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Identification of Factors Contributing to the Decline of Traffic Fatalities in the United States from 2008 to 2012 (2019)

Chapter: Appendix D State-level MNCS model prediction vs. performance

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Suggested Citation:"Appendix D State-level MNCS model prediction vs. performance." 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:"Appendix D State-level MNCS model prediction vs. performance." 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:"Appendix D State-level MNCS model prediction vs. performance." 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:"Appendix D State-level MNCS model prediction vs. performance." 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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Page 99 Appendix D State-level MNCS model prediction vs. performance The panels in this Appendix compare the predicted number of fatalities for each state with the number actually experienced, computed as the ratio between observed and predicted. The MNCS (model not considering state) model was used for the purpose, because the goal was to compare how states differed from the prediction, in order to identify states that had more or fewer traffic fatalities than predicted by the model. In the panels, the horizontal line represents no difference from predicted. The dashed line represents the value obtained by dividing the observed number of traffic fatalities by the number of fatalities predicted by the MNCS model. Lines above the horizontal line represent a greater number than predicted, and those below represent fewer traffic than predicted. The greyed band represents the 90% confidence interval of the ratio. Small states with relatively few traffic fatalities tended to have more volatility in their number of traffic fatalities, so the ratios were less stable. Predictions for larger states tended to be more stable and showed less fluctuation. For several states, the ratio was close to the horizontal line (of no difference), showing that the MCS model prediction was close to the outcome. In these states, the model explained most of the variation. These states included Alabama, Colorado, Florida, Mississippi, North Carolina, and Pennsylvania. In other states, the ratios were persistently less than one. These states may have some features or programs that consistently resulted in a safer traffic environment. These states include Indiana, Massachusetts, Michigan, Minnesota, New York, Ohio, and Vermont. In other states, the dash line was consistently above the horizontal line, indicating that the number of fatalities was persistently greater than predicted by the MNCS model. A comparison of states that had fewer traffic fatalities than predicted by the model with the states that had more would be useful to identify characteristics, programs, and interventions that contributed to the difference in safety environment.

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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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