Many bridge rails in the United States are outdated with respect to the Manual for Assessing Safety Hardware (MASH ^[1]). It is not economically feasible to completely replace the obsolete bridge rails with newer MASH-compliant designs. Oftentimes, state transportation agencies may need to utilize a crash-worthy bridge rail that is retrofitted to the existing bridge deck when an obsolete bridge railing needs to be replaced for a MASH-compliant bridge rail system. In the preceding research (referred to as ‘Phase 1’ herein), TTI has designed and successfully crash-tested a new thrie beam retrofit bridge rail design to be used on obsolete bridges for MASH TL-3 ^[2].  Details of Phase 1 crash-tested design are shown in Figure 1.

In a second Phase 2 project ^[3], Several conditions such as no curb, taller curb, wider curb, changes in deck thickness and reinforcing steel, and the location of existing obsolete bridge rails left in place different from the as-tested design were considered. Thus, the following questions arose to apply this thrie beam bridge rail retrofit to more bridge conditions in the field:

• Can the as-tested design be used for bridge rails without a curb at TL-3?
• How does the as-tested design perform for MASH TL-4?
• What changes are needed to the as-tested design to meet MASH TL-4?

In this Phase 2 study, these questions were answered.  Changes were made to the current design to improve the crash performance for MASH TL-4.  MASH TL-4 design details were developed as part of this Phase 2 project.  The purpose of this Phase 3 Project will be to construct and test the design developed in Phase 2 for MASH TL-4 acceptance.  Details of the design developed in Phase 2 and planned for full-scale crash testing for this project are shown in Figure 2.

Objective

The main objective of this project will be to perform full-scale crash testing on the new MASH TL-4 design developed in Phase 2 for MASH TL-4 acceptance.

Benefits

The main benefit of this project will be to have a thrie beam retrofit bridge rail design that meets the performance requirements of MASH TL-4.

Products

A test report summarizing the full-scale crash testing of the MASH TL-4 Thrie Beam Retrofit Design developed in Phase 2 will be provided as part of this project.

Work Plan

For this project, TTI plans to fabricate and construct the MASH TL-4 Thrie Beam Retrofit Bridge Rail design developed in Phase 2.  Reuse of the test installation from Phase 1 is planned for this project.  The work plan is as follows:

Task 1 – Engineering Design and Details
Engineering design, and details for terminating the top structural steel tube at the ends of the thrie beam retrofit bridge rail. Two design options will be considered for this task.

Task 2 – Construction of the MASH TL-4 Test Installation
TTI will fabricate the 43-inch tall thrie beam retrofit bridge rail using the existing installation from Phase 1. The installation length will be increased for MASH TL-4 testing.  One of the design options from Task 1 will be selected and constructed on both ends of the test installation. The thrie beam guardrail will transition to a Texas Department of Transportation (TxDOT) Downstream Anchor Terminal (DAT), similar to the guardrail transition installed during Phase 1. TxDOT DATs will be constructed on both ends of the test installation.

Perform MASH Test 4-12 only.  MASH Tests 4-10 and 4-11 will not need to be performed since tests 3-10 and 3-11 were performed and passed as part of Phase 1.

Prepare a comprehensive test report including design details of the MASH TL-4 crash tested Thrie Beam Retrofit Bridge Rail and all the test data and a summary of the results from the test.

Time Schedule

Started: May 2026 Time frame: 20 Months

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May 19, 2026