Biomechanical Analysis of a Bicycle/Bus Accident

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Robert J. Nobilini, Ph.D. ::::

Case Synopsis:   A cyclist was struck and then run over by the rear tandem wheels of a bus.  Witnesses reported that the bus stopped after the man was initially run over by the first set of wheels.  At this point the man was trapped between the wheels of the two tandem axles.  The bus was then moved forward a second time in an attempt to free the man.  A biomechanical analysis was requested to reconstruct the dynamics of the man’s interaction with the rear wheels of the bus to determine whether the man’s fatal injuries occurred during the first or second movement of the bus.

Expert Analysis:  The medical examiner’s report listed the cause of death as a flailed right chest.  Other injuries included an open fracture of the right arm with a degloving of the right forearm and upper arm.  The medical examiner’s photographs revealed black marks and bruises on the right hand and arm and a tire mark that extended from the lower right abdomen up and across the right chest. The police report and photographs of the incident site documented certain physical evidence at the scene including blood marks and various parts of the bicycle. There was testimony regarding the position of the man’s body at various times during the incident.  However, the witnesses were not able to explain the details of the man’s interaction with the rear wheels of the bus. 

A 3D computer model of the incident bus and location were created based on high definition laser scans.  The path of the bus and the locations of the physical evidence were located in the model.  An articulated model of a human male with the man’s physical dimensions was used to recreate the various positions of the body and bus that were described by the witnesses.  The man’s injuries were then matched up to the physical evidence and the wheels of the bus to determine the dynamics of the man’s interaction with the bus during the incident.   

Based on this analysis it was determined that the man’s right arm was initially run over by the front set of wheels.  His forearm became pinched between the dual tires of the forward axle.  As the bus continued to move forward, the man’s arm was rotated upward with the wheels and his body was pulled up against the under carriage of the bus.  At this point the bus stopped.  When the bus was moved the second time, the man’s right arm was pulled forward, causing his right torso to be pulled into the path of the rear wheel.  The rear wheel then mounted the man’s lower right abdomen, ran over his right chest, dismounted over his right shoulder, and stopped approximately 1 foot forward of the plaintiff’s right hand. 

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Result: Once the dynamics of the man’s interaction with the bus were determined, the sequence of events was animated for demonstrative purposes.  The animation provided a means to visualize and further verify the complex dynamics of this incident.  Ultimately, the analysis revealed that the man’s fatal injuries occurred during the second movement of the bus, when the rear wheel rolled over his chest.
      

 

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