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Accident Reconstruction/Bio-Mechanics

The Role of Bio-Mechanical Evidence and Recreation in Injury Trials

While liability for many vehicular/trucking collisions is clear, accident reconstruction and workup of the biomechanics of injury are nonetheless required in the proper trial presentation in virtually all such cases.

The Scarlett Law Group works with top experts in the world on this subject. For example, many are surprised to learn that most SUVs and pickup trucks maintain a rigid bumper system which clearly can result in much greater injury to occupants in even low speed impact collisions.

Analyzing Bumper Damage

The presence or absence of motor vehicle bumper damage is usually thought to be an important consideration when estimating the severity of a low speed, or minimal damage collision. There are, however, several types of bumpers. Most passenger car bumpers contain elements designed to dissipate the impact energy, such as shock absorber-like isolators, foam cores or lattice cores. A number of studies have provided insight into analyzing collisions involving these kinds of bumpers.

A rigid bumper system, such as contained on most SUV and pickup trucks, typically consist of a steel bumper beam attached to the vehicle frame either directly or by mounting brackets. Rigid bumpers are common on pickup trucks, vans, and sport utility vehicles.

In one study, full-scale impact testing was selected as a method of investigating the performance of rigid bumper systems during low-speed collisions. A vehicle-to-vehicle test is clearly the best facsimile of the actual collision. However, barrier impacts are widely used in mandatory standards compliant tests, and the relative ease of conducting a barrier test makes it an attractive alternative to a vehicle-to-vehicle test when assessing the behavior of a rigid bumper.

In at least one study, comparison was made between the damage produced in barrier and vehicle-to-vehicle test of a similar severity to assess the viability of barrier testing when analyzing real-world collisions involving rigid bumpers. The Scarlett Law Group, together with its experts, maintains constant review of all literature in this area, and when re-enactment, via computerized projection or actual vehicle reenactment is performed for forensic purposes, the Scarlett Law Group and its expert chooses the most viable option available.

Testing Bumper Damage in Vehicle Collisions

For example, in one study 5 pickup trucks were subjected to barrier impacts and vehicle-to-vehicle impacts on both their front and rear bumpers. Prior to each test, replacement bumpers and mounting hardware were installed by a local auto body shop.

The vehicles tested included:

  • 1980 Ford F-150 Pickup
  • 1981 GMC C-1500 Pickup
  • 1983 Toyota Half-Ton Pickup
  • 1983 Chevrolet S-10 Pickup
  • 1984 Ford Ranger
  • and a 1993 Ford Crown Victoria.

Original equipment manufactured parts were used for all of the vehicles. Speed, damage, and high-speed video were recorded for each test. Impact force was recorded for the barrier test.

A Macinnis Engineering Associates “fifth wheel” was attached to each test vehicle to measure speed during the collisions. Collected at 256Hz, this device provides speed resolution of about 0.04km/h.

The barrier was equipped with two uni-axial lode cells to measure impact force. This data was collected at 256Hz.

All test vehicles were weighted axe-by-axel using an 11kN load cell with a resolution of 10N.

Video of the bumper impacts was recorded using an omniSpeed HS motion capture system and high speed digital cameras. Video data were recorded at 250 frames per second, using a shutter speed of 1/1000.

First, the front and rear barrier impacts were conducted with all vehicles, followed by front and rear impacts with the rear and front bumpers, respectively, of the 1993 Ford Crown Victoria 4-door sedan.

The test vehicles were pulled into impact by a speed control electronic winch and a steel cable attached to the undercarriage. Just prior to impact, the winch was turned off, so the vehicle coasted into contact.

The barrier consisted of a horizontal steel beam with a rectangular cross-section attached by two lode cells to a rigid frame. The frame was bolted to a concrete floor. The height of the impact beam was adjusted so that the center of the beam was approximately level with mid-height of the bumper.

A 1993 Ford Crown Victoria was used for vehicle-to-vehicle collisions with the pickup trucks. In each of rear bumper test, a stationary pickup truck with a struck by the front of the Crown Victoria. The Crown Victoria was towed to the required speed by the electric winch, and released just before impact. For each front bumper test, the pickup truck was towed into the rear of the stationary Crown Victoria in a similar manner.

The striking vehicle impact speed for each vehicle-to-vehicle test was selected so that the speed change experienced by the pickup truck would nearly match the speed change observed in the corresponding barrier test. Coefficients of resolution were predicted using approved methodology.

The striking and target vehicle bumper heights matched in all tests.

The differences between the damage caused in the vehicle and barrier test was found to be generally attributable to the difference in the shape of the barrier and the Crown Victoria’s bumpers. The Crown Victoria’s bumpers were curved and these curvatures resulted in non-uniform loading of the bumper beam and the mounting brackets. In many of the tests the horizontal curvature caused greater deformation between the bumper mounts than the barrier test.

The bumper damage was similar in vehicle and barrier tests if the bumper mounts buckled. The exception was the Toyota rear bumper, which rotated in opposite directions in vehicle and barrier tests, though with about equal magnitude. However, if the bumper mounts did not fail, or if the bumper was mounted directly to the frame rails, then bumper damage was different in the vehicle and barrier test. In these cases, the bumper beams tended to bow between the unyielding mounts and when contacted by the rounded vehicle bumper, while they remained flat after the barrier impact.

The test data presented in this study established that both front and rear bumpers of five pickup trucks sustained at least localized damage when subjected to nominal 8km/h speed changes in collisions with a fixed barrier or another vehicle. Full-sized pickup trucks sustained less bumper damage than compact trucks for equivalent speed changes, though there was variation in compact truck performance. Nonetheless, given the rigid nature of the bumper itself, little damage to the bumper did not equate to the forces subject to the occupants of the vehicles itself. In fact, through utilization of appropriate biomechanical testing, it was determined that the absence of bumper damage on a rigidly mounted bumper did not in any way rule out the probability of serious injury, including brain injury, to the
occupants therein.

Accordingly, by utilizing appropriate experts, and by staying abreast of current literature, the Scarlett Law Group is able to educate juries as to why serious injuries occur with seemingly little property damage.

Even in cases involving significant property damage, for example where the Jaws of Life has been utilized in order to extricate the occupants of a vehicle, biomechanical analysis must still occur. Whether the collision involves a large truck, a school bus, a pickup truck, or a small sedan, the Scarlett Law Group, and its team of experts, stand ready to assist you in your time of need.

If you or someone you know has been injured as the result of an auto accident or car crash, you need the assistance of the Scarlett Law Group. Call (415) 688-2176 today to speak with a San Francisco car accident lawyer.

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