Expertly Speaking


Fifth-Wheel Decoupling

R. Scott King, BSME, Principal Automotive / Mechanical Engineer ::::

A commercial semi-trailer detached from its tractor and came to rest within the roadway, blocking several travel lanes. Before the tractor-trailer operator could place her reflective warning devices on the roadway, the operator of an oncoming passenger vehicle approaching the detached trailer steered sharply to avoid it and in doing so, lost control of her vehicle resulting in significant injuries to herself and the occupants within the vehicle. A post-incident investigation revealed the tractor-trailer combination had recently departed its terminal and traveled several miles before detaching. Police investigators concluded that the sole cause of the separation was that the operator failed to properly connect the tractor and trailer before departing for the trip. Forensic engineers, however, came to a more detailed conclusion.

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3D Collision Reconstruction – A Dashcam Video Case Study Breakdown

Laurence R. Penn, Senior Forensic Animation/Video Specialist ::::

Thanks to powerful software, forensic video specialists at DJS Associates are able to analyze surveillance and dashcam video footage in three dimensions, with high levels of accuracy, in order to reconstruct the circumstances of an accident. Although multiple factors may complicate the process, tenacity and an eye for detail can yield rewarding results. In this case study, the original dashcam video footage showed evidence of lens distortion which needed to be corrected in order to proceed with detailed videogrammetric analysis. After a few phases of lens correction, environment features represented by the red crosses were placed in the undistorted video frame and matched to their locations in the 3D scan data. Once refined the virtual camera is placed accurately within the 3D environment. Trackers represented by the green and yellow crosses were placed on features of the vehicles for each frame in the video. Again, these positions were matched to their relative locations on the 3D vehicle scan data. The final analysis allows 3D vehicles to be placed in the 3D environment spatially and temporally in order to view the circumstances from alternate angles, and even from the operators or eye witness point of view.

Laurence R. Penn, Senior Forensic Animation/Video Specialist at DJS Associates, can be reached via email at or via phone at 215-659-2010.

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Product Liability Expert Witness

Forensic Biomechanics/Functional Anatomy/Physiology Analysis of Erectile Dysfunction: A Defense Perspective in a Product Liability Case

Patrick Hannon, Ed.D., Biomechanical Expert ::::

In forensic biomechanics, most of us who provide expertise in this discipline have a large percentage of vehicle accident cases [1]. Certainly, as experts we appreciate unusual cases and new challenges outside the box of auto accidents. This specific case involved the defense of a bicycle seat manufacturer in a claim involving a middle aged man who reported that after an approximate 30 mile ride, the nose of his bicycle seat saddle had deformed during the last few miles of his ride resulting in his chronic erectile dysfunction (i.e. ED).

Read the full article here – A Defense Perspective in a Product Liability Case

Patrick Hannon, Ed.D., Biomechanical Expert with DJS Associates, can be reached via email at or via phone at 215-659-2010.

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OSHA Expert Witness

Assessing Construction Site Safety: Who’s Responsible?

Lt. Col. Bryan J. Smith, PE, Construction Site Safety Expert ::::

Case Description/Summary: During the performance of a project to construct a multi-unit apartment complex, a second tier subcontractor foreman was injured while removing temporary stairs. One temporary stair riser section collapsed while he was working upon it to free it for removal, resulting in his twenty foot fall and severe personal injury.

Expert Analysis: Long after the incident, a site survey was conducted to inspect all of the removed temporary stair sections. No evidentiary findings could be made from the inspection. A review of all involved parties’ responsibilities revealed that the represented defendant firm was not responsible for this portion of contract work though they did have responsibility for all underground utilities and site improvements. The general contractor (GC) for the building portion of the project is held responsible for overall site safety by OSHA.

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Mississippi Moon

Robert T. Lynch, PE, Principal Collision Reconstruction Engineer ::::

…won’t you keep on shinin’ on me

When evaluating nighttime collisions, a reconstructionist may choose to visit the accident location under similar conditions in order to observe the artificial light sources (i.e. street lights, nearby business lighting, traffic lights, etc.) to get a sense of what a driver could have seen leading up to a collision. Where a well-lit intersection could illuminate the roadway as if it had the appearance of daytime, a driver on a dark roadway may not have sufficient time and distance to perceive, react and avoid a dark-clothed pedestrian crossing the roadway.

While the historical moon data is researched and taken into consideration for a similar conditioned inspection, the moon is often not a factor in contributing to the overall useful illumination of the roadway. The definition of “useful” illumination is often taken to be an area of the roadway illuminated above 3.2 LUX, the dark limit of civil twilight (~30 minutes after sunset). Research has shown that beyond the limit of civil twilight, visual recognition functions deteriorate rapidly. The term “twilight envelope” has been coined to describe the useful extent of the vehicle headlight beam effecting a driver’s visibility at night.

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River Rafting Expert Witness

High School Student Drowns on River Rafting Trip

Tom Griffiths, Ed.D., Aquatic Safety Expert ::::

Case Synopsis: A high school Senior participated on a Senior class rafting trip approximately two hours away from the school. Because he was a non-swimmer his father refused to sign the permission slip to go on the field trip. The victim wanted to go badly because his friends were going, so he forged his father’s signature and as a result, the school allowed him to attend. Although the weather was sunny and warm, the river was extremely high and fast due to heavy rains earlier in the week. All six participants in the victim’s raft removed their lifejackets shortly after launching. Soon after removing their lifejackets, the raft rode up the face of a large standing wave and all six students were ejected into the raging river. All students managed to get to shore safely except for the victim who was found dead several days later. The cause of his death was drowning.

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