National Cooperative Highway Research Program

NCHRP Report 350

Recommended Procedures for the Safety Performance Evaluation of Highway Features

Transportation Research Board National Research Council

TRANSPORTATION RESEARCH BOARD EXECUTIVE COMMITTEE 1992

OFFICERS

Chairman: William W. Millar, Executive Director, Port Authority of Allegheny County, Pennsylvania Vice Chairman: A. Ray Chamberlain, Executive Director, Colorado Department of Transportation Executive Director: Thomas B. Deen, Transportation Research Board

MEMBERS

MICHAEL ACOTT, President, National Asphalt Pavement Association (ex officio) ROY A. ALLEN, Vice President, Research and Test Department, Association of American Railroads (ex officio) MARION C. BLAKEY, National Highway Traffic Safety Administrator, U.S. Department of Transportation (ex officio) GILBERT E. CARMICHAEL, Federal Railroad Administrator, U.S. Department of Transportation (ex officio) BRIAN W. CLYMER, Federal Transit Administrator, U.S. Department of Transportation (ex officio) FRANCIS B. FRANCOIS, Executive Director, American Association of State Highway and Transportation Officials (ex officio) JACK R. GILSTRAP, Executive Vice President, American Public Transit Association (ex officio) DOUGLAS B. HAM, Research and Special Programs Acting Administrator, U.S. Department of Transportation (ex officio) THOMAS H. HANNA, President and Chief Executive Officer, Motor Vehicle Manufacturers Association of the United States, Inc (ex officio) THOMAS D. LARSON, Federal Highway Administrator. U.S. Department of Transportation (ex officio) WARREN G. LEBACK, Maritime Administrator. U.S. Department of Transportation (ex officio) THOMAS C. RICHARDS, Federal Aviation Administrator, U.S. Department of Transportation (ex officio) ARTHUR E. WILLIAMS, Chief of Engineers and Commander, U.S. Army Corps of Engineers (ex officio) JAMES M. BEGGS, Chairman, SPACEHAB, Inc.

KIRK BROWN, Secretary, Illinois Department of Transportation DAVID BURWELL, President, Rails-to-Trails Conservancy L. GARY BYRD, Consulting Engineer, Alexandria, Virginia L. STANLEY CRANE, former Chairman and CEO of CONRAIL RICHARD K. DAVIDSON, Chairman and CEO, Union Pacific Railroad JAMES C. DELONG, Director of Aviation, Philadelphia International Airport JERRY L. DEPOY, Vice President, Properties & Facilities, USAir THOMAS J. HARRELSON, Secretary, North Carolina Department of Transportation LESTER P. LAMM, President, Highway Users Federation LILLIAN C. LIBURDI, Director. Port Department, The Port Authority of New York and New Jersey ADOLF D. MAY, JR., Professor and Vice Chairman, Institute of Transportation Studies, University of California. Berkeley WAYNE MURI, Chief Engineer, Missouri Highway & Transportation Department (Past Chairman, 1990) CHARLES P. O'LEARY, JR., Commissioner. New Hampshire Department of Transportation NEIL PETERSON, Executive Director. Los Angeles County Transportation Commission DELLA M. ROY, Professor of Materials Science, Pennsylvania State University JOSEPH M. SUSSMAN, JR East Professor of Engineering, Massachusetts Institute of Technology JOHN R. TABB, Director, Chief Administrative Officer, Mississippi State Highway Department JAMES W. VAN LOBEN SELS, Director, California Department of Transportation C. MICHAEL WALTON, Paul D. & Betty Robertson Meek Centennial Professor and Chairman, Civil Engineering Department, University of Texas at Austin (Past Chairman, 1991) FRANKLIN E. WHITE, Commissioner, New York State Department of Transportation JULIAN WOLPERT, Henry G. Bryant Professor of Geography, Public Affairs and Urban Planning, Woodrow Wilson School of Public and International Affairs, Princeton University ROBERT A. YOUNG III, President, ABF Freight Systems, Inc

NATIONAL COOPERATIVE HIGHWAY RESEARCH PROGRAM

Transportation Research Board Executive Committee Subcommittee for NCHRP WILLIAM W. MILLAR, Port Authority of Allegheny County (Chairman) A.

RAY CHAMBERLAIN, Colorado Department of Transportation FRANCIS B. FRANCOIS, American Association of State Highway and Transportation Officials

THOMAS D. LARSON, U.S. Department of Transportation C. MICHAEL WALTON, University of Texas at Austin L. GARY BYRD, Consulting Engineer THOMAS B. DEEN, Transportation Research Board

Field of Design Area of Vehicle Barrier Systems Project Panel C22-7

ROGER L. STOUGHTON, California Department of Transportation (Chairman) JAMES E. BRYDEN, New York State Department of Transportation CHARLES E. DOUGAN, Connecticut Department of Transportation DENNIS L. HANSEN, Hennepin Co. Department of Transportation, Minn.

