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                Safety Performance Function Development Guide: Developing Jurisdiction-Specific SPFs
**Description:**
        This document is a “how-to” guidebook for agencies that are developing jurisdiction-specific safety performance functions (SPFs). The guidebook discusses the statistical issues associated with the development of jurisdiction-specific SPFs and provides a step-by-step procedure that states can use to develop jurisdiction-specific SPFs. Statistical issues covered in this guidebook include:

Over-dispersion.
	Selection of Explanatory Variables.
	Functional Form of the Model and Explanatory Variables.
	Over-fitting of SPFs.
	Correlation among Explanatory Variables.
	Homogenous Segments and Aggregation.
	Presence of Outliers.
	Endogenous Explanatory Variables.
	Estimation of SPFs for Different Crash Types and Severities.
	Goodness of Fit.Intended users include safety practitioners, consultants, and researchers. Users are expected to have more than a basic understanding of statistics.
    
          **Tool Type:**
        Application Guide
    
    
    
          **Owner Source:**
        federal
    
          **Sponsor/Owner:**
        Federal Highway Administration (FHWA)
    
        **Published:**
      2013
    
        **Availability:**
      The guide is available free of charge at the following link: SPF Development Guide. U.S. DEPARTMENT OF TRANSPORTATION

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