Safe Speed Forums

Hi there,

I was driving (admitedly I think 45mph in a 30mph zone due to my lack of attention) towards a speed camera on the otherside of the road.

Both lane had the usual white speed camera lines on the floor.

Now the speed camera flashed as I drove by.. I've heard it is impossible to get done for speeding when you are driving TOWARDS a speed camera?

Is this true?

Or have I just earnt myself 3 points!! ?

Regards.

Nick

What on earth were you doing speeding on the wrong side of the road in a 30 zone?

People have a habit of looking right when walking into a road, had you hit anyone you would now be detained at Her Majesty's finest, rightly so!

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Views expressed are personal opinions and are not necessarily shared by the Safe Speed campaign

Steady on Smeggy. I 'might have', allegedly, overtaken someone recently at 60mph in a 30mph zone. It might have been on the far side of a village with the 30mph zone extended uselessly into an entirely rural setting with no buildings and no pavements.

The bottom line is that 30 zones ain't what they used to be.

And for the OP, no, gatsos cannot gather legal evidence of the speed of an approaching vehicle.

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Paul Smith
Our scrap speed cameras petition got over 28,000 sigs
The Safe Speed campaign demands a return to intelligent road safety

I took this to mean that the camera was on the other side of the road, not the driver.

If it was a Gatso (two quick flashes , bright light) he should have nothing to worry about; but it might be worth keeping a bit nearer to the limit in future - if I may suggest that.

Best wishes all,
Dave.

Yes, I too read this as the camera, not the driver, being on the other side of the road.

If we haven't scared him off already, perhaps crE can clear this up?

Ahhh no! I am sorry, I re-read my post - no I wasnt driving on the right hand side of the road, dear god!

I am glad to hear that ... although I am curios - why did it flash?

Does it have the CAPABILITY of recording my speed?
Is it unlawful to prosecute me for it?
Does it record it but I'm too far gone for it to see my number plate?

I am sure it wasnt traffic on the otherside of the road, as it was a transit van slowing down to turn into a side street going at most 20mph... or perhaps it was random? I do occasionally see gatso's on the otherside of the dual carriage way randomly going off when no-one is there!!

Nick

Might be a reflection of radar waves off the van that reached your car and went back.

Also I seem to remember reading that dummy gatsoes flash speeders in both directions.

Ah.. reflections like that can happen?? Crazy gatso's!!

Dummy gatso's - as in gatso's that arent rigged up to catch speeders may flash in both directions?

Another question someone might know.. Can gatso's catch you if there are no lines on the floor?

That's one i've always wondered..

oops, my bad. I see what you mean now. Apologies to you CRE

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Views expressed are personal opinions and are not necessarily shared by the Safe Speed campaign

Not a problem smeggy!! I've not gone on a mad road rage frenzied killing spree just yet.

My understanding is that the 'reflections' (which may be common with laser devices) do not affect radar devices, like gatsos, which use doppler shift to calculate speed (the degree to which a known frequency is rarefied by vehicles travelling away).

I have heard that the cheap dummy flash units they put in non-camera gatsos will flash both directions, although I thought they had been discontinued due to the risks of them dazling drivers at night (fast and blind would presumably be more dangerous than a little over the limit).

There could conceivably be secondary reflections, but chances are they would be swamped by the primary due to the extra attenuation from the additional bounce. It wouldn't matter anyway because if the sensor really was wildly affected then the secondary check (photos of the car on the lines) would foil the prosecution anyway.


Let us know if you do get a NIP, it might make you famous as it would be a UK first

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Views expressed are personal opinions and are not necessarily shared by the Safe Speed campaign

Now that I think of it, I remember something in the news ages ago about a lorry being caught stationary when a car whizzed along the other way.

I don't know if there's any chance that a van could have the same effect. But I think that smeggy is right since the van wasn't stationary thus the main doppler would be from it.

Is it not the case that the gatso, being mounted at the side of the carriageway, is angled to cover the lane(s) in front of it; consequently the radar beam will encroach over the lane(s) in the opposite direction? Certainly (on single carriageways anyway) it is possible to trigger the camera from the opposite direction..........and to my knowledge not all (if any) of those are dummies

And that is not saying that my knowledge derives from any points tally - whatever my direction of travel!!