JAMES H. HATTON, JR., Federal Highway Administration WALTER J. JESTINGS, Parsons, Brinckerhoff Quade & Douglas, Georgia JAMES F. ROBERTS, Jefferson City, Missouri

F. J. TAMANINI, Energy Absorption Systems, Inc., Virginia THOMAS TURBELL, VTI, Sweden HARRY W. TAYLOR, Federal Highway Administration (The late) EDWARD N. POST, University of Nebraska-Lincoln MARTY HARGRAVES, FHWA Liaison Representative FRANK R. McCULLAGH, TRB Liaison Representative

Program Staff

ROBERT J. REILLY, Director, Cooperative Research Programs ROBERT B. MILLER, Financial Officer LOUIS M. MAcGREGOR, Program Officer DANIEL W. DEARASAUGH, JR., Senior Program Officer AMIR N. HANNA, Senior Program Officer

CRAWFORD F. JENCKS, Senior Program Officer KENNETH S. OPIELA, Senior Program Officer DAN A. ROSEN, Senior Program Officer

SCOTT SABOL, Senior Program Officer EILEEN P. DELANEY, Editor

National Cooperative Highway Research Program

Report 350

Recommended Procedures for the Safety Performance Evaluation of Highway Features

H. E. ROSS, JR., D. L. SICKING, and R. A. ZIMMER Texas Transportation Institute Texas A&M University System

College Station, Texas and

J. D. MICHIE

Dynatech Engineering Inc.

San Antonio, Texas

Research Sponsored by the American Association of State Highway and Transportation Officials in Cooperation with the

Federal Highway Administration

TRANSPORTATION RESEARCH BOARD

NATIONAL RESEARCH COUNCIL

NATIONAL ACADEMY PRESS

Washington, D.C. 1993

NATIONAL COOPERATIVE HIGHWAY RESEARCH

PROGRAM

Systematic, well-designed research provides the most effective approach to the solution of many problems facing highway administrators and engineers. Often, highway problems are of local interest and can best be studied by highway departments individually or in cooperation with their state universities and others. However, the accelerating growth of highway transportation develops increasingly complex problems of wide interest to highway authorities. These problems are best studied through a coordinated program of cooperative research.

In recognition of these needs, the highway administrators of the American Association of State Highway and Transportation Officials initiated in 1962 an objective national highway research program employing modern scientific techniques. This program is supported on a continuing basis by funds from participating member states of the Association and it receives the full cooperation and support of the Federal Highway Administration, United States Department of Transportation.

The Transportation Research Board of the National Research Council was requested by the Association to administer the research program because of the Board's recognized objectivity and understanding of modern research practices. The Board is uniquely suited for this purpose as: it maintains an extensive committee structure from which authorities on any highway transportation subject may be drawn; it possesses avenues of communications and cooperation with federal, state and local governmental agencies, universities, and industry; its relationship to the National Research Council is an insurance of objectivity; it maintains a full-time research correlation staff of specialists in highway transportation matters to bring the findings of research directly to those who are in a position to use them.

The program is developed on the basis of research needs identified by chief administrators of the highway and transportation departments and by committees of AASHTO. Each year, specific areas of research needs to be included in the program are proposed to the National Research Council and the Board by the American Association of State Highway and Transportation Officials. Research projects to fulfill these needs are defined by the Board, and qualified research agencies are selected from those that have submitted proposals. Administration and surveillance of research contracts are the responsibilities of the National Research Council and the Transportation Research Board.

The needs for highway research are many, and the National Cooperative Highway Research Program can make significant contributions to the solution of 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.

Note: The Transportation Research Board, the National Research Council, the Federal Highway Administration, the American Association of State Highway and Transportation Officials, and the individual states participating in the National Cooperative Highway Research Program do not endorse products or manufacturers. Trade or manufacturers names appear herein solely because they are considered essential to the object of this report.

NCHRP REPORT 350

Project 22-7 FY'89

ISSN 0077-5614

ISBN 0-309-04873-7

L. C. Catalog Card No. 92-61950

Price $13.00

Areas of Interests

Bridges, Other Structures, Hydraulics and Hydrology Materials and Construction Safety and Human Performance

Modes

Highway Transportation

NOTICE

The project that is the subject of this report was a part of the National Cooperative Highway Research Program conducted by the Transportation Research Board with the approval of the Governing Board of the National Research Council. Such approval reflects the Governing Board's judgment that the program concerned is of national importance and appropriate with respect to both the purposes and resources of the National Research Council.

The members of the technical committee selected to monitor this project and to review this report were chosen for recognized scholarly competence and with due consideration for the balance of disciplines appropriate to the project. The opinions and conclusions expressed or implied are those of the research agency that performed the research, and, while they have been accepted as appropriate by the technical committee, they are not necessarily those of the Transportation Research Board, the National Research Council, the American Association of State Highway and Transportation officials, or the Federal Highway Administration, U.S.

Department of Transportation.

Each report is reviewed and accepted for publication by the technical committee according to procedures established and monitored by the Transportation Research Board Executive Committee and the Governing Board of the National Research Council.

Published reports of the

NATIONAL COOPERATIVE HIGHWAY RESEARCH PROGRAM

are available from:

Transportation Research Board

National Research Council 2101 Constitution Avenue, N.W.

Washington, D.C. 20418

Printed in the United States of America

FOREWORD

By Staff

Transportation Research Board

This report is recommended to highway design engineers, bridge engineers, safety engineers, maintenance engineers, researchers, hardware developers, and others concerned with safety features used in the highway environment. It contains recommended procedures for evaluating the safety performance of various highway safety features.

These procedures are based on a comprehensive literature review, an analysis of the state of the art for performance evaluation (including procedures adopted by foreign agencies), and the advice of a selected group of acknowledged experts. It is believed that this report will contribute toward providing safer highways.

