The Traffic Accident Reconstruction Origin -ARnews-
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The Traffic Accident Reconstruction Origin -ARnews-
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I'd be a little cautious in using the "blood trail" as an indicator of any
true distances (end of airborne phase, beginning of slide phase)... ever cut
your finger with a piece of paper?... notice that it took perhaps 1/2 to maybe
a second to start bleeding?... 1/2 to a full second of time interprets to
considerable distance when related to the rate of travel for the striking vehicle.
As is often the case, determination of the actual area of impact may be difficult
with regard to a ped/car impact. Add to this some of the reconstruction community's
observations about the shape of the front of the striking vehicle, whether the
impact was of "forward projection" or "wrap" configuration, and the fact that
the vehicle was not slowing during and shortly after impact, and you have a difficult task in
estimating the vehicle's speed as easily as might be the case with skid, etc.
Professor Appel's work in concert with the Searle studies and a host of others
might be of assistance in "converting" the "raw" equation answer. Many of the
available methods/equations in fact reveal the approximate speed of the pedestrian's
body after impact and not necessarily the speed of the striking vehicle...
Any indications of rotation (such as secondary strikes to the hood/windshield)
reveal that the body/vehicle interface was not centered or co-linear...
in short its somewhat of a "glancing blow" with some of the energy being employed
to move the body forward and other portions of the energy being employed to
spin the body... As most of the "airborne" equations are related to displacement and
not spin, they fall a bit short. Some other equations are tweaked to account
for empirical observations and at least claim to provide closer results. I and
apparently many others don't entirely trust any single equation or method and
tend to employ several to come up with probable ranges for vehicle speed.
Here's some good reading to begin with:
"Influence of Impact Speed and Vehicle Parameters on Injuries of Children and Adults
in Pedestrian Accidents," Appel, H., Sturtz, G. and Gotzen, L., Proceedings 2nd
International IRCOBI Conference, 1976, pp 83-100
"The Trajectories of Pedestrians, Motorcycles, Motorcyclists, etc., Following a
Road Accident," Searle, John A, and Angela, SAE paper #831622
Ed Livesay
elivesay@alltel.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.