NCHRP Research Report 1138	National Cooperative Highway Research Program

Evaluating the Performance
of Longitudinal Barriers on Curved,
Superelevated Off-Ramps

TRANSPORTATION RESEARCH BOARD 2024 EXECUTIVE COMMITTEE*

OFFICERS

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NATIONAL COOPERATIVE HIGHWAY RESEARCH PROGRAM

Evaluating the Performance of Longitudinal Barriers on Curved, Superelevated Off-Ramps

Dhafer Marzougui
Cing Dao (Steve) Kan
Fadi Tahan
Christopher Story
CENTER FOR COLLISION SAFETY AND ANALYSIS (CCSA)
GEORGE MASON UNIVERSITY
Fairfax, VA

Kenneth S. Opiela
Springfield, VA

Subscriber Categories
Design • Highways • Safety and Human Factors

Research sponsored by the American Association of State Highway and Transportation Officials in cooperation with the Federal Highway Administration

NATIONAL COOPERATIVE HIGHWAY RESEARCH PROGRAM

Systematic, well-designed, and implementable research is the most effective way to solve many problems facing state department of transportation (DOT) administrators and engineers. Often, highway problems are of local or regional interest and can best be studied by state DOTs individually or in cooperation with their state universities and others. However, the accelerating growth of highway transportation results in increasingly complex problems of wide interest to highway authorities. These problems are best studied through a coordinated program of cooperative research.

Recognizing this need, the leadership of the American Association of State Highway and Transportation Officials (AASHTO) in 1962 initiated an objective national highway research program using modern scientific techniques—the National Cooperative Highway Research Program (NCHRP). NCHRP is supported on a continuing basis by funds from participating member states of AASHTO and receives the full cooperation and support of the Federal Highway Administration (FHWA), United States Department of Transportation.

The Transportation Research Board (TRB) of the National Academies of Sciences, Engineering, and Medicine was requested by AASHTO to administer the research program because of TRB’s recognized objectivity and understanding of modern research practices. TRB is uniquely suited for this purpose for many reasons: TRB maintains an extensive committee structure from which authorities on any highway transportation subject may be drawn; TRB possesses avenues of communications and cooperation with federal, state, and local governmental agencies, universities, and industry; TRB’s relationship to the National Academies is an insurance of objectivity; and TRB maintains a full-time staff of specialists in highway transportation matters to bring the findings of research directly to those in a position to use them.

The program is developed on the basis of research needs identified by chief administrators and other staff of the highway and transportation departments, by committees of AASHTO, and by the FHWA. Topics of the highest merit are selected by the AASHTO Special Committee on Research and Innovation (R&I), and each year R&I’s recommendations are proposed to the AASHTO Board of Directors, the FHWA, and the National Academies. Research projects to address these topics are defined by NCHRP, and qualified research agencies are selected from submitted proposals. Administration and oversight of research contracts are the responsibilities of NCHRP.

The needs for highway research are many, and NCHRP can make significant contributions to solving highway transportation problems of mutual concern to many responsible groups. The program, however, is intended to complement, rather than to substitute for or duplicate, other highway research programs.

NCHRP RESEARCH REPORT 1138

Project 22-29B
ISSN 2572-3766 (Print)
ISSN 2572-3774 (Online)
ISBN 978-0-309-73155-3
Library of Congress Control Number 2024952871
Digital Object Identifier: 10.17226/28589

© 2025 by the National Academy of Sciences. National Academies of Sciences, Engineering, and Medicine and the graphical logo are trademarks of the National Academy of Sciences. All rights reserved.

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Authors herein are responsible for the authenticity of their materials and for obtaining written permissions from publishers or persons who own the copyright to any previously published or copyrighted material used herein.

Cooperative Research Programs (CRP) grants permission to reproduce material in this publication for classroom and not-for-profit purposes. Permission is given with the understanding that none of the material will be used to imply TRB, AASHTO, APTA, FAA, FHWA, FTA, GHSA, or NHTSA endorsement of a particular product, method, or practice. It is expected that those reproducing the material in this document for educational and not-for-profit uses will give appropriate acknowledgment of the source of any reprinted or reproduced material. For other uses of the material, request permission from CRP.

NOTICE

The research report was reviewed by the technical panel and accepted for publication according to procedures established and overseen by the Transportation Research Board and approved by the National Academies of Sciences, Engineering, and Medicine.

This material is based upon work supported by the FHWA under Agreement No. 693JJ32350025. The opinions, findings, and conclusions or recommendations expressed or implied in this publication are those of the researchers who performed the research and are not necessarily those of the Transportation Research Board; the National Academies of Sciences, Engineering, and Medicine; the FHWA; or the program sponsors.

The Transportation Research Board does not develop, issue, or publish standards or specifications. The Transportation Research Board manages applied research projects which provide the scientific foundation that may be used by Transportation Research Board sponsors, industry associations, or other organizations as the basis for revised practices, procedures, or specifications.

