Accident Reconstruction


Accident Reconstruction/Bio-Mechanics is one of the most essential part of almost all cases. Though liability for many vehicular/trucking collisions is clear, accident reconstruction and workup of the biomechanics of injury are required for proper trial presentation. To give every case their best, 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 can result in much greater injury to occupants in even low speed impact collisions.

The presence or absence of motor vehicle bumper damage is usually considered to be important while estimating the severity of a low speed, or minimal damage collision. There are several types of bumpers. Bumpers on most passenger cars contain elements designed to dissipate the impact energy. Some examples of such elements are shock absorber-like isolators, foam cores or lattice cores.

A number of studies have provided insight into analyzing collisions involving these kinds of bumpers. Most SUVs, vans and pickup trucks have a rigid bumper system. This system consists of a steel bumper beam attached to the vehicle frame either directly or by mounting brackets. There are two methods used for investigating the performance of rigid bumper system during low speed collisions. Vehicle-to-vehicle test is considered the best replica of the actual collision. However, barrier impacts are widely used in mandatory standards compliant tests. 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.

Accident Reconstruction

In one study, damage produced in barrier and vehicle-to-vehicle test of a similar severity was compared 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. When re-enactment, either via computerized projection or actual vehicles is performed for forensic purposes, the Scarlett Law Group and its expert choose the most viable option available.

For example, in one study 5 pickup trucks (a 1980 Ford F-150 Pickup, a 1981 GMC C-1500 Pickup, a 1983 Toyota Half-Ton Pickup, a 1983 Chevrolet S-10 Pickup, a 1984 Ford Ranger, and a 1993 Ford Crown Victoria) 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. 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.

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 load 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 was 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.

Accident Reconstruction

The differences between the damage caused in the vehicle-to-vehicle and barrier tests 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-to-vehicle and barrier tests if the bumper mounts buckled. The exception was the Toyota rear bumper, which rotated in opposite directions in both vehicle-to-vehicle and barrier tests, 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-to-vehicle and barrier test. In these cases, the bumper beams tended to bow between the unyielding mounts 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 all five pickup trucks sustained at least localized damage when subject ed to nominal 8 km/h speed changes in collisions with a fixed barrier or another vehicle.

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