The Traffic Accident Reconstruction Origin -ARnews-

Re: Speedometer Locked in Position Following a Collision

Steve Pustay (mvengpit@sgi.net)
Fri, 6 Feb 1998 18:27:08 -0500 (EST)

I've recently been struggling with the same type of question.

Northwestern Univ. Traffic Inst., Traffic Accident Investigation Manual,
Volume I, has a couple Figures and states simply that the needle's position
on a speedometer locked as the result of impact damage may, or may not, mean anything.
I definitely would vote for the needle's position being essentially worthless.
"If it were zero, would that neccessarily indicate that the car was stoppped?"

The second layer of the onion is more difficult. Many of the police deptartments
accept the needle "slap" mark as evidence of the needle's position at impact. I haven't
found any reference that can substantiate that claim. Considering the inherent uncertainty
of the speedometer, the influence of the angle of the impact and the rotational components of
the impact, I can't see how the "Slap" position can be accurate. Only in dead center
head-on frontal impact would the needle deflection be straight toward the face of the panel.

Where's the beef? With all the crash tests conducted under controlled conditions, we
need an investigator to do a statistical analysis of the speedometer needle marks.

Good luck,

Steve Pustay
mvengpit@sgi.net

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