From Viz Top Tips, regarding bombing through an average speed camera, one correspondant recommended a solution of pulling over for a spliff. First class!

“Most car speedos are miles out”

Some, not all.
Most German car speedos are very accurate.
Certain Japanese manufactures can over read by as much as 7-8mph at about 70-80mph.

flatboy – yep, that’s why speed cameras have a certain leeway. It’s to account for the possibility that you may think you’re driving at 30mph because your speedo says so, but you’re doing 35 actually (though normally it’s the other way around).

The other halfs Nissan is shockingly inaccurate. Seventy in her car is same as 70 in mine. The signs that tell you what speed you are doing reckon at 30 she needs to be registering 35 on the speedo.

And the traffic cop next door agrees. Reckons the Tom Tom he has in the civilian car is as accurate as the properly calibrated speedo in his jam sandwich.

exactly. apparently my initial claim that they are allowed to be slightly inaccurate either way is wrong, i’ve just found out that they’re allowed to read too high a speed but not too low, so if anything you’re going slower than you thought, rather than the opposite. makes sense.

Yes, so the cameras are linked (paired) and they don’t have to be linked to another camera in the same lane, or to the next subsequent camera in the same lane, or other lane.

This is what I said originally.

A single camera is only linked to another single camera, not each and every camera in the section of roadworks.

So there’s a good chance you won’t be prosecuted if you speed (either in the same lane, or by moving lanes)…just the luck of how they’re linked.

SPECS have just cleverly worded it on their website. They’re not going to opening publicise it are they 🙂

Although I do see that SPECS have submitted a new design for HomeOffice approval which will link all cameras via a database:

http://www.speedcheck.co.uk/SPECS3_overview.pdf

So watch out in the future!

Cumbria Safety Cameras
Press Release
Safety Cameras Slash Speed at M6 Roadworks
Tiny Percentage Of Drivers Caught Speeding

Static safety cameras operating at two roadwork sites on the M6 proved a highly effective deterrent to speeding motorists, analysis by Cumbria Safety Cameras has revealed.

Average speed over distance SPECS cameras near to Junction 36, which operated over 26 days between October and November, caught 282 offenders out of an estimated traffic volume of 1,040,000 cars between those two dates –0.03 per cent of the total traffic exceeding the speed threshold. The highest speed recorded in this 40mph limit was 80mph.

Digital RedSpeed cameras operating between November 05 and March 06 caught 2761 offenders from a total traffic volume of 4,640,000 over 116 days – 0.06 per cent of the total traffic exceeding the speed threshold. The highest speed recorded in this 50mph limit was 96mph.

Kevin Tea, Communications Manager for Cumbria Safety Cameras commented:” The cameras were installed at the request of the Highways Agency following the deaths of four workers at roadworks in the first half of 2005.

“Looking at the traffic figures and the proportionately small number of cars caught speeding, we know that we were successful in encouraging drivers to slow down in the roadworks and didn’t record one injury accident in the time the cameras were operating.”

He added that while roadworks on motorways were frustrating to drivers, the majority were aware of the safety aspects and complied with the temporary limits and all partners concerned would like to thank motorists for their consideration.

Temporary lower speed limits are placed on motorways as roadworks because contra flows and chicanes are changed on a regular basis and slower speeds than the normal 70mph are safer for both drivers and road workers.

End

For further information Contact:
Kevin Tea 01768 217791
Steve Callaghan 01768 217630

The other halfs Nissan is shockingly inaccurate. Seventy in her car is same as 70 in mine. So yours is ‘shockingly inaccurate’ too?

The changing lanes thing was legalistic rather than technical – they’ve always been able to track you across multiple lanes, it’s just that they weren’t able to prosecute you if you had changed lanes as legally the cameras had to be paired.

Note I wrote “was”, “weren’t” and “had”!

Gary_M – Member

Most car speedos are miles out Where did you read this piece of nonsense? Do car manufacturers not bother making speedos properly then?

Not read, fact. I’ve never been in a car/motorbike which reads accurately at all speeds. Best being within 5%. However my current car is accurate at 70-80mph. Many speedo’s accuracy changes depending on speed, they can be more accurate in some ranges.

How do you know your satnav is 100% accurate.

I work in the marine industry, deal and using GPS units upto military standard. I have a better idea than most. It won’t be 100% accurate, but on level ground, constant speed, travelling in a straight line and with nothing to obscure reception a modern unit will be within 1%.

That 16 miles of it on the M1 is tedious
50 gets to feel very slow indeed

Like others have said I use GPS for accurate speed readings & just set my cruise control to an indicated 50 using that [56 on the main speedo]

5% isn’t ‘miles out’ though is it. If you stated ‘fact’ in your first post which was backed up by some evidence it would have made more sense.

