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surely the laser is just a carrier for the signal?
Only if it is being fired by a postman.
Rachel
The bit I don't get is what constitutes a separate offence/instance of speeding. If they set up 4 of the non-average cameras along a short stretch of road presumably you could lose your license straight away if you got done by all of them. But if they were average speed cameras it would only be one offence.
On a similar note, I've often wondered how you can be prosecuted for exceeding 50 miles per hour, when you haven't travelled 50 miles or travelled for an hour ? Surely a speed limit of metres per second would be more appropriate
Because you are travelling at a RATE of 50mph. No judge or jury would side with your argument.
SImilar to the fact that ALL laser devices have not been type approved for use on motorcycles yet they are....
The smaller front area and lack of sufficiently large reflective areas causes real issues for a correct reading.
Causes issues on my garage door opener too - sets it off and makes all sorts of noises... 
If you spread jam on your bonnet it will absorb the laser beam, marmalade may also work.
IMO, the best thing about the ambiguity (as demonstrated by all these threads) of average speed cameras through roadworks is that because very few drivers are absolutely sure how they work, if they're switched on, etc, that the great majority slow down to the indicated limit and traffic flows at much higher densities than when they used gatsos.
My brother has just been done on the one on the M5 jcts 6-4. FYI.
Jam doesn't work due to the build up of wasps.
it dosent work by Doppler, it's timed (so an average again for the pedants). Funny post though, might have to spread thatsurely the laser is just a carrier for the signal?
Heisenberg got stopped by the police, who asked him how fast he had been going.
"No.", he said, "But I know exactly where I was".
They don’t tell you these things, do they???
Can you jam* the signal
* not that kind of jam
Can you jam* the signal* not that kind of jam
<whispers> - when was the last time you saw a pink car getting a speeding ticket?
I didn’t tell you this…
Rachel
And this is before we start the discussion about in fact being stationary and allowing the world to rotate beneath us at several thousand mph
Now, the trouble is; if you are driving a blue car, blue light is a higher frequency than red light and it has the effect of changing the reflected laser light that little bit more than a red car does and means you can be measured doing a higher speed than you actually are.That’s why they have to have some leeway in the system.
They don’t tell you these things, do they???
Because it's wrong.
A laser beam is an exact single frequency of light, and it's a single wave rather than the confused mess you get from a filament lamp that's why it's used, you can count the number of waves as a very accurate 'clock' between the light being emitted and returned. 2x pulses give your 2x distances and a a time and therefore speed.
They're not dopler effect. That only works (at car/plane speeds) with Radar.
As the laser is a single frequency of light it won't be absorbed by the car's paint unless it happens to be exactly the right color for the laser, in which case it'll absorb it completely, a bit like radar absorbing paint, to the radar/laser it would just appear 'black', it won't change the frequency.
Even cameras with lines on the road are measuring and instantaneous (to all intents) speed, they measure it as you pass the camera, then the 2 flashes are just photographic evidence, the speed recorded is the one measured by the laser/radar.
Hilariously, they make naff all sense on the M3 when you spend 30 minutes crawling at 15 mph or less. I'm not sure what the maths is but I wonder what speed you could drive at to average 50mph by the time you get to the M25.
Juamann absorber...its the only way to maybe possibly be sure
Though paradoxically a delorean may also negate receiving a ticket
or stealth
have you noticed how they generally aren't being removed once the roadworks have finished.
how long before a national network of speed averaging cameras...
thisisnotaspoon - Because it's wrong.
You mean everything I said was wrong? Oh no - how could that be? I’m so embarrassed…
🙄
Rachel
We've got some road widening controlled by some average speed cameras.
The poor Merc driver beside me yesterday got his calculations badly wrong when he forgot he wasn't at the last set of cameras, but the second last when he gunned it. I don't think slamming on the brakes right beside the last set was going to make much difference to his rather large average speed...
The bit I don't get is what constitutes a separate offence/instance of speeding. If they set up 4 of the non-average cameras along a short stretch of road presumably you could lose your license straight away if you got done by all of them. But if they were average speed cameras it would only be one offence.
To get done more than once, I think there has to be some evidence that you slowed down to below the limit between each instance of getting caught over it, otherwise the argument is that it is one continuous offence. Things such as going in the opposite direction, stopping at services, going through a town, that sort of thing. I can't recall any case law but I think that's right.
I heard the following last week, which I find hard to believe. The story went 'of the avg speed cameras on the A9, only three pairs are working at any time. You can get a SatNav which tells you whether you're at one, and you can ignore the others.'
I'm guessing they are only cameras, maybe with IR lighting at night for clarity, logging number plates* and it sounds like BS. Can anyone confirm?
They seem to work, lots of cars at the same speed and well spread out. It remains obvious that lots of drivers don't know how to overtake except on the dual sections.
*Didn't the Gov buy the technology from TrafficMaster yonks ago?
The poor Merc driver beside me yesterday got his calculations badly wrong when he forgot he wasn't at the last set of cameras, but the second last when he gunned it. I don't think slamming on the brakes right beside the last set was going to make much difference to his rather large average speed...
depends how many cameras! if he went through 9 cameras at 50mph, and then one final stretch at 80mph, he'd still only have averaged 53mph across the whole thing*.
if there were only 4 sets of cameras though, he's probably jiggered 😉
*if the cameras were equally spaced etc etc
OP, we had a thread before and yes STWers have been done
Foreign plates anyone ?
gosh, quite a response (couldn't find the previous thread)
Loving the physics chat, do let us know when you have revolved the idea of an instantaneous speed
IMO, the best thing about the ambiguity (as demonstrated by all these threads) of average speed cameras through roadworks is that because very few drivers are absolutely sure how they work, if they're switched on, etc, that the great majority slow down to the indicated limit and traffic flows at much higher densities than when they used gatsos.
