What You Don’t See Can Hurt You-Undercarriage Crashes


Expertise Includes:

    • Human Factors & Safety
    • Vehicle/Pedestrian/Bicycle Crash Investigations
    • Illumination Evaluation
    • Workplace Injuries
    • Codes and Standards
    • Risk Assessment
    • Slips, Trips and Falls

A 43-year-old man driving his small vehicle northbound in the right lane of a rural two-lane paved road, was on his way to his favorite hunting spot in the early morning. He had two passengers with him—one in his front passenger seat and one in his back left seat. It was dark outside, and the weather was clear and dry. Along the rural two-lane road were large wooded private properties with no ambient lighting illuminating the roadway. Further up the road, a log truck began to turn left onto the road. Unable to entirely turn left in one fluid movement, the log truck stopped and began to back up in order to successfully make the left turn without falling into a roadside drainage ditch. While the log truck driver was maneuvering his truck and trailer, the empty black colored log trailer was positioned perpendicular to the roadway, and the truck itself was positioned southbound in the left travel lane. While the truck driver was maneuvering, the northbound small vehicle driver collided with the empty log trailer, resulting in an undercarriage collision and fatal injuries to all three people in the small vehicle. According to data obtained from the vehicle, the driver started braking only 0.5 seconds before impact. Due to the speed of the vehicle, the driver was unable to fully arrest the vehicle before impact. What factors were involved in tis specific incident? Why did the small vehicle driver fail to see the large trailer in his path?

Depiction of the incident. The log truck was turning left into the southbound lane of the road while the smaller vehicle was traveling northbound in the right lane. Photo courtesy of “Southern Loggin’ Times.”

One factor involved in this undercarriage collision is that the human visual system is not adapted to perform well in the dark. Light is required for color perception and visual acuity (ability to see fine detail). As the environment darkens, accurate color perception and visual acuity both diminish. This makes the highly visual task of driving difficult for drivers to successfully perform at night. In order to aid in driver nighttime performance, relevant objects, such as road signs, roadway markings, taillights, and headlights are designed to be visible in dark conditions. However, objects that were not designed to remain visible in low luminance environments are extremely difficult to detect. In this incident, the driver of the small vehicle was likely unable to detect the presence of the dark and unmarked empty log truck trailer due to its lack of contrast within the environment as well as the small surface area facing the small vehicle driver. These visual and environmental factors resulted in the collision. Had the log trailer been marked with retroreflective material or active lighting, the undercarriage crash could have been avoided due to the log trailer’s increased contrast, therefore increased visibility within the roadway. The increased visibility of the log trailer with retroreflective markings would have afforded the small vehicle driver earlier detection of the trailer’s presence, granting more time for the driver appropriately react to the hazardous trailer and avoid a collision.

Log trucks often make wide turns to accommodate for their trailers. This can lead to trucks and trailers positioned perpendicular to the roadway causing significant hazards for other drivers.

In addition to the low visibility of the log trailer, the perception of the truck’s location based on its headlights led the small vehicle driver to believe the roadway was clear of hazards. As the small vehicle driver was approaching the truck, it would have appeared as if the truck was located in the left lane and oncoming toward the driver. An oncoming vehicle in the opposing travel lane does not typically present a threat to drivers. Additionally, the higher visibility of the truck’s trailer headlights likely attracted the attention of the small vehicle driver away from the low visibility log trailer hazard in the northbound land. The log truck headlights also produced excessive glare for the small vehicle driver. It is established in research that excessive glare from oncoming vehicles has the potential to negatively impact the driving performance and the ability to detect roadway hazards of drivers. In this instance, the glare from the log truck headlights further diminished the driver’s ability to see the dark, empty log trailer in his travel path.

A human factors analysis of the incident facts revealed significant factors contributing to the undercarriage crash. Those factors included the dark surrounding environment, the low visibility of the log trailer, and the perceived location of the truck. The undercarriage collision would likely have been avoided if the trailer was equipped with visibility aids such as retroreflective material or active lighting to assist in the small vehicle driver’s perception in the challenging environment.

Ellen Szubski, Ph.D., CXLT, CPSI, AHFP, is a human factors consultant at The Warren Group. She earned a Doctorate of Philosophy in Human Factors Psychology and a Master of Science in Applied Psychology from Clemson University.  She did her dissertation on “The Influence of Pedestrian Biological Motion on Time-To-Collision Estimates at Night”.  She is also a Certified XL Tribometrist, Certified Playground Safety Inspector and and a Certified Associate Human Factors Professional (AHFP). Prior to entering the forensic field, Ellen planned and conducted experiments for a major bicycle manufacturer. She also conducted laser strike perception studies for the Department of Defense.  Ellen applies her experience in Human Factors to the analysis of crash investigations and other personal injury matters. These matters often include collisions involving vulnerable road users and drivers, driver distraction, and slips, trips, and falls. She utilizes her knowledge of OSHA regulations, codes, and standards in her analysis of premises liability incidents and safety consulting.  Ellen is a current member of the Human Factors and Ergonomics Society (HFES) and it’s Forensic Professional Technical Group.

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