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TonyD
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 Posted: Mon Jan 26, 2009 11:35 am Post subject: Basic question about average speed cameras |
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Do average speed cameras as used in motorway roadworks work with both average speed and instantaneous speed ? i.e. if you average 50 through a 50 section but happen to go past one camera at 60, do you get clocked.
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falkirk81
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| Posted: Mon Jan 26, 2009 11:44 am Post subject: |
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No, the cameras are used to time your entry time and exit time, and from that work out your average speed through the road works.
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TonyD
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| Posted: Mon Jan 26, 2009 11:53 am Post subject: |
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| falkirk81 wrote: | | No, the cameras are used to time your entry time and exit time, and from that work out your average speed through the road works. |
That's good news. So if you get stuck behind someone doing 40 for the first half you can speed up to 60 for the second half (hypothetically of course). Oh, and before someone points it out, I realise that has to be half the time and not half the distance.
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falkirk81
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| Posted: Mon Jan 26, 2009 12:03 pm Post subject: |
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I guess so hypothetically half the time you could do 40 and half the time you could do 60. I personally wouldnt risk it, but in principle you should be ok.
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TonyD
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| Posted: Mon Jan 26, 2009 12:10 pm Post subject: |
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| falkirk81 wrote: | | I guess so hypothetically half the time you could do 40 and half the time you could do 60. I personally wouldnt risk it, but in principle you should be ok. |
Are you sating you wouldn't risk it because what you said may be wrong ?
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falkirk81
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| Posted: Mon Jan 26, 2009 12:21 pm Post subject: |
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Im saying that i wouldn't risk doing 40 for half the distance and 60 for the other half. Just in case i am wrong. Also bear in mind, some SPECS installations have middle cameras which further complicate your hypothetical situation.
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TonyD
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| Posted: Mon Jan 26, 2009 12:49 pm Post subject: |
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| falkirk81 wrote: | | Im saying that i wouldn't risk doing 40 for half the distance and 60 for the other half. Just in case i am wrong. Also bear in mind, some SPECS installations have middle cameras which further complicate your hypothetical situation. |
I think what I'm really saying in practice is that I tend to drive at an indicated 55mph on the basis that my speedo over reads 10%, but occasionally I find my speed has drifted up a little so I then under speed a while to compensate, but I don't want to find that a brief few seconds of 55-60 coinciding with a camera is going to give me a problem.
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DennisN
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| Posted: Mon Jan 26, 2009 1:52 pm Post subject: |
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| TonyD wrote: | | I think what I'm really saying in practice is that I tend to drive at an indicated 55mph on the basis that my speedo over reads 10% |
You mean that on your inaccurate speedo, you can rely on it being accurately 10% over?  If you were taking your driving test, would you drive round town at an indicated 33mph?
On your TomTom,
Change Preferences,
Status Bar Preferences,
Show max speed next to speed
and it will show your speed as true as you can get.
PS One safe method with specs is to drive under the speed limit, not up to it - works every time. 
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Dennis
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TonyD
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| Posted: Tue Jan 27, 2009 1:20 am Post subject: |
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| DennisN wrote: | | TonyD wrote: | | I think what I'm really saying in practice is that I tend to drive at an indicated 55mph on the basis that my speedo over reads 10% |
You mean that on your inaccurate speedo, you can rely on it being accurately 10% over?
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Yes. I have been using GPS in my car for 14 years and by experience I know I can trust it to show my true speed is at all times.
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GPS_fan
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| Posted: Tue Jan 27, 2009 1:40 am Post subject: |
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The speedo in my car is almost spot on, compared with GPS speeds, and is certainly no more than 5% different.
Just to play safe, I assume that the car speedo is spot on, 100% accurate, so that I KNOW I'm always under the speed limit.
Not all police forces apply the 10% +2mph 'rule', so it's better to be under, rather than 'on' the speed limit.
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TonyD
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| Posted: Tue Jan 27, 2009 8:45 am Post subject: |
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| GPS_fan wrote: | The speedo in my car is almost spot on, compared with GPS speeds, and is certainly no more than 5% different.
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Yes, my wife has just got a new Honda Jazz and I notice that that speedo is virtually spot on - the first car I've had where this has been the case. Probably reflects the fact that modern speedo technology is more accurate and therefore no need to build in a 10% over read.
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Darren
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| Posted: Tue Jan 27, 2009 8:57 am Post subject: |
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| TonyD wrote: | | Yes, my wife has just got a new Honda Jazz and I notice that that speedo is virtually spot on - the first car I've had where this has been the case. Probably reflects the fact that modern speedo technology is more accurate and therefore no need to build in a 10% over read. |
Speedos have long since been accurate enough to display exact speed but legislation makes it far easier for manufacturers to calibrate them to over read.
This allows for tyre wear and other factors to be taken into account without breaching the law.
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DennisN
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| Posted: Tue Jan 27, 2009 9:34 am Post subject: |
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My "One safe method" described above has also been found to work for ordinary flashing and mobile speed cameras. This business of driving at 55 in a 50 zone is the basis for all those people who claim that speed cameras cause "accidents" because they force them to concentrate on their speedo instead of the road in case they "accidentally" drift over. It's not accidental, it's deliberate, it's negligence, - if they are expert enough to drive at a constant 55, they are expert enough to drive at a constant 50. It's why I disapprove of the 10%+2 attitude and I have no problem with the zero tolerance approach of some. Why set a speed limit and then say you are allowed to exceed it (sometimes, in some places)? To be trapped in a 50 limit it appears that they have to have a speedo showing 63/64. What sort of driving is that? I repeat, is an indicated 86/87mph acceptable for the driving test along a dual carriageway? Is it acceptable for the Institute of Advanced Motorists?
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Dennis
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Darren
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| Posted: Tue Jan 27, 2009 9:40 am Post subject: |
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| DennisN wrote: | | I repeat, is an indicated 86/87mph acceptable for the driving test along a dual carriageway? Is it acceptable for the Institute of Advanced Motorists? |
Hmm, ponder the fact that the Police Advanced Driver course instructors would penalise you in some circumstances if you adhered to speed limits when road and other conditions permitted more rapid progress. The National Limit signs were not nicknamed GLF signs without reason!
Anyway, this discussion is drifting way OT so lets leave the preaching out please.
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DennisN
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| Posted: Tue Jan 27, 2009 9:56 am Post subject: |
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I withdraw, speechless!
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