The Traffic Accident Reconstruction Origin -ARnews-
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The Traffic Accident Reconstruction Origin -ARnews-
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Now let's look at what you have said. First you say that the pedestrian slide a distance of 52 feet. Are you assuming that the pedestrian was impacted and ended up a total of 52 feet? By definition a pedestrian impact in a two phase model (fall and slide) is struck travels in the air during the fall distance and then hits the ground sliding to a stop over the slide distance. (For information there is a third phase breaks up the "Fall distance" into two additional phase of carry on the vehicle and then falling to the initial ground contact. What NWUTI equation did you insert the 52 feet is the slide distance? If you started with the top df = then remember that the slide distance is only the ds value and only then unless you are using the 4th NWUTI equation Vs = srt(2*f*g*ds). You also qustion as does others on this thread the use of .45 - .6 slide friction as found in Lynn Fricke's book. I can tell you that the way the test data was conducted that just sliding a pedestria
n across a surface you will find comperable results as .45 - .6. In fact in the lat 1980's Boise State University did a similiar set of tests as to NWUTI and the values were comparable in the .43 - .64. However in actual pedestrian impact tests these low slide values are not found for normal asphalt or concrete dry surfaces. One problem is that in the NWUTI and Boise State tests the pedestrians were slid always on the horizontal direction. There was no initial vertical force as found when the pedestrian needs to fall to the ground either from its standing height ie forward projection or in a wrap when the pedestrian is raised to an apex height and then falls to the ground. In 1966 D. Severy at UCLA did 9 pedestrian crash tests. In the data collected from these tests the initial ground contact was between 20-40 g's. They also found the pedestrian slding friction was between .8 - 1.2 on a nominla .7 asphaltic roadway. Additionally other authors have also agreed when discussing t
he slide friction within a range of .7 - 1.2. Other authors describe friction values of between .4 - .66 discussing the average friction for the pedestrian over the total throw distance.
Finally, if you want to send me an email with the above questions I can give you a good range of values. I would really need to know the distance from initial contact to the pedestrian's final resting point distance.
If I assume that the 52 feet is the sliding friction then the minimum speed would be about 33 mph. Along with this thread you have my email address and I would be happy to have you contact me to discuss your questions. I can also send you to some sources with SAE and a couple of other papers and books that describe this situation. Also for your information, Rusty Haight and I have done over 180 ped or bike versus auto crash tests. I have also located over 100 additional tests done by other authors. I can tell you that for a roadway surface dry not contaimnated for with a non ABS friction of .7 NWUTI's formula will always be 15-25% below the actual impact speed. Additionally because of their low sliding frictions the actual fall and slide distances are quite aways off from the actual tested condition. Also I have looked a 7 real pedestrian vs. auto video taped collisions, and in real life the post impact slide friction for the pedestrian is always been above the NWUTI high end
value.
Jerry Eubanks
JerryEubanks@worldnet.att.net
For example, to continue this discussion look for a thread titled
Pedestrian Accident Reconstruction
If this thread does not exist in the current archive, you can begin another one by using that title.