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FHWA Home / Safety / Transportation Safety Planning (TSP) / Transportation Safety Planning (TSP)

Transportation Safety Planning (TSP)

Graphical header that has the title: Applying Safety Data and Analysis to Performance-Based Transportation Planning.

Figure D.1 Chart. Example of Regression to the Mean

Long Description

Figure D.1 is a chart showing three different types of data. Years are on the x-axis and the number of crashes is on the y-axis. One line shows hypothetical 1990 to 2010 annual crash frequency at a site. The crash frequency varies up and down from year to year. The second line represents the long-term average crash frequency at the same hypothetical site. The long-term average stabilizes at approximately 14 crashes per year. The third line represents the five-year rolling average number of crashes per year. The first five-year average is from 1990 to 1994 and is plotted in 1994, the second is from 1991 to 1995 and plotted on 1995. As shown, the five-year rolling average more closely approximates the long-term average than the annual crash frequency alone.

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Page last modified on December 11, 2015
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Federal Highway Administration | 1200 New Jersey Avenue, SE | Washington, DC 20590 | 202-366-4000