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NATIONAL COOPERATIVE HIGHWAY RESEARCH PROGRAM

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COOPERATIVE RESEARCH PROGRAMS

CRP STAFF FOR NCHRP RESEARCH REPORT 1138

Monique R. Evans, Director, Cooperative Research Programs

Waseem Dekelbab, Deputy Director, Cooperative Research Programs, and Manager, National Cooperative Highway Research Program

Roberto Barcena, Senior Program Officer

Anthony P. Avery, Senior Program Assistant

Natalie Barnes, Director of Publications

Heather DiAngelis, Associate Director of Publications

NCHRP PROJECT 22-29B PANEL
Field of Design—Area of Vehicle Barrier Systems

Chris Poole, Iowa Department of Transportation, Ames, IA (Chair)

John C. Durkos, Road Systems, Inc., Stow, OH

Lyman L. Hale, New York State Department of Transportation, Gansevoort, NY

Charles F. McDevitt, McDevitt Consulting, Matthews, NC

David Spence Rayburn, National Transportation Safety Board (NTSB), Washington, DC

Michael J. Smelker, New Mexico Department of Transportation, Las Cruces, NM

Teri Lynn Soos, Maryland State Highway Administration, Frederick, MD

Ana Maria Eigen, FHWA Liaison

AUTHOR ACKNOWLEDGMENTS

The George Mason University (GMU) project team wishes to acknowledge the Federal Highway Administration Office of Safety Research and Development for the support of this research by allowing testing at the Federal Outdoor Impact Laboratory and Mr. Eduardo Arispe who handled all the details to make it possible. The testing was important toward addressing the questions related to longitudinal barriers deployed on curved, superelevated off-ramps. The GMU project team also thanks the many persons from state departments of transportation, industry, and academia who provided the insights, information, and data used in this project.

FOREWORD

By Roberto Barcena
Staff Officer
Transportation Research Board

NCHRP Research Report 1138: Evaluating the Performance of Longitudinal Barriers on Curved, Superelevated Off-Ramps presents insights and guidelines related to the performance of longitudinal barriers placed on varying curved, superelevated ramp sections. The insights and guidelines were developed using vehicle dynamics analyses, finite element crash simulations, and full-scale crash testing.

This report will be of immediate interest to highway designers and safety staff at transportation agencies who seek safer practices in designing, selecting, and deploying longitudinal barriers on curved, superelevated off-ramps.

Longitudinal barriers are roadside safety devices commonly used to prevent errant vehicles from impacting hazards located alongside the traveled way. These barriers have been placed along the roadway, ranging from rigid concrete parapets to semi-rigid beam guardrails to relatively flexible wire rope barriers. Historically, the development and testing of longitudinal barriers have been conducted under the assumption that the barriers are installed in relatively straight sections parallel to the roadway. While the barriers designed under this assumption have performed well, their behavior when installed on curved roadways is largely unknown.

In NCHRP Project 22-29, “Performance of Longitudinal Barriers on Curved, Superelevated Roadway Sections” and NCHRP Project 22-29A, “Evaluating the Performance of Longitudinal Barriers on Curved, Superelevated Roadway Sections,” vehicle dynamics analyses and crash simulations were applied to determine the effects of typical vehicles leaving the roadway and impacting roadside barriers to evaluate vehicle-to-barrier interfaces and crash impact outcomes for a broad range of conditions (e.g., speed, impact angle, surface profile, vehicle type, barrier designs, and road features).

Under NCHRP Project 22-29B, “Evaluating the Performance of Longitudinal Barriers on Curved, Superelevated Off-Ramps,” George Mason University was asked to propose guidelines for selecting and designing traffic barriers for curved, superelevated off-ramps.

In addition to the report published as NCHRP Research Report 1138, the following deliverables can be found on the National Academies Press webpage for NCHRP Research Report 1138: Evaluating the Performance of Longitudinal Barriers on Curved, Superelevated Off-Ramps (https://doi.org/10.17226/28589) under “Resources at a Glance”:

• Appendices A–C
• Appendix D
• Appendices E–J
• A presentation with a summary of the project findings, including embedded simulation animations and crash-testing videos

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CONTENTS

Chapter 1 Introduction

1.1 Background

1.2 Objective

1.3 Research Approach

1.4 Organization of Final Report

Chapter 2 Background Studies

2.1 Literature Review

2.2 Agency Survey

2.3 Review of Typical Sites

2.4 Overview of Background Study Findings

Chapter 3 Vehicle Dynamics Analyses

3.1 Vehicle Dynamics Analyses

3.2 Vehicle Dynamics Analyses Results

3.3 Aggregated VDA Metrics for CSORs

Chapter 4 Crash Simulation Analyses

4.1 Crash Simulation Analysis Requirements

4.2 Crash Simulation Analyses

4.3 Computer Simulation Analysis for CSORs

4.4 Applicability of Results to Practice

Chapter 5 Full-Scale Crash Testing

5.1 Test Article and Installation Details

5.2 Test Vehicles

5.3 Test Summaries

5.4 Conclusions

Chapter 6 Research Conclusions and Guidelines for Longitudinal Barriers on CSORs

6.1 Analyses of Vehicle Dynamics Effects of Barrier Interface on CSOR Ramps

6.2 CSOR Simulations

6.3 Proposed CSOR Guidelines

6.4 Conclusions

6.5 Needs for Future Research

References

Appendices

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