some speed cameras have an loop in the floor to detect weight and some have a height sensor on the top of the camera
Taken from the website at speed-trap.co.uk/FAQ/FAQ.htm
Driving a high sided vehicle. Gatso’s seem to have problems with trucks/high sided vehicles and will give an inaccurate speed reading - even if the truck is stationary! The police are meant to carefully revue all high sided vehicle NIP’s before sending them out - so if you get a NIP and you were not speeding (or even moving!), request the photographs and this evidence should easily clear you. Also if you truck has a tacho. check it and if it proves you were not speeding then send them a copy.
I have to say that people who get caught by these cameras amaze me. As 95% are painted a very vivid yellow on the back, how do you get caught by them? Surely, if you are whizzing along and you see a camera, you slow down for it■■? You aren’t telling me, you see a camera and still go past it above the relevant speed limit?? If so, you deserve to lose £60!! This isn’t about whether you were speeding or not… it’s about road observation.
Just a thought from someone who has never been done by a Gatso simply because when I AM ‘nipping’ along, even if it is something silly o’clock, I keep my eyes open for square boxes on poles on the roadside that have very bright yellow backs.
I suppose the fact we are on foreign plates helps as well teeheeheeheee no one on our firm has ever had a NIP
A556 Tabley nr Knutsford M6 J19 is one local to me.
I got a NIP for 46mph, I rang the Central Ticket Office to request photos, and spoke to a very nice Lady (too nice to be plod) who told me:
Although four lanes, no central reservation means single carriage way, 60 mph limit for cars, but the camera switchs to 40 mph when sensors in the road prior to the fixed camera detect any vehicle with close spaced axles. 
Since then I have noticed other small vehicles (e.g. cars vans 4wd’s) towing twin axle trailers getting flashed.
I put my request in writing for photos along with the signed NIP, and I got a letter by return of post informing me the NIP had been cancelled. 
Manwell wrote
“but the camera switchs to 40 mph when sensors in the road prior to the fixed camera detect any vehicle with close spaced axles.”
So why are 7.5 tonners getting tickets? Surely their axles aren’t that close together?
Just wondering 
One of the drivers at our place said something about there being cameras ‘over the road’ around the Bawtry to Gainsborough area (A631 I think it is) which are supposed to check the time it takes for vehicles to travel between one camera and the next over some distance. This is supposed to put a stop to people speeding upto one camera, then slowing down, then speeding upto the next and so. I’d not heard of this before so I don’t know how true it is, if anyone else has heard anything similar or even if it is true then please clarify!
Cheers,
Paul.
Yeti:
One of the drivers at our place said something about there being cameras ‘over the road’ around the Bawtry to Gainsborough area (A631 I think it is) which are supposed to check the time it takes for vehicles to travel between one camera and the next over some distance. This is supposed to put a stop to people speeding upto one camera, then slowing down, then speeding upto the next and so. I’d not heard of this before so I don’t know how true it is, if anyone else has heard anything similar or even if it is true then please clarify!Cheers,
Paul.
they are called specs cameras mate been around for a while now
simon
Yeti have you never been to Nottingham or Northampton?, i dont know where else they are but they are up in the sky looking down on you similar to a cctv.
I have found the best way to not get caught by the gatso is to stick to the speed limits whatever they might be until they have the presence of mind to change them 
TheBear wrote:
I have to say that people who get caught by these cameras amaze me. As 95% are painted a very vivid yellow on the back, how do you get caught by them?
I’ll have to ask that to the person who decided to overtake me last night heading into Thorney towards Peterboro on the A47 as 30mph was waaaay too slow for him even though the 30, slow down signs jump out at you and there are 2 highly visible Gatsos dotted throughout the village in each direction. Not to mention the mini roundabout, zebra crossing, traffic lights and villagers. Must only take you about two or three minutes or so to travel from one end to the other.
Ah well, you live and learn. I learned that the cameras deffo do work and he learned that putting your brakes on after the double flash is just a teensy weensy bit too late to stop you gettin’ a ticket… if there’s any film in it of course!
I am still trying to find out the technology behind these cameras, the strips in the road measure distance/time and not the weight or axle spacings(unless someone can prove otherwise, and not hearsay). Buses advertise various goods and services but do not sell them, so for a website to state that a speed camera can tell the difference between a car and a truck without factual evidence does not mean a thing, other than adding fuel to the fire. How do they differentiate between heights of vehicles when they are activated by the speed of a vehicle, distance/time?
