Accident Investigation for Private Investigators One
From The "X" FILES by Chris Voeglie of Forensic Associates, Inc.
www.cybercomm.net/forensic
A recent conversation with a fellow licensed investigator, raised my
curiosity regarding those who have ventured into the field of Accident
Investigation. I was introduced to this gentleman through a mutual friend.
I will refer to him as Investigator X. Investigator X has been a licensed
investigator for nearly 10 years and retired from some 20 years of law
enforcement experience. Through our conversation, Investigator X was clearly
a knowledgeable and experienced investigator, who has probably forgotten
more about the private investigation industry than I have yet to learn.
That was until he mentioned this great opportunity available to investigators,
Accident Investigation. Well, that's where my expertise came into play
and my concern mounted. Investigator X began explaining, that although
once intimidated by the technical jargon and reputation of the math involved
in accident reconstruction, he found it to be a rather simple. So far I
was still listening, however this is also where my concern turned to fear.
Investigator X at this point has no idea that I am a Traffic Accident Reconstructionist
and that my practice specializes in Accident Investigation & Reconstruction.
He advised me that after reading various publications, which appeared
to have been written for insurance investigators or adjusters, he was able
to easily determine a vehicle's speed from skid marks left at the scene.
Although our discussion became rather entangled and involved numerous topics
I wish to address this particular subject matter. The science and procedures
of accident reconstruction are based on scientifically approved methods
that are derived from the physics developed by Sir Isaac Newton. In recent
years many individuals have surfaced, proclaiming to be Accident Investigators
and or Reconstructionists. Some of these individuals are indeed well trained
and knowledgeable in the field and as this example will demonstrate some
not so knowledgeable. This unfortunate case is a perfect example of the
old saying "a little knowledge is worst than no knowledge at all"
and will prove deadly in a litigation matter.
When I was working in the traffic division many times I was asked "how
can you prove that," when I had determined a vehicle's minimum speed.
I will not, and can not encompass the entire subject matter of speed from
skid marks, but I will attempt to provide a basic understanding of how
it can be calculated and the details needed to make your estimates more
accurate and less susceptible to legal attack.
A vehicle's speed from skidding can be calculated with a multitude
of different formulas. The simplest formula to discuss and utilize is that
of : The square root of 30df. This was also the method utilized by Investigator
X. What this equation states is that the square root of the sum of: 30
x d x f will equal the vehicle's speed calculated from skid marks. What
this means is that the formula calculates a vehicle's speed if it had skidded
to a stop without striking anything. This formula, when used properly,
will determine a vehicle's minimum speed in order to skid the given distance
without taking into account the speed of the vehicle at impact.
This calculation, when used alone will provide a lower than actual
speed, thereby providing the driver with the benefit. In most cases, except
for impacts which result in little or no damage, it will provide speeds
substantially lower than that of the actual initial speed. Elements of
the equation are this:
S= speed 30 is a constant d = distance of skid f
= coefficient of friction or drag factor
EXAMPLE
Let's use Investigator X's case as an example to help understand the
use of this equation: Vehicle #1 was traveling westbound in a posted 25
mph school zone and skidded 35' prior to striking the rear of Vehicle #2
that was stopped at the crosswalk. After impact both vehicles did not move
significantly although there was minor damage noted to both vehicles.
APPLYING THE FORMULA
In order to apply the formula we must first determine the values of
our variables. We have determined the skid distance from the given example
but not the drag factor of the roadway. Let's assume that the roadway characteristics
are that of normal bituminous concrete (asphalt) construction, level and
dry. Various tests can by performed by the investigator in order to determine
the drag factor of the roadway. There are basically 3 ways to determine
a roadway's coefficient of friction or drag factor.
1) Is to perform actual skid testing at the accident site, preferably
with the same or similar type vehicle configuration, at the same location
and direction of travel.
2) Utilize an investigative tool called a drag sled.
3) Utilize a range of values that have been approved and accepted
through previous testing.
