They Did What?! Analyzing Human Behavior from a Human Factors Perspective by Dr. Nancy Grugle Adriver who drowned after driving into a river, a fire at a manufacturing plant and a driver who was killed by a train after stopping on active train tracks — these cases seem to have nothing in common at first glance. However, all of these cases involve human factors issues related to human behavior and performance (e.g., vision, attention, perception, information processing and decision-making) despite their seemingly unrelated circumstances. To provide some insight into how a human factors expert evaluates human performance and behavior in a variety of circumstances, I describe my role as a human factors expert in three of the most interesting cases I have worked on over the last 10 years. Human factors is the scientific study of how humans interact with technology and their environment. Human factors experts can evaluate human behavior and performance in various circumstances, addressing why people behave in a certain way, how the environment affects their behavior and what actions they are likely to take. Regardless of the specific type of case I am working on, I am frequently asked to evaluate whether a person’s actions or inactions were “reasonable.” However, it is important to differentiate between a reliable human factors opinion on the reasonableness of a person’s actions and a jury’s consideration of whether the person’s actions were reasonable. From a human factors perspective, the reasonableness of a person’s actions is determined by whether their actions are consistent with the known capabilities and limitations of human beings and/or consistent with other people’s actions under similar circumstances. For example, a jury might consider driving after only five hours of sleep to be “reasonable” from their perspective, but scientific research indicates driving after only five hours of sleep dangerously increases crash risk. Or a jury might consider it “unreasonable” for a commercial truck driver to make a driving error because they are trained, professional drivers. However, scientific research shows professional drivers are subject to the same inherent human capabilities and limitations as any human driver regardless of their training. Thus, a human factors analysis of the reasonableness of a person’s actions can not only provide reliable, scientific support for opinions related to a person’s behavior, but it can also dispel common misconceptions among the jury. Why Would a Person Drive Off the End of a City Street into a River Unless They Were Too Drunk to Drive? In this case, a young woman disappeared on her way home from a night out drinking with friends in the city. After 9 days, the police were able to track the last known location of her cell phone to the bank of a river at the end of a dead-end city street. Surveillance video from a nearby business showed her car driving down the dead-end street, over a curb and down an embankment into a river below. I was asked to evaluate whether the roadway environment provided a driver with sufficient information to be able to determine the street dead-ended into a river. As part of my investigation, I applied the human factors constructs of wayfinding, expectancy and positive guidance to my evaluation of the roadway environment. On this street, there were no advanced warning signs to inform a driver it was a dead-end street; there were no barriers to prevent a driver from driving off the end of the roadway; there were no warning signs where the roadway ended; and there was only a small curb to mark the end of the street which was covered in vegetation. In other words, there was no visual information available to a driver that differentiated this dead-end street from any other street in the city that did not dead-end into a river. In addition, the embankment after the curb sloped downward to the shoreline away from the driver and the water level of the river was approximately seven feet below street level, completely preventing a driver from detecting its presence. Perhaps most importantly, this incident occurred at night and the view looking straight ahead from a driver’s perspective appeared to show a continuation of the roadway on the other side of the river. Street lights, buildings and vehicles all seemingly continued DR. NANCY GRUGLE is a human factors expert witness specializing in transportation, premises safety and product warnings. She works at Evidence Solutions, Inc., 333 N. Wilmot Rd, Suite 340, Tucson, AZ 85711. She can be reached at ngrugle@evidencesolutions.com and 720-879-1162. 44 Trial Lawyer | Winter 2025
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