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Old 20th Jan 2019, 09:41
  #86 (permalink)  
Join Date: Oct 2004
Location: mids
Age: 53
Posts: 0
Strange that our local traffic police say different. I'll have to tell them tesco says they are wrong. Another of your many talents.
The traffic cops are not that hard to confuse, the engineers they use only slightly harder. I used to do the analysis for my boss for his professional witness stuff. He used to run rings round them.

What is true to say is its not cost effective these days to do it and its better when the person is only going to get a smack on the wrists and some points to not waste the cash.

If the person is doing 100 in a 50 then the results are pretty straight forward as its a Vsqr energy function . But when it comes to proving that some one was doing 40 in a 30 the measurement errors become more than the difference your trying to prove and that goes for normal brakes never mind ABS.

If its none fatal its a waste of cash to go through the process. Better to just tell everyone that they can't do it, below 40mph its debatable if your going to get a result which you can defend.

Last one I did was a lorry door swinging open while it was driving down a road which was a big dip between two rises at the bottom the chassis flexed enough due to it having a forklift fitted to the back for the door to come out of its rails and the deceleration as it started up the hill swung it outwards. This led to a pedestrian getting decapitated. I did the work to prove that the chassis could flex enough for the door to come out due to having a lump mass off the back while doing legal speeds. Which got the driver off the hook legally but not mentally. Then it became a case between the coachworks company that built the thing and Volvo the maker of the lorry. Think the coachworks company got done in the end, we were out of it after the driver was off the hook.

Another one was a Porsche went up the back of a fully loaded C+E with drill pipe on. The lorry driver was getting done for leaving the scene of an accident. The speed of the Porsche we calculated at 110mph when braking started and 85 mph when he hit the back end of the trailer which was moving at 50. Net effect of the hit on the lorry was the same as missing a gear and clipping a cog or hitting a pot hole. So within possibility that the driver never noticed. 2 dead in the Porsche due to it lifting the trailer and going under it then the trailer getting dragged off. That case is the one I learned about the capability's of measuring braking of cars with ABS, the driver had bent the steering wheel while pressing on the brake which actually required a super human level of strength but the forensic pathologist said was not unusual.

Both cases it was a 10k plus bill for me and my supervisor and a couple of days experimental with accelerometers. About 5 hours work for him including 3 hours in the court and 30 hours for me making models up and experimental. If it wasn't for the fact that people had died they were very fun engineering to be involved with. Easy to forget and then you see a door with brains splattered all over it.

So it really doesn't surprise me that the traffic cops say they can't do it. If some one wants to fight it then 1k will easily purchase the services of a Uni Professor for an afternoon, who will utterly destroy the Traffic Police Forensic person if they haven't taken into account experimental error.

This case proving the difference between 60 and 70+ is relatively simple because the braking distances change so much between the two speeds. But as there was nobody killed it will just be left to deal with as a civil matter.
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