:Hello chaps
I have just loged on to trucknet for the fist time in the hope that someone out there might be able to help me .
Can anybody tell me if speed cameras can tell the differance between cars and trucks as i have just been caught on one on the A5 south from Atherstone. I was doing 48mph in as far as i know a nat speed limit single track road. the ticket said that i was going over the limit for that class of vehecle i dont dispute that what i do dispute is that if i was in a nat speed limit zone why did the camera flash me at 48mph if anyone can help plese get back to me ASAP thak,s Ronnie.
Speed cameras can tell the difference between large and small vehicles.
They do this by using an induction loop which is buried in the road. Where this has been retro-fitted, you can see it, situated around 30 feet forward of the camera. Look for a grid of freshly laid tar, similar to the type which is situated at traffic lights, which causes them to change as a vehicle approaches.
Hope this helps,
Vince
Ronnie the speed limit for a truck on a single track road is 40 mph providing of course its over 7.5 ton. 
Yes they can and they are using the fact that most HGV drivers travel nearer 50mph on single carriageway roads as a way of getting more convictions.
Tell me about it. I have been driving rigids for years and have never been flashed by a camera doing 50 on the A1 (single carriageway bit) until a few weeks ago when - in an artic - I got flashed!!! Dagnammit!! 
It`s worth pointing out here that the police can only bring a successful prosecution in a camera-based case if they can provide a photograph from which the motor vehicle can clearly be identified.
One problem which the police always face when attempting to prosecute the driver of an articulated lorry is that their photograph will not clearly show a motor vehicle, since this is always obscured by the semi-trailer, which is not, in itsself a motor vehicle, regardless of any temporary number-plate it may be displaying. Another driver may be falsely using your number plate, for example.
So you should always ask for a copy of the photograph before proceeding with the defence of a speeding case.
In my experience, if this flaw in the supplied photograph is pointed out to the police, then they will drop the case.
However, it would be morally incorrect for any truck driver to defend a speeding charge using this defence, if it was untrue.
Hope this helps.
Vince
I believe you can only ask for the photo if you are going to take the case to court. The risk of deciding to do this is a bigger fine and more points of still found guilty.
However I think Vince has a point the number plate on a trailer is mobile therefore you can try and claim that it might not be your unit on the front. The only thing is that Gatso photos from the rear, but Tuvelo take a picture from the front.
I was thinking of asking the same question myself recently. 5 weeks ago I was heading west across the A30 at Goss Moor at 6.40 in the morning. Just me and one car on the road. He flew past me, spotted the camera, braked and went through, speeding up when he got past. I was thinking “nearly got you mate” as I passed the camera when the early morning was lit up by two bright flashes. I looked at my speedo and read 50MPH. As this was a Nat speed limit road and he definately went through faster than me I was a bit peeved. From the other answers I can now see that this camera can tell the difference in size. I was in a 7 and half tonner but with a ten ton drag attached so I did not question the £60 ticket when it dropped on the mat. However, reading the replies to this post makes me think it might have been worth questioning the ticket. Too late now, 30 years driving (25 with HGV), and my first points. Spoilt my whole week.
muckles:
I believe you can only ask for the photo if you are going to take the case to court. .
No, the police will provide you with a copy of the photograph if you ask for one, and this will not affect their decision with regards to prosecution.
If the police cannot provide you with a photograph from which the motor vehicle can be identified, then you will receive an email like this.
I have made enquiries and can confirm that the case was discontinued
following investigations. I apologise that the supervisor who dealt
with the matter omitted to send confirmation of this to you, I will be
dealing with the supervisor over this issue. Please accept my apologies
for any inconvenience caused, the matter is closed so will not affect
any insurance policy.
Bryan Pritchard
Hope this helps,
Vince