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Discussion Starter #1
Travelling back on the M1 last night, I had to travel through a very long roadworks stretch in Yorkshire/Derbyshire. The speed limit is 50mph and monitored by average speed cameras...so I simply set my cruise control to 50mph and sit there (albeit slightly frustrated that it seems too slow when traffic is free flowing).

I'm often shocked by the number of drivers that zoom by....and I'm not talking about those doing marginally more that may not have cruise control and experiencing parallax error on the speedo, I'm talking about those that are obviously doing 70mph or more. Are they:
a) idiots that don't understand the meaning of 'average'
b) willing law breakers
c) have insider knowledge eg that the cameras aren't working or infractions will not be pursued?
 

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Well if you apply Occam's Razor,

Occam's razor (also written as Ockham's razor and in Latinlex parsimoniae) is a principle of parsimony, economy, or succinctness used in problem-solving devised by William of Ockham (c. 1287–1347). It states that among competing hypotheses, the one with the fewest assumptions should be selected.

Its would seem Option B is the correct one, however I think in this case Option A is the most likely :)
 

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No idea, but I sit tight like you do too.

I've never had any points on my license, and I've never arrived late due to a lack of speeding.

Weird that, I plan my journeys based on potential hold-ups and not driving like a loon and arrive on time... wish more people could apply the same logic more often.
 

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Classic case of YMMV.

I've never been knobbled by the variable speed limit on the M25 which has been in place or average speed cameras even when I've occasionally slightly transgressed from absent mindedness or being late at night with no one around. Maybe I've been lucky, or the cameras have been operated with less of a revenue focus and more of their intended safety emphasis.

For anyone transiting M4/M5 interchange the variable speed congestion controls are being aggressively policed and the cameras are active ALL the time. IMHO it's a massive money making scam, the speedlimits are used on a daily basis on a hair-trigger, as a result congestion is worse than before IMHO - but revenues are up :mad:

http://m.bbc.co.uk/news/uk-england-bristol-28329966
 

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Discussion Starter #5
On the way up I had an HGV that was literally 80cm from my boot. All I could see was the Renault logo in my rear view mirror he was THAT close. As I was in the middle lane (going past people doing 45mph in the inside lane) he couldn't overtake me.

As soon as I got chance I pulled into the inside lane and he speeded up to get past at about 60 mph.

It was a Polish HGV.

It's no wonder there are so many motorway accidents with tw*ts like this driving. Unfortunately the specs cameras will do nothing about this. More unmarked police cars and ACTUALLY prosecuting tail gaters is a much better solution. Word will soon spread!
 

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I do think a lot of the road work specs cameras are for show, although I'm not taking the risk. Have you seen the new signs at roadworks? along the lines of a child's drawing and "My daddy works on this site, please don't speed"

The cameras on the M1 variable speed limit definitely work when the variable limit is in force I've seen them flash and a few guys at work have the bits of paper to prove it. I still see people speeding through them though.
 

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Something I have some inside knowledge of. The issue seems to be two fold, a mix of driver ignorance of what SPECS cameras are, and others believing, sometimes rightly, sometimes wrongly, that they are not operational.

Sadly the first version of SPECS, SPECS2, where deployed for temporary installations, was only rarely every connected. It seems that, initially, the need to provide power, and to have them networked together by cables as well as move them as work progressed made it an expensive task and so they simply hoped that their mere presence was enough.

But SPECS3, the standard now used, is much simpler to deploy and almost always live and operational.

Like you I always set the limiter or cruise to a GPS indicated 50 and am amazed at how many breeze past, often at speeds much much higher than the temporary limit. I just wish I could be there when they get the NIP :)
 

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There are a number of margins that come into play in this scenario.
  • Your speed is not 50mph. (Your satnav wil give you a more accurate speed). The law defines the upper limit for a speedometer as Zero and a margin on the lower side (see http://www.legislation.gov.uk/uksi/1996/3013/schedule/2/made section 19), so all speedometers reflect this with an underspeed reading. (this is predominantly around 10% under-read) if your gauge says 50 you are in reality going slower. so a 50mph Reading may only be 45mph.
  • The ACPO Recommended Prosecution limit is 10%+2 ie for 50mph a prosecution for speeding would only be recommended at 50+5+2 = 57mph. Of course if you are being stupid or annoy a police officer you can be prosecuted at the limit!
  • Roadworks speed limit enforcement is not the same a standard speed camera enforcement. There is a vast range of conditions & criteria to meet to use a speed camera for speed enforcement, road safety cameras at roadworks are there not to enforce the speed limit but to catch lunatics/dangerous drivers consequently the threshold on roadworks speed cameras can be much higher that on standard speed trap cameras. (I don't have actual figures but it may be twice the ACPO limit).

