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Crash Modification Factors: Instructions

This page introduces the Federal Crash Modification Factors Clearinghouse web site and provides guidance on how best to use that site.

The Home Page
Engineering analysis, expertise and judgment are your tools for selecting the most appropriate factor for each project.
The source for countermeasures is the FHWA Crash Modification Factors Clearinghouse.  This is now the standard resource for the crash modification factors used for the cost-benefit analysis in submitting projects for safety funding.


Using the Quick Search

The CMF Clearinghouse Home page offers information about the program, a quick search, and updates.  There will be newly posted studies with crash modification factors on this page, as well as access to FAQs and other aids in using the site.
The Quick Search shown on the Home page is good for general searches such as browsing through all countermeasures for rural multi-lane roads.
It’s not recommended when searching for countermeasures at a site you have studied and have crash data for.  It’s the best search when you have a crash measure in mind and want to find the studies related to that mitigation measure.  The Quick search will endeavor to find countermeasures that meet all of the parameters given.  Since adding parameters can mean no or few countermeasures meet all of the parameters, this search yields the best results searching only one parameter at a time.


Selection Criteria

There is a Quality Rating of 0-5 stars for the reliability of the data.  ODOT standard is to use only those factors with a 3-star rating or greater. 

You can screen results for the star rating only if you use the Advanced Search discussed below.  If there are no 3+ star rated listings, run your search again with progressively lower ratings.  Often a lower rating reflects lack of depth in the research rather than poor quality control.  Keep your work used to determine the crash modification factor(s) to support your choices if needed.

Advanced Search

For most searches, the Advanced Search screen is where you want to start. Here you can target higher rated results by your road or crash type.  Since the search considers the list of parameters as connected by logical ‘AND’s, filling in as few parameters as possible will net the most results.  It is suggested that you first search by only the Roadway Type or the Crash Type to get a list with the greatest number of possibilities. 
You do not need to enter Search Terms unless you select a Search Area.  If you’re looking for a specific study from a list you previously downloaded or a specific type of countermeasure, the Search Area can help narrow the results list.  Keep the Search Terms to one or two key words for best results.
You may also want to look for only those CMFs which are included in the Highway Safety Manual if you are looking at countermeasures during design of a project.  This option selects a very limited group of studies to search from, so you will probably not want to check this box for initial searches.

Working with Search Results

When you run the search, the result is a page showing a list of categories with the number of countermeasures listed for that category.  You can look at the list of countermeasures in a category using the ‘+’ tab.  Expand the results list to view the complete information by Category>Countermeasure>Study by clicking on Expand All option at the top.

Saving a Selected CMF List

Once the list is expanded, you can review the studies that were pulled and determine if you have enough information or run a new search.
At the bottom of the expanded list will be a link to export all results to Excel.  Download and save the list for your project then cull every listing except those that seem a possible fit with the crash history of the site you're analyzing. 
Refine and narrow the possible factors further by specific crash types you are trying to impact.  Use the 'ALL' crash type related factors if there aren't any factors specifically associated with the crash types you're concerned with.  In this case, you will need to include all crashes in your benefit cost analysis, not just the crashes you're hoping to reduce.

More Search Tips
If you are considering a countermeasure that does not show up in your results list:
delete all other search parameters and search only by keywords for that countermeasure.  In some cases, you may have to try several keywords to find the ones that were entered with that countermeasure.  Trying keywords one at a time will net the most possible listings. 
In order to select a countermeasure when there is more than one study you want to use but without a 3+ star rating:
access each study using the right hand link and look at the executive summary to determine if that study looked at sufficiently similar situations to the one you're working with.  Caution at using unrated or low rated studies is recommended, especially if the study method did not have good control sites or is based on only one or two installations.  If you do use low or unrated CMFs, document the basis for your decision.

All the Links
The advanced search screen is here:  http://www.cmfclearinghouse.org/advsearch.cfm
You can access the main Crash Modification Factors Clearinghouse site here:   http://www.cmfclearinghouse.org/index.cfm
Engineering analysis, expertise and judgment are required in selecting the most appropriate factor for each project.