I agree, they do work and that's because we are all scared. There is no flash, so no feedback, so we err on the side of caution. I can see some people here have been done...but the question remains: how fast could you go through them? If you took the racing line (which is legal) and they give you a bit of speedo error could you go through at 60 in a 50 I wonders?
I was told years ago by people living there that this is one of the reasons why motorists in France had a habit of picnicking by the side of the road. If you stop for half an hour on the road you can then drive as fast as you want as you'll never make it back up to the average speed.Hilariously, they make naff all sense on the M3 when you spend 30 minutes crawling at 15 mph or less. I'm not sure what the maths is but I wonder what speed you could drive at to average 50mph by the time you get to the M25.
how fast could you go through them?
I always put the cruise at 55mph, and I always get overtaken.
if he went through 9 cameras at 50mph, and then one final stretch at 80mph, he'd still only have averaged 53mph across the whole thing*.
You do realise that's not how it works, right? It's an average between two successive cameras, not across all of them.
how fast could you go through them? If you took the racing line (which is legal) and they give you a bit of speedo error could you go through at 60 in a 50 I wonders?
You can go through a SPECS camera as fast as you like. They don't measure the speed of passing traffic, they just know how long it's been since you passed through the last one.
You do realise that's not how it works, right? It's an average between two successive cameras, not across all of them.
😳
nope, didn't know. although now i come to think of it, there'd be no point in having any interim cameras if it was just treated as one single block...
You'd still need repeaters next to entry / exit lanes, but yes.
[quote=Cougar said]
You do realise that's not how it works, right? It's an average between two successive cameras, not across all of them.
Not necessarily successive cameras! The system operates with camera pairs, entry and exit which might be grouped with overlap.
The system design is such that the cameras can only operate in pairs, each pair can only monitor one lane of a multi lane road.[7] It is therefore, at least in theory, possible to escape detection by changing lanes between the entry and exit cameras since the exit will be captured by the exit camera of a different pair.[7] However, in reality, the authorities are able to easily defeat this tactic by arranging for two or more sets of pairs of cameras to have overlapping areas of monitoring.[7] Since the driver cannot tell which cameras are 'entry' and which are 'exit', as they look identical, they cannot tell where to change lane to escape detection.
I didn't know that, but it makes sense (I did know about the lane thing though).
Since the driver cannot tell which cameras are 'entry' and which are 'exit', as they look identical, they cannot tell where to change lane to escape detection.
what about the hard shoulder. if i swerve violently onto the hard shoulder every time i see an average speed camera array, will they pick me up then?
[quote=theotherjonv said]will they pick me up then?
I imagine someone will Jon 😉
I was told years ago by people living there that this is one of the reasons why motorists in France had a habit of picnicking by the side of the road. If you stop for half an hour on the road you can then drive as fast as you want as you'll never make it back up to the average speed.
They don't have average speed cameras on French roads, just hundreds of the standard radar ones. The rumour of timing on the peage is I think nonsense as the toll booths are so far apart apart - often more than 200km
On a quantum level could you argue that you were both there and not there at the same time, as a defence to your speeding?
I wasn't caught, having been zapped a couple of months ago by a roadside camera and discovered a newfound respect for the law your honour, but there's a 500 m stretch of the A90 at laurencekirk that has had a 50 zone put in to protect the really awkward offset junction there - there were a couple of deaths IIRC that prompted it, so well sited IMO.
anyways, last time I was up there, having hit the 50 zone which is 400m short of the camera and reduced the cruise to 52 or thereabouts, i spotted a mobile van sitting right under the fixed speed camera at the junction - obviously looking to zap the idiots doing 70+ in the 50 zone, just before surfing down for the short stretch covered by the camera.
sneaky
Yes, I think that would work. The quantum thing.
I have used a Laser speed camera.
One by a manufaturer approved for supply to UK Police forces.
Very , Very simple to use . Aim at the front of the car. Pull trigger . Laser beam goes very , very fast toward car for literally a millisecond.
Reciever in camera 'sees' the 'bounce' of the light reflection. Usually the fromt number plate as its a highly reflective flat surface of a given size ( there is the reason why they are BS spec). If it isnt the number plate the reflective rear of the light clusters are very reflctive too, then the paint ( I have got readings from flat matt wrapped cars , just a tiny bit slower )
Laser then pings car again a few milleseconds later , and times the response . The difference is calculated into MPH.
Total acquisition time is very, very fast. Less than 2 seconds , sometimes less than 1.
This is as I uderstand it. I am not a policeman or physicist
If they set up 4 of the non-average cameras along a short stretch of road
That would be the Elland bypass.
That's basically it STM
They do throw false readings on certain vehicles.
Certain OEM and aftermarket door opening systems cause them to flag an error too as they often use the 902nm band.
Obviously I have no idea what ones they could be....
Years ago the average speed cameras used to only cover a particular lane so you could go at any speed, swop lanes at each camera and not get caught.
So the urban myth went anyway.
They changed the software a few years ago along with the type approval to remove that loophole.