Tractor-Trailer Sustains Severe Fire Damage

Tractor Trailer Fire Damage

R. Scott King, BSME, Principal Automotive / Mechanical Engineer ::::
A commercial tractor-trailer sustained severe fire damage during an overnight stay in a parking area of a heavily traveled interstate. No one was in the truck at the time of the fire; however, security surveillance cameras recorded the event and the video became an important element of the ensuing investigation.
A preliminary engineering review included a study of the truck’s recent maintenance and repair records, as well as an interview with the truck owner. This identified two areas on the truck that warranted a detailed visual examination. It also identified potentially relevant parties for the subsequent, joint-expert examination. Specifically, the truck owner produced service records reflecting battery and starter repairs performed one month before the loss. He also reported that after those repairs, he had trouble starting the truck, along with other electrical problems. He returned to the shop that performed the repairs; however, those complaints went unremedied. Continue reading “Tractor-Trailer Sustains Severe Fire Damage”

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. Continue reading “Fifth-Wheel Decoupling”

Watch Where You Stand

Off-Tracking of Right Turning Tractor-Trailer

Steven M. Schorr, P.E., President of DJS Associates ::::
A tractor-trailer operator was executing a right-hand turn at a four-way intersection in a major city. As he was completing his turn and heading straight down the roadway onto which he turned, he was flagged down by a person who advised him that his truck contacted a pedestrian.
The physical evidence indicated that indeed the right side of his trailer did contact the pedestrian and knocked him down whereupon the pedestrian was run over by the right rear trailer tires of the right-turning tractor-trailer.
These dynamics are consistent with the properties of a right (or left) turning tractor-trailer wherein the tractor pulls the trailer. The trailer itself has no steering therefore as a result, in a right-hand turn, the right rear tires of the trailer will always track to the inside of the path of the right front tires of the tractor. This concept is referred to as “off-tracking”. The longer the trailer, the further to the inside (of the front tractor tires) the rear trailer tires will “off-track”. Continue reading “Watch Where You Stand”