Effective traffic barrier systems, end treatments, crash cushions, breakaway devices, truck-mounted attenuators, and other hardware must be used to achieve the highest levels of highway safety. Many devices have been developed by state agencies, universities, and private firms to address particular roadside safety concerns. New systems are continually emerging to address safety problems, and traditional devices and practices for their use are being improved in response to an increased understanding of safety performance, a changing vehicle fleet, the emergence of new materials, and other factors. Full-scale impact testing has been and will continue to be the most common method of evaluating the safety performance of guardrails, median barriers, bridge railings, crash cushions, breakaway supports, truck-mounted attenuators, work zone traffic control devices, and other hardware. Because a number of agencies in the United States conduct such tests, there is a need for uniformity in the procedures and criteria used to evaluate traffic barriers and other roadside safety features. There are also important precedents for promoting international harmonization of procedures to take advantage of relevant experience and research findings in other countries.

Procedures for full-scale vehicle crash testing of guardrails were first published in Highway Research Correlation Services Circular 482 in 1962. This one-page document specified vehicle mass, impact speed, and approach angle for the crash tests. Although Circular 482 did bring a measure of uniformity to traffic barrier research then being performed at several research agencies, a number of questions arose that were not addressed.

NCHRP Project 22-2 was initiated at Southwest Research Institute in 1973 to address the questions that were not covered in Circular 482. The final report was published as "Recommended Procedures for Vehicle Crash Testing of Highway Appurtenances," NCHRP Report 153. This 16-page document was based on technical input from more than 70 individuals and agencies as well as extensive deliberations by a special ad hoc panel.

Several parts of the document were known to be based on inadequate information, but coverage of these areas was included to provide a more complete set of testing procedures.

These procedures gained wide acceptance following their publication in 1974, but it was recognized at that time that periodic updating would be needed; and, in January 1976, TRB Committee A2A04 accepted the responsibility for reviewing the efficacy of the procedures. Questionnaires were submitted to committee members to identify areas of the document that needed revision. The responses generally fell into two categories: (1) minor changes requiring modified treatment of particular problem areas; and (2) major changes that would require broadening the scope to include, for example, testing with trucks and buses, reevaluating the criteria for impact severity, and treating special highway appurtenances such as construction barriers. The committee addressed the minor changes through special committee action; and Transportation Research Circular 191, published in 1978, was the product of this effort.

NCHRP Project 22-2(4) was initiated in 1979 by Southwest Research Institute to address the major changes. Its objective was to review, revise, and expand the scope of Circular 191 to reflect current technology. The final report of NCHRP Project 22-2(4) was published as NCHRP Report 230, "Recommended Procedures for the Safety Performance Evaluation of Highway Safety Appurtenances," in 1980. This 36-page document incorporated new procedures, updated the evaluation criteria, and brought the procedures up to date with available technology and practices. This document served as the primary reference for full-scale crash testing of highway safety appurtenances in the U.S. and in many other parts of the world.

In 1987, American Association of State Highway and Transportation Officials (AASHTO) recognized that the evolution of roadside safety concepts, technology, and practices necessitated an update to Report 230. The reasons included significant changes in the vehicle fleet, the emergence of many new barrier designs, increased interest in matching safety performance to levels of roadway utilization, new policies requiring the use of safety belts, and advances in computer simulation and other evaluation methods.

NCHRP Project 22-7 was approved to consider these factors and to prepare the update to Report 230.

The research team of Principal Investigator Dr. Hayes Ross, Jr., Texas A & M University, and Co-Principal Investigator Mr. Jarvis Michie, Dynatech Engineering, began this effort in 1989 with a series of white papers on the subjects of the test matrix, assessment procedures and criteria, specification and control of test parameters, in-service evaluation, use of surrogate test vehicles, computer simulations and other evaluation procedures, instrumentation of crash testing, the purpose of the document, and conversion to SI units. (Unedited drafts of these documents can be obtained on request from the NCHRP.) The panel reviewed each white paper and provided comments on the issues raised in them. A meeting of the panel was held to discuss the various issues, debate the implications for an updated set of procedures, and develop a consensus on the procedures that would be incorporated in the update. The research team prepared the first draft of the updated procedures after this meeting. This draft was thoroughly reviewed by the panel and a second meeting was held to discuss the report and establish panel consensus on the updated procedures.

The second draft of this document was mailed to some 100 individuals, and comments were received from about 65. The project panel met a third time to consider the review comments and determine where changes were needed in the updated procedures.

Although the report originated with the research agency, each recommendation has the consensus endorsement of the NCHRP Project Panel. Where recommendations are founded on less than clear-cut evidence, the judgment of the project panel prevailed.

NCHRP Report 350 represents a comprehensive update of the procedures for safety performance evaluation. Report 350 differs from Report 230 in the following ways:

1. It is presented as an all-metric document in anticipation of the U.S. conversion to SI units of measurement. Hard conversions were made in the update process, which will alter the mass, speeds, and tolerances used in testing. For example, tests previously specified for 60 mph (97 km/h) are now specified at 100 km/h. The impacts of such increases of speed on the kinetic energy of the tests were recognized and appropriate criteria adjustments made.

2. It provides a wider range of test procedures to permit safety performance evaluations for a wider range of barriers, terminals, crash cushions, breakaway support structures and utility poles, truck-mounted attenuators, and work zone traffic control devices.

