The Traffic Accident Reconstruction Origin -ARnews-

Re: Speed from crush, roof of vehicle

Wilt Nelson ([email protected])
Tue, 6 Oct 1998 15:32:41 -0400 (EDT)

<<Speed from a yawmarks put the vehicle at 64 MPH.
Hit a curb and took out two trees approx 10" in diameter. Good
intrusion, 19" +/- into the engine compartment laterally. Vehicle went
onto drivers side and hit another tree. Passenger space intrusion of
about 37". My question is, what formula would I use to figure the speed
at this point? Everything I've got talks about barriers, fixed objects
etc but not how to measure when the tree snaps off. Would a basic
formula work? 1.02xcrush, or whatever it is>>
Just a few words of caution. Never quote a speed of, e.g.; 64 mph. Use a range of speeds based on the variables, e.g.; 62 to 67 mph. Your drag factor certainly was a range, and if you made more than one measurement of the M.O. you have some variation there.
Never use an equation like 1.02Xcrush= speed. These are hoaxy and I can give you the history of how the got started and why they are incorrect if we have more time later.
The earlier advice you rec'd is good. You don't need 5 different ways to show the speed, you're the expert, do it the best way you know how. No tests have ever been done to evaluate speed for the damage pattern you describe. A roof is easily crushed, it is not designed as energy absorbing. Given the wt of the car at 10 mph drop test could produce 37" of crush from a tree (narrower than a barrier).
Wilt
Wilt Nelson
[email protected]

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