Roadway Design

New Technology in the Evaluation of a Guiderail Collision

Case Synopsis: A southbound vehicle leaves the roadway to the left in the area of an exit and strikes a guiderail at an angle of approximately 85 degrees [almost perpendicular].  The vehicle breaks through the guiderail, travels down a ravine, and rolls over, killing the operator.  The claim versus the governing authority was that the guiderail had been previously damaged and, as a result, was weakened.  Further, the claim was that had the guiderail been in its proper, undamaged condition the vehicle would not have broken through and would not have ultimately rolled over and the operator would not have been killed.

Expert Analysis: The physical evidence included tire tracks defining the path and impact orientation of the vehicle as it struck the guiderail,  the damage to the vehicle that defined the rollover orientation, and data captured on the Sensing and Diagnostic Module -SDM [the airbag module] of the vehicle.  The SDM data [after being properly evaluated and correlated to the field data from the collision] noted the speed of the vehicle, prior to the airbag deployment, to be 67 mph [17 mph over the speed limit].  Further, the SDM data and the reconstruction analysis noted the speed of the vehicle at the time of the collision with the guiderail was approximately 60 mph.  Engineering references, including specific crash test videos, established that guiderails are defined to be effective when impacted at speeds of 65 mph and at angles of 25 degrees or less.  In this case, the guiderail was impacted at an angle of 85 degrees, almost perpendicular, not an angle and speed that the guiderail was designed to withstand.  Finite Element Analysis [FEA] was completed to analytically evaluate the capabilities of the guiderail to hold at 60 mph and 85 degrees.

Conclusion: The FEA analysis confirmed the research data indicating that, despite the claims by the Estate of the driver, due to the speed and angle of the collision, even a properly maintained guiderail would not have prevented the tragic and fatal rollover.

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