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                Recommended Protocols for Developing Crash Modification Factors
**Description:**
        This guidebook outlines a process for developing high-quality crash modification factors for inclusion in the Highway Safety Manual (HSM) and the Crash Modification Factor (CMF) Clearinghouse. The purpose is to define what factors in a study design make a quality CMF that will attain high ratings in the CMF Clearinghouse and will be acceptable for inclusion in the HSM. The document specifies recommended protocols that should be used in developing CMFs, what research details should be documented, and how various potential biases should be addressed. The following is a summary of the documentation requirements detailed in the CMF Protocols:
CMF and Countermeasure

Countermeasure Name and Description
	Crash Modification Factor or Function
	Measures of Precision for the CMF
	Prior ConditionsSite Characteristics

Roadway Class
	Road Division Type
	State
	Municipality
	Area Type
	Number of Through Lanes
	Speed Limit
	Traffic Volume Range
	Traffic Control (if applicable)
	Intersection Type
	Intersection Geometry
	Other Relevant DetailsCrash Characteristics

Crash Type
	Crash Severity
	Time of DayStudy Details

Years of Data
	Type of Methodology
	Site Selection Criteria
	Sample Size Used (Crashes)
	Sample Size Used (Sites)The guidebook is written for those responsible for developing or overseeing the development of CMFs. It may be difficult to understand the implications of statistical methods and potential sources of bias for those who do not possess a background in statistics and road safety.
    
          **Tool Type:**
        Informational Guide
    
    
    
          **Owner Source:**
        organization
    
          **Sponsor/Owner:**
        National Cooperative Highway Research Program (NCHRP)
    
        **Published:**
      2012
    
        **Availability:**
      The guidebook is available free of charge at the following link: Recommended Protocols for Developing CMFs.
    
          **Disclaimer:**
        This information is disseminated under the sponsorship of the U.S. Department of Transportation in the interest of information exchange. The U.S. Government assumes no liability for the use of the information contained herein. This information does not constitute a standard, specification, or regulation. The U.S. Government does not endorse products or manufacturers. Trademarks or manufacturer's names appear in this information only because they are considered essential to the objective of this publication.
          Any opinions, findings, and conclusions or recommendations, and translations thereof, expressed in this publication are those of the author(s) and do not necessarily reflect the views of the Federal Highway Administration. U.S. DEPARTMENT OF TRANSPORTATION

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