Accuracy of GPS Speed indicators

arthurking83 · Occasional Visitor Joined: Nov 27, 2005 Posts: 3

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.

bazza_c · Posted: Wed Dec 21, 2005 2:15 am Post subject:

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.

Robin2 · Posted: Fri Dec 23, 2005 3:34 pm Post subject:

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!
Robin
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Strawbs · Posted: Thu Jan 12, 2006 5:55 pm Post subject:

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.

neil01 · Posted: Sat Jan 14, 2006 1:29 am Post subject:

adam808 · Occasional Visitor Joined: Mar 31, 2006 Posts: 12

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

adam808 · Occasional Visitor Joined: Mar 31, 2006 Posts: 12

Ako · Posted: Fri Mar 31, 2006 8:12 pm Post subject:

Adam808 wrote:

astrocompass · Posted: Fri Mar 31, 2006 9:18 pm Post subject:

Ako · Posted: Fri Mar 31, 2006 9:34 pm Post subject:

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 · Posted: Fri Mar 31, 2006 11:05 pm Post subject:

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 · Posted: Fri Mar 31, 2006 11:30 pm Post subject:

Astrocompass wrote:

Skippy · Posted: Sat Apr 01, 2006 2:10 am Post subject:

Skippy · Posted: Sat Apr 01, 2006 2:12 am Post subject:

astrocompass · Posted: Sat Apr 01, 2006 2:13 pm Post subject:

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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