NAT'L INST. OF STAND & TECH Emergency Vehicle Publication Warning Systems 480-37 Reference NBS Publl - cations 1 I Law Enforcement Technology i U.S. DEPARTMENT OF COMMERCE National Bureau of Standards •QC 100 ,U57 NO. ^80-37 1981 ABOUT THE TECHNOLOGY ASSESSMENT PROGRAM The Technology Assessment Program is sponsored by the Office of Development, Testing, and Dissemination of the National Institute of Justice (NIJ), U.S. Department of Justice. The program responds to the mandate of the Justice System Improvement Act of 1979, which created NIJ and directed it to encourage research and development to improve the criminal justice system and to disseminate the results to Federal, State, and local agencies. The Technology Assessment Program is an applied research effort that determines the technological needs of justice system agencies, sets minimum performance standards for specific devices, tests commercially available equipment against those standards, and disseminates the standards and the test results to criminal justice agencies nationwide and internationally. The program operates through: The Technology Assessment Program Advisory Council (TAPAC) consisting of nationally recognized criminal justice practitioners from Federal, State, and local agencies, which assesses technological needs and sets priorities for research programs and items to be evaluated and tested. The Law Enforcement Standards Laboratory (LESL) at the National Bureau of Standards, which develops voluntary National performance standards for compliance testing to ensure that individual items of equipment are suitable for use by criminal justice agencies. The standards are based upon laboratory testing and evaluation of representative samples of each item of equipment to determine the key attributes, develop test methods, and establish minimum performance requirements for each essential attribute. In addition to the highly technical standards, LESL also produces user guides that explain in non-technical terms the capabilities of available equipment. The Technology Assessment Program Information Center (TAPIC) operated by the International Association of Chiefs of Police (lACP), which supervises a national compliance testing program conducted by independent agencies. The standards developed by LESL serve as performance bench marks against which commercial equipment is measured. The facilities, personnel, and testing capabilities of the independent laboratories are evaluated by LESL prior to testing each item of equipment, and LESL helps the Information Center staff review and analyze data. Test results are published in Consumer Product Reports designed to help justice system procurement officials make informed purchasing decisions. All publications issued by the National Institute of Justice, including those of the Technology Assessment Program, are available from the National Criminal Justice Reference Service (NCJRS), which serves as a central information and reference source for the nation's criminal justice community. For further information, or to register with NCJRS, write to the National Institute of Justice, National Criminal Justice Reference Service, Washington, DC 2053L Paul Cascarano, Director Office of Development, Testing, and Dissemination National Institute of Justice ACKNOWLEDGMENTS This report was prepared by the Law Enforcement Standards Laboratory of the National Bureau of Standards under the direction of Jared J. Collard, Acting Manager, Selected Systems Program, and Lawrence K. Eiiason, Chief of LESL. The contributions of Jacob J. Diamond, Charles A. Douglas and Thomas L. Quindry, formerly at the National Bureau of Standards, are gratefully acknowledged. The preparation of this report was sponsored by the National Institute of Justice, Lester D. Shubin, Standards Program Manager. NBS Special Emergency Vehicle JUN i 5 1931 Publication Warning Systems by Arthur I. Rubin Gerald L. Howett Center for Building Technology National Bureau of Standards and the Law Enforcement Standards Laboratory Center for Consumer Product Technology National Bureau of Standards Washington, DC 20234 prepared for the National Institute of Justice U.S. Department of Justice Washington, DC 20531 / 'I issued May 1981 U.S. DEPARTMENT OF COMMERCE, Malcolm Baldrige , Secretary NATIONAL BUREAU OF STANDARDS Ernest Ambler, Director Library of Congress Catalog Card Number: 81 -600059 National Bureau of Standards Special Publication 480-37 Nat. Bur. Stand. (U.S.) Spec. Publ. 480-37, 25 pages CODEN: XNBSAV U.S. GOVERNMENT PRINTING OFFICE WASHINGTON: 1981 For sale by the Superintendent of Documents U.S. Government Printing Office, Washington, DC 20402 Price $2.25 (Add 25 percent for other than U.S. mailing) FOREWORD The Law Enforcement Standards Laboratory (LESL) of