American Association of State Highway and Transportation Officials

Special Committee on Research and Innovation

FY2023 NCHRP PROBLEM STATEMENT

Problem Number: 2023-C-02

Problem Title

Determination of barrier deflections for lower speeds

Background Information and Need For Research

Deflection of permanent and temporary barrier systems often influence the design of the surrounding roadside. Utility poles and other fixed objects may have to be relocated to avoid the zone of intrusion for W-beam guardrail, free-standing portable concrete barriers, etc. Additional construction phases may need to be added to account for portable concrete barriers that would otherwise be located too close to a drop-off condition. These scenarios, and ones like them, contribute to added costs and delays to construction.

Minimum offset requirements are typically based upon crash test results. MASH testing criteria requires TL-3 tests to be performed at 62 mph and TL-2 tests at 44 mph. However, there are many instances where vehicles may be expected to travel at speeds that are lower than what was crash tested, so the offset requirements from the MASH testing may be overly conservative. Furthermore, most of the commonly used barriers are not tested for the lower-speed TL-2. The behind-the-barrier offset requirements for the barriers are based on testing at a much higher 62 mph impact speed. Understanding what the deflection would be at lower speeds will help DOTs to make more informed decisions and could ultimately reduce construction costs by minimizing utility relocations, changes to roadside design, and potentially eliminating unnecessary construction phases.

Literature Search Summary

Roadside Design Guide’s (RDG) Zone of Intrusion (ZOI) guidelines were developed using results of NCHRP Report 350 testing with longitudinal barriers. These guidelines provide zones on top and behind the barrier, where an impacting vehicle or the barrier may intrude into during a crash. Ongoing NCHRP Project 22-34 has been tasked to update the ZOI guidelines using the MASH testing criteria. However, the research effort to update the ZOI guidelines is significantly different from the one being proposed under this problem statement. ZOI research is focused primarily on Test Level 3 or higher, which is suitable to high-speed roadways. Furthermore, in addition to flexible or semi-flexible barrier systems, ZOI related research and guidance is influenced by inclusion of rigid or nearly rigid barriers such as bridge rails, permanent concrete barriers, etc. These barriers have close to zero maximum dynamic deflection. In contrast, typical W-beam guardrail or free-standing portable concrete barriers have several feet of dynamic deflection, which can be significantly reduced for lower speed impacts.

Research performed by Weiland et al. (MwRSF Report TRP-03-314-15) focused on determining the working width and maximum dynamic deflection of the MGS guardrail system for MASH TL-2 and TL-1 impact conditions using simulation analysis. This research can be expanded further to include other barrier systems. Furthermore, while the MASH testing standard specifies impact speeds of 62 mph (TL-3), 44 mph (TL-2) and 31 mph (TL-1), in many situations, roadside barriers are placed on roadways with intermediate or lower design speeds. There is currently not much information on the working width or barrier deflection for these lower and intermediate speeds. This new problem statement proposes to research and provide this missing information, which will be of significant benefit in reducing the minimum offset requirements behind the barriers on low-speed roadways.

Research Objective

This research should result in guidance on the required distance needed behind different types of MASH compliant barriers, based on the roadway design speed. The design speeds should range from 25 mph to 62 mph. The research activities should involve the following major tasks in developing this guidance.

- The research should perform a thorough literature review of the different barrier types that have been crash tested to MASH TL-3, but are also used on lower-speed roadways, and it would be beneficial for state DOTs and user agencies to know their clear offset requirements for lower-speeds. Examples of such systems are W-beam guardrail, free-standing portable concrete barrier systems, etc. The literature review should also include any MASH testing performed on such barrier systems at lower test levels (TL-2 or TL-1) of MASH.

- To develop the guidance for lower-speed impacts, the research team should identify MASH TL-3, and whenever possible, MASH TL-2 crash tests performed on these barrier systems. The research team should develop detailed finite element models of the selected barrier systems and perform impact simulations using MASH TL-3 and/or TL-2 test impact conditions. The results of the simulations should be compared to the test results to establish the validity of the models. In doing so, the research team should use the verification and validation methods described in NCHRP Web Only Document 179. Validation should be established for the barrier’s dynamic deflection, permanent deflection, and the MASH work width of the system.

- Once the barrier system models have be adequately validated using previously available MASH TL-3 and/or TL-2 crash test data, the research team should perform additional impact simulations with lower impact speeds. The research team should use these lower-speed impact simulations to establish the MASH working width and dynamic deflection of the various barrier systems.

- Results of the simulations with lower speeds should then be used to develop the desired guidance for barriers installed on lower-speed roadways.

Urgency and Potential Benefits

All State DOTs take barrier deflection into consideration during the design and placement of both permanent and temporary roadside barriers. On low-speed roads, additional and sometimes unnecessary work may be required to accommodate these deflections that are based on high-speed testing. Conducting this research may allow states to reduce costs and time associated with overly conservative decisions associated with the limited knowledge about deflection that exist today.

This research is ranked number 4 out of 5 by the AASHTO Technical Committee on Roadside Safety. This research is endorsed by the AASHTO Committee on Design.

Implementation Considerations

The State DOT Highway, Roadside Design, Traffic, and/or Work Zone engineers will benefit from these research results. Using this new data, states may be able to update design manuals and construction drawings. Furthermore, AASHTO Roadside Design Guide can include more guidance emanating from this research for installation of barriers on lower speed roadways.

Recommended Research Funding and Research Period

The recommended research funding is $350,000.

The recommended research period is 2 years.

Problem Statement Author(s): For each author, provide their name, affiliation, email address and phone.

Nauman M. Sheikh, P.E.

Texas A&M Transportation Institute

n-sheikh@tti.tamu.edu

+1-979-317-2695

James Danila, P.E.

Massachusetts Department of Transportation

james.danila@state.ma.us

+1-857-368-9640

Potential Panel Members: For each panel member, provide their name, affiliation, email address and phone.

James Danila, Massachusetts DOT, james.danila@state.ma.us, 857-368-9640

Erik Emerson, Wisconsin DOT, Erik.Emerson@wi.gov, 608-266-2842

Tim Moeckel, Washington DOT, moecket@wsdot.wa.gov, 360-704-6377

Shawn Debenham, Utah DOT, sdebenham@utah.gov, 801-965-4590

Chris Lindsey, Texas DOT, Christopher.Lindsey@txdot.gov, 512-416-2750

Ali Hangul, Tennessee DOT, Ali.Hangul@tn.gov, 615-741-0840

Hassan Raza, Pennsylvania DOT, HRaza@pa.gov, 717-783-5110

Christopher Henson, Oregon DOT, Christopher.S.Henson@odot.state.or.us, 503-986-3561

Kurt Brauner, Louisiana Transportation Center, Kurt.Brauner@la.gov, 225-379-1933

Derwood C. Sheppard, Jr., Florida DOT, Derwood.Sheppard@dot.state.fl.us, 850-414-4334

Bob Meline, Caltrans, Bob.Meline@dot.ca.gov, 916-227-7031

Person Submitting The Problem Statement: Name, affiliation, email address and phone.

Kristin Schuster, P.E.

Michigan Department of Transportation

Chair, AASHTO Technical Committee on Roadside Safety

Phone: 517-315-4421

Email: schusterk@michigan.gov