CRASH MODIFICATION FACTORS CLEARINGHOUSE

Searching for CMFs on the CMF Clearinghouse

What is the best way to use search terms and search types?

Searching the Clearinghouse for CMFs is the most important and often the most challenging task for Clearinghouse users. With thousands of CMFs in the database, it is critical to use the best search techniques to find the most appropriate CMF information. The Clearinghouse provides various options to assist users in searching effectively, such as searching by countermeasure, study title, or keywords in the study abstract.
The CMF Clearinghouse search function allows a user to search the database for CMFs related to the topic of interest. A user should enter a search term in the text box on the home page and select an option in the pull-down menu as to what field to search. The search term to be entered depends on what field is being searched. The default search field is “Countermeasure Name”. Users can leave the search field on this default setting to get a more focused set of results. Users with more experience may wish to use one of the other search fields. Table 1 below presents additional information on each search field.

See the video below for a demonstration on how to conduct a search for CMFs on the CMF Clearinghouse.

Table 1. Types of Search Fields Available on the CMF Clearinghouse

Search field	Description	Example search terms that could be used	Example of actual entry from CMF Clearinghouse
Countermeasure Name	Only the countermeasure name and related keywords will be searched. Related keywords are assigned by the Clearinghouse team to aid searches in finding countermeasure that may be called by various names (e.g., HAWK signal and Pedestrian Hybrid Beacon)	roundabout or signal	Convert signalized intersection to modern roundabout
Study Abstract	Only the study abstract field will be searched. The abstract is a paragraph or two of text summarizing the study that produced the CMF.	converted, intersections, or empirical Bayes	(excerpt) “...Several States helped to identify signalized intersections that were converted to roundabouts in the recent past. In total, 28 conversions were identified in the United States. The empirical Bayes (EB) method was employed in an observational before-after study to estimate the safety effects...”
Study Citation	Only the study citation field will be searched. This may be useful if you want to search a particular author’s name.	Uddin or roundabouts	Uddin, W., J. Headrick, and J.S. Sullivan. "Performance Evaluation of Roundabouts for Traffic Flow Improvements and Crash Reductions at a Highway Interchange in Oxford, MS." Transportation Research Board 91st Annual Meeting Compendium of Papers, Washington, D.C., 2012.
Single CMF ID	Each CMF has a unique ID number in the Clearinghouse. Using this search field means that only the CMF ID field will be searched. This is intended to allow you to jump straight to a particular CMF if you know the ID number.	213	213
All Fields	All of the above fields except CMF ID will be searched. This will provide the widest set of search results, but many of them may not be closely related to the topic of interest.	Any of the above examples except CMF ID.	Any of the above examples except CMF ID.

Multiple Search Terms
When more than one search term is used (e.g., wide edgeline), the Clearinghouse applies an AND condition between the words. In the example of searching