Gary_M – Member

5% isn’t ‘miles out’ though is it. If you stated ‘fact’ in your first post which was backed up by some evidence it would have made more sense.

is one of your relatives a car speedometer? miles out/up to 10% out (which i understand is the permitted variation), who gives a shit?

You, obviously.

5% isn’t ‘miles out’ though is it. If you stated ‘fact’ in your first post which was backed up by some evidence it would have made more sense.

5% being the best I’ve seen. I’ve driven cars out by 10% or more. That would account for some passing you at 7mph faster in a 50 limit zone. Your car would be reading 50mph when you’re actually driving at 45mph. The driver with a GPS driving at a real 52mph.

As the theflatboy, why take it so seriously! I’d say a gauge that is 5% out IS miles off the mark.

why take it so seriously 🙄 from the person who spends his time driving with one eye on the speedo and the other on his satnav.

Not quite, only need to check the car once at various speeds to see how accurate it is.

Sorry, just to clarify my typo – 70mph in a Nissan is 60mph in my Golf.

have always assumed some people don’t know what average means – similar near here on bypass people go past and brake at the cameras – (possibly) interestingly this is a 3 lane single road so max speed is 60mph but many drive at 70 – you can get the stats on local police website

presume those that do know what it means and drive fast pay someone in the pub to take the points or get their spouse to, to some people its a minor expense

do get fed up with the HGVS doing their limited max which involves periods of tailgatng you – yes i do know can see over top but i’ve seen enough accidents to realise this doesn’t work all the time especially in narrow lanes with knobby manoevres

uplink – Member
That 16 miles of it on the M1 is tedious
50 gets to feel very slow indeed

You need a plan. Switch GPS on, bring speed up to limit, engage cruse control, nod off for a bit.

Can I just be the first to say that if you simply obey the speed limit then there is no need to fret about the technicalities of speed camera systems. I actually view them as a metaphor for deviance and society. There are always those who try to bend the law as far as they can and those are the people who should be punished. If 50mph is actually 45mph then anyone who drives at a real 50mph should be punished as severely as if they were driving at 55mph. The alternative is simply to allow society to implode.

Furthermore, motorcycles shouldn’t really be allowed on motorways. They’re both unstable and dangerous and if they can’t be effectively policed by average speed cameras, they should simply be banned until such time as they are.

Can I just be the first to say:

The alternative is simply to allow society to implode.

Furthermore, motorcycles shouldn’t really be allowed on motorways. They’re both unstable and dangerous and if they can’t be effectively policed by average speed cameras, they should simply be banned until such time as they are.

first and last, with a bit of luck 😆

I was wondering about these things too.

Ignoring the science for a minute. I have been done by normal speed & traffic light cameras & so have some people i know. However, i personally do not know of anyone that has been caught by these average jobbies, nor it seems, does anyone else. Which does start to make you think, that are very effective or do not generate prosecutions (for whatever reason).

I had begun to assume that all those who sped through average speed camera areas did it because they knew they were untraceable because they had no driving licence or were on cloned plates, rather than just being worryingly unobservant behind the wheel.

I also thought it potentially sneaky that in the 2 sets on the M4 near Swindon, one set is at 40mph and the other 50mph. I would expect it is likely that people could easily forget which limit applies to the zone they are in, especially in the dark when the speed repeaters are not clearly visible.

I’m liking mos and IanMunro!

However, i personally do not know of anyone that has been caught by these average jobbies, nor it seems, does anyone else. Which does start to make you think, that are very effective or do not generate prosecutions (for whatever reason).

A much more likey option though is that they simply don’t have any average speed cameras installed in the first place.

…..diverting us away from arguments about the accuracy of speedometers, although relevant in a way, back to the original post!

AIUI speedos are required by law to read between 0% and +10% over the speed limit ie under reading is not permitted. Hence most manufacturers err at about +5%.

If you do the math, the tread wear on a tyre from new to bald works out at a few % difference in speed reading with worse (higher %) variation for small diameter tyres. So even with the best ‘german’ car you’ll get a few % variance depending on how badly worn the tread is as the speedo assumes a constant circumference wheel from which it calculates the speed.

However, i personally do not know of anyone that has been caught by these average jobbies, nor it seems, does anyone else. Which does start to make you think, that are very effective or do not generate prosecutions (for whatever reason).

They had some on the M27 recently. It is impossible to speed through them due to sheer numbers of sanctimonious pansies chugging along at 50 or less. Even weaving between lanes I never managed a decent pace. As someone rightly pointed out, these morons have no idea of the meaning of average speed as they never speed up to 100+ once a tailback clears.

