speed camera on dual carriageway

[regulators]

if there is a speed camera on a dual carriageway or motorway does it check speed on more than one lane, and how do they tell the difference on a single carriageway between a car that can do 60 mph and a hgv that can only do 40mph

[Hippy]

Cameras are able to see three lanes if set up correctly. It's just a function of the distance from the camera to the litlle painted spots on the road and the angle of the camera.

It may not be an universal truth, but on A1 up to Scotland through Northumberland & Berwickshire the cameras are linked to pressure sensors in the road (like the ones that count traffic and trigger traffic lights) and the weight of the approaching vehicle alters the speed tolerance of the camera. Even if it gets it wrong and a car or heavy van (not HGV) gets flashed, the photograph will show this up and be discarded.

The biggest mystery to me is how it can tell the difference between HGVs and PCVs that are both large heavy vehicles but are subject to different speed restrictions. Without doubt, the clever cameras are able to do this!

Another "by the way" is that in Brighton I saw central reservation cameras that, as we know can only "see" in one direction, but are painted to look like the blank side is the business end! Sneeeeaky!

[Joanne-G]

There are several types of speed camera, the ones that have the strips painted on the road which show the speed by two pictures (hence the double flash) But these only work taking your picture from behind, you can drive towards them at any speed, personal experience and no tickets posted to me!, and trigger the box to flash but as one is past the cam when the 2nd flash fires your speed cannot be poven, but the nice peeps who operate thes cams have a nice pic of your car and face..(the invasion of privacy act rears it's head) And the nasty ones that are set up between two points that take a first at cam 1 and a second at cam 2 and the time it takes between both proves your average speed, the third (the REALLY NASTY) is using lazer and can record your speed without a flash and you can be going towards and away from it (now THAT is nasty!)

[joules99]

I dont think they do distinguish between cars and hgv, but it is a legal requirment for hgv in the uk and most of europe to be fitted with speed restrictors anyway.

[Oneeyedvic]

They can tell the difference between hgv and cars as they will flash a hgv going at 50 on a single carriage way road (where national speed restrictions apply) where as they won't flash a car doing 50 on the smae road.

I'm sorry but I don't know how it works!

[Tim Baxter]

Arguing from a privileged position of ignorance, I don't think that most speed cameras can generally tell the difference, they just flash (twice) and have done.  I think the distiction is drawn by the people who interpret the photo's later.

[Kos]

And if 2 cars go through the speedtrap together on a dual-carriageway, how do they know if it is one or both that is breaking the speed limit? Or even on a single carriageay fro that matter,a s both may be breaking the limit

[UsAndStuff]

in reply to joules99
Although LGV's are restricted to 56mph, the speed limits that apply to roads are as follows.
Single Carriageway roads are 40mph
Dual carriageway roads are 50mph
Motorways are 56mph
so they are still capable of going 16mph over the speed limit (and the majority of them do!)

[UsAndStuff]

Oops, I meant 60mph on Motorways!

[Del68]

Right! here we go. Most of the newer cameras are linked to a central computer which in turn is linked to either the PNC (Police National Computer System) or throught to DVLA. This enables automatic tickets to be printed and sent to the registered owners address. It also says what the vehicle is, i.e. car, lorry van, ambulance etc. The software won't normally allow a ticket to be issued to a car travelling at 65-70 mph on a M/way but would issued to say a HGV . The older film type cameras need to be "read". This can be done by a person or as is becoming the norm, scanned through computers using similar technology as Optical Character Recognition as in home scanners that allow you to scan directly into a word document. The computer then "decides" whether or not to issue the ticket based on it's programming. These type of cameras are being replaced by the newer digital direct linked ones. Phew! How do I know? I work for a company that makes the camera's!!!! Don't all hate me at once, need to make a living somehow!