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Suggested Citation:"Front Matter." National Academies of Sciences, Engineering, and Medicine. 2020. Identification of Factors Contributing to the Decline of Traffic Fatalities in the United States from 2008 to 2012. Washington, DC: The National Academies Press. doi: 10.17226/25590.
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Suggested Citation:"Front Matter." National Academies of Sciences, Engineering, and Medicine. 2020. Identification of Factors Contributing to the Decline of Traffic Fatalities in the United States from 2008 to 2012. Washington, DC: The National Academies Press. doi: 10.17226/25590.
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Suggested Citation:"Front Matter." National Academies of Sciences, Engineering, and Medicine. 2020. Identification of Factors Contributing to the Decline of Traffic Fatalities in the United States from 2008 to 2012. Washington, DC: The National Academies Press. doi: 10.17226/25590.
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Suggested Citation:"Front Matter." National Academies of Sciences, Engineering, and Medicine. 2020. Identification of Factors Contributing to the Decline of Traffic Fatalities in the United States from 2008 to 2012. Washington, DC: The National Academies Press. doi: 10.17226/25590.
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Suggested Citation:"Front Matter." National Academies of Sciences, Engineering, and Medicine. 2020. Identification of Factors Contributing to the Decline of Traffic Fatalities in the United States from 2008 to 2012. Washington, DC: The National Academies Press. doi: 10.17226/25590.
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Suggested Citation:"Front Matter." National Academies of Sciences, Engineering, and Medicine. 2020. Identification of Factors Contributing to the Decline of Traffic Fatalities in the United States from 2008 to 2012. Washington, DC: The National Academies Press. doi: 10.17226/25590.
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Suggested Citation:"Front Matter." National Academies of Sciences, Engineering, and Medicine. 2020. Identification of Factors Contributing to the Decline of Traffic Fatalities in the United States from 2008 to 2012. Washington, DC: The National Academies Press. doi: 10.17226/25590.
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Suggested Citation:"Front Matter." National Academies of Sciences, Engineering, and Medicine. 2020. Identification of Factors Contributing to the Decline of Traffic Fatalities in the United States from 2008 to 2012. Washington, DC: The National Academies Press. doi: 10.17226/25590.
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Suggested Citation:"Front Matter." National Academies of Sciences, Engineering, and Medicine. 2020. Identification of Factors Contributing to the Decline of Traffic Fatalities in the United States from 2008 to 2012. Washington, DC: The National Academies Press. doi: 10.17226/25590.
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Suggested Citation:"Front Matter." National Academies of Sciences, Engineering, and Medicine. 2020. Identification of Factors Contributing to the Decline of Traffic Fatalities in the United States from 2008 to 2012. Washington, DC: The National Academies Press. doi: 10.17226/25590.
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2020 N A T I O N A L C O O P E R A T I V E H I G H W A Y R E S E A R C H P R O G R A M NCHRP RESEARCH REPORT 928 Identification of Factors Contributing to the Decline of Traffic Fatalities in the United States from 2008 to 2012 Daniel Blower Carol Flannagan University of Michigan transportation research institUte Ann Arbor, MI Srinivas Geedipally Dominique Lord Robert Wunderlich texas a&M transportation institUte College Station, TX Subscriber Categories Planning and Forecasting • 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 departments of transportation (DOTs) 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 transporta- tion results in increasingly complex problems of wide interest to high- way 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 ini- tiated 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, 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 com- mittee 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, univer- sities, and industry; TRB’s relationship to the National Academies is an insurance of objectivity; and TRB maintains a full-time staff of special- ists 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 Federal Highway Administration. 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 Direc- tors 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 surveillance of research contracts are the responsibilities of the National Academies and TRB. 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. Published research reports of the NATIONAL COOPERATIVE HIGHWAY RESEARCH PROGRAM are available from Transportation Research Board Business Office 500 Fifth Street, NW Washington, DC 20001 and can be ordered through the Internet by going to http://www.national-academies.org and then searching for TRB Printed in the United States of America NCHRP RESEARCH REPORT 928 Project 17-67 ISSN 2572-3766 (Print) ISSN 2572-3774 (Online) ISBN 978-0-309-48111-3 Library of Congress Control Number 2020931211 © 2020 National Academy of Sciences. All rights reserved. COPYRIGHT INFORMATION 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, FAA, FHWA, FMCSA, FRA, FTA, Office of the Assistant Secretary for Research and Technology, PHMSA, or TDC 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. The opinions and conclusions expressed or implied in this report 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; or the program sponsors. The Transportation Research Board; the National Academies of Sciences, Engineering, and Medicine; and the sponsors of 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 the report.

