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
>
>
> >
> >A rolling tire provides more stopping force than a skidding one.
> Being
> >able to steer is a bonus.
> >
> >--- "Mr. Plow" <adam_is_mr_plow@hotmail.com> wrote:
> > > Well, maybe it's my ignorance, but i'm going to disagree here.
> > > It is my understanding that the reason to let up just before
> locking
> > > the
> > > brakes is to avoid skidding and maintain directional control of
> the
> > > vehicle.
> > > Anti-lock brake were developed to continue to be ablt to steer
> the
> > > car/truck at maximum braking. If you lock the fronts up, you
> cannot
> > > steer,
> > > you just slide in that direction.
> > >
> > > But that's just my opinion, i could be wrong, if so please
> enlighten
> > > me.
> > >
> > >
> > >
> > > >
> > > >If you have made the mistake of locking your brakes then the
> only
> > > >thing that is going to slow you down is the kinetic friction of
> your
> > > >tire against the road which is MUCH lower that the static
> friction
> > > of
> > > >your tire rolling on the ground.
> > > >
> > > >This is why we were all told to ease up on the pedal if you
> lock up
> > > >the brakes in order to stop faster. But I do agree that a
> stronger
> > > >braking system would allow us to get closer to the edge of
> skidding
> > > >with enough modulation to stop a lot faster.
> > > >
> > > >NITF
> > >
> _________________________________________________________________
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> >
> >=====
> >-andy
> >
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