Injury Risk of Road Departure Crashes using Modeling and Reconstruction Methods

Each year roughly there are roughly 40,000 traffic-related fatalities. Common roadside objects such as trees, poles, guardrails, embankments, culverts, and fences result account for roughly 46% of these fatalities. Efforts to reduce to injury risk and risk exposure in these crashes have been hampered by the difficulty in performing reconstructions.

To address the need for accurate reconstructions in order to assess injury risk, a vehicle-specific stiffness database was added to the WinSmash reconstruction program. This single modification increased the average estimated delta-V by 8% and reduced error from 23% to 13% on average. A method to extend the WinSmash energy-based reconstruction approach to poles and trees that were damaged or broken was implemented to provide delta-V estimates for these crashes. The error of the pole and tree reconstruction component was roughly 44% but still represented a significant step forward for these crashes which previously could not be reconstructed.

The use of strong-post w-beam guardrail along roadsides is the primary method by which exposure to risk is reduced. Efforts to model guardrails using finite element methods were hampered by the large number of unknowns and lack of knowledge about the sensitivity of the crash outcome to each variable. Through a parametric study the soil properties and rail mesh density were identified as the most significant influences in simulation outcome. This knowledge was applied to finite element models of damaged guardrail to identify when the damage compromises the guardrail ability to prevent risk exposure. Models of guardrail with rail deflection, missing posts, and missing blockouts identified rail deflection over 6 inches and any number of missing posts as hazardous conditions. The removal of a single blockout was found to be acceptable if not desirable.

These findings have far-reaching implications. The enhanced WinSmash reconstruction program has been adopted by NASS/CDS to generate delta-V estimates used by researchers in all areas of transportation research. The identification of hazardous guardrail was of great interest to transportation agencies responsible for prioritizing and performing repairs of damaged guardrail.