Richard I've heard my police buddy who is an AI for the department
talk about drag coefficients and crush factors. I assume they
determine inpact speed from how badly the vehicle is "crumpled" and
add that in whith what they find for the skidmarks. So if you never
hit your brakes the crush factor would indicate a high rate of impact
speed. Say you leave 50 yards of skid marks and the crush factor
looks to be around 30mph.... just figure out the speed for 50yards of
skids and tack on the 30mph impact.
That's my GUESS anyway.
--Mike
www.mikesdakota.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
>>
>>
>> >
>> >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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This archive was generated by hypermail 2b29 : Fri Jun 20 2003 - 12:02:06 EDT