Improved method for roadside barrier length of need modeling using real-world trajectories

Area of Science:

• Road safety engineering
• Traffic engineering
• Transportation safety

Background:

• The 2011 AASHTO Roadside Design Guide (RDG) procedure for length of need (LON) is widely used but has limitations.
• The RDG procedure employs a simplified vehicle departure model and lacks explicit protection level specification.
• Existing methods may not accurately reflect real-world crash scenarios or offer designers precise control over safety outcomes.

Purpose of the Study:

• To introduce and evaluate a novel procedure for determining the length of need (LON) for roadside barriers.
• To address the limitations of the 2011 AASHTO Roadside Design Guide (RDG) procedure, specifically its simplified vehicle departure model and lack of explicit protection levels.
• To provide a more realistic and customizable approach to roadside safety design.

Main Methods:

• Development of a new LON procedure based on recent, real-world road departure trajectory data.
• Utilization of departure data in a more realistic simulation model.
• Comparison of LON recommendations from the new procedure against the 2011 RDG procedure.

Main Results:

• The 2011 RDG procedure provides LON sufficient to intercept 80-90% of right-side departures for hazards at 10m on 55 mph roads.
• The RDG procedure's protection level varies with hazard offset, becoming more conservative closer to the roadway.
• The improved procedure offers a consistent protection level irrespective of hazard location.

Conclusions:

• The new LON procedure offers a more accurate and adaptable method for roadside safety design.
• It allows for specifying protection based on crash frequency, injury severity, or cost.
• This approach ensures a predictable and consistent level of safety for roadside features.