3. It uses a 3/4-ton pickup truck as the standard test vehicle in place of the 4500-lb passenger car to reflect the fact that almost one-quarter of the passenger vehicles on U.S. roads are in the "light truck" category. This change was made recognizing the differences in wheel bases, bumper heights, body stiffness and structure, front overhang, and other vehicular design factors.

4. It defines other supplemental test vehicles including a mini-compact passenger car (700 kg), single-unit cargo trucks (8000 kg), and tractor-trailer vehicles (36,000

kg) to provide the basis for optional testing to meet higher performance levels.

5. It includes a broader range of tests for each category of safety feature to provide a uniform basis for establishing warrants for the application of roadside safety hardware that consider the levels of use of the roadway facility. Six basic test levels are defined for the various classes of roadside safety features, and a number of optional test levels are defined to provide the basis for safety evaluations to support more or less stringent performance criteria.

6. The report includes guidelines for the selection of the critical impact point for crash tests on redirecting-type safety hardware.

7. It provides information related to enhanced measurement techniques related to occupant risk and it incorporates guidelines for device installation and test instrumentation.

8. The three basic evaluation criteria categories remain the same. The occupant risk criteria retains the use of the flail space model, but defines preferred and maximum levels of occupant impact velocity and acceleration. The lateral occupant impact velocity limits were altered to be equivalent to longitudinal limits to reflect recent research findings. The redirection criteria were altered to incorporate a limiting 12 m/s vehicular velocity change requirement in the longitudinal direction.

9. It reflects a critical review of methods and technologies for safety-performance evaluation, such as surrogate test vehicles and computer simulations, and incorporates state-of-the-art methods in the procedures.

10. It provides optional criteria, established by others, for side impact testing.

The evolution of the knowledge of roadside safety and performance evaluations is reflected in this document. Inevitably, parts of this document will need to be revised in the future, but it is the consensus opinion of the project panel and the many reviewers of these procedures that this document will effectively meet the needs for uniform safety performance evaluation procedures into the 21st century.

