|TTI Research Supervisor: |
Nathan D. Schulz, Ph.D.
Assistant Research Scientist
Texas A&M Transportation Institute
Texas A&M University System
College Station, Texas, 77843-3135
|Pooled Fund Technical Representative:|
Senior Civil Engineer (Transportation)
PA Department of Transportation
400 North Street, 7th Floor
Harrisburg, PA 17120
The American Association of State Highway and Transportation Officials (AASHTO) published an updated 2016 edition of the Manual for Assessing Safety Hardware (MASH) document. 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.
PennDOT and other state DOTs have encountered situations where strong post median guide rail must be connected to a median F-Shape concrete barrier. No MASH testing and evaluation have been conducted on this type of system. Establishing a MASH compliant transition between strong post median guide rail and an F-Shape concrete barrier would provide the safest possible transition for state DOTs to use.
The purpose of this research is to develop and evaluate a MASH TL-3 transition from strong post median guide rail to median F-Shape concrete barrier.
The 2016 MASH edition is the latest in a series of documents that provided guidance on testing and evaluation of roadside safety features (1). The original MASH document was published in 2009 and represents a comprehensive update to crash test and evaluation procedures to reflect changes in the vehicle fleet, operating conditions, and roadside safety knowledge and technology (2). The MASH documents supersede the National Cooperative Highway Research Program (NCHRP) Report 350, ‟Recommended Procedures for the Safety Performance Evaluation of Highway Features” standards (3).
The FHWA issued a January 7, 2016 memo mandating the AASHTO/FHWA Joint Implementation Agreement for MASH with compliance dates for installing MASH hardware that differ by hardware category. After December 31, 2019, all roadside safety devices must have been successfully tested and evaluated according to the 2016 MASH standard edition. The Federal Highway Administration (FHWA) will no longer issue eligibility letters for highway safety hardware that has not been successfully crash tested according to the 2016 MASH edition evaluation criteria.
MASH was developed to incorporate significant changes and additions to procedures for safety-performance evaluation, and updates reflecting the changing character of the highway network and the vehicles using it. For example, MASH increased the weight of the pickup truck design test vehicle from 4,409 lb. to 5,000 lb., changed the body style from a ¾-ton, standard cab to a ½-ton, 4-door, and imposed a minimum height for the vertical center of gravity (CG) of 28 inches. The impact conditions for the small car test have also changed. The weight of the small passenger design test vehicle increased from 1,800 lb. to 2,420 lb.
Previous testing was conducted on a median guardrail transition to a median Single Slope concrete barrier (4). Figure 1 shows the transition system. A total of four full-scale successful crash tests were performed to evaluate the MASH compliance of the system. The crash tests were performed with different MASH test vehicles at different locations along the transition. The transition system was found to be compliant for MASH TL-3.
The purpose of this research is to evaluate and develop guidelines for a MASH TL-3 compliant transition from strong post median guide rail to various heights of precast/cast-in-place median F-Shape barrier. The analysis and evaluation of these systems will be conducted with finite element computer simulations and full-scale crash testing.
PennDOT and other state DOTs use transitions from strong post median guide rail to median concrete F-Shape barriers. There is a need to develop and evaluate a transition system for this application and determine if it is compliant for MASH TL-3 evaluation criteria. This would provide consistency and maximum safety for a transition being made between these systems. Guidance would be provided for transitioning median guide rail to various median F-Shape concrete barrier heights.
The TTI research team will provide composite video and photographic documentation of the crash test and a final report documenting the research and testing performed. The TTI research team will provide standard drawings of the transition system evaluated through full-scale crash testing. The TTI research team will include the guidelines, recommendations, and engineering opinion for MASH compliance for other less critical concrete F-Shape barrier heights in the final report
Task 1: Design Concept and Evaluation.
The TTI research team will review current state DOT standards for median guide rail to median concrete barrier transitions. This review will also include a questionnaire survey of the Roadside Safety Pooled Fund state DOTs to gather information on their use of median concrete barrier shapes and median concrete barrier heights when transitioning to median guide rail. If state DOTs indicate usage of median vertical concrete barrier when transitioning to median guide rail, then the vertical concrete shape will be included in the computer simulation analysis and discussed in the final guidelines and recommendations.
In addition, the TTI research team will conduct a review of the MASH TL-3 TxDOT Median Transition to Single Slope Barrier. Some of the system details and components from this MASH compliant system may be utilized for this study.
The TTI research team will develop a design concept for the median guide rail to median F-Shape concrete barrier transition system. One variable for the design will be the height of the F-Shape concrete barrier. To evaluate the performance of the transition system and the varying heights of the F-Shape concrete barrier, the TTI research team will conduct finite element computer simulations. Computer simulations will be performed on the transition system with an F-Shape barrier height of 32 inches, 42 inches, and 50 inches. A MASH performance assessment will be given for each transition system. While the simulations will only be evaluating three barrier heights, the final guidelines and recommendations will consider a range of acceptable barrier heights.
The TTI research team will select the critical F-Shape barrier height for full-scale crash testing. In addition, design consideration will be given to the installation of the median F-Shape concrete barrier. The TxDOT median transition system Single Slope barrier was doweled into a concrete block. The TTI research team will consider and evaluate other design preferences (e.g., keyed into asphalt) for the test installation. It is expected that engineering opinion for MASH compliance for alternative design conditions would be provided in the final guidelines and recommendations.
Task 2: MASH Test 3-21 – Full-Scale Crash Test.
The TTI research team will perform a full-scale crash test on the median guide rail to median F-Shape concrete barrier transition system according to MASH 2016 Test 3-21. The full-scale crash test will involve a 5,000-lb pickup truck impacting the transition system at 62 mph nominal speed and a 25° impact angle. The performance of the transition system will be evaluated according to the criteria set in MASH 2016 standards.
Task 3: Reporting Results (includes Guidelines & Recommendations).
The TTI research team will generate a final report of the findings from the research and crash testing evaluation. The TTI research team will report the crash test results in terms of transition system performance, vehicle stability, and occupant risk factors and will compare the results with respect to MASH 2016 crashworthiness criteria. The TTI research team will make an assessment for MASH TL-3 compliance of the transition system. The TTI research team will include the guidelines and recommendations in the final report for variations in F-Shape barrier heights.