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 Conditions
Site 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 Details
Crash Characteristics
- Crash Type
- Crash Severity
- Time of Day
Study 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:
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.