The National Academies

NCHRP 17-72 [Completed]

Update of Crash Modification Factors for the Highway Safety Manual

  Project Data
Funds: $845,000
Research Agency: University of North Carolina - Chapel Hill
Principal Investigator: Raghavan Srinivasan
Effective Date: 8/31/2015
Completion Date: 7/4/2022

Highway safety practitioners were given a significant new tool in 2010 with the publication of the first edition of the AASHTO Highway Safety Manual (HSM). In Part D of the HSM, crash modification factors (CMFs) are provided for a variety of treatments. These CMFs provide practitioners with the means to estimate the safety effects of countermeasures. By the time the second edition HSM is published, many more important CMFs will have been developed. It is critical that the next edition of the HSM incorporate these CMFs in order to continue to push forward this significant tool. In the first edition HSM, only the best available CMFs for individual treatments are provided. Questions that have arisen since the first edition of the HSM include:

a. Do the inclusion criteria need to be revised?
b. Should more than one CMF be presented for a particular countermeasure?
c. Is uncertainty of the CMFs adequately represented?
d. Should CMFs from multiple studies for the same treatment be combined and if so, how?

There is a need to establish inclusion criteria for CMFs and guidelines on how CMFs should be incorporated in the next edition of the HSM. Also, CMFs for use in the second edition of the HSM need to identified, assembled, and documented.
The objectives of this research are to:

a. Assess the current criteria and existing process for evaluating and identifying the quality of CMFs for appropriate use with the HSM.
b. Develop proposed revisions to the criteria and process, including how existing and new CMFs may be incorporated in the HSM. Provide guidance for practitioner application of the revised process.
c. Apply the evaluation criteria to identify and assess CMFs and develop a list of appropriate CMFs for the HSM.

CMFs to be studied are those listed in the FHWA CMF Clearinghouse. The research results are intended for possible inclusion in a future second edition of the HSM.
STATUS: Research Completed. 

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