This shouldn't be the case: Mega-quick radar 101:

When the radar waves bounce off a stationary object, they return to the unit at the same frequency they were emitted, this can be calculated as zero speed. If they hit something moving away from the unit then the wave gets 'dragged out' as is bounces, and results in a reduced frequency being returned to the unit, which is used to calculate speed. If something coming towards the unit is hit, then the wave 'bunched up' as it reflects, and the returned frequency is higher. This is known as the Doppler Effect, and is easily demonstrated by noting the reduction in pitch of vehicle engines/sirens/horns as they pass a stationary observer.

Obviously its important that Gatsos measure the frequency shift accurately; its the very essence of their operation. With that in mind, one would expect that a bona-fide camera unit would be able to tell the difference between a vehicle moving towards or away from the unit. As for the dummy units, presumably its cheaper to produce logic that triggers the flash if the frequency returned varies from the datum by more than x, rather than trigger the camera/flash only when the return is rarefied to a frequency below y.

As for reflections, its a whole different ball game than laser, and certainly not so intuitive. Granted there will still be a certain degree of specular reflection, but the degree to which each vehicle's movement affects the frequency in an oblique strike, between vehicles moving in opposite directions, would tend to return the frequency towards datum (giving a slower speed reading). The oblique angle of incidence would also mean that the Doppler Effect is less pronounced than if it were perpendicular, also lowering the effective speed of each vehicle. There are also other ways in which a metal car would re-radiate radar energy. All these 'other' returns would be much weaker than the return from an almost perpendicular surface or a re-entrant structure, and so I would not expect the unit to take any notice of them.

In conclusion, a real camera must know if you are travelling towards or away, and should only flash if you're moving away.

As smeggy alludes to, if your car was to appear in two Gatso photos taken from the other side of the road, triggered by a vehicle moving in the other direction, they would still have proof of your speed, using the road markings. It is, however, our experience that the scameraships do not routinely check the photos, so would be unlikely to pick it up. If they did, I would still be unsure of the admissability of the evidence, due to it's collection being outside the type rating of the device.

Would they? Wouldn’t the measured directions be in conflict? If so then the corroboration must be invalid as the readings won’t match (must be within 10% IIRC).

Other than that I would go with all of that post

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Views expressed are personal opinions and are not necessarily shared by the Safe Speed campaign

From what I have seen in photos, the real Gatso control box has a switch to select whether to catch Receding or Approachig traffic, or both directions.
It records this on the film as a letter "R" or "A".
The dummy (jounior) unit does not have this switch.

I don't know the technical details of how radar gets inaccurate readings but I know that it does.

Every case I remember seeing on PePiPoo where someone says "I was caught by a gatso which said I was doing xx speed and I'm sure I wasn't, here's the photos" has an HGV or large van in frame. Large metal surfaces? Reflecting? Vibrating?

There's a reason these things take two photos - the radar reading on its own is not accurate enough at all.

I read a Home Office FoI response a few months ago which stated that the only speedmeter type approved for front photography is the Truvelo Combi SMc.

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Andrew.

This is known as The shutter effect. Panels vibrating with great enough frequency and amplitude will create enough doppler shift to fool the sensor.
Say the beam is aimed at a large panel, the engine vibrating it at 50Hz and that it is at resonance such that the displacement is +/-1cm (that would be a lot for that frequency). Some quick maths state the panel would have a peak speed of ..... only 7mph? That doesn't quite tie up with the claim in article



I can't figure out this one

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Views expressed are personal opinions and are not necessarily shared by the Safe Speed campaign

The detection method is to sum the send and return radar signals. The difference frequency is in the audio range and the speed is calculated from this audio frequency.

The vibrating panel does not do doppler but modulates the return signal which gives rise to a spurious audio frequency signal. The audio frequency passes through the filter and gets measured.

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Paul Smith
Our scrap speed cameras petition got over 28,000 sigs
The Safe Speed campaign demands a return to intelligent road safety

I don't now the maths but I've seen it happen. (Unless of course someone managed to do 35+MPH and stop before hitting the bus without making a loud screech. Which I don't think was possible.)

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Andrew.