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Application
of Accelerometers for Accident Investigation
By
Rick Jobe
Drag Factor
 Measuring
drag factor is the #1 application for an accelerometer in traffic
crash investigation. There are 4 measures of physics to measure
the braking force of a vehicle.
- Acceleration
(G-force).
- Speed
- Distance
- Time
A unique
trait of the Vericom is that the Vericom employs all 4 measures.
This is crucial if the data collected from the accelerometer is
challenged in court. The investigator must always be prepared
to exhibit to the court that he/she used the accelerometer device
correctly and the accelerometer was accurate. The initial braking
speed that the Vericom calculated can be verified with a radar
gun, thus confirming the accuracy of the accelerometer. Because
the Vericom calculates the speed from the acceleration, and a
radar gun verifies the calculated speed the Acceleration Factor
(drag factor) is accurate.
Lateral
Acceleration
Perhaps the most underrated application for the accelerometer
in traffic crash investigation is measuring lateral G. The turning
ability of a vehicle can be measured by doing a simple skid pad
test. This is done by turning and holding the steering wheel at
270 degrees, driving the car in a circle and increasing the speed
until the rear tires side slid. Measured lateral G can be applied
to circular motion equations for turn away and lane change situations.
In the absents of a measured lateral G most schools recommend
a default value of .15G or .2G be used. If yaw marks are clear
a roadway friction value may be used, but if no skid or yaw marks
occur the value could be as high as .6 G to .9 G.
Positive
Acceleration
Measuring positive acceleration is the #2 application for an accelerometer
in traffic crash investigation. When an accident occurs after
a stop sign the Vericom becomes a valuable tool for measuring
speed and time over a given distance. As objective information
we can measure maximum vehicle speed and average acceleration
time. Sometimes it can be proven the violator did not stop for
at the stop sign. Subjective conclusions may be derived from this
information that will add or diminish the credibility of an eyewitness.
Slope
Measuring Grade and Superelevation is the #3 application for the
traffic crash investigator. An accelerometer can be used as an
inclinometer to measure slope. The new VC3000 has additional features
so that it can be used as a slope meter or a turn and bank indicator.
Checking banked turns for the posted reduced speed can help analysis
and prevent accidents.
Reaction
Time
Reaction time can of course be measured independently from acceleration.
However ultimately reaction time is used to determine how long
it take the driver to go from constant velocity or positive acceleration
to braking or deceleration. A reaction time switch is offered
as an accessory to the Vericom VC3000.
Low
speed impacts
Measuring the G force during low speed impacts is becoming more
popular as a means of discouraging deception insurance claims.
A 10 G tri axis accelerometer can be connected to the Vericom
VC3000DAQ for measuring impact force.
Written
by Rick Jobe, President of Vericom Computers. Mr. Jobe has been
giving training class for the use of accelerometers in Traffic
Crash Investigation since 1991.
For
addition information about the Vericom VC3000 go to www.vericomcomputers.com
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