Airborne Motorcyclist: Was Speed an Issue?

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Curt M. Beloy, MSME ::::

Case Synopsis: Eastbound motorcyclist on a two-lane road encounters a left hand curve and fails to properly navigate it. He leaves the road to the south and enters a grass field where he makes contact with a fixed object, severely injuring himself. At the scene, the police document the physical evidence with total station survey equipment, including rest positions of the motorcycle and operator, contact damage to the fixed object, and the tire marks left by the motorcycle in the grassy field. A lawsuit was filed against the property owner (i.e. fixed object) and as a result, speed of the motorcycle became a major issue.

Expert Analysis: DJS Associates was retained to analyze the physical evidence and render an opinion, if possible, regarding motorcycle speed. Early in the analysis a site inspection was completed and a high definition survey [HDS] laser scan of the roadway and neighboring grass field was performed. The police survey points were later plotted on the site scan data to establish the path of the motorcyclist as he left the roadway and continued to impact. Analysis of the data revealed that the field had a complicated profile; a gap in the tire mark in the middle of the grassy field was consistent with the motorcycle becoming airborne during its path to the point of rest.

The vertical profile of the field along the path of the motorcycle was taken from the HDS laser scan data and accurately modeled in three-dimensions within vehicle dynamics simulation software. The motorcycle motion over the terrain was analyzed to determine a range of speeds required to result in the motorcycle becoming airborne as defined by the gap in the tire marks. The simulation results were consistent with manual calculations completed utilizing the physical evidence including the vehicle damage and post impact dynamics. The ultimate opinion was that the motorcycle was traveling in excess of the speed limit at the time it left the roadway.

 

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