Forensic Engineering Analysis of a Crash Caused by Swingout of an Articulated Booster on a Semi-Trailer


  • DONALD FOURNIER Forensic Engineering Technologies, LLC
  • Shawn Ray SEAlimited
  • Steven Mitchell Forensic Engineering Technologies, LLC
  • Reza Vaghar Forensic Engineering Technologies, LLC



Truck-tractor, lowboy semi-trailer, swingout, booster axle, dolly, rolling lateral friction, cross over collision , forensic engineering


An unloaded lowboy trailer with an articulated booster axle was traversing a curved exit ramp when the trailer tires lost traction, and the booster axle redirected the rear of the trailer into oncoming traffic. The reconstruction used a detailed analysis of roadway geometry, truck geometry, and suspension characteristics to determine the cause of the trailer swingout. A comprehensive topographical map was created from 3D laser scans. The interaction of each tire with the pavement surface was used to determine the individual wheel loads. Dynamic analysis of the curved path quantified the speed required to cause loss of traction and subsequent swingout.

Author Biographies

DONALD FOURNIER, Forensic Engineering Technologies, LLC

Donald Fournier, P.E. is president of Forensic Engineering Technologies. His 30 year career as a mechanical engineer includes positions in industry, academia, and consulting.  His work as a forensic engineer includes traffic accident investigation and reconstruction, evaluation of industrial and consumer products, and premises liability claims.

Shawn Ray, SEAlimited

Shawn Ray is a Senior Mechanical Engineer and has been evaluating mechanical failures and performing accident reconstruction for more than 30 years. 

Steven Mitchell, Forensic Engineering Technologies, LLC

Steven Mitchell, Ph.D., P.E. is a project manager at Forensic Engineering Technologies where he investigates and reconstructs traffic accidents involving heavy vehicles, passenger vehicles, bicycles, pedestrians, and traffic signal operation. 

Reza Vaghar, Forensic Engineering Technologies, LLC

Reza Vaghar, Ph.D., P.E. is a project manager at Forensic Engineering Technologies. With more than 18 years of experience as a mechanical engineer, he investigates events related to vehicle accidents, walkway safety, product failure, and safety analysis. He applies the principles of physics, engineering, and safety to the evaluation of walkways, consumer products and manufacturing processes. Dr. Vaghar has reconstructed many accidents involving automobiles, motorcycles, pedestrians, and commercial vehicles.


A Policy on Geometric Design of Highways & Streets AASHTO, 6th Edition, 2011.

Measurement of Vehicle-Roadway Frictional Drag, SAE J2505, 2010.

Use of the Critical Speed Formula, SAE J2969, International, Society of Automotive Engineers, Jan 2017.




How to Cite

FOURNIER, DONALD, Shawn Ray, Steven Mitchell, and Reza Vaghar. 2022. “Forensic Engineering Analysis of a Crash Caused by Swingout of an Articulated Booster on a Semi-Trailer ”. Journal of the National Academy of Forensic Engineers 38 (2).