The American Association of State Highway and Transportation Officials (AASHTO) published an updated 2016 edition of the Manual for Assessing Safety Hardware (MASH) document (1). Along with this, the Federal Highway Administration (FHWA) and AASHTO developed a revised joint implementation agreement which establishes dates for discontinuing the use of safety hardware that has met earlier crash testing criteria for new installations and full replacements on the National Highway System (NHS). Although some barrier testing was performed during the development of the updated criteria, many barrier systems and other roadside safety features have yet to be evaluated under the proposed guidelines. Sign support systems were developed and investigated according to Test Level 3 (TL-3) criteria per previous NCHRP Report 350 standard requirements. Most of the acceptance for NCHRP Report 350 devices was based on dynamic pendulum impact testing. Some of these sign support systems have been tested and evaluated under the current MASH Test Level 3 standard criteria. A recent TTI project evaluated a breakaway sign support system on a 6H:1V slope according to MASH TL-3 (Silvestri-Dobrovolny et al. 2023). The system was found to perform satisfactorily for the MASH criteria. Only one slope configuration was evaluated in the crash test. Additional investigation and analysis are required to understand the performance of breakaway sign support systems on varying slope configurations. The information compiled from this research will provide the FHWA and State Departments of Transportation with an increased understanding of the performance of sign support systems placed on slopes for MASH Test Level 3 conditions.

 

The project objective is to evaluate how roadside geometry can influence performance of breakaway sign support systems. Specifically, this project will evaluate the MASH TL-3 crashworthiness of breakaway sign support systems with different slope configurations. The evaluation will be initially focused on large guide signs. However, the analysis and results will also be considered for placement of other breakaway sign support systems on slopes.

Benefits

The results of this project will provide agencies with guidance on the placement of breakaway sign support systems on roadside slopes.

Products

The TTI research team will provide a final report that will include the results of the computer simulation analyses and guidance for the placement of breakaway sign support systems on slopes.

Work Plan

The work plan for this research includes the following tasks.

Task 1: Model Development and Validation
TTI’s research team will review the previous testing of a large guide sign on a 6H:1V slope (Silvestri-Dobrovolny et al. 2023). The research team will also conduct a review of any other relevant sign support testing on slopes. Further, the research team will review details and configurations for roadside ditch configurations. This will consist of state DOT standard detail review and available research literature. The research team will develop a finite element (FE) model of the large guide sign support system. The research team will also develop a representative model for the roadside ditch profile. The research team will perform a computer simulation replicating the impact conditions from the full-scale crash test (612261-05-2) to validate the FE model. The research team will compare the results from the computer simulation to the full-scale crash test. The comparison will focus on breakaway performance, vehicle trajectory, occupant risk metrics, vehicle deformation, and any other key metrics. The research team will make the adjustments to the finite element models, if needed, to improve the model performance.

Task 2: Computer Simulation Analysis of Slope Configurations
Using the validated FE model from Task 1, TTI’s research team will analyze the performance of the large guide sign support system on different ditch configurations. The number of ditch configurations analyzed will consist of the following:

The research team will base the selection of the parameters for the above list on the Task 1 findings and consultation with the Pooled Fund technical representative.

For each configuration, the research team will evaluate the system according to MASH TL-3. This will consist of impacting the system with the 1100C FE model and 2270P FE model. The impact speed will be 62 mi/h and the impact angle will be 25 degrees. Each computer simulation will be assessed according to the MASH TL-3 evaluation criteria. The research team will develop guidelines for placement of large guide signs on slopes based on the computer simulation findings. The research team will review the results of the computer simulations to identify trends and commonalities that indicate key crashworthy performance characteristics. The research team will consider these characteristics for application to other roadside sign support systems.

Task 3: Final Report
TTI’s research team will generate a final report of the findings from the research. The reporting results will include the model develop and validation and computer simulation analysis of breakaway sign support systems on slopes. The research team will include guidelines and recommendations in the final report for the placement of breakaway sign support systems on slopes.

Time Schedule

Started: March 2025
Time frame: 18 months

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March 20, 2025