CONTENTS

1 SUMMARY

3 CHAPTER ONE Introduction

1.1 Purpose and Scope, 3

1.2 Development of a Safety Feature, 3

1.3 Performance Goals, 4

1.4 Performance Limitations, 4

1.5 Organization of Report, 4

1.6 International Harmonization of Performance Standards, 6

7 CHAPTER TWO Test Parameters

2.1 General, 7

2.2 Testing Facility, 7

2.2.1 Soil, 7

2.2.1.1 Standard Soil, 7

2.2.1.2 Special Soils, 7

2.2.1.3 Embedment of Test Article, 8

2.2.2 Special Structures, 8

2.3 Test Article, 8

2.3.1 General, 8

2.3.2 Installation Details, 8

2.3.2.1 Longitudinal Barriers, 8

2.3.2.2 Terminals and Crash Cushions, 9

2.3.2.3 Support Structures, Work Zone Traffic Control Devices, and Breakaway Utility Poles, 9

2.3.2.4 Truck-Mounted Attenuators (TMAs), 9

2.4 Test Vehicles, 10

2.4.1 Description of Test Vehicles, 10

2.4.1.1 Production Model Test Vehicles, 10

2.4.1.2 Surrogate Test Vehicles, 12

2.4.1.3 Truck Used in TMA Test, 12

2.4.2 Mass Properties, 12

2.4.2.1 Test Vehicle, 12

2.4.2.2 Ballast, 13

2.4.3 Propulsion and Braking, 13

2.4.4 Guidance, 13

2.5 Surrogate Occupants, 14

15 CHAPTER THREE Test Conditions

3.1 General, 15

3.2 Test Matrices, 15

3.2.1 Longitudinal Barriers, 15

3.2.1.1 General, 15

3.2.1.2 Description of Tests, 17

3.2.2 Terminals and Crash Cushions, 17

3.2.2.1 General, 17

3.2.2.2 Description of Tests, 17

3.2.2.3 Orientation of Terminal/Crash Cushion, 19

3.2.2.4 Other Terminal/Crash Cushion Designs, 20

3.2.3 Support Structures, Work Zone Traffic Control Devices, and Breakaway Utility Poles, 20

3.2.3.1 General, 20

3.2.3.2 Description of Tests, 25

3.2.4 Truck-Mounted Attenuators (TMAs), 27

3.2.4.1 General, 27

3.2.4.2 Test Descriptions, 27

3.2.5 Roadside Geometric Features, 28

3.3 Tolerances on Impact Conditions, 30

3.3.1 General, 30

3.3.2 Longitudinal Barriers, 30

3.3.3 Terminals and Crash Cushions, 30

3.3.4 Support Structures, Work Zone Traffic Control Devices, and Breakaway Utility Poles, 30

3.3.5 Truck-Mounted Attenuators (TMAs), 32

3.4 Impact Point for Redirective Devices, 32

3.4.1 General, 32

3.4.2 Longitudinal Barriers, 32

3.4.2.1 Tests with the 700C, 820C, and 2000P Vehicles, 32

3.4.2.2 Tests with the 8000S, 36000V, and 36000T Vehicles, 34

3.4.3 Terminals and Redirective Crash Cushions,

3.5 Side Impact Tests, 34

41 CHAPTER FOUR Data Acquisition

4.1 Typical Parameters, 41

4.2 Pretest Parameters, 41

4.2.1 Test Vehicle, 41

4.2.2 Test Article, 41

4.2.2.1 General, 41

4.2.2.2 Longitudinal Barriers, 41

4.2.2.3 Terminals and Crash Cushions, 47

4.2.2.4 Support Structures, Work Zone Traffic Control Devices, and Breakaway Utility Poles, 47

4.2.2.5 Truck-Mounted Attenuators (TMAs), 47

4.3 Test Parameters, 47

4.3.1 General, 47

4.3.2 Electronic and Photographic Instrumentation Specifications, 47

4.3.3 Accelerometer Placement and Data Reduction for Test Vehicles 700C, 820C, and 200P, 49

4.4 Post-Test Parameters, 51

4.5 Additional Parameters, 51

52 CHAPTER FIVE Evaluation Criteria

5.1 General, 52

5.2 Structural Adequacy, 52

5.3 Occupant Risk, 52

5.4 Post-Impact Vehicular Trajectory, 55

5.5 Geometric Features, 56

57 CHAPTER SIX Test Documentation

6.1 General Reporting Recommendations, 57

6.2 Electronic Data, 62

63 CHAPTER SEVEN Implementation and In-Service Evaluation

7.1 Purpose, 63

7.2 Objectives, 63

7.3 Characteristics of Trial Installations, 63

7.4 Discussion, 64

65 APPENDIX A Commentary

82 APPENDIX B Soil Specifications B1 Standard Soil, 83 B2 Weak Soil, 85 B3 Compaction Guidelines, 88

89 APPENDIX C Electronic and Photographic Instrumentation Specifications

100 APPENDIX D Analytical and Experimental Tools D1 Useful Techniques, 100

D1.1 Structural Design, 100 D1.2 Static Tests, 100 D1.3 Computer Simulations, 101 D1.4 Laboratory Dynamic Tests, 102 D1.5 Gravitional Pendulum, 102 D1.6 Drop Mass/Dynamic Test Service, 103 D1.7 Scale Model, 103 D1.8 Bogie Test, 103 D2.0 Comparison of Techniques, 103

104 APPENDIX E Occupant Compartment Deformation Index

106 APPENDIX F Determination of the THIV, the PHD, and the ASI 110 APPENDIX G Side Impact Test and Evaluation Procedures for Roadside Structure Crash Tests

127 APPENDIX H References and Bibliography

130 APPENDIX I Glossary of Terms

132 APPENDIX J SI Conversions

SUMMARY

RECOMMENDED PROCEDURES FOR

THE SAFETY PERFORMANCE

EVALUATION OF HIGHWAY FEATURES

Procedures are presented for conducting vehicle crash tests and in-service evaluation of roadside safety features or appurtenances. The features covered by these procedures include (1) longitudinal barriers such as bridge rails, guardrails, median barriers, transitions, and terminals; (2) crash cushions; (3) breakaway or yielding supports for signs and luminaries; (4) breakaway utility poles; (5) truck-mounted attenuators; and (6) work zone traffic control devices. The purpose of the procedures is to promote the uniform testing and inservice evaluation of roadside safety features so that highway engineers may confidently compare the safety performance of designs that are tested and evaluated by different agencies. These procedures are presented in the form of guidelines that describe how a feature should be tested and evaluated. The identification of specific new, existing, or modified features for testing and evaluation; the selection of a level of service that the feature is to meet; and the establishment of acceptable performance criteria for an agency are policy decisions that are beyond the purview of this document. The procedures are directed at the safety performance of roadside safety features; other service requirements such as economics and aesthetics are not considered here.

These procedures are devised to subject roadside safety features to severe vehicle impact conditions rather than to typical or average highway situations. Although the innumerable highway-site and safety-feature application conditions that exist are recognized, it is impractical or impossible to duplicate these in a limited number of standardized tests.

Hence, the approach has been to normalize test conditions: straight longitudinal barriers are tested although curved installations exist; flat grade is recommended even though installations are sometimes situated on sloped shoulders and behind curbs; idealized soils are specified although roadside safety hardware are often founded in poor soil or frozen ground. These normalized test conditions have a significant effect on a feature's performance but are of secondary importance when comparing results of two or more systems.

For vehicle crash testing, specific impact conditions are presented for vehicle mass, speed, approach angle, and point on the safety feature to be hit. Standard test vehicle types are defined for mini-compact and subcompact passenger cars, standard ¾-ton pickup trucks, single-unit trucks, and tractor-trailer cargo trucks. Impact speeds range from 35 to 100 km/h (approximately 20 to 60 mph), and approach angles vary from 0 to 25 degrees.

Three primary appraisal factors are presented for evaluating the crash test performance:

structural adequacy, occupant risk, and after-collision vehicle trajectory. Depending on the safety feature's function, it should contain, redirect, permit controlled penetration of the impacting vehicle, or permit a controlled stop in a predictable manner to satisfy structural adequacy requirements. Occupant risk relates to the degree of hazard to which occupants in the impacting vehicle would be subjected. It is measured in terms of the velocity at which a hypothetical unrestrained occupant strikes some part of the vehicle interior such as the instrument panel, window, or door, and the subsequent occupant ridedown accelerations. The after-collision vehicle trajectory is assessed based on the probable involvement of other traffic due to the path or final position of the impacting car and on the chances of undesirable post-impact vehicle behaviors such as pocketing or snagging. It is recognized that vehicle crash tests are complex experiments and are difficult to replicate because of the imprecise control of test conditions and the sometimes random and unstable behavior of dynamic crush and fracture mechanisms. Accordingly, care should be exercised in interpreting the results.

