As shown in Figure 1, sidewalk is often present in front of guardrail along the roadways and on bridges, creating challenges in ensuring the safety and structural integrity of the barrier-to-guardrail transition. These transitions need to be designed to accommodate the presence of sidewalks while maintaining compliance with current testing standard, Manual for Assessing Safety Hardware (MASH) [1].

Previous research conducted by the Texas A&M Transportation Institute (TTI) for Massachusetts Department of Transportation (MassDOT) included the design and successful testing of a Test Level 4 (TL-4) transition featuring a flared concrete barrier end, as shown in Figure 2 [2]. While this design offers a valuable reference, bridge barrier ends are not always flared and there is a need for a transition system with no flare.

This research aims to develop and evaluate a bridge barrier-to-guardrail transition with sidewalk for MASH TL-3 conditions. The design will be a concrete bridge barrier-to-thrie-beam-to-W-beam guardrail transition system. The concrete bridge barrier will be 42-inch high vertical wall barrier without a flared end. The barrier transition will be tapered down to 32-inch high to create smooth connection to thrie-beam guardrail (see Figure 3). The sidewalk will be 6 inches high, with a 1-inch offset and a minimum width of 5 feet.

Benefits

A successful transition design will provide state DOTs with a MASH TL-3 compliant design for bridge barrier-to-guardrail transitions with sidewalk. The outcome of this research will help state DOTs improve safety and functionality in transition zones while accommodating both vehicular and pedestrian traffic.

Products

The TTI research team will provide a final report that will include the results of the computer simulations, testing performed under the project, and final design details of the transition system.

Work Plan

The work plan for this research includes the following tasks. Task 1: Literature Review Task 1 involves a comprehensive review of previous studies and design standards related to bridge barrier-to-guardrail transitions with sidewalks. This includes examining existing transition designs from agencies such as MassDOT, CALTRANS, and PennDOT, as well as ongoing research by MwRSF. Special attention will be given to evaluating the upstream end transition where the guardrail attaches to the concrete bridge barrier, as this is a critical component for ensuring structural integrity and safety. The review will also include other transition elements, such as the thrie-beam-to-W-beam connection. Task 2: Engineering and Simulation Analysis This task involves developing a full-scale finite element (FE) transition model, evaluating the system model under MASH TL-3 conditions, modifying designs, and finding the most critical impact conditions. The research team will first evaluate the PennDOT transition design, which connects the 42-inch tall concrete bridge barrier to the thrie-beam guardrail [3]. The concrete barrier transition will include a tapering section to have 32-inch height at the end of the barrier to smoothly transit and connect to 31-inch high thrie-beam guardrail (Figure 3). The transition will be evaluated under MASH TL-3 conditions with 6-inch tall x 1 inch offset x 5 ft width sidewalk. If the design could not meet the MASH evaluation criteria, at least two thrie-beam guardrail modification concepts will be proposed to ensure structural continuity and MASH TL-3 compliance. Once the modification concepts are available, the research team will discuss pros and cons of each concept with technical representatives to decide the one for further investigation by considering state preferences, constructability, etc. for further investigation. Prior to evaluating the transition design, FE vehicle and system models will be validated by comparing them to the previously test data for the transition system connecting a 42-inch tall concrete bridge rail with sidewalk to a thrie-to-W-beam transition (e.g. Test No. H42ST-2 conducted by MwRSF [4]) to ensure accuracy and reliability of FE models. Once the FE models were validated, the final transition model will be developed. The research team will evaluate the system and investigate the trajectory profile to identify the critical sidewalk width, with a minimum of 5 ft restriction. The evaluation process will focus on optimizing the transition configuration with a sidewalk and identifying critical impact conditions to recommend for the full-scale crash test. Task 3: Crash Testing In this task, a selected transition design will be constructed and tested under MASH TL-3 conditions. According to MASH 2016, two full-scale vehicle crash tests are recommended for evaluating a transition system:

• Test 3-21: A 2270P vehicle weighing 5000 lb impacting the longitudinal barrier while traveling at 62 mph and 25 degrees.
• Test 3-20: An 1100C vehicle weighing 2420 lb impacting the longitudinal barrier while traveling at 62 mph and 25 degrees.

While Test 3-21 with pickup truck is required, Test 3-20 with the small car is optional in the MASH 2016. However, due to the presence of a sidewalk, it may undergo additional instability that is not fully understood from past tests and research. Therefore, the research team recommends performing Test 3-20 in this research. In MASH 2016, the testing for the transition design incorporating two significant stiffness changes has illustrated the importance of evaluating two different transition regions: (1) the downstream stiffness transition where the thrie-beam connects to the end of concrete bridge rail and (2) the upstream stiffness transition where the W-beam guardrail transitions to a thrie-beam section. However, the upstream stiffness transition from thrie-beam to W-beam was designed to replicate the MASH compliant MGS stiffness transition [5]. Thus, crash testing of the upstream stiffness transition was deemed non-critical and only the downstream stiffness transition will be tested.

 

Task 4: Final Report In Task 4, the final report will be prepared. The deliverables will include the literature review, design details, the result of simulation and tests, performance evaluation data, and practical guidelines for implementation of the transition with a sidewalk.  

Time Schedule

Started: May 2025
Time frame: 20 months

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May 22, 2025