The Traffic Accident Reconstruction Origin -ARnews-

Re: Pedestrian Ride Times

Jerry Eubanks (JerryEubanks@worldnet.att.net)
Sat, 26 Jul 1997 20:05:06 -0400 (EDT)

You may be able to determine a speed range using the blood trail. If you were able to determine the pedestrian's first contact with the ground and then it's position at final rest you may be able to just use a slide to stop equation. A couple of things to determine that the first point of ground contact is available and used for the slide distance calculation. Additionally make sure that no other outside force has either accelerated or decelerated the pedestrian during the slide. Such as the pedestrian being run over by accident or another vehicle, or the pedestrian for instance does not have it's velocity changed by hitting a curb or striking a parked vehicle. Once all of those factors are determined then you are ready to atttempt to determine a pedestrian sliding drag factor. There are a number of papers and book that describe pedestrian throw distance and sliding frictions ranges. Most papers will discuss from the POI (ICP) to POR for the pedestrian between a .4 - .71 frict
ion range over the total throw distance. However this is from POI to POR, and in your case you don't know the impact position. In this case that is one thing you are trying to obtain. Finally, if you are looking at a very conservative friction during the time the pedestrian is sliding, bouncing and tumbling on the ground, you can use the vehicle / roadway friction value assuming a non-ABS vehicle. Now for a closer speed range assuming that the pedestrian trajectory is not a forward projection as described by Ravani (SAE #811024). As the difference between the peestrian's center of mass to leading edge of the vehicle increases, the sliding friction actually increases due to the initial ground impact forces being in the 20 - 40 g range as written by Severy SAE (660080). Frictions for a non forward projection range between .7 - 1.2 (Limpert Motor Vehicle Accident Reconstruction and Analysis 4th ed, The Mitchie Company Publishers). Most of the time in testing we find that .8 - 1.2
(Severy SAE 660080)may slightly over estimate at the top end .8 - 1.1 ranges seem to fit the slide to stop pedestrian friction for about 180 crash tests that Rusty Haight and I have conducted. By the way this also seems to fit on most of the real life pedestrian impacts we have from video tape of real people being struck. If you have any other questions please let me know via my e-mail address. If you want to attempt to use a pedestrian equation to solve for throw distance from a known impact speed try using Stcherbatcheff, Collision, Searle, and the fall and slide formula as written wihtout using the quadratic equation. Initially all equations solved for the throw distance with other known values. If you need all those formulas you can get them from SAE 921591. Good luck
Jerry Eubanks
JerryEubanks@worldnet.att.net

NOTE: You are reading in an archived session of ARnews. It is possible that this topic is still being discussed. To see if this topic is still active, or of there were any more recent posts on this topic, check later archives of ARnews.

If there is no current post, and you would like to add to this topic, link to the Current ARnews Discussion and begin a new thread. Be sure that if you are starting a new post that the thread title does not contain the abbreviation RE: Placing RE: at the beginning of a new post will confuse Hypermail and prevent others from answering your post in the future.

For example, to continue this discussion look for a thread titled

Pedestrian Ride Times

If this thread does not exist in the current archive, you can begin another one by using that title.