In-service evaluation is used in the final stage of develoment of new or extensively modified roadside safety features and has the purpose of appraising actual performance during a broad range of collision, environmental, operational, and maintenance situations for typical site and traffic conditions. This report updates the guidelines for in-service evaluation first provided in NCHRP Report 230, recognizing the complex nature of vehicular accidents and the limited resources of agencies responsible for monitoring the performance of new or modified safety features.

Appendices to this report provide (a) a commentary on the basis for the procedures; (b) soil specifications for the installation of safety features; (c) specifications for the instrumentation of the tests; (d) a summary on the analytical and experimental tools that can be used in the research and development phase for safety features; (e) a methodology for quantifying the damage to the occupant compartment of a test vehicle; (f) a description of calculation procedures for alternate measures of occupant risk (e.g., THIV, PHD, and ASI); and (g) a methodology for conducting and evaluating side impact tests.

CHAPTER 1

INTRODUCTION

1.1 PURPOSE AND SCOPE

The purpose of this report is to present uniform guidelines for the crash testing of both permanent and temporary highway safety features and recommended evaluation criteria to assess test results. Guidelines are also presented for the in-service evaluation of safety features. These guidelines and criteria, which have evolved over the past 30 years, incorporate current technology and the collective judgment and expertise of profes-sionals in the field of roadside safety design. They provide (1) a basis on which researchers and user agencies can compare the impact performance merits of candidate safety features, (2) guidance for developers of new safety features, and (3) a basis on which user agencies can formulate performance specifica-tion for safety features.

Although these guidelines are representative and applicable to an array of highway features and traffic conditions, they should not be viewed as all-inclusive. Experience has shown that as new designs are developed, current test procedures may not properly evaluate critical conditions for these designs. Experience has also shown that evaluation and testing of features not addressed by the current guidelines will be made. Therefore, specific features and site con-ditions may arise that require special tests and evaluation criteria.

Deviations from the guidelines are warranted when other tests or evaluation criteria are more appropriate and representative of site or design conditions.

With the guidelines, a given feature may be tested to one of six "test levels." A test level is defined by impact conditions (speed and angle of approach) and the type of test vehicle (ranging in size from a small car to a fully loaded tractor-trailer truck). A feature de-signed and tested for a low test level would generally be used on a low service level roadway; for example, a rural collector or local road, an urban street, or perhaps in a restricted work zone. A feature designed and tested for a high test level would typically be used on a high service level roadway; for example, a freeway.

It must also be noted that features that meet a given test level will generally have different performance characteristics. A concrete barrier and a cable barrier can be designed to satisfy a given test level, but it is obvious that the cable barrier will deflect much more, impact forces will be less for the cable barrier, and vehicle trajec-tory will certainly not be the same for both barriers. A terminal can be designed to have full redirection capabilities along its entire length (termed a nongating terminal), or it can be designed to allow controlled penetration along a portion of its length (termed a gating terminal). Both designs can be made to satisfy a given test level. A crash cushion can be designed to redirect a vehicle impacting the side of the cushion (termed a redirective crash cushion), or it can be designed to decelerate the vehicle to a stop when impacted on the side (termed a nonredirec-tive crash cushion). While the guidelines were formulated pur-posely to offer the user considerable latitude in the design and test-ing of a feature, it is not the purpose nor is it within the purview of this document to determine where a feature, satisfying a given test level and having specific performance characteristics, would have application. That determination rests with the appropriate transpor-tation agency responsible for the implementation of the safety fea-ture.

These guidelines supersede those contained in NCHRP Report 230 (1). Major revisions incorporated herein relative to Report 230 include (a) changes to the test vehicles, (b) changes to the number and impact conditions of the test matrices, (c) adoption of the con-cept of "test levels" as opposed to "service levels," (d) changes to the evaluation criteria, (e) inclusion of test guidelines for additional features, and (e) adoption of the International System of Units (SI).

The SI was adopted in concert with national efforts to convert the English system of units to the internationally accepted SI.

Procedures presented herein involve vehicular tests to evaluate the impact performance of permanent and temporary highway safety features. Performance is evaluated in terms of the degree of hazard to which occupants of the impacting vehicle would be ex-posed, the structural adequacy of the safety feature, the hazard to workers and pedestrians that may be behind a barrier or in the path of debris resulting from impact with a safety feature, and the post-impact behavior of the test vehicle. Other factors that should be evaluated in the design of a safety feature, such as aesthetics, costs (initial and maintenance), and durability (ability to withstand envi-ronmental conditions such as freezing and thawing, wind-induced fatigue loading, effects of moisture, ultraviolet radiation, etc.) are not addressed.

1.2 DEVELOPMENT OF A SAFETY FEATURE

Development of a safety feature from its inception to the time it becomes operational is often a long and arduous process. Depend-ing on its developmental phase, a feature is generally placed in one of three categories: (1) research and development, (2) experimen-tal, and (3) operational. During the research and development phase, the design evolves and is eventually subjected to a set of crash tests. Results of the crash tests are assessed in accordance with a set of evaluation criteria. If the feature satisfies the evalua-tion criteria, it is then placed in the experimental phase. Subject to interest by user agencies, it may then be installed, often on a lim-ited basis. The purpose of the experimental phase is to closely monitor the in-service performance of the feature. If it performs satisfactorily in service, it may then be placed in the operational phase; but its performance should con-tinue to be monitored.