the National Bureau of Standards (NBS) furnishes technical support to the National Institute of Justice (NIJ) program to strengthen law enforcement and criminal justice in the United States. LESL's function is to conduct research that will assist law enforcement and criminal justice agencies in the selection and procurement of quality equipment. LESL is: (1) Subjecting existing equipment to laboratory testing and evaluation and (2) conducting research leading to the development of several series of documents, including national voluntary equipment standards, user guides, and technical reports. This document is a law enforcement equipment report developed by LESL under the sponsorship of NIJ. Additional reports as well as other documents are being issued under the LESL program in the areas of protective equipment, communications equipment, security systems, weapons, emergency equipment, investigative aids, vehicles, and clothing. Technical comments and suggestions concerning this report are invited from all interested parties. They may be addressed to the Law Enforcement Standards Laboratory, National Bureau of Standards, Washington, DC 20234. Lawrence K. Eliason, Chief Law Enforcement Standards Laboratory iii CONTENTS Foreword iii Introduction 1 The Warning Signal Problem 2 Signal Effectiveness 2 Signal Variability 2 An Analysis of Warning Systems 4 Factors Contributing to a Good Warning System 5 Reactions of Drivers to Warning Signals 5 Messages Transmitted by Warning Systems 7 Emergency Vehicle Warning Lights 7 Emergency Vehicle Sirens 9 Electronic Sirens With Dual Speakers 12 National Standardization of Warning Light Signals 12 Meaning of the Signals 13 Color Selection 13 Recommended Colors, Configurations, and Duty (On-Off) Cycles 14 Recommended Flash Rates 17 Recommended Minimum Intensities 17 Improving Visual and Audible Effectiveness 19 Appendix A—References 21 V EMERGENCY VEHICLE WARNING SYSTEMS Arthur I. Rubin* Gerald L. Howett* National Bureau of Standards, Washington. DC 20234 The subject of visual and auditory warning devices (lights and sirens) for emergency and service vehicles is surveyed from a broad perspective. The report should provide directly useful information at all levels from the selection of hardware to a general understanding of the psychophysical factors determining the effectiveness of these devices. Topics covered include: an analysis of warning signals; the present situation and the need for uniform national standards; suggested performance standards for warning light systems and for sirens, including the reasons for the principal requirements; recommendations for actions that can be taken to improve the signal effectiveness of emergency vehicles; and brief summaries of some of the physical measurements that are made on a selection of lights and sirens. Key words: Conspicuity; effective intensity; emergency warning lights; flashing lights; lights, warning; sirens; sound level; warning lights; warning signals. INTRODUCTION The typical emergency vehicle warning system consists of lights and sirens, which are used to clear a path through traffic for a police or other emergency vehicle. A 1972 national survey of police departments [1]' pointed out their need for relevant, objective technical information when purchasing warning systems. In response to this need, the National Bureau of Standards Law Enforcement Standards Laboratory initiated a project to develop performance standards for lights and sirens used as emergency vehicle warning systems. The identification of performance attributes of warning lights and sirens, the establishment of the methods of testing and measuring each attribute and the evaluation of the minimum performance levels for each one are essential steps in the development of meaningful performance standards. These procedures are usually straightforward and clearly understood. Attempts, however, to apply these procedures to technology which involves the visual and auditory senses is especially difficult, not only due to human variables, but also because of the large number of combinations and configurations of warning lights and sirens on the market. Warning systems have been used for many years by a large number of departments and considerable operational experience has been accumulated. Although there have been interdepartmental exchanges of information, no single system has been evolved as the "best" warning system. In fact, the plethora of systems would seem to indicate that each department has reached its own solution independently. This report discusses the problems associated with the functional use of emergency vehicle warning systems and a recommended national standard system of warning light signals. It also describes in general terms the types of lights