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Paul Abelson

Through finite element analysis, engineers determine the forces and vectors causing the distortion of the original vehicle structure. It is not uncommon for an engineering firm to test parts and tweak the computer program many times, crumpling fenders, bumpers, trunks, and doors until they recreate the damage done at the scene.

It's one thing to have an expert testify as to what the witness believed happened, and quite another to show an animation, then compare the actual with the recreated image. But best of all is bringing in a damaged test part that is virtually identical to the part from the crash.

There were many sessions in accident reconstruction at the recent International Congress of the Society of Automotive Engineers (SAE). A common theme was that one successful test is worth 10,000 expert opinions.

The engineers also examine all pertinent paperwork, the crash scene, and climate records. They'll interview the driver, if possible, and other fleet personnel, especially in maintenance.

Using failure analysis, forensic engineers can examine damaged or failed parts to determine if parts were damaged or weakened before the incident or as a result of it. They examine the vehicle's maintenance paperwork. For larger trucks, this includes the drivers' vehicles inspection reports, required in parts 392.7, 396.11, and 396.13 of 40 CFR, or the Federal Motor Carrier Safety Regulations.

If discrepancies are reported in a post-trip report, there must be a record that they were addressed. If not, the other side can use that against you.

Other factors

Weather and road conditions can play a big role in the cause and magnitude of crashes, even when it was dry and sunny. In one case described at SAE, a stretch of dry asphalt road generated 0.58g (forces of gravity, a measure of traction) but dust blown onto it reduced that to about 0.33g. In sections, wet clay had been dropped from dump trucks. It reduced traction below half that of the dry road.

Either side may depose drivers and maintenance personnel, and they may have to testify about safety training, maintenance practices, and other factors that may have affected the crash. These interviews could be fishing expeditions, but they could uncover a fleet practice that contributed to the crash.

New trucks have electronic data recorders that monitor throttle position and rate of change of pedal movement, and the same for the brake pedal. Some also log steering wheel angle and rate of change of steering. Recorders lock data into memory for a given number of seconds before and after the crash.

When the forensic engineers are done, they can go to court with a virtual reality model of the crash. Using these data, engineers can reconstruct the driver's actions, often with greater accuracy than the driver can recall.

In one case, the engineers presented an overhead view of the crash. Each witness, including the vehicle occupants, stated that the crash did not occur quite that way. But when lawyers asked where each observer was and the computer was programmed to present the scenario as seen from each witness's position, all agreed that the simulation was exactly what happened.

Accident reconstruction is a double-edged sword. It can cut for you, destroying the claims made by your opposition, or it can cut against you, proving the other side's case if they are right. Just remember, in a crash involving injury or death, reconstructions by forensic engineers will most certainly be entered as evidence.

— Paul Abelson is a former director of the Technology and Maintenance Council of the American Trucking Associations. You can e-mail him at truck writer@anet.com.