The Roadside Safety Pooled Fund recently funded a research project evaluating the MASH compliance of reduced post spacing Midwest Guardrail Systems (MGS). However, states would benefit from an expansion of that research to evaluate the reduced post spacing MGS when installed with a sloped roadside. While MASH (1) Test Level 3 (TL-3) is the desired impact severity, an evaluation of TL-2 deflections of this barrier system is also beneficial as this system can often be found on lower speed roadways. The desired effort is to first evaluate the reduced post spacing with the posts at the slope break point. If successful, then evaluate the crashworthiness if the posts are shifted onto the sloped face.

Objective

The project objective is to evaluate the crashworthiness of reduced post spacing MGS installed with sloped terrain. The primary objective is a TL-3 evaluation of this system. If project resources allow, an additional TL-2 computer simulation evaluation to predict dynamic deflections will be performed.

Benefits

Reduced post spacing systems are utilized when roadside obstacles, such as trees and poles, prohibit the clear space required for standard post spacing MGS dynamic deflections. In certain locations, these obstacles are located near slopes, which requires an evaluation of the reduced post spacing MGS with sloped terrain. A report describing the results of the computer simulations and crash testing for reduced post spacing MGS, specifically with deflections from the various analyses, will aid states with the objective of MASH implementation.

Products

The TTI research team will provide a final report that will include the results of the computer simulations and crash tests. The report will include dynamic deflection measurements from the crash testing and computer simulations.

Work Plan

The work plan for this research includes the following tasks:

Task 1: Literature Review
The Task 1 objective is to review previous literature and testing related to crashworthiness of guardrail systems with sloped terrain. The TTI research team will accomplish this review through various means, including use of internet search engines, as well as databases like the Roadside Safety Pooled Fund MASH database and the Midwest Roadside Safety Facility library of research projects. This reviewed information will lay the foundation for the analyses in Task 2.

Task 2: Computer Simulations

The TTI research team will first develop a detailed finite element analysis (FEA) model of the MGS installed with sloped terrain. The posts will be located at the slope break point similar as was evaluated in Midwest Roadside Safety Facility test MGSS-1 (2). Subsequently, the TTI research team will use the explicit finite element code LS-DYNA (3) to perform initial impact simulations using the developed barrier model and currently available vehicle models. The TTI research team will compare these initial simulations to previous crash testing identified in the Task 1 Literature Review to ensure proper predictive capability. If needed, the TTI research team will make modifications to these models to improve predictive capability. Once the models’ predictive capability has been confirmed, the TTI research team will develop variations of the model to include quarter-post spacing (18.75 inches) and half-post spacing (37.5 inches). These models will then be used in computer simulations of MASH tests 3-11 and 3-10 to predict the crashworthiness and dynamic deflection of the variations. The models will then be modified to place the posts on the slope face so the w-beam rail is aligned with the slope break point. This model will then be used in computer simulations of MASH tests 3-11 and 3-10 to predict the crashworthiness and dynamic deflection of the reduced post spacing variations. The research team will then select the critical system (quarter- or half-post spacing) for crash testing based on the computer simulation results

 

Upon approval of the testing plan by the technical representative, the TTI research team will install the critical system (as determined by computer simulations in Task 2) at the Texas A&M University System RELLIS Campus. The TTI research team currently plans to perform both MASH tests 3-11 and 3-10 on the critical system.

 

This task includes the reporting and documentation of the project’s effort. The TTI research team will prepare and submit a research report fully documenting the work completed within this project. This documentation includes a professional opinion for the reduced post spacing configuration which was evaluated through computer simulation, but not physically crash tested. This justification will be provided if the physical crash tests of the critical system are successful and there is positive correlation between the computer simulation and physical testing. The TTI research team will submit this report to the technical representative of the Roadside Safety Pooled Fund for review and approval.

Time Schedule

Started: August 2024
Time frame: 18 months

 

 

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Updated January 15, 2025