Based on the above a driver reading 50mph on his speedo (true speed 45mph), may be overtaken by a driver going 5mph faster (seems like 55mph but a true 50mph), or 12mph faster (seems like 62mph but a true 57mph) to meet ACPO limit at a speed camera, or even as fast as 19mph (seems like 69mph but a true 64mph) faster at a roadworks camera, with no penalties being issued.

Of course these are limit speeds based on perfect margins if there is a single 1% error your in for a ticket! so use this information at your own risk. if you stick to indicated speed you will be extremely unlikely to break these margins (by over-inflated tires or the wrong size wheels) - which is why you don't need to slow to 45mph for a 50mph camera "Just To Be Safe" you already are safe!

(you may also notice that lorry speed limiters are set to true speed not speedo speed. hence they always seem to be going faster than allowed, in reality you are just going slower than you think.)
 

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Discussion Starter #9
ACPO guidelines also state that when using hand held speed guns, the officer should be wearing a hi vis vest and be in plain sight. Yet they RARELY adhere to this. Indeed I've seen them literally hidden in a bush wearing all black uniform.

Maybe I'll go at satnav indicated speed in future because I believe the Ampera over-reads by 10%.

I had been told that motorway tickets are not valid because it takes an act of parliament to change motorway speed limits but I don't believe this and can find no info to support the argument.
 

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Discussion Starter #11
I'm hoping I won't have to bank on it. I'm sure the pareto principle applies....80% of motorists drive safely and within the speed limits. Unfortunately there is the other 20% that don't drive safely....and that can include going too slow. It's not speed per se that kills, it's the SUDDEN loss of it in most cases. And that occurs when you drive too close to the vehicle in front.

The prats that try to bully people out of the way by accelerating up to a bumper (making no stereo types about German car drivers) are the ones that annoy me.
 

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Maybe I'll go at satnav indicated speed in future because I believe the Ampera over-reads by 10%.
It's coincidental that you mention that. I suspected that was the case, and on Friday did a test against Sat Nav (Actually, Google My Tracks vs Cruise Control) on M1, and, yes, it's about 10% over. CC set to 66mph but My Tracks recorded constant 60mph.

Strangely enough though, the distance travelled on the Energy Info screen was spot on. I expected that to be over by the same percentage.
 

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Discussion Starter #14
You should visit Milton Keynes some time. 70 mph across town is not fast enough for more people than you'd think!
I did last year. WAAAYY too many roundabouts. Cars accelerating/decelerating regularly are dreadful for the environment....especially ICEs.
 

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It's coincidental that you mention that. I suspected that was the case, and on Friday did a test against Sat Nav (Actually, Google My Tracks vs Cruise Control) on M1, and, yes, it's about 10% over. CC set to 66mph but My Tracks recorded constant 60mph.

Strangely enough though, the distance travelled on the Energy Info screen was spot on. I expected that to be over by the same percentage.
Your speedo (by law, as I understand it) must never UNDER read, but can over ready by something like 10% max (or even more).

So your speedo is basically rarely completely accurate due to having to over read regardless of types, wheel spec etc at the factory. Some speculate the margin is changed depending on car spec (tyres, wheels etc) but this seems to rarely, if ever, be shown in "real world" tests.

GPS is pretty accurate, but also can be wrong in terms of changes in gradient and so on (incline/decline a lot and your car will be going x speed, but only going across the earth at x - some clever calculation).

In general I'd say GPS is more likely to be accurate, but you're supposed to go by car readouts.
 

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Out of interest the law is here (section 19):
http://www.legislation.gov.uk/uksi/1996/3013/schedule/2/made

So if you work out the median target value that the manufacturers would be aiming for is as follows:
Code:
Real  Min    Max    Target    Error
25    25    33.75    29.375    18%
30    30    39.25    34.625    15%
35    35    44.75    39.875    14%
40    40    50.25    45.125    13%
45    45    55.75    50.375    12%
50    50    61.25    55.625    11%
55    55    66.75    60.875    11%
60    60    72.25    66.125    10%
65    65    77.75    71.375    10%
70    70    83.25    76.625    9%
Of course if you have a very accurate speed reading adding a straight 10% would put you close enough to that target. Which is what I believe they do on the Ampera.

A much more accurate true speed is available on the ODBII data and would be used for all the mpg calcs etc. its just not legal to use it on the Dash Speedometer. (my old ford fiesta could display it on dash in test mode.)
 

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A much more accurate true speed is available on the ODBII data and would be used for all the mpg calcs etc. its just not legal to use it on the Dash Speedometer. (my old ford fiesta could display it on dash in test mode.)
You could do that in the original new MINI too, before they introduced digital speed displays. Wonder if the LEAF Spy etc can show this too?
 

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The prats that try to bully people out of the way by accelerating up to a bumper (making no stereo types about German car drivers) are the ones that annoy me.
Me too! When I'm overtaken by someone doing nearer to 100 than 70, it's almost always a German car. Our other car is a VW BTW.
 

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I think the range on my German car would suffer if I spent too long at "nearer to 100"! I think it's limited to prevent this.
 
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