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Roadway Friction Accident
Reconstruction Expert
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Accident Reconstruction
Crash Data Retrieval
About Our Experts
Illinois has nearly 139,000 miles of roads -
the fourth most in the nation.
-
FHWA
Fraud Investigation
Some surfaces offer excellent braking conditions, such as the dry concrete roadway surface on
the right.  Other surfaces present far less ideal friction, such as the wet and well traveled asphalt roadway or the
grass shoulder.

Experts must consider the surface upon which a vehicle is slowing when reconstructing the speed at which a
vehicle was traveling.

To view a copy of a Vericom VC4000 accelerometer drag factor test conducted by our accident reconstruction
experts, please
click here.
Traffic accidents can occur on a variety of
surfaces and under an assortment of
weather conditions.

Our accident reconstruction experts utilize
the Vericom VC4000 (precision
accelerometer)  to measure and document
roadway/surface friction.

Accurate measurement of such data is an
intricate part of at-scene accident
investigation.
Grass Shoulder Friction
Wet Asphalt Roadway Friction
Cement Roadway Friction
With regard to accident reconstruction, experts will often refer to frictional relationships with terms
like Coefficient of Friction (μ) or Drag Factor (f).  While the two terms are related, they are not interchangeable.  By
definition, the coefficient of friction is the ratio of the tangential (parallel) force applied to an object sliding across a
surface to the normal (perpendicular) force.

In the English system, force is measured in pounds. For example, if a square block were set on a level surface, the
block would apply a measureable force down due to gravity.  Based on its own weight, if the block applied five
pounds of force down while requiring three pounds of parallel force to slide it across a level surface, then its
coefficient of friction on said surface would be 0.6 (3 ∕ 5 = 0.6).

The idea of an object’s drag factor, however, is somewhat more complicated.  A drag factor, like a coefficient of
friction, is actually a non-dimensional number, but is often used in conjunction with the acceleration rate of an object
due to gravity (32.2 ft/sec²).  Therefore, many accident reconstructionists add a unit of measurement for gravity
represented by the letter g.  So, if a vehicle experiences a 0.6 drag factor while slowing, then it is decelerating at a
rate of about 0.6g or 19.32 ft/sec² (32.2 ft/sec² × 0.6 = 19.32 ft/sec²).
VC4000 Accelerometer Accident Reconstruction
Crash Data Retrieval Training
Disclaimer: Crash Data Services, LLC and crashdataservices.net provide the information in this web site for informational purposes only. The information is not intended to be legal advice or an expert
opinion and should not be construed as such.  The use of this site does not create a contractor/client relationship with any employee of Crash Data Services, LLC.   Each investigation is different. Case
results depend on a variety of factors unique to each case.  The results of any investigation/reconstruction do not guarantee or predict a similar result in any future case undertaken by Crash Data Services,
LLC
Our experts are always available to fulfill your accident reconstruction needs  Call today for a free consultation:  (847)-217-6644 or reach our reconstruction experts by email