Shown in Figure 1.1 is a flow chart illustrating the process through which a new safety feature is typically subjected. Steps 1 through 4 involve the research and development phase. Factors that should be considered and design techniques that may be used during this phase are indicated. Note that during step 3 it may be beneficial to use analytical and experimental tools described in Appendix D. Step 4 is addressed in Chapters 2 through 6. If a de-vice meets the recommended impact performance criteria, it is then classified as experimental and steps 6 through 9 may then be per-formed. If acceptable to a user agency, standard plans are prepared (step 8) and the feature is installed on a limited basis. Step 9 in-volves in-service evaluation, and recommended procedures for conducting this evaluation are given in Chapter 7. This step is per-haps the most important part of the development of a feature. If its in-service is acceptable, it may then be classified as operational (step 11) and fully implemented. However, monitoring of the in-service performance of the device should continue in this phase (step 12).

To be noted is that, while there are specific guidelines (as pre-sented herein) for determining if a device is acceptable as an ex-perimental device, there are no widely accepted, specific criteria to assess its in-service performance. Consequently, considerable judgment must be exercised in determining when a device has met the in-service requirements and thus becomes operational. Some agencies may choose to skip steps 9 and 10, declaring the feature operational on the basis of expert opinion. However, it is strongly recommended that step 12 never be omitted.

1.3 PERFORMANCE GOALS

A goal of a highway safety feature is to provide a forgiving roadway and roadside for an errant motorist. The safety goal is met when the feature either contains and redirects the vehicle away from a hazardous area, decelerates the vehicle to a stop over a relatively short distance, readily breaks away or fractures or yields, allows a controlled penetration, or is traversable, without causing serious injuries to the vehicle's occupants or to other motorists, pedestrians, or work zone personnel.

Ideally, the roadside would be clear of all obstructions, including unnecessary roadside hardware, and be traversable so that an errant motorist could recover control of the vehicle and stop or return to the pavement. However, there are numerous roadside areas that cannot practically be cleared of all fixed objects or made traver-sable. At these sites, the use of an appropriate safety feature or safety treatment is intended to reduce the consequences of a run-off-the-road incident.

As discussed in Section 1.2, the safety performance of a highway feature cannot be measured by a series of crash tests only. Testing must be viewed as a necessary but not sufficient condition to qual-ify a feature for operational status. Tests results are judged on the basis of evaluation criteria presented in Chapter 5.

1.4 PERFORMANCE LIMITATIONS

Even the most carefully researched device has performance limits dictated by physical laws, crashworthiness of vehicles, and limitation of resources. For example, at some sites, sufficient space is lacking to safely decelerate a vehicle, regardless of the crash cushion design. Irrespective of the breakaway feature, certain tim-ber utility poles may be so massive that the impacting vehicle is abruptly decelerated, thus limiting achievable safety performance without a change in support technology. There is no assurance that a feature meeting the test recommendations herein for a tracking vehicle will perform satisfactorily if impacted by a vehicle sliding sideways. Some vehicle types may lack sufficient size or mass or necessary crashworthiness features such as interface strength, stiffness, controlled crush properties, and stability to provide occu-pants with an acceptable level of protection. Note that no provi-sions are made herein for the design and testing of safety features for two-wheeled vehicles-powered or unpowered. Longitudinal barriers that will contain and redirect the smaller passenger cars and yet have strength capability to redirect a tractor-trailer or inter-city bus are relatively expensive. Seemingly insignificant site con-ditions such as curbs, slopes, and soft soil conditions can cause or contribute to the unsuccessful performance of a safety feature.

For these reasons, safety features are generally developed and tested for selected idealized situations that are intended to encom-pass a large majority, but not all, of the possible in-service colli-sions. Even so, it is essential that test results be evaluated and in-terpreted by competent researchers and that the evaluation be guided by sound engineering judgment.

While it is to be expected that certain features, meeting all test and evaluation criteria recommended herein, will have untested "windows of vulnerability" in service, the corollary of this is also to be expected. That is, it is to be expected that certain features not meeting all test and evaluation criteria recommended herein will still be cost-effective alternatives for selected in-service applica-tions.

1.5 ORGANIZATION OF REPORT

Chapter 2 describes the test parameters, including those associ-ated with the test facility, the test article, and the test and its simu-lated occupants. Chapter 3 gives the test conditions recommended for each of the respective features. It also presents recommended tolerances on impact conditions and a procedure for identifying the critical impact point for certain features. Chapter 4 describes the data acquisition systems recommended and identifies parameters that should be measured before, during, and after the test. The evaluation criteria used to assess test results are contained in Chapter 5. Chapter 6 recommends the manner in which a given test and its results are to be documented. Chapter 7 contains guidelines on how the in-service performance of a feature should be evalu-ated. Appendix A is a commentary on those items contained in Chapters 2 through 6 and presents further elaboration and discus-sion. Appendix B contains soil specifications, reproduced with permission from the American Association of Highway and Trans-portation Officials, and Appendix C contains instrumentation specifications, reproduced with permission from the Society of Automotive Engineers, Inc. Appendix D summarizes analytical and experimental tools that can be used in the research and devel-opment phase; Appendix E contains a methodology for quantifying the damage to the occupant compartment; Appendix F describes calculation procedures for the Theoretical Head Impact Velocity (THIV), Post-Impact

Head Deceleration (PHD), and the Acceleration Severity Index (ASI); and Appendix G contains a methodology for conducting and evaluating side impacts. Appendix H contains the references and bibliography, and Appendix I is a glossary of terms. Sample SI conversion factors are presented in Appendix J.