The National Academy of Sciences was established in 1863 by an Act of Congress, signed by President Lincoln, as a private, non- governmental institution to advise the nation on issues related to science and technology. Members are elected by their peers for outstanding contributions to research. Dr. Marcia McNutt is president. The National Academy of Engineering was established in 1964 under the charter of the National Academy of Sciences to bring the practices of engineering to advising the nation. Members are elected by their peers for extraordinary contributions to engineering. Dr. John L. Anderson is president. The National Academy of Medicine (formerly the Institute of Medicine) was established in 1970 under the charter of the National Academy of Sciences to advise the nation on medical and health issues. Members are elected by their peers for distinguished contributions to medicine and health. Dr. Victor J. Dzau is president. The three Academies work together as the National Academies of Sciences, Engineering, and Medicine to provide independent, objective analysis and advice to the nation and conduct other activities to solve complex problems and inform public policy decisions. The National Academies also encourage education and research, recognize outstanding contributions to knowledge, and increase public understanding in matters of science, engineering, and medicine. Learn more about the National Academies of Sciences, Engineering, and Medicine at www.national-academies.org. The Transportation Research Board is one of seven major programs of the National Academies of Sciences, Engineering, and Medicine. The mission of the Transportation Research Board is to provide leadership in transportation improvements and innovation through trusted, timely, impartial, and evidence-based information exchange, research, and advice regarding all modes of transportation. The Board’s varied activities annually engage about 8,000 engineers, scientists, and other transportation researchers and practitioners from the public and private sectors and academia, all of whom contribute their expertise in the public interest. The program is supported by state transportation departments, federal agencies including the component administrations of the U.S. Department of Transportation, and other organizations and individuals interested in the development of transportation. Learn more about the Transportation Research Board at www.TRB.org.

C O O P E R A T I V E R E S E A R C H P R O G R A M S AUTHOR ACKNOWLEDGMENTS This research was performed under NCHRP Project 17-67 by the University of Michigan Trans- portation Research Institute (UMTRI) and the Texas A&M Transportation Institute (TTI). The authors acknowledge the contributions of David Eby, Lidia Kostyniuk, and John Sullivan at UMTRI for their subject matter expertise in identifying in a comprehensive way the factors that contributed to traffic safety over the period, as well as their assistance in identifying and digesting the major relevant literature. The authors also acknowledge Reneé St. Louis for her assistance in organizing the literature and Alice Elliott for her assistance in locating and compiling data series for the project. Finally, the team thanks the Panel for their many useful insights and suggestions. CRP STAFF FOR NCHRP RESEARCH REPORT 928 Christopher J. Hedges, Director, Cooperative Research Programs Lori L. Sundstrom, Deputy Director, Cooperative Research Programs Mark S. Bush, Senior Program Officer Eileen P. Delaney, Director of Publications Natalie Barnes, Associate Director of Publications NCHRP PROJECT 17-67 PANEL Field of Traffic—Area of Safety Robert E. Hull, Cambridge Systematics, Inc., Salt Lake City, UT (Chair) Raymond J. Khoury, Virginia DOT, Richmond, VA Nicole L. Charlson, Oregon DOT, Salem, OR Anthony R. Giancola, Washington, DC Susan B. Herbel, SBH Consult, Fort Meyers, FL Jennifer A. Inzana, Massachusetts DOT, Boston, MA Raj V. Ponnaluri, Florida DOT, Tallahassee, FL Brian C. Tefft, AAA Foundation for Traffic Safety, Washington, DC Jin Wang, Atkins, San Francisco, CA Thomas M. Welch, Leidos, Fairfield Bay, AR Monique R. Evans, FHWA Liaison Kelly K. Hardy, AASHTO Liaison Bernardo Kleiner, TRB Liaison

This report describes a comprehensive analysis of the factors associated with fatality rates in states, especially as they relate to the substantial drop in fatalities occurring in the years from 2008 to 2011. The analysis included predictors representing a wide variety of potentially related factors including travel, demographics, the economy, vehi- cle safety systems, and state spending on several categories of infrastructure and safety improvements. Understanding the broad array of factors that influence traffic safety in the United States is particularly important for state highway safety planning. From 2008 to 2011, the United States, along with several other countries, experienced a substantial drop in annual traffic fatalities. State departments of transportation are keenly interested in capturing the key contributing factors to this decline so that the information can be used to help focus resources on effective countermeasures in future years. Safety countermeasures are implemented in a wide variety of ways—changing behavior (e.g., through driver education), changing vehicles (e.g., with Electronic Stability Control and other safety technologies), and changing the environment (e.g., improving roadways, laws, and enforcement). Safety can be influenced by factors other than safety efforts themselves, so it can be difficult to know which changes are responsible for overall reductions in fatalities. Under NCHRP Project 17-67, the research conducted by the University of Michigan, with support from Texas A&M was asked to provide a multidisciplinary analysis of the relative influence of the types of factors that contributed to the national decline in the number of highway fatalities and rates in the United States during the years of 2008–2011. The research team used the Haddon matrix to identify a large number of potential travel, demographic, economic, vehicle, and infrastructure influences on fatalities. Data on these factors were then collected from data sources publicly available at the state level (e.g., FHWA Highway Statistics). Annual state-level measures of these factors were compiled into a database covering the years from 2001 to 2012 and matched with fatalities from the Fatality Analysis Reporting System (FARS) database. These data were analyzed using statistical methods to predict fatalities in states as well as changes over time. Because the statistical models closely approximated the reduction in fatalities from 2008 to 2011, the factors could then be evaluated in terms of their individual (and combined) contributions to fatalities. This report covers the scope of the problem, the data obtained to measure each factor, the statistical models, and the interpretation of results to understand how different factors play a role in total fatality counts. The knowledge gained from this process can be used to predict future fatality levels for planning at the state level and to provide insight into factors influencing these levels and actions that might reduce them. F O R E W O R D By Mark S. Bush Staff Officer Transportation Research Board

