Roadway Friction Accident Reconstruction Experts

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Roadway Friction Accident
Reconstruction Expert

Providing Quality Accident Reconstruction and Investigation

Illinois has nearly 139,000 miles of roads -
the fourth most in the nation.
- FHWA

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.

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

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