The Traffic Accident Reconstruction Origin -ARnews-

Re: Speed range from head-strike in pick-up vs. pedestrian collision

Jerry Eubanks (JerryEubanks@worldnet.att.net)
Sun, 22 Jun 1997 01:43:47 -0400 (EDT)

It sounds like there is very little evidence in this case. If you are going to attempt to use any of the pedestrian throw distance equations you must know the
distance from the initial contact point to the final resting point of the ped. If you only have a estimated distance of 45-60 feet that may not be good enough!
Is it possible with that short of a distance that you may have the body of the ped may have been a prtial impact, ie. where not the whole body is struck. For
usually a throw distance of 75 feet should have a speed range in the area of 30-35 mph, for a "wrap series" impact. There are equations that can be written to
solve for throw distance, you can look at SAE 921591, by Rusty Haight and myself. Some of those equations will work to give you an estimate of the throw distance.
Then using those estimates there is a qudratic equation where if you know and estimate of the distance the pickup moved from impact to its final rest and you can
ask the driver a couple of questions 1. when did you first know of the impact. ie I heard it, then use what ever perpcetion and Reaction time you deem as appropriate
and then 2. How he braked post impact post impact, ie I braked like going into a stop sign, tests have shown that friction to be in the range of .25, you then can come
up with a known velocity.
Another factor might be to look and see if on the front pelvic area of your pedestrian there is "stretch markings". A coroner in Green Bay discussed stretch markings
we observed in impact speed in the 25-30 mph range. This might help define a range of speeds. Also you might look at whether or not the pedestrian was involved in a forward
projection, or a wrap trajectory. The definitions can also be found in the above mentioned SAE paper or in an SAE paper by Ravini #811024.
If you would like to give me a call my number is (619) 275-1455.

Jerry Eubanks
JerryEubanks@worldnet.att.net

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