1.6 INTERNATIONAL HARMONIZATION OF

PERFORMANCE STANDARDS

Concurrent with the preparation of this report, the European Committee for Standardization (CEN) was preparing a similar document (77). Discussions were held to explore ways impact per-formance standards between the U.S. and CEN could possibly be harmonized. However, scheduling deadlines precluded the devel-opment of substantive agreements. Nonetheless, based on ex-pressed interests by U.S. government agencies and CEN agencies, it is expected that common standards will be adopted in future re-ports, at least for certain elements of the test and evaluation proc-ess. Toward this end, it was decided to incorporate the SI system of units herein. Furthermore, it is suggested that certain evaluation criteria adopted by CEN be calculated and reported for tests in the U.S. for purposes of comparison with comparable U.S. criteria (see Section 5.3).

CHAPTER 2

TEST PARAMETERS

2.1 GENERAL

Highway safety features are evaluated for a particular test level through a series of vehicular crash tests for a limited range of impact conditions, as presented in Chapter 3. Many important test parameters have been standardized to arrive at practical stratification of tests (test matrices) and to enhance the degree of test replication. Care must be exercised in the interpretation of test results and in the projection of the results to in-service performance. Good performance under ideal test conditions does not ensure comparable performance under in-service conditions. As discussed in Chapter 1, the evaluation process should not stop with successful completion of tests recommended herein. In-service evaluation of the feature is perhaps more important than crash test evaluation and should be pursued as recommended in Chapter 7.

2.2 TESTING FACILITY

A flat surface, preferably paved, should be used when accelerating the test vehicle to the desired speed and to provide for unrestricted trajectory of the vehicle following impact. The surface should be free of curbs, swales, ditches, or other irregularities that could influence impact or post-impact behavior of the vehicle except when test conditions require such features.

If necessary, a flat compacted soil or sod surface should adjoin the paved approach area to replicate conditions for safety features normally surrounded by an unpaved surface, so that post-impact vehicular behavior can be properly assessed.

2.2.1 Soil

Impact performance of some features depends on dynamic soil-structure interaction. Longitudinal barriers with soil embedded posts and soil-embedded support structures for signs and luminaires are such features. When feasible, these features should be tested with soil conditions that replicate typical inservice conditions. Unfortunately, soil conditions are known to vary with time and location, even within relatively small geographical areas. Therefore, except for special test conditions, it is necessary to standardize soil conditions for testing. In the absence of a specific soil, it is recommended that all features whose impact performance is sensitive to soil-structure interaction be tested with soil described in Section 2.2.1.1. Product developers and user agencies should assess the potential sensitivity of a feature to foundation conditions, and if the feature is likely to be installed in a soil that could be expected to degrade its performance, testing in one or more of the special soils described in Section 2.2.1.2 may be appropriate.

For tests involving soils recommended in Sections 2.2.1.1 and 2.2.1.2, the length, width, and depth of the embedment material should be sufficient to effectively eliminate influence of native soil on impact performance. If these dimensions cannot be determined, it is recommended the test soil depth be approximately 1.2 times the embedment length of the test article and that the lateral extent of the test soil, outside an envelope of the embedded portion of the test article, be approximately 1.3 times the embedment length.

2.2.1.1 Standard Soil

It is recommended that the standard soil meet AASHTO standard specifications for "Materials for Aggregate and Soil Aggregate Subbase, Base and Surface Courses," designation M 14765 (1990), grading A or B (see Appendix B, Part 1). It should be compacted in accordance with AASHTO Guide Specifications for Highway Construction, Sections 304.05 and 304.07 (see Appendix B, Part 3). The soil should be recompacted, as necessary, before each test to meet density requirements of the Guide Specifications. The soil should be well drained at the time of the crash test. The test should not be performed if the ground is frozen or if the soil is saturated unless the test is specifically designed to evaluate these conditions (see next section).

2.2.1.2 Special Soils

The following guidelines may be used to evaluate a feature in a weak, saturated, or frozen soil.

Weak Soil. It is recommended the weak soil meet AASHTO standard specification for "Fine Aggregate for Portland Cement Concrete," AASHTO designation M 6-87 (see Appendix B, Part 2). The soil should be compacted in accordance with AASHTO Guide Specifications for Highway Construction, Sections 304.05 and 304.07 (see Appendix B, Part 3). The soil should be recompacted, as necessary, before each test to meet density requirements of the Guide Specifications. The soil should be well drained at the time of the crash test.

Saturated Soil. The "standard soil" and "weak soil" previously described may be used to evaluate impact performance of a feature under saturated soil conditions. Moisture content of the soil should replicate expected in-service conditions.

Frozen Soil. The "standard soil" and "weak soil" described may be used to evaluate impact performance of a feature under frozen soil conditions. The degree to which the soil is frozen, measured in terms of depth and temperature, and its moisture content should replicate expected in-service conditions.

2.2.1.3. Embedment of Test Article

Within the range of expected in-service conditions, the depth and method of embedment should be those likely to reveal the poorest performance of the test article. This may not be predictable, in which case testing should be done under sufficient embedment conditions to reveal the worst performance.