1 Summary 8 Chapter 1 Statement of the Problem 9 Chapter 2 Analytical Approach 9 2.1 Risk vs. Exposure 10 2.2 Use of the Haddon Matrix 10 2.3 Economic Framework 11 2.4 Study Outline 12 Chapter 3 International Parallels 14 Chapter 4 Trends in Risk and Exposure 17 Chapter 5 Data 17 5.1 Crash Data 17 5.2 Sources of Other Data Used 22 Chapter 6 Trends in Contributing Factors 22 6.1 Age 25 6.2 Changes in Vehicles and Person Types Involved in Fatal Crashes 27 6.3 Roadway Class and Type 29 6.4 Vehicle Design and Model Year 32 6.5 Restraint Use 33 6.6 State Regulation of Driver Behavior, Alcohol Consumption 36 6.7 Economic Factors, National Trends 39 6.8 Highway and Infrastructure 42 Chapter 7 Modeling 43 7.1 Factor Analysis to Identify Parameters for the Models 44 7.2 Regression Models 57 Chapter 8 Discussion of Results 58 8.1 Variable Influence Estimated from the Count Models 70 8.2 Variable Influence Estimated from the Change Model 73 8.3 Implications for Reducing Fatalities and Crash Risk 74 Chapter 9 Limitations 76 Chapter 10 Data Needs and Future Research 76 10.1 Data Needs 77 10.2 Future Research 79 References C O N T E N T S

82 Appendix A Factor Analysis Details 84 Appendix B Descriptive Statistics 87 Appendix C State-Specific Parameters for the MCS Model 91 Appendix D State-Level MNCS Model Prediction vs. Performance Note: Photographs, figures, and tables in this report may have been converted from color to grayscale for printing. The electronic version of the report (posted on the web at www.trb.org) retains the color versions.

A B B R E V I A T I O N S 3R/4R Relocation, resurfacing, restoration, rehabilitation and reconstruction AIC Akaike information criterion BAC Blood alcohol concentration CMF Crash modification factor CPI Consumer Price Index DUI Driving under the influence EMS Emergency medical service ESC Electronic stability control FARS Fatality Analysis Reporting System FMVSS Federal Motor Vehicle Safety Standards GDL Graduated driver licensing GDP Gross domestic product GES General Estimates System (of the National Automotive Sampling System) GLM Generalized linear model GOF Goodness-of-fit HSIP Highway Safety Improvement Program IIHS Insurance Institute for Highway Safety IRTAD International Traffic Safety Data and Analysis Group LTV Light truck vehicle MAD Mean absolute deviation MCS Model controlling for state MCSAP Motor Carrier Safety Assistance Program MNCS Model not controlling for state MSPE Mean squared prediction error NB Negative binomial (model) NBER National Bureau of Economic Research NCAP New Car Assessment Program NHTS National Household Travel Survey NOPUS National Occupant Protection Use Survey OECD Organization for Economic Cooperation and Development PC Principal component PCA Principal Components Analysis QIE Quasi-induced exposure SUV Sport utility vehicle TTI Texas A&M Transportation Institute UMTRI University of Michigan Transportation Research Institute VIN Vehicle identification number VMT Vehicle miles traveled

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Identification of Factors Contributing to the Decline of Traffic Fatalities in the United States from 2008 to 2012 Get This Book
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Between 2005 and 2011, the number of traffic fatalities in the U.S. declined by 11,031, from 43,510 in 2005 to 32,479 in 2011. This decline amounted to a reduction in traffic-related deaths of 25.4 percent, by far the greatest decline over a comparable period in the last 30 years.

Historically, significant drops in traffic fatalities over a short period of time have coincided with economic recessions. Longer recessions have coincided with deeper declines in the number of traffic fatalities. This TRB National Cooperative Highway Research Program's NCHRP Research Report 928: Identification of Factors Contributing to the Decline of Traffic Fatalities in the United States from 2008 to 2012 provides an analysis that identifies the specific factors in the economic decline that affected fatal crash risk, while taking into account the long-term factors that determine the level of traffic safety.

A key insight into the analysis of the factors that produced the sharp drop in traffic fatalities was that the young contributed disproportionately to the drop-off in traffic fatalities. Of the reduction in traffic fatalities from 2007 to 2011, people 25-years-old and younger accounted for nearly 48 percent of the drop, though they were only about 28 percent of total traffic fatalities prior to the decline. Traffic deaths among people 25-years-old and younger dropped substantially more than other groups. Young drivers are known to be a high-risk group and can be readily identified in the crash data. Other high-risk groups also likely contributed to the decline but they cannot be identified as well as age can.

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