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Suggested Citation:"Contents." National Academies of Sciences, Engineering, and Medicine. 2019. 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:"Contents." National Academies of Sciences, Engineering, and Medicine. 2019. 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:"Contents." National Academies of Sciences, Engineering, and Medicine. 2019. 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:"Contents." National Academies of Sciences, Engineering, and Medicine. 2019. 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:"Contents." National Academies of Sciences, Engineering, and Medicine. 2019. 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:"Contents." National Academies of Sciences, Engineering, and Medicine. 2019. 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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iii Contents Summary ...................................................................................................................................................... ix  Chapter 1.  Statement of the problem ...................................................................................................... 1  Chapter 2.  Analytical approach .............................................................................................................. 3  2.1  Risk vs. exposure .......................................................................................................................... 3  2.2  Use of the Haddon Matrix ............................................................................................................. 4  2.3  Economic framework .................................................................................................................... 5  2.4  Study outline ................................................................................................................................. 5  Chapter 3.  International parallels ............................................................................................................ 7  Chapter 4.  Trends in risk and exposure .................................................................................................. 9  Chapter 5.  Data ..................................................................................................................................... 12  5.1  Crash data .................................................................................................................................... 12  5.2  Sources of other data used .......................................................................................................... 12  Chapter 6.  Trends in contributing factors ............................................................................................. 18  6.1  Age .............................................................................................................................................. 18  6.2  Changes in vehicles and person types involved in fatal crashes ................................................. 21  6.3  Roadway class and type .............................................................................................................. 24  6.4  Vehicle design and model year ................................................................................................... 27  6.5  Restraint use ................................................................................................................................ 30  6.6  State regulation of driver behavior, alcohol consumption .......................................................... 32  6.7  Economic factors, national trends ............................................................................................... 35  6.8  Highway and infrastructure ......................................................................................................... 38  Chapter 7.  Modeling ............................................................................................................................. 42  7.1  Factor analysis to identify parameters for the models ................................................................ 43  7.2  Regression models ...................................................................................................................... 45  7.2.1  Regression of factors on vehicle miles traveled .................................................................. 45  7.2.2  Regression of factors on fatalities ....................................................................................... 49  7.2.3  Model of annual change in factor levels on the annual change in fatalities. ....................... 56  Chapter 8.  Discussion of results ........................................................................................................... 60  8.1  Variable influence estimated from the count models .................................................................. 62  8.2  Variable influence estimated from the change model ................................................................. 75  8.3  Implications for reducing fatalities and crash risk ...................................................................... 79  Chapter 9.  Limitations .......................................................................................................................... 81  Chapter 10.  Future research and data needs ........................................................................................... 83 

iv 10.1  Data needs ................................................................................................................................... 83  10.2  Future research ............................................................................................................................ 84  References ................................................................................................................................................... 87  Appendix A Factor analysis details ............................................................................................................ 91  Appendix B Descriptive statistics ............................................................................................................... 93  Appendix C State-specific parameters for the MCS model ........................................................................ 95  Appendix D State-level MNCS model prediction vs. performance ............................................................ 99  List of Tables Table ES-1 Explanatory factors and expected mechanisms of activity ..................................................... xiii  Table ES-2 Effects of Count Model Factors .............................................................................................. xiv  Table ES-3 Effects of change-model predictors for 2007-2011 ................................................................ xiv  Table 2-1 Haddon Matrix to organize factors related to crash risk and severity .......................................... 4  Table 3-1 Reduction in traffic fatalities, selected European countries and the U.S., 2007-2011 ................. 7  Table 5-1 Exposure data series ................................................................................................................... 13  Table 5-2 Economic data series .................................................................................................................. 14  Table 5-3 Driver- and vehicle-related framework ...................................................................................... 15  Table 5-4 Highway expenditures ................................................................................................................ 16  Table 6-1 Fatality rates per 100 million VMT, by roadway function class, 2001-2012 ............................. 25  Table 6-2 State highway expenditures per highway mile, 2010-2012, in 1000s of 2013 dollars ............... 41  Table 7-1 Summary of predictors and correlations ..................................................................................... 44  Table 7-2 Correlation of VMT with different variables .............................................................................. 45  Table 7-3 Parameter estimates for the total VMT model ............................................................................ 46  Table 7-4 Parameter estimates for the urban VMT model .......................................................................... 47  Table 7-5 Parameter estimates for the rural VMT model ........................................................................... 48  Table 7-6 Parameter estimates for the MNCS model, VMT offset ............................................................ 53  Table 7-7 Parameter estimates for the MCS model with VMT as exposure ............................................... 54  Table 7-8 Parameter estimates for the MCS model with population as exposure ...................................... 55  Table 7-9 Parameter estimates for change model ....................................................................................... 58  Table 7-10 Effects of change-model predictors for 2007-2011 .................................................................. 59  Table 8-1 Explanatory factors and expected mechanisms of activity ......................................................... 61  Table 8-2 Grouping of Variables ................................................................................................................ 62  Table 8-3 Proportion of Predicted and Observed Reduction of Fatalities accounted for by groupings of Count Model Variables ............................................................................................................................... 63  Table 8-4 Effects of Individual Economic Factors ..................................................................................... 71  Table 8-5 Effects of Individual Regulatory Factors .................................................................................... 74 

