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View Full Version : Ave Speed Cameras...how the feck do they work ?



methven999
12.03.2012, 08:23 PM
I've posted this before on a similar, now mothballed site, and still haven't come up with an answer.

I commute sometimes down to sunny Embra from my Highland hideaway in Perthshire and we have 40 MPH ave speed cameras on the M90 for about 4 miles leading up to the Forth Road bridge.

my question is... how do these cameras work? I know they don't work with bikes...no number plate...no shit sherlock, but what do they do? Do they read a number plate somehow, store it away and do some clever maths or take a picture of the whole car?? Or are they just magic...? What do they do ?

the first person to come back with Distance equals speed times time or similar O level maths should be removed from the forum.....? :rolleyes:

Guido
12.03.2012, 08:31 PM
Here you go...............

http://www.speedcamerasuk.com/specs.htm

golddesk
12.03.2012, 08:33 PM
Just magic, they not even there, just make you think you saw them and drive like a d*** for 4 miles

Andrew H
12.03.2012, 08:34 PM
Unfortunately the o level maths is the basis for any speed and distance calculation - the distance is a known constant so the maths is pretty straightforward. The camera's themselves if they are 'specs' are high end number plate recognition cameras - they just track your plate through a known distance and work out the speed - seemples.

The thing about changing lanes DOES NOT confuse them anymore and yes they can ticket you between any 2 points, that could be camera 1 & 2 - or camera 2 and 5 doesnt matter - clever software works it out.

Sensible thing to do is just slow down and chill out - unless your on a bike and then [email protected]%k them - just watch out for other cameras though the highways agency ones could always be tasked to watch out for anyone being silly

miloVanMultistrada
12.03.2012, 08:38 PM
Each camera is constantly scanning (recording images many times a second) one or two lanes and as soon as it sees something that looks like a numberplate, it attempts to read the digits - it's like way a barcode scanner is constantly scanning until it finds something that looks like a barcode.

When they read a numberplate, they record the exact time. Because the camera locations are fixed, the distance between them is known, and the data about what time each numberplate passed each camera is shared between the cameras, it's easy enough to work out your average speed, between any two cameras in the "chain", or across the whole lot.

They use infrared, so aren't affected by darkness:

http://en.wikipedia.org/wiki/SPECS_(speed_camera)

Because most of the cameras read the front numberplate, they don't work on bikes, but there are a few down south that read the rear plate rather than the front - so always check the way the camera lenses are pointed before you open the thottle - I've also seen traffic police sitting on bridges, presumably watching for someone obviously speeding (stand out like a sore thumb) on the M90, so be warned.

RobbieT
12.03.2012, 08:40 PM
Distance equals speed times

more like speed = distance/time???

yeah yeah I know ban me know but thats just it.

Multiple cameras multiple sites at known distances apart = clock you moving from A-B-C-D (wherever they may be) and wey-hey the computer gets your average speed.

Simples?

methven999
12.03.2012, 08:43 PM
more like speed = distance/time???

yeah yeah I know ban me know but thats just it.

Multiple cameras multiple sites at known distances apart = clock you moving from A-B-C-D (wherever they may be) and wey-hey the computer gets your average speed.

Simples?

You're Barred ! Moderator....reveal yourself..

Andrew H
12.03.2012, 08:44 PM
As a piece of friendly advice from a traffic cop friend of a friend if you know what i mean "don't be the fastest car on the road" if your obviously speeding as Miles says above your asking for it, that's just like painting a target on your car and if your "under 80 your fine" (in a 70 of course) - I once heard about a 10% +/- 2mph rule for calibration of speedo's but not sure how true that is.

RobbieT
12.03.2012, 08:44 PM
whats even more puzzling how this thread has got 0 views but 5 replies?
7902
eh???

time travel????

Andrew H
12.03.2012, 08:45 PM
The Doctor is on the forum

miloVanMultistrada
12.03.2012, 08:47 PM
As a piece of friendly advice from a traffic cop friend of a friend if you know what i mean "don't be the fastest car on the road" if your obviously speeding as Miles says above your asking for it, that's just like painting a target on your car and if your "under 80 your fine" (in a 70 of course) - I once heard about a 10% +/- 2mph rule for calibration of speedo's but not sure how true that is.

