For The Defense, November 2012 - DRI Today

Product Liability
• low static stability factor (SSF);
• inadequate rollover resistance; or
• inadequate occupant protection.
Low Static Stability Factor (SSF)
Opposing experts, at times, may compare
ROV static characteristics to on-road passenger
vehicle safety metrics. For example,
they might claim that an ROV is
Today,appropriate
dedicated equipment
exists that can be used
to recreate real-world
motions in an ROV in a
laboratory environment.
Tests such as these
can be used to quantify
and comprehend the
performance of the
restraint systems better.
flawed because its static stability factor
(SSF)—a vehicle’s center of gravity (CG)
height divided by one-half of its track
width—is too low. In reality, most ROVs
have a lower SSF than on-road passenger
vehicles. The function and utility of ROVs
and on-road passenger vehicles are quite
different and, therefore, comparing their
static safety metrics, such as SSF, is not
justifiable.
Correctly determining a vehicle’s CG
height to calculate its SSF is no trivial
task. There are numerous opportunities
for error, and simplifying assumptions can
lead to incorrect results. Yet, to address
claims made against a vehicle’s CG height
and SSF properly, it is necessary to have
accurate measurements. With appropriate
equipment and adherence to proper techniques,
it is possible to measure the effect
that certain design parameters may have
74 ■ For The Defense ■ November 2012
on an ROV’s CG height, SSF, and inertia
properties. This includes, but is not limited
to, the installation of tires not recommended
by the manufacturer, applying tire
pressures counter to what is prescribed, or
exceeding the manufacturer’s limits for
occupant and cargo loading.
Inadequate Rollover Resistance
Cases against ROV manufacturers may
also involve claims that the vehicles do not
have adequate rollover resistance based
on their performance during severe driving
maneuvers. Allegations that an ROV
is flawed because it tips up at lateral accelerations
below those necessary to tip up
an on-road passenger vehicle suffer from
the same lack of foundation as the low SSF
claims. The two different vehicle classes
have significant differences in their function
and utility. Therefore, it is imperative
to know the limits of a specific ROV’s capabilities
during maneuvers that take it to the
threshold of tipping up, and as importantly,
to know what type of driver inputs are necessary
to do so.
Equipping an ROV with test instrumentation
and “putting it through its paces” in
a suite of dynamic field tests can answer
the necessary questions regarding its overall
lateral stability and rollover resistance.
More importantly, dynamic field- testing
can be used to demonstrate the magnitude
of driver inputs, such as the vehicle speed
and steering requirements necessary to
take the vehicle up to its limits of response.
This knowledge is useful in gauging the
inherent margin of safety that a vehicle
has under various driver conditions, including
while being driven on various offroad
terrains. Further, this information
can be helpful to address how a vehicle
responds under driver inputs that might
be made by an alert, responsible, and prudent
driver, as well as indicate what types
and ranges of driver inputs are necessary to
cause or to contribute to a particular accident.
Finally, data obtained can be applied
to address differences between ROVs and
on-road vehicles.
Inadequate Occupant Protection
Sometimes lawsuits against ROV manufacturers
involve assertions that the vehicles
do not have adequate occupant restraint
systems. Allegations may posit that ROV
original equipment manufacturer (OEM)
seat belts, hip and shoulder restraints,
doors and nets, or a combination of these
are inadequate or defective, and plaintiffs
allege that they can show “redesigns” that
could have prevented the injuries from
occurring. Often the allegations and the
“redesigns” are not based on facts supported
by physics or by rigorous biomechanical
evaluation. Clearly, the foremost
issue to evaluate is whether or not the
restraint system was present and properly
used at the time of an accident. It is necessary
to have a sound understanding of the
safety benefits and characteristics, as well
as the limits, of each restraint and occupant
protection component on the ROV.
Even more beneficial is knowing how the
elements work together to provide overall
occupant protection and thereby prevent
injury.
The translational and rotational forces
that act on an ROV and its occupants before
and during an accident lead to very complex
vehicle and occupant motions, displacements,
velocities, and accelerations.
For example, in most ROV rollover situations,
it is not sufficient simply to test or
model the vehicle and occupant as they
might respond during a “pure roll” motion;
most rollovers involve important components
of longitudinal and lateral accelerations
and motions as well. Studies of
three- dimensional states of motion and
forces are required to evaluate occupant
restraint systems properly. Tipping (rolling)
a vehicle at 45 degrees, or to any other
quasi- static angle for that matter, without
any longitudinal or lateral acceleration,
is not adequate to determine how well a
restraint system works during an accident
scenario. Doing so may result in misleading
conclusions. Today, appropriate dedicated
equipment exists that can be used
to recreate real-world motions in an ROV
in a laboratory environment. Tests such as
these can be used to quantify and comprehend
the performance of the restraint systems
better.
Being armed with reliable and scientifically
valid information on how restraint
systems actually work in real-world rollover
events can be the backbone of a strong
defense against opinions based on inaccurate
theories or science.