That gets very tricky. And quite messy. But in short it involves
"Including these "shadows", or as I would call them, "impending tire marks",
in the total length laid down by each tire of the vehicle does not pose a
problem in the analysis. This is due to the fact that during these impending
tire marks, the vehicle is at it's maximum braking efficiency (near static
friction) until the tires lose traction and begin to slide on the roadway at
the locked wheel co-efficient. By including these impending tire marks in
the total slide distance, we are still giving every consideration to the
driver of the vehicle by using the locked wheel co-efficient of friction
over the total skid distance, obtaining a lower speed." (Taken from an
article Dan Kemble a nine year veteran of the Los Angeles Police Department
wrote up)
and also the other persons skid marks. I will ask my dad who who knows much
more than me on the subject and get back to you on it. I know the basic
coefficent stuff where the skid marks are easy to trace.
Ill get back on it shortly with an answer for you.
-------------
Dakota Dodge
Profile at:
http://www.twistedbits.net/WWWProfile/dakota/XgAJPmbQu2jpA/profile.htm
Truck Home Page: http://www.dakota2.4mg.com
>I've always wondered about that - determining vehicle speed from skid
>marks. I know it makes sense based upon physics - take the weight of the
>vehicle and then measure the skid marks to determine the speed of the
>vehicle, etc. What has always been a question in my mind, though, is
>suppose the person is a little slow in the reflexes and the skid marks
>are short because the impact happened more suddenly? In other words, say
>in normal conditions my reaction time is .32 seconds, but some chick
>distracts me and when I finally turn my attention back to the road ahead,
>I'm about to impact another vehicle. Under normal circumstances I would
>have begun to apply the brakes maybe 30 yds sooner and my skid marks
>would have been longer. As someone knowledgeable in this area can you
>enlighten me as to how the speed can be determined when one never really
>knows the reaction time of the driver leaving the skid marks and the fact
>that the driver may have impacted the other vehicle before running out of
>skid?
>
>Thanks!
>
>Richard in San Antonio
>
>
>On Thu, 12 Jul 2001 16:58:08 -0000 "Dakota Dodge"
><dakotasdodge@hotmail.com> writes:
> > As a safety engineer, along with my dad, we have looked at many MVA's
> > (Motor
> > Vehicle Accidents) in the past and I would guess 95% of them all
> > have one
> > thing in common. And that is they leave tire (skid) marks from the
> >
> > accident. Those that can control there brakeing and stay in control
> > without
> > skidding will be MUCH LESS likely to be involved in a crash. The
> > coeficient
> > of friction for tires is approx .95, and once they start to skid
> > (which if
> > you look at it in slow motion...the tires are skidding on the
> > burning
> > rubber) the coeficient of friction drops down to the area of water
> > (ever
> > hydroplaned in your DAK?...same idea as skidding on rubber)
> > Well there. A little in depth stuff for any of you interetsted.
> > BTW - if
> > you are ever in a car wreck and leave skid marks and there is a
> > question
> > about your speed...through the use of the coefficent of friction the
> > police
> > (or myself as an investigator) can tell if you were speeding or not.
> > Pretty
> > neat stuff huh?!
> >
> > -------------
> > Dakota Dodge
> > Profile at:
> > http://www.twistedbits.net/WWWProfile/dakota/XgAJPmbQu2jpA/profile.htm
> > Truck Home Page: http://www.dakota2.4mg.com
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