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Impact of Shoulder Width and Median Width on Safety (2009) / Chapter Skim
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Appendix A - Using Prediction Models to Determine Relative Safety of Design Element Choices
Pages 36-37

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From page 36...
... In this step, the choice of shoulder widths, median widths, median presence, and shoulder type are determined in order to identify the possible roadway geometric design elements to be evaluated. • Step 3: Estimate the number of crashes for each condition to be evaluated using the appropriate prediction model for each segment of concern.
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From page 37...
... Flow chart of model application. Crashes Segment Length ADT Shoulder Obs Exp 1 0.25 12,000 6 4 2.38 2 0.30 10,000 4 3 3.02 3 0.44 16,000 8 6 4.51 4 0.20 18,000 8 4 2.36 … … … … … … … … … … … … … … … … … … 100 0.42 17,000 6 6 6.09 Total 70 50 Table A-1.
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Key Terms

  • roadway section
  • roadway project
  • design elements
  • calibration process
  • rural highways

  • geometric design
  • prediction models
  • expected values
  • relative safety
  • safety implications

  • design choices
  • using prediction
  • evaluated using
  • determine relative
  • ing factor

  • sample data
  • total crashes
  • values obtained
  • local conditions
  • width occurs

  • adt shoulder
  • requires dividing
  • appropriate prediction
  • simply summing
  • set calculations

  • individual predictions
  • obs exp
  • shoulder obs
  • model estimates
  • entire roadway


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