The Traffic Accident Reconstruction Origin -ARnews-
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The Traffic Accident Reconstruction Origin -ARnews-
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Friction coefficients (also known as the drag factor in most contexts related to reconstruction) simply mathematically describe the friction offered by a given surface to a car tire dragging slipping or skidding across it. Drag factor is often described in two forms.... an engineer might specify a drag factor of 20 feet-per-second-per-second (20fps^2). This describes the RATE of acceleration (which also includes slowing down while a car skids). Policemen/non-engineer reconists often use the more easily understood FACTOR (i.e. .62 or 62%). The factor is a decimal number describing the acceleration with respect to one G or G-force which is 32.2 fps^2. And so a roadway might be described as offering a resistance of 20fps^2 (rate) or the equivalent .62 drag factor (factor).
Stiffness coefficients are mathematical descriptions of how stiff the surface/components of a vehicle are. Speed from crush (damage) methodologies rely upon Hooke's Law (F=kx or Force = Spring-stiffness multiplied by distance over which the spring is compressed or stretched). In short crush methods consider the surface of a car to be a multitude of springs postioned in a perpendicular fashion in relation to the car's surface. A particular type of car has a certain stiffness strength or power. Hooke's law simply says that in order to push one (or several) of the spring(s) a certain distance inward (damage depth) requires a certain amount of Force (lbs). Add some considerable mathematical conversions and the result is speed required to compress the spring(s). Again in short measure the depth and width of the damaged areas on a car's surface determine the stiffness coefficents (spring stiffnesses) from past staged/controlled collisions do some math-a-magic and a useable s
peed ESTIMATE can result.
Friction coefficients and stiffness coefficients have no relationship with each other. Your query leaves me with the impression that your opponents may be employing photogrammetry methods to provide estimates of distances angles etc. to create a scale-diagram. The scale-diagram would in turn be used to provide measurements for use in a conservation of linear momentum type of speed estimate for the vehicles involved (an energy analysis involving crush/stiffness coefficients would be extremely complicated). Photogrammetry is actually a VERY mathematically complex surveying technology which can indeed be used with some accuracy and efficiency (provided good photographs with proper data visible... but they would almost certainly need to visit the scene to obtain certain data-points). Your opponents must be using several photographs must have some data about the scene such as a map from the Division of Highways (or your State's equivalent) etc. and must be employing quite a few assum
ptions.
They (your opposition) will be hard-pressed to present opinion testimony ACCURATE TO A REASONABLE DEGREE OF ENGINEERING CERTAINTY with only a single (or even two) photograph(s) no site or vehicle examinations and with the significant assumptions implied. They might indeed present simple opinions based solely upon the limited evidence to the insurer's claims rep but they will be in deep kimshee in the formal court environment with proper interogatives and cross-examination.
Hope this message is not too late and is of some value to you. I wish you and your client justice. I am
Sincerely yours
Ed Livesay
Integrity Intelligence Services
PO Box 3394
Sanford NC 27331-3394
(919) 774-6024
Ed Livesay
EdLivesay@worldnet.att.net
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Speed calculation based on photographs
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