Safe Speed Forums

Hi All,

I was recenly nabbed in a temporary 30 limit at 42 (allegedly). On the photographic evidence as viewed over the web (and I've not requested any paperwok or video evidence at this stage) it shows a speed of 42mph , then states nr for new recording but the image is frame 01 of the recording.
The time on the data panel in the picture shows 15:00:28 for the time in hours minutes and seconds but the info posted beside it in the explanatory notes shows 15:00:27 so there's a one second discrepancy (they have the rest of the info correct). Assuming the LTI 20/20 shoots standard PAL video that's 25 frames per second so there's either another second of video and another recording that I'm not being told about or they've got the time wrong.
It says in the notes on the 20/20 that it requires 300 milliseconds to complete its process but frame one of a PAL video is only 40 milliseconds
Another interesting thing... the laser system is said to have a beam divergence of 1200mm at 400m range and this is without atmospheric considerations such as relative humidity and airborne pollution, both of which are known factors affecting beam divergence.
From the above it seems reasonable to assume a minimum divergence of 600mm at 200m range, which is exactly the range at which I was shot. There is not 600mm of my car visible in the photograph, only the very end of the bumper and the (very) close side of the car ahead and another behind.
They give a +/- 1mph tolerance on the speed calculation on the laser and a similarly low tolerance on the ranging but no tolerance is offered on the aiming...
The second picture is shot at much closer range, seventeen seconds later and is frame 13 of the recording but the speed has been omitted.
I am an engineer and have used laser light for cutting steel, wood and plastic for fifteen years. I have also appeared as an expert witness for the prosecution on the subject of acoustic imaging. Not quite same as laser ranging in air but sound propagation in water follows virtually identical rules and I smell a very big rat with the above. Anyone want to comment?

Bill

Mmm, I have also noticed that even if the laser devices are 100% accurate, they are often used by a human in a van with suspension next to the side of the road.

I believe there have been people successful in proving the device can give invalid readings in some circumstances.

_________________
Andrew.