I do not believe it is not possible I just want hard facts as all the sites I have found so far mention distance/time, no mention of height, weight, axle spacings only a simple mathematical calculation.
apophis:
I would suggest the drivers caught have been done so by manned cameras where a person can see the size and type of vehicle commiting any offence.
I wait to be proved wrong.
Have a drive through lincolnshire then 
90% of their cameras have rubber strips or wire loops built into the tarmac preceding them. If the radar & sensor matches the speed to the appropriate weight and recognises it as going at a naughty pace, it takes its photos.
I know from seeing the blighters, speaking to a friendly bike copper I meet now and again at local bike nights, and from my older brother who got nicked by one earlier this year.
The A15 is now populated nicely with dozens of lorries doing 40mph, and desperate cagers trying to squeeze past in unfeasably small gaps and time-frames. SAFETY camera? not bloody likely.
apophis:
I am still trying to find out the technology behind these cameras, the strips in the road measure distance/time and not the weight or axle spacings(unless someone can prove otherwise, and not hearsay). Buses advertise various goods and services but do not sell them, so for a website to state that a speed camera can tell the difference between a car and a truck without factual evidence does not mean a thing, other than adding fuel to the fire. How do they differentiate between heights of vehicles when they are activated by the speed of a vehicle, distance/time?
I do not believe it is not possible I just want hard facts as all the sites I have found so far mention distance/time, no mention of height, weight, axle spacings only a simple mathematical calculation.
It may say bisto on buses but no sale goes on, but equally it doesn’t say “asthma attack inducer for the afflicted” either…
It’s easy to explain how its all working though.
you approach a set of traffic lights - look down, and see the diagonal sets of black lines that meet up and head toward the kerb. They detect pressure and set priority for lights that may be red to turn green, if sensors on the other approach aren’t showing any traffic flow.
The amount of pressure exerted through them can be measured by the sensor simply by how many micrometers the cable moves from default and as such determine mass of the vehicle, should the relevant sensor package be installed. This is then set up with a speed camera and away it goes. All the same basic technology.
Of course, the instant link digital set-ups like SPECS use ANPR (automated number plate recognition) against the registered mass of the vehicle displaying that plate and should it be exceeding its designated limit, then it’ll issue a ticket. You can see these and not need to worry about different masses due to the 40 limit on the Nottingham ring road, a well as on a road you DO need to worry about them, on the road linking Junction 35A on the M1 in toward Sheffield/Wentorth business park
Some new units using GATSO style housings are real-time linked to DVLA via ANPR database but record straight to DVD any offences and so don’t need strips due to the plate recognition.
Much of this I know through taking an unhealthily keen interest in not accruing more points (I’m sat on 9 right now), and through my contact with a local bike cop, as well as my old MAC instructor (a former police grade1 examiner - still in the loop as it were).
I hope this helps in keeping noses, and licenses clean!
There are several ways to use the cameras!
An induction loop in the road is one way that can measure weight or axles.
The cameras can be set at different speed limits in different directions and the height sensors are used as well. The type of truck can be distinguished from the rear by the type of reflective markings it has.
And if that doesnt work, the registration plate can be checked against the DVLA Computer by a real live person 
if they cant tell the difference how can it say on the nip for “class of vehicle ■■” ALL speed camaras can tell the class of vehicle, its not rocket sicence to see how its done,as has been said there are pressure lines in the road also the white lines are at different lengths,these can all be used to check the length and the weight of the vehicle,as you all know the axle spread of HGVs is set by law,so a simple deduction is made 5/6 axles hitting the lines marked or the pressure loops set in the road will reset the camaras set speed ie 60 to 40mph…once the camara flashes it will reset to the set speed for the road,and we dont live in a police state ■■?
Manwell:
but the camera switchs to 40 mph when sensors in the road prior to the fixed camera detect any vehicle with close spaced axles.
Since then I have noticed other small vehicles (e.g. cars vans 4wd’s) towing twin axle trailers getting flashed.
The nice lady also told me that any driver or operator of a vehicle that was not classed as a HGV and had been flashed had only to send the plating cerificate or log book to her office and the ticket would be cancelled.
So in essence, everybody who gets flashed gets an NIP, and its up to any innocent parties to cry foul and prove they are not guilty, or else pay the fine.
if you get flashed your reg is sent to the dvla for verifiction as to the class of vehicle if it is regesterd as an goods vehicle and has exceeded the speed for its class it will be sent a nip