Introduction to the CMF Clearinghouse

What is the purpose of the CMF Clearinghouse?

The CMF Clearinghouse serves three important roles for the transportation safety field.

1. Provides CMF Data
The CMF Clearinghouse is a comprehensive and searchable database of published CMFs. It contains all CMFs published in 2010 or after as well as many CMFs published before that date, such as those compiled in the first edition of the AASHTO Highway Safety Manual and the FHWA Desktop Reference for Crash Reduction Factors. It provides information on all available CMFs, such as the CMF value and all published details about the CMF; citations and related information about the study that produced each CMF; and a star rating that provides an indication of the quality of each CMF. It is regularly updated to include newly published CMFs.

2. Educates CMF Users
The CMF Clearinghouse provides guidance material to instruct users about the appropriate use of CMFs. Through a series of Frequently Asked Questions, the Clearinghouse provides answers to many important CMF-related questions posed by city and state transportation engineers, planners, and researchers. The CMF Clearinghouse also sponsors an annual webinar to provide guidance on appropriate use of CMFs and best practices from state agencies. In addition to the guidance provided from the Clearinghouse, the website also provides links to many external resources in categories such as “How to Develop and Use CMFs”, “Cost-Benefit Analyses”, and “Training”.

3. Facilitates CMF Research
Researchers often use CMF Clearinghouse data to determine if there are any CMFs existing on a potential research topic and where research gaps are present. To direct future research, the CMF Most Wanted List is provided to show researchers and funding agencies the countermeasures and topics that are high priority to Clearinghouse users but not present in the Clearinghouse data. The CMF Clearinghouse also provides safety researchers with a mechanism to submit CMFs for inclusion in the Clearinghouse.

What kind of CMFs does the CMF Clearinghouse include?

It is important to understand what the Clearinghouse does and does not include. The CMF Clearinghouse presents CMFs from studies that meet the following criteria:

  • The study must be based on crash data, not surrogate measures of safety such as speed reductions, near misses, or yielding behavior.
  • The study must have the objective of quantifying the safety effect of a roadway feature or characteristic (i.e., as opposed to an academic exercise of comparing model forms).
  • The study must be focused on determining the safety effect of an infrastructure characteristic, feature, or modification that would fall under engineering responsibilities (e.g., not planning-level or area-wide characteristics such as land use or demographics; not safety efforts unrelated to engineering such as public safety awareness campaigns or law enforcement efforts).
  • The study must explicitly present quantified CMF values or CMFunctions (i.e., the Clearinghouse team does not derive CMFs if they are not explicitly reported by the author).The Clearinghouse presents the CMFs as they are presented by the author in the original source document. There is no modification made to the CMF value or adjustment to any reported standard error.

Where DO CMFs come from?

The CMF Clearinghouse team, which consists of engineers with many years of safety research experience, identifies eligible CMFs through a regular review process of published reports and professional journals. The review cycle is conducted four times per year and consists of reviewing papers from the following sources:

Quarter 1
  • Transportation Research Board Annual Meeting Compendium of Papers (past meeting)
  • User-submitted studies (past 3 months)

Quarter 2
  • American Society of Civil Engineers Journal of Transportation Engineering (past 6 months)
  • Institute of Transportation Engineers Journal (past 6 months)
  • Accident Analysis and Prevention (past 6 months)
  • Journal of Safety Research (past 6 months)
  • User-submitted studies (past 3 months)

Quarter 3
  • Searches on the Transport Research International Documentation (TRID, formerly TRIS)
  • User-submitted studies (past 3 months)

Quarter 4
  • American Society of Civil Engineers Journal of Transportation Engineering (past 6 months)
  • Institute of Transportation Engineers Journal (past 6 months)
  • Accident Analysis and Prevention (past 6 months)
  • Journal of Safety Research (past 6 months)
  • User-submitted studies (past 3 months)

The process for each review cycle is:

  • Study Identification – The Clearinghouse team reviews the resources (published reports, journal articles, etc.) for the appropriate quarter and identifies papers that appear eligible based on title and abstract.
  • Preliminary Review – The Clearinghouse team performs an in-depth review of each identified study to determine if it meets the eligibility criteria and if so, to record all CMFs from the study into an administrative database.
  • Critical Review – The Clearinghouse team performs a critical review on the recorded CMFs to assign a star quality rating to each CMF.
  • Review by FHWA Subject Matter Experts – The final reviewed list of CMFs is submitted for review by a team of subject matter experts (SMEs) at FHWA for a final check.
  • Add to CMF Clearinghouse – With concurrence from FHWA, the final CMFs are posted to CMF Clearinghouse on a quarterly basis.

Prior to its launch in 2010 and the start of a regular review cycle, the Clearinghouse was initially populated with CMFs from two major resources, the first edition of the AASHTO Highway Safety Manual (HSM) and the FHWA Desktop Reference for Crash Reduction Factors. The Clearinghouse provides a page of information on the relationship to the HSM, including the scopes of the two resources and details on how star ratings were applied to CMFs from the HSM.

Next Chapter: Searching for CMFs on the CMF Clearinghouse -->