Two DTRs-parallel parking and a rear ender

Mar 1, 2010 by

# 1: The parallel parking DTR

The insured backed his small SUV into the side of the claimant’s sedan during parallel parking.  The claimant and his passenger both claimed injury.

GEI was assigned to examine the supplied documents and photographs to determine the impact speed, g-forces, and likelihood of injury.

The photographs and estimate for the insured’s SUV showed no damage. The claimant’s sedan was slightly damaged.  His photographs showed an 8 to 10 inches wide, 1/2-inch deep dent in the left door skin.

The weight and stiffness values for vehicles were researched and speeds were calculated.   Since there was no damage to the insured’s SUV, all of the energy used in the impact was used in deforming the claimant’s sedan.

The speed of the insured’s SUV, at impact to the claimant’s sedan was calculated as 1.4 mph.  This is less than the values given for 15th percentile pedestrian-street-crossing, walking speeds.  This value was not high enough to move the claimant’s sedan sideways, a requirement for the production of an injury.  The actual movement of the claimant’s sedan immediately post impact was only to slightly rock on its springs.

How did these values apply to the production of an injury?

Vehicle g-forces are not a direct measurement of forces to the occupant.  The force transmitted to the affected areas of an occupant’s body are more important.  Seat back restitution, interior padding, seat belts, air bag restraints, and headrest positioning are all factors that influence occupant g-forces.  In this case, the forces as experienced by the claimant’s vehicle were so low that the occupant g-forces in this event were far less than those required for injury.

How do these data compare with published threshold injury data?  Research has determined that in a retroflex impact, a normal occupant needs a speed change of over 7 mph coupled with a force of over 14 g to produce complaints of pain to healthy test subjects.  Lateral load requirements are a little lower.

To give the reader a feel for what forces are involved, we can compare this event with those forces experienced by riders in amusement park bumper cars.  Speed changes (omni-directional) of about 4.7 mph, and g-forces of about 2.13 g are normal and routinely experienced.
Federal New Car Assessment Program (NCAP) data tells us the act of simply stepping off a curb produces g-forces of about 5 g.  Other examples of g-loading are as follows: sneeze, 2.9 g; being jostled in a crowd, 3.6 g; hopping off a step, 8.1 g. This incident was well under these values.

In order for an occupant to suffer an injury, the occupant must either undergo a speed change or a direction change within a very short period of time.  This particular incident provided no mechanism for these changes.  This was not an injury-producing event, as the forces and speeds exchanged between the vehicles were just too low.

# 2: The rear ended DTR

The insured (V1) was rear-ended (by V2).  Neither supplemental restraint system deployed.  The CHP responded, interviewed the participants, listed no independent witnesses, recorded no roadway evidence, and classified the damage to both vehicles as “minor”.  Their report located the damage on the insured’s vehicle as being in the center-rear.  When the claim got to the desk of the adjuster, the insured’s vehicle was heavily damaged on the right rear corner.

GEI was assigned to make an independent examination of the supplied documents and photographs to determine the impact speed, and to answer the question, “Could the vehicles have collided as described?”

We examined the photographs and the repair estimates for both vehicles, researched the published weight and measurement data, and the NHTSA stiffness values.

NHTSA stiffness values are data based upon controlled test crashes designed to produce data relative to speed from damage assessments.

The photographs for V2 showed the front bumper assembly to have been undamaged.  The center portion of the leading edge of the hood/grille assembly was pushed to the rear 2 inches.  The structural portions of the front-end were not engaged, as the force of the impact went over the bumper and into the soft, unsupported hood and grille over a width of about 40 inches.  The radiator core support was damaged. The top of the front bumper was listed as being 20 inches high.  V2 required zero hours of frame work repairs.  The 2.5 mph rated bumper’s energy absorption system was not touched.

V1 was damaged to a much greater degree. Photographs and repair estimates showed that there was damage to the rear bumper cover, to the energy absorption system, and 8 hours of work on the frame.  The floor pan and other rear quarter parts were damaged.  The right rear tail lamp was damaged, requiring replacement, and the right rear sheet metal was pushed to the front about 6 inches.    The damage seen on the right rear tail lamp was grossly disproportionate to the damage found on V2’s matching counter-point, the hood/grille.

After assessing the damage to V1, we calculated the kinetic energy needed to produce the damage to the vehicle.  This value came out to be 9,975 pounds per feet of energy.  The energy estimated from the crush values for the damage to the front end of V2 was calculated to be 1,722 pounds per feet.   Since Newton’s Third Law of Uniform Motion states that for every force there must be an equal and opposite force, the same force seen on V1 must be present on V2.   In this case, they were not.   Even when one accounts for errors in estimating damage levels, the levels could not be reconciled.  The difference was about 579 percent.

These two calculations showed the values to be so grossly divergent that they were far beyond any reasonable percentage of error. This event claimed (that required 8 hours of frame work to repair) was clearly not caused by V2.  The CHP officer saw one event, but another later event was turned in to the insurance company for payment of repairs.  Any claim of damage or injury to V1, or its occupants from V2, was just that –  a claim that was in no way supported by evidence or physics.

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