Investigator X simply used the given distance stated in the police
report and a value he ascertained from an article he read regarding this
topic. After ascertaining the drag factor he proceeded with the equation
by substituting the variables with the determined values. 30 X 35' X .80
= 840 The square root of 840 is 28.98 Thus he determined that the vehicle
was exceeding the posted 25 mph speed limit. It all seems simple enough
right! Well, I could not help asking how he determined the roadway characteristics
needed to apply published data to without visiting the site and what his
experience was in determining a roadway surface characteristic?. Did you
apply a range of values to determine the sensitivity of the results regarding
a drag factor? Was there a grade in the roadway that needs to be considered
in determining a resultant drag factor? Did you determine the location
of the vehicle's center of mass including its occupants and load, and did
you apply it in determining weight shift during braking? How did you determine
the percentage of braking, were all wheels locked and sliding? If not,
which wheels left the skid marks? How much braking can be contributed to
the skidding wheels? If the other wheels were not skidding, does it mean
they were not contributing to the slowing of the vehicle? What percentage
of braking can be contributed to the non skidding wheels? How much additional
kinetic energy was possessed in order to facilitate the damage done to
the vehicles at impact. How would you convert kinetic energy to velocity
or speed? How did you determine the speed at impact? What method was used
to combine these findings? Did you simply add them together? The list goes
on and on, and I'm sure you get the gist of it. These types of questions
mount up quickly depending on the complexity of the accident.
This example is one of the simplest accidents to determine speed from.
Let's throw in maybe a tractor trailer combination with some braking problems,
a child chasing after his ball and a speeding motorcyclist who was thrown
from his cycle 150 ft with an unknown takeoff angle, and slid an additional
80ft once he hit the ground. Once Investigator X realized he was placed
in such an uncomfortable position by a young man nearly half his age and
over all experience, he realized he was lucky to have not been put on the
stand concerning this "new opportunity." Opportunity yes, but
definitely not for everyone. I now provide his office with these services.
This is why we spend years in training, attending and participating in
independent studies including actual crash testing, not to mention reading
every article and book about the subject we can get our hands on. Some
of us eat, sleep and drink facts, figures, procedures, formulas and theories
of physics. For those of you who are interested in, or have ventured into
this field use caution in providing your findings and conclusions. There
is a fine line that once crossed will transform you from Investigator to
Reconstructionist. This instant change in title will expose you to a world
of experts most of which posses extensive formal and specialized educations,
and who are knowledgeable in forensic engineering, ready and willing to
pounce on easy prey.
If you wish to conduct accident investigations by all means do so,
but be conscious of the fact that after spending years building your reputation
and clientele you may be the next "Investigator X "on the stand.
There is a lot more involved than what first meets the eye. I strongly
suggest employing the services of a Reconstructionist when presenting any
evidence whether physical or assumed which will be considered above the
evidence gathering and reporting level. For some I may have discouraged
you, and for others, peeked your curiosity. My intentions are neither.
For those interested in pursuing this investigative opportunity I have
a few friendly words of advice. One must craw before he can walk, and walk
before he can run. A great deal of credible reference material is available
to you without breaking the bank. Most reference books and courses are
indeed geared toward the police officer who has the luxury of investigating
the accident when it happens. We, as Private Investigators on the other
hand, may not get to see the case for years. For this reason I mention
fellow NAIS member Jack Murray. Jack Murray has written several books,
two of which, and he tells me a third is in the works, encompass accident
investigation in the private sector written exclusively for private investigators.
Jack was very helpful to me, in my transition from law enforcement to the
private sector. Although I was extensively trained in accident investigation
and reconstruction and could be admitted as an expert in court, I did not
know how my potential clients needed their information presented. Jack
was more than willing to assist me and for this "Jack I thank you
very much!" Both of his books "Accident Investigation in the
Private Sector Vol. I," which was also named "Best Investigative
book of 1994"; and "Accident Investigation in the Private Sector
Vol. II," which was just released, to which I posses the first issue
sold along with a friendly hello from the author, are well written and
are easily understood. Jack has a way of writing factual and informative
material in such a way as to allow you to read on! Both of these books
are available through Thomas Investigative Publications, Inc. PO Box 33244,
Austin Texas 78764, www..pimall.com/nais/home.html. I have read both his
writings and strongly suggest to those new to this field to purchase them.
An additional initial necessity will be the "Traffic Accident Investigation
Manual Vol. I," by Jay Stannard Baker & Lynn B. Fricke, Northwestern
University Traffic Institute, 405 Church St. PO Box 1409, Evanston, IL
60204, www.nwu.edu/traffic/. The combination of these three books will
undoubtedly provide you with a wealth of information and best of all, will
not cost you a whole lot of money. All three publications will probably
run around $120 and an excellent addition to any investigator's library.
SKID MARK
ANALYSIS