GPS speed is accurate – it’s independent of it’s positional accuracy as it works on the Doppler effect* exhibited in the carrier wave. It’s been shown to be accurate to a 1-2 mm a second… I’d say that was accurate!

The speedo on my old merc is about 1mph off at 70mph. Good job I checked as the speedo in the(much newer 05 plate) fiesta was off by about 9mph at 70mph….

http://gauss.gge.unb.ca/papers.pdf/ionntm2004.serrano.pdf

I always assumed the SPECS cameras could only cope with one lane for computional reasons – image recognition is only so good, so if you have 1 lane to compare, you’ll have less false positives than 3 lanes.

*Unless you have a sh1t one that doesn’t use the doppler effect.

Assuming our GPS is spot on, our Audi reads bang on the money for speed, if the speedo says 70, it’s doing 70. Our Honda reads freaking miles out. If the speedo says 70, the gps says 63-64 (so the 10% rule seems accurate). My Hyundai when I had it was about 2mph out at 70.

I always assumed the SPECS cameras could only cope with one lane for computional reasons – image recognition is only so good, so if you have 1 lane to compare, you’ll have less false positives than 3 lanes.

I dunno about that. The roadside vans doing car tax evaders can collect and assimulate plates ridiculously quickly, I’ve been talking to the police men while it was beeping away as a stream of cars went past. As the car went past, it beeped instantly having done a plate capture, sent it to the dvla, got the results back and forumlated a beep. I assume it’s the same technology.

The speedo in the wife’s car under reads by about 8 mph, 60 on the clock is about 52 on speed traps. Why is this more serious than over reading?

Coupleof yrs ago I got flashed at 57mph in a 50 area as the driver was on my bumper.

3 points later and £65 fine in the post-I learned to ignore the driver on my bumper.

Ignore the idiots-anyway concentrate on your driving!

Besides it could be an emergency-they have reasons for speeding-if it’s serious/life threatening call the cops to get there for you-don’t risk yourself or others!

If you’re just late then you speed you get caught or crash into someone or arrive a few minutes earlier.-Someones life isn’t worth it and workmen could get runover.

Someones life isn’t worth it and workmen could get runover.

The vast majority of times when I go through roadworks speed limits on motorways, it’s only the cones which are at risk of getting run over.

if all this lane swapping was so true, how come there on 2 camera’s on a 3 lane motorway.. shouldn’t there be three or is one lane not checked?

I use that section of the m5, very annoying it is too whn it’s part of a 100mile journey (but safety first for the workmen, my inconvenience is insignificant), but I’m not going to be the one to test the lane swapping theory…. watched some driver trying to dodge around them the other day, by speeding between cameras then trying to hide behind lorries at the next set… how long can you hold that up for?

Lane swapping is true…read the info on the Specs website.

Only 2 cameras on a 3 lane motorway must mean one lane isn’t monitored. Still doesn’t help you know how they’ve linked the cameras though, if they always pointing at the same two lanes etc. It’s still a lottery as to whether you get caught.

I used to have a Ford Puma, and if you held the odometer button down on start-up it switched to diagnostic mode, which included a digital tacho and digital speedo. These were spot-on accurate, and I checked my speed against the digital speedo several times, and the analogue one consistently read 10% fast, so I could guarantee at an indicated 80mph I was doing a genuine 72, and 80 at indicated 90. I’ve yet to check the speed accuracy of my Octavia with the GPS HUD app on my iPhone, but going to have a go soon just to see if it follows the same 10%, which I generally assume it does.

Okay, we used the SPECS sytem a few times. This is how it actually works.

The cameras read ALL lanes.

Only 2 ‘sets’ are used. They are one after the other. For example there are something like 11 sets near Ayr but only 1 section at any one time is active. You never know which one though.

Lane changing did work a few years ago – it was due to poor programming. The software has been modified to correct this.

They do work and very well too. On one section of the M8 (during re-surfacing) one direction caught over 300 speeders. The opposite direction only 7!

So now you know.

ACPO recommend only prosecuting/fixed pen at 57 in a 50 (10% +2). Does that guidance apply to the average speed cameras?
Guidance Here

I always set CC to 55 on a 50 average speed and haven’t been fined yet. No idea what the actual speed of my Volvo is compared to indicated. I do know I’m usually moving faster than most other cars though. I’m probably only doing 50

Gary_M – Member

why take it so seriously [:roll:] from the person who spends his time driving with one eye on the speedo and the other on his satnav.

don’t you need to keep one of your eyes on the road? 😀