v List of Figures Figure ES-1 Traffic fatalities, 2001-2012 .................................................................................................... ix  Figure ES-2 Motor vehicle traffic fatalities and periods of recession, 1966-2012 ....................................... x  Figure ES-3 Fatality rates by VMT and vehicle registrations, and fatalities, normalized to 2001 .............. xi  Figure ES-4 Ratio of traffic fatalities by age groups, normalized to 2001 ................................................. xii  Figure 1-1 Traffic fatalities, 2001-2012 ........................................................................................................ 2  Figure 4-1 Trends in crashes, fatal crashes, and fatalities, 2001-2012 ....................................................... 10  Figure 4-2 Trends in traffic fatalities, VMT, and vehicle registrations, 2001-2012 ................................... 10  Figure 4-3 Fatality rates by VMT and vehicle registrations, and fatalities, normalized to 2001 ................ 11  Figure 6-1 Percentage of driver age bands by crash year in fatal crashes .................................................. 19  Figure 6-2 Ratio of traffic fatalities by age groups, 2001 to 2012 .............................................................. 20  Figure 6-3 Estimated reduction in traffic fatalities, 2008-2012, by age ..................................................... 21  Figure 6-4 Passenger car, LTV, truck, motorcycle, bus, and other motor vehicle involvements in fatal crashes, 2001-2012 ..................................................................................................................................... 22  Figure 6-5 Trends in vehicle involvements in fatal crashes, 2001-2012 .................................................... 22  Figure 6-6 Distribution of fatalities by person type, 2001-2012 ................................................................. 23  Figure 6-7 Trends in fatalities by person type, 2001-2012 ......................................................................... 24  Figure 6-8 Trends in VMT by area and road type, 2001-2012 ................................................................... 25  Figure 6-9 Estimated reduction in traffic fatalities 2008-2012 by road type .............................................. 26  Figure 6-10 Ratio to 2001 of traffic fatalities in urban and rural areas, 2001 to 2012 ................................ 26  Figure 6-11 Estimated reduction in traffic fatalities 2008-2012 by area type ............................................ 27  Figure 6-12 Age of vehicles in fatal crashes, 2001-2012 ............................................................................ 29  Figure 6-13 Fleet penetration of ESC (adapted from (Highway Loss Data Institute 2014)) and penetration of post-1991 model year ............................................................................................................................. 29  Figure 6-14 Driver safety belt use: Observed, drivers in fatal crashes, & fatally-injured drivers .............. 31  Figure 6-15 Trends in observed safety belt use by state, 2001-2012 .......................................................... 32  Figure 6-16 Safety belt laws rating index by state and year, 2001-2012 .................................................... 33  Figure 6-17Alcohol laws rating index by state and year, 2001-2012\ ........................................................ 34  Figure 6-18 Per capita consumption of beer, spirits, and wine ................................................................... 35  Figure 6-19 Trends in median household income and GDP/capita, 2001-2012 ......................................... 37  Figure 6-20 Unemployment rate by age ..................................................................................................... 37  Figure 6-21 Fuel prices, constant 2013 dollars, 2001-2012 ........................................................................ 38  Figure 6-22 Highway spending per mile of highway, 2001-2012 .............................................................. 40  Figure 7-1 Predicted total VMT versus reported total VMT, 2001-2012 ................................................... 46  Figure 7-2 Predicted urban VMT versus reported urban VMT, 2001-2012 ............................................... 47  Figure 7-3 Predicted rural VMT versus reported rural VMT, 2001-2012 .................................................. 49  Figure 7-4 Model predictions versus actual fatalities, 2007-2012 .............................................................. 56  Figure 8-1 Observed Traffic Fatalities versus Fatalities with Constant Exposure or Risk ......................... 60  Figure 8-2 Quantification of Economic Effects on Fatalities ..................................................................... 64  Figure 8-3 Quantification of Effects of Safety Expenditure on Fatalities ................................................... 65 

vi Figure 8-4 Quantification of Effects of Capital Expenditure on Fatalities ................................................. 66  Figure 8-5 Quantification of Effects of Regulatory Effects on Fatalities ................................................... 67  Figure 8-6 Quantification of Effects of Vehicle Improvements on Fatalities ............................................. 68  Figure 8-7 Fuel prices, constant 2013 dollars, 2007-2012 .......................................................................... 72  Figure 8-8 Trends in median household income, 2007-2012 ..................................................................... 74  Figure 8-9 Change model prediction of variable effect on reduction in traffic fatalities, 2007-2011 ........ 76 

vii Acknowledgements The research report herein was performed under NCHRP Project 17-67 by the University of Michigan Transportation Research Institute (UMTRI) and the Texas A&M Transportation Institute (TTI). The authors would like to 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; 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.

viii Acronyms AIC  Akaike information criterion  BAC  Blood alcohol concentration  DUI  Driving under the influence  FARS  Fatality Analysis Reporting System  GDP  Gross domestic product  GES  General Estimates System (of the National Automotive Sampling System)  GOF  Goodness‐of‐fit  HSIP  Highway Safety Improvement Program  LTV  Light truck vehicle  MAD  Mean absolute deviation  MCS  Model controlling for state  MNCS  Model not controlling for state  MSPE  Mean Squared Prediction Error  NB  Negative binomial (model)  NCAP  New Car Assessment Program  NCHRP  National Cooperative Highway Research Program  NHTSA  National Highway Traffic Safety Administration  NIAAA  National Institute on Alcohol Abuse and Alcoholism  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 report from the National Cooperative Highway Research Program, 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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