I think the 10% +/- 2mph is official ACPO "advice" that most UK forces follow. It's not the law though, so it you are being a bit of tit and/or get lippy with the officer who stops you, you could end up being done for less...

Just do what I do, fit some plates with Andrew's number on and never worry about speeding again. ;)

RobbieT
12.03.2012, 08:48 PM
I once heard about a 10% +/- 2mph rule for calibration of speedo's but not sure how true that is.

Same...only I heard it was 10% +/- 3mph

miloVanMultistrada
12.03.2012, 08:49 PM
whats even more puzzling how this thread has got 0 views but 5 replies?
7902
eh???

time travel????

I could tell you, but then I'd have to kill you.

Oh, go on then:

It's cheaper than Horlicks and will get you off to sleep quicker:

http://en.wikipedia.org/wiki/Database_caching

RobbieT
12.03.2012, 08:50 PM
You're Barred ! Moderator....reveal yourself..

:dunno:

:whistle::whistle::whistle::whistle::whistle::whistle:

RobbieT
12.03.2012, 08:51 PM
I could tell you, but then I'd have to kill you.

Oh, go on then:

It's cheaper than Horlicks and will get you off to sleep quicker:

http://en.wikipedia.org/wiki/Database_caching

seriously???

do you want me to start posting articles about global warming again???

Andrew H
12.03.2012, 08:55 PM
Haha - Who says there are no interesting threads on DuN :dunno:

RobbieT
12.03.2012, 09:01 PM
Haha - Who says there are no interesting threads on DuN :dunno:

bet you're just gald I ain't talking about them pixies and fireflies again eh?????

RobbieT
12.03.2012, 09:04 PM
The Doctor is on the forum

strange combination....

http://www.bbc.co.uk/doctorwho/medialibrary/s2/images/1024/s2_10_wal_09.jpg?size=1024&promo=/doctorwho/medialibrary/s2/images/main-promo/s2_10_wal_09.jpg&purpose=Computer%20wallpaper&summary=Bit%20of%20a%20legend.&info=&tag_file_id=s2_10_wal_20 http://good-wallpapers.com/pictures/2760/46%20The%20Doctor.jpg

Andrew H
12.03.2012, 09:09 PM
I knew you wouldn't be able to resist that one

:lol2:

Anteater
12.03.2012, 09:55 PM
Every time I go through the avcams in the car I just set the cruise control and chill. They dont bother me or wind me up anymore, driving by buttons, sounds awful but works.

lidlika
12.03.2012, 10:27 PM
forgive me for stating "the obvious" but if u know they are there(cameras) just obey the speed limit........allow extra time,calm yourself down......go fast when you know you can!

Derek
13.03.2012, 08:46 AM
I once heard about a 10% +/- 2mph rule for calibration of speedo's but not sure how true that is.


Same...only I heard it was 10% +/- 3mph


I think the 10% +/- 2mph is official ACPO "advice" that most UK forces follow. It's not the law though, so it you are being a bit of tit and/or get lippy with the officer who stops you, you could end up being done for less...

And for the record re. calibration of speedos. They are allowed to read up to +10% but -0%, i.e they must not read slow. Consequently most speedos are set by the manufacturers to read about 5% fast. So if it says 70mph you're probably only doing about 66mph.

mbg
13.03.2012, 11:31 AM
What happens if you fit larger size wheels to a vehicle? How does that affect the speedo readings?

Derek
13.03.2012, 12:12 PM
Larger wheels means less revolutions of the wheel per mile, so the speedo will read slow which could get you in a dodgy situation with speed cameras and also means your speedo is illegal.

miloVanMultistrada
13.03.2012, 01:45 PM
What happens if you fit larger size wheels to a vehicle? How does that affect the speedo readings?

The thing to watch for Mary is not the wheel size, but the "rolling radius", this is the wheel + the tyre.

When you are fitting bigger wheels (say going from a 17" to an 18") on a car, you typically fit a lower profile tyre so the radius of the wheel and tyre is the same as the original.

If you don't do this on a modern car with traction control, they'll throw a wobbler. Fitting bigger wheels to a bike often ruins the handling anyway, and any fitted with TC / ABS, etc will probably do the same unless wheel size + tyre is the same radius as the outgoing combo.

