Many pooled fund states need a professional assessment of their roadside safety hardware and barrier system. The purpose of this project is to provide engineering support services and recommendations for various roadside safety hardware and barriers that pooled fund member states request be evaluated.
There is a need for an assessment of roadside safety barrier systems and hardware without necessarily performing full-scale crash testing. TTI recently completed NCHRP 20-07 Task 395, “MASH Equivalency of NCHRP Report 350-Approved Bridge Railings”. Under the NCHRP 20-07, TTI surveyed numerous state DOT’s and prioritized bridge rail systems that were evaluated for MASH equivalency. Three different criterions were established for these bridge rail systems considered. These criteria consist of stability, rail geometrics, and strength. The analysis methodologies used to evaluate these criteria are presented below.
For a bridge rail system to be considered a MASH acceptable barrier, a minimum height must be met to ensure stability of the vehicle. The height of the bridge rail system being analyzed was acquired from the detailed drawings of that specific bridge rail system and compared to the minimum height requirement for the specified test level.
The geometric relationships for bridge railings contained in Section 13 AASHTO LRFD Bridge Design Specifications (Figure 1) were applied to evaluate rail geometry. These relationships pertain to the potential for wheel, bumper or hood snagging on elements of the bridge rail system. Severe snagging can lead to a number of undesirable consequences including increased occupant compartment deformation, higher accelerations and occupant risk indices, and vehicle instability.
For each bridge rail system analyzed, post setback distance, ratio of contact width to height, and vertical clear opening were determined or calculated from the provided bridge rail details and plotted against the current AASHTO LRFD Section 13 geometric criteria.
Section 13 of the AASHTO LRFD Bridge Design Specifications contains procedures for analyzing the structural capacity of different types of bridge railings (e.g., steel, concrete). Using these procedures, an analysis of the strength of the rail system was performed. For concrete parapet railings, the yield line method was applied to determine the ultimate strength of the system. Metal rail systems were analyzed using plastic strength analysis methods. The strength of the rail members, posts, and post connections were analyzed to obtain the overall strength of the rail system.
Analysis methodologies similar to the one introduced above for the NCHRP 20-07 project will be utilized in this research study to assess the adequacy of the roadside safety barriers and hardware chosen by the pooled fund member states.
As part of this study, TTI will assess the performance of not only bridge rail systems, but other roadside safety issues that pertain to roadside safety hardware and barrier systems that are prioritized by the member states.
The objective of this research is to provide engineering support services and recommendations for those roadside safety barrier hardware and barrier systems that are prioritized/requested by pooled fund member states. TTI will assess the performance of this hardware and barrier systems and provide professional evaluation and recommendations as necessary to meet the MASH performance criteria. TTI will gather information pertaining to the roadside safety barriers from the pooled fund member states, research facilities, and other sources. TTI will evaluate each roadside feature/safety barrier based on current details of the barrier and/or similar barriers, previous data and information gathered from past research studies of the barrier, and assessment methodologies similar to the one introduced in the previous section.
This project will provide engineering support services and recommendations for those roadside safety barriers and hardware that are requested by pooled fund member states for a professional evaluation. In addition, detailed engineering drawings will be developed for implementation as needed.
TTI will generate a brief technical report for each activity/assessment performed for this project. These brief reports will provide the assessment methodologies used and the final recommendations for each roadside safety hardware and barrier systems for this project.
TTI researchers will gather information pertaining to the roadside safety hardware and barrier system selected from the pooled fund member states, research facilities, and other sources. The information necessary for TTI to conduct a thorough assessment of a roadside safety barrier and hardware system includes but is not limited to detailed engineering drawings, test reports, engineering calculations, and simulation results of the barrier and hardware system under review. TTI will perform literature reviews as necessary to complete this work. A review of previous crash history will be performed. The information gathered from this task will be summarized in the individual technical reports generated for this project.
Each roadside safety barrier and hardware system chosen by the pooled fund member states will be evaluated based on current details of the barrier and hardware system, previous data and information from past research studies of the system, or similar systems will be considered in each evaluation and assessment. Assessment methodologies similar to the one introduced in the previous section will be used to complete this work. The information gathered in Task 1 will be used to conduct the evaluation of the roadside safety barriers and hardware.
|TTI Research Supervisor:
William F. Williams, P.E.
Associate Research Engineer
Texas A&M Transportation Institute
College Station, Texas 77843-3135
|Pooled Fund Technical Representative:
Jim Danila, P.E.
Assistant State Traffic Engineer
Traffic and Safety Engineering Section
Massachusetts Highway Division
10 Park Plaza, Room 7210
Boston, MA 02116