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Beyond the Obvious- Human Factors in Accident Reconstruction


Human factors, those variables that affect a driver’s ability to operate the vehicle effectively, are often the most important and complex issues involved in understanding how and why a collision occurred. Addressing these factors can re-veal the underlying causes of a collision and help clarify questions of liability. The following example comes from a Sintra Engineering file, one that proceeded to court and is now part of the public record. At first glance, the incident seemed to have an obvious explanation. The outcome of the legal proceeding supported a very different explanation, which shows how advanced collision analysis can dramatically affect the way liability is ultimately apportioned.

The incident occurred early on a Monday morning along a single-lane, divided high-way just outside Calgary. There were three vehicles involved: a tow-truck with a lone occupant (McCabe Truck), a passenger vehicle with a lone occupant (Hewitt vehicle), and a passenger vehicle with seven occupants (Mossfeldt vehicle). The tow-truck was travelling westbound and the other two vehicles were eastbound. The tow-truck and the Mossfeldt vehicle collided in the eastbound lane. The collision was serious - six fatalities from the Mossfeldt vehicle and injuries to the tow-truck driver. The survivor in the Mossfeldt vehicle had been riding in the trunk and did not see the collision, and the tow truck driver recalled little about the incident.

Upon attending the accident scene, the attending police officers found that the people in the Mossfeldt vehicle had been partying at a campsite the night before. In addition there was evidence that the Mossfeldt vehicle was driving in the westbound lane, struck a guardrail on the north side of the road and returned to the eastbound lane where it collided with the tow truck. The markings on the roadway were clear; it appeared that both the tow truck and the Mossfeldt vehicle were in the eastbound lane immediately prior to the collision. The roadway markings suggested that the Mossfeldt vehicle was speeding.

This appeared to be an open and shut case: a carload of young kids, the driver - possibly drunk - was speeding, lost control of the vehicle or fell asleep and caused a fatal collision. Case closed.

The open and shut case began to turn on witness information provided by the driver of the third vehicle, Mr. Hewitt. He stated that he was almost run off the road by the tow-truck in the moments immediately preceding the collision. In fact, he saw the tow-truck swerve back into the westbound lane prior to the collision. A detailed time and reaction analysis by Sintra Engineering found that the sequence of events initially proposed did not fit with Hewitt’s observations.

A second, more likely scenario, emerged: the tow-truck driver lost control of his vehicle and swerved into oncoming traffic in the eastbound lane. To avoid a collision, the driver of the Mossfeldt vehicle initially steered into the westbound lane and then swerved back into the eastbound lane.  The high-speed impact occurred when both vehicles returned to the eastbound lane.

Because there were two versions of events, the matter proceeded to trial where it was revealed that the tow-truck driver suffered chronic pain in his leg, caused by a previous accident. To deal with the pain, he would take large quantities of Tylenol 3 with Codeine and was prone to binge drinking. In the hours prior to the collision, he had done both.

This information, combined with Mr. Hewitt’s description, supported the possibility that the tow-truck driver fell asleep while driving (from the alcohol and Codeine) and lost control of his vehicle. While trying to regain control, he almost drove Mr. Hewitt off the road before fishtailing and then coming back into the lane that the Mossfeldt vehicle had moved into.

During the trial, the human factors of the incident became significant. The timing of the collision, what could be seen by Mr. Hewitt, and how the drivers maneuvered their vehicles were critical. In the end, what appeared to be an open and shut case turned into a three week  trial. Liability was split between the two drivers - a big change from the initial presumption that the driver of the Mossfeldt vehicle was 100% responsible.

Accident reconstruction is as much a study of the people driving as it is of the dynamics of their vehicles. Every case is different. An analysis of the human factors influencing each collision allows for a fuller understanding of what happened, beyond the seemingly obvious, to reveal liability issues that weren’t readily apparent.


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