Derek
13.03.2012, 01:51 PM
If you don't do this on a modern car with traction control, they'll throw a wobbler. Fitting bigger wheels to a bike often ruins the handling anyway, and any fitted with TC / ABS, etc will probably do the same unless wheel size + tyre is the same radius as the outgoing combo.
I don't think that's quite true Miles. If they have the same size back and front there is generally no problem but if there is a difference between the tyre sizes on the front and back they get shirty about it.

RobbieT
13.03.2012, 05:10 PM
What happens if you fit larger size wheels to a vehicle? How does that affect the speedo readings?

I heard a story once about a taxi firm that fitted smaller wheels to their cabs so that the distance clocked was more than actually travelled.
not sure if it was true though....

PhilLew
13.03.2012, 07:21 PM
to return to the topic...:lol2:

does anyone have first hand experience;) ...or know anyone who has actually been charged with speeding on the evidence of avarage speed, speed cameras?

gordj65
13.03.2012, 07:21 PM
your all missing the important bit. why do some drivers slam on the brakes when they see the cameras, boot it down the road to the next cameras, where they brake like a loony then keep on doing the same for each set?

PhilLew
13.03.2012, 07:32 PM
your all missing the important bit. why do some drivers slam on the brakes when they see the cameras, boot it down the road to the next cameras, where they brake like a loony then keep on doing the same for each set?

Because a lot of people don't know how they work.....




I commute sometimes down to sunny Embra from my Highland hideaway in Perthshire and we have 40 MPH ave speed cameras on the M90 for about 4 miles leading up to the Forth Road bridge.

my question is... how do these cameras work?


I rest my case! :D:D:D

.

RobbieT
13.03.2012, 07:37 PM
Because a lot of people don't know how they work.....

I do......

lots of tiny little pixies live in the cameras and they all sit and guess your speed then phone up the polis to send you a ticket

Derek
13.03.2012, 07:50 PM
I do......

lots of tiny little pixies live in the cameras and they all sit and guess your speed then phone up the polis to send you a ticket
Have you been reading Terry Pratchett again :D

239desmo
13.03.2012, 08:08 PM
I do......

lots of tiny little pixies live in the cameras and they all sit and guess your speed then phone up the polis to send you a ticket

:D

Should you not give that stuff a miss on a school night? ;) :)

ShedBob
13.03.2012, 09:13 PM
Easy to work out how they work on a motorway but what about the A77 down towards Ayr & beyond. There are roundabouts & traffic lights & all sorts on that bit. 3 different speed limits too. I can't believe they can compensate for all that. I reckon the computer just has a "bogey time" & if you beat it you're done.
If they're switched on past Prestwick at all of course................

methven999
13.03.2012, 10:53 PM
From a simple 'how do they work?' this thread has produced the 10% +/- rule, the calibration of speedos (no not the budgie smugglers), the rolling radius of oversized tyres, a picture of David Tennent (Who ?), tiny pixies and fire flies and of course - first reply - the answer I was looking for.....

Where else, other than a secure ward, would one find such a random set of replies to what could have been considered - a reasonably straight forward question.

Thank you one and all..

Andrew H
13.03.2012, 11:04 PM
My pleasure - hope you enjoyed as much as we did

RobbieT
14.03.2012, 05:14 PM
From a simple 'how do they work?' this thread has produced the 10% +/- rule, the calibration of speedos (no not the budgie smugglers), the rolling radius of oversized tyres, a picture of David Tennent (Who ?), tiny pixies and fire flies and of course - first reply - the answer I was looking for.....

Where else, other than a secure ward, would one find such a random set of replies to what could have been considered - a reasonably straight forward question.

Thank you one and all..


No problemo, was a pleasure, although are you sure they were random???


:D
Should you not give that stuff a miss on a school night? ;) :)

A school night??? oh sh1t.....oops


Have you been reading Terry Pratchett again :D

what do you mean again? who is this terry pratchet??????

Derek
14.03.2012, 06:39 PM
Have you been reading Terry Pratchett again :D


what do you mean again? who is this terry pratchet??????
For your enlightenment Robbie http://en.wikipedia.org/wiki/Terry_Pratchett
At first glance his books may seem simple fantasy stuff with lots of wizzards ;) and witches but most of them are very perceptive parodies of life, magic and folklore.

He also comes up with amazingly funny alternative technology, like cameras that have an imp inside them that paints the picture and grumps if you take them in bad light.

lots of tiny little pixies live in the cameras and they all sit and guess your speed then phone up the polis to send you a ticketCould have come straight out of a Terry Pratchett book. :D
Unfortunately he is now afflicted with Alzheimer's but is still writing. It will be a sad day when he has to stop.

And that is another off-topic subject we've managed to fit in this thread :D

gordj65
14.03.2012, 06:42 PM
I do......

lots of tiny little pixies live in the cameras and they all sit and guess your speed then phone up the polis to send you a ticket

Dont be so fecking stupid. Everybody knows pixies and elfs are helpfull creatures. its nasty goblins that live in evil speed cameras!!!!

RobbieT
14.03.2012, 07:12 PM
For your enlightenment Robbie http://en.wikipedia.org/wiki/Terry_Pratchett
At first glance his books may seem simple fantasy stuff with lots of wizzards ;) and witches but most of them are very perceptive parodies of life, magic and folklore.

He also comes up with amazingly funny alternative technology, like cameras that have an imp inside them that paints the picture and grumps if you take them in bad light.
Could have come straight out of a Terry Pratchett book. :D
Unfortunately he is now afflicted with Alzheimer's but is still writing. It will be a sad day when he has to stop.


Thanks.
Without looking at the thread the name rings a bell and something to do with hitchhicking or something through the galaxy???
I have heard people talk about it but avoided anything. Might give it a try...
Funny coz my reference was actually to Dara O'Brien and I just took it from there and expanded it a bit...maybe thats were he got it from???
http://www.youtube.com/watch?v=LbY7GODI5Dw

239desmo
14.03.2012, 07:20 PM
or something through the galaxy???

Munching?

Can you still buy Galaxy chocolate? :confused:



How much further off topic can this go??

Derek
14.03.2012, 07:25 PM
You're thinking of the "Hitchhiker's Guide to the Galaxy". Originally a radio comedy broadcast on BBC Radio 4 in 1978, written by Douglas Adams, alas now deceased. There was subsequently a "trilogy" of five books published between 1979 and 1992. I like Terry Pratchett better though. :)

Cateran
14.03.2012, 07:26 PM
Munching?

Can you still buy Galaxy chocolate? :confused:



How much further off topic can this go??

They're called 'Munchies' and it's no' a 'Topic' it's a 'Marathon' :p

239desmo
14.03.2012, 07:28 PM
You're thinking of the "Hitchhiker's Guide to the Galaxy". Originally a radio comedy broadcast on BBC Radio 4 in 1978, written by Douglas Adams, alas now deceased. There was subsequently a "trilogy" of five books published between 1979 and 1992. I like Terry Pratchett better though. :)

"John" the newsreader with Terry Wogan for years (also as featured in Janet & John Stories with TW) was the voice of the programme I'm told.

239desmo
14.03.2012, 07:29 PM
it's a 'Marathon' :p

So is this thread! :p :lol2:

PhilLew
14.03.2012, 09:01 PM
"John" the newsreader with Terry Wogan for years (also as featured in Janet & John Stories with TW) was the voice of the programme I'm told.

John 'Boggy' Marsh :D

Andrew H
14.03.2012, 09:29 PM
Read my first Pratchet book when I was about 16 'The Colour Of Magic' bought and read them all since, fantastic author, very dark social comments, hilarious grown up humour wrapped up in a disguise of fantasy writing, try it!

So back on topic

"What's got a hazelnut in every bite?"

molenz
15.03.2012, 12:56 PM
is it something to do with squirrels :)

239desmo
15.03.2012, 01:12 PM
is it something to do with squirrels :)

You're thinking of the old joke "Why do squirrels swim on their backs?" ;) :)

Trish
15.03.2012, 03:08 PM
what do you mean again? who is this terry pratchet??????[/QUOTE]


:eek:
you don't know who Terry Pratchett is shame on you .....................im off to get Granny Weatherwax to sort you oot ;) or would I be better with Rob Anybody Andrew?

gordj65
16.03.2012, 07:50 PM
Munching?

Can you still buy Galaxy chocolate? :confused:

How much further off topic can this go??

Galaxy chocolate, the best brittish chocolate you can buy, remember Galaxy counters. beats that cadbury buttons rubbish hands down everyday