuted for doing 71mph in a 70mph area - this is less than 2%! I do not know the exact circumstances.


sadly the 10% + 2mph is a bit of an urban myth.

it stems from way back when, a real police officer would pull you over & make a judgement call on your behaviour.

they used to use the 10+2 formulae.

cameras don't make this distinction

(they are just after money, no one tell me that sending some1 an NIP 14 days AFTER they were speeding saves lives, thats just a useless threat, i might get nicked if i speed - same as i might go to prison if i burgle DOESN'T stop burglries... i digress)

I'd like to think no copper who has even the vaguest notion of community policing would nick ya for 1mph over, but a camera is has a base setting & if you exceed that it will get you!

cheers
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Ako
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PostPosted: Fri Mar 31, 2006 8:12 pm    Post subject: Reply with quote

Adam808 wrote:
Quote:
I'd like to think no copper who has even the vaguest notion of community policing would nick ya for 1mph over, but a camera is has a base setting & if you exceed that it will get you!


But what do you reckon the base setting is? I have had the misfortune (or lucky escape) to accidentally go through a 30mph limit camera at 35 (well!!! aproximately 35) and it didn't flash. So from what I can see, the 10% + 2 rule stands. That's not to say that I'm not open to persuation. Can anyone in the know confirm or deny it? (off the record of course).

Dave
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astrocompass
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PostPosted: Fri Mar 31, 2006 9:18 pm    Post subject: Reply with quote

Quote:
30mph limit camera at 35 (well!!! aproximately 35) and it didn't flash.


Probably wasn't loaded with film or switched on. These cameras don't operate 24/7.

The 10% + 2mph is guidance, nothing more, and applies more to Police traffic vehicles/mobile units than cameras. Circumstances dictate whether or not it is invoked. And it's interpreted differently according to which Force area you're in.

Some areas set their cameras with a low threshold, others differently. Depends on location, policy at the time, and whether or not there's a campaign against speeding in a particular location. Regrettably there's not a "one size fits all" rule to apply here.

Best you can do is apply the camera database and heed the warnings. Oh, and don't speed, of course.
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Ako
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PostPosted: Fri Mar 31, 2006 9:34 pm    Post subject: Reply with quote

Astrocompass wrote:
[/quote]Probably wasn't loaded with film or switched on. These cameras don't operate 24/7.[quote]

The thing is I know this camera works as I have seen it flash other people when I've been going the other way. Also it was during the day so it is not likely that it was switched off. The possibility of no film is there I suppose but it would still flash wouldn't it? I agree that there is no consensus but in this particular case it seems likely that it is the threshold setting.

Dave
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astrocompass
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PostPosted: Fri Mar 31, 2006 11:05 pm    Post subject: Reply with quote

Hi Dave

My understanding is no film = no flash. "Switched off" applies to digital cameras rather than film ones.

Could well be the threshold, as you say - there's no consistency across the patch on this. But please don't let this lull you into believing that you can always pass this particular (or any other) cam even marginally above the limit. The settings can be changed easily enough, and thresholds change even within a Force area. The cynic in me might lead me to believe that if a Camera Partnership isn't generating sufficient revenue to cover costs, then thresholds get lower.......unlikely to be the case in reality, though. Just take care out there, keep the cam database updated, and avoid those points!
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Ako
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PostPosted: Fri Mar 31, 2006 11:30 pm    Post subject: Reply with quote

Astrocompass wrote:
Quote:
My understanding is no film = no flash. "Switched off" applies to digital cameras rather than film ones.


Fair enough. I may have been under the wrong impression. As you say, no consistency except for them making money out of us.

Quote:
But please don't let this lull you into believing that you can always pass this particular (or any other) cam even marginally above the limit.


God no!!!! When I went through this one it was a case of "I'm only going local and I know where all the cam's are" The you start thinking of something else because you haven't got the reminder popping up.

Dave
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Skippy
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PostPosted: Sat Apr 01, 2006 2:10 am    Post subject: Reply with quote

astrocompass wrote:
My understanding is no film = no flash.


Sorry, you are wrong. You can clearly see the camera in the gatso's and a dark area on the ones which don't.

I do understand the 10% plus 2 guideline but a friend who rides a motorcycle can confirm that they do all flash, but the trigger point is often well above the speed limt (ie 40 in a 30 area).
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Skippy
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PostPosted: Sat Apr 01, 2006 2:12 am    Post subject: Reply with quote

Skippy wrote:
Sorry, you are wrong. You can clearly see the camera in the gatso's and a dark area on the ones which don't.


I meant to add that they DO all flash, including vehicles coming towards the camera where they can't take photos (no calibration lines on the road and theh second flash would not even capture a picture of the vehicle)
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astrocompass
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PostPosted: Sat Apr 01, 2006 2:13 pm    Post subject: Reply with quote

Skippy, you may well be right - in your neck of the woods. As I think I hinted, there's no consistency in application, so what may be right for you is not necessarily correct elsewhere.

I'm cursed with occasional travel on the M25, and am regularly overtaken on those post-gantry road markings by vehicles travelling at a speed which makes Scotty's Warp Drive look positively glacial - but no flashes.

Plus I know of one camera that NEVER flashes - because it's a very convincing replica built and installed by a local business with a view to slowing traffic down - hope it's not in the Camera database! (Can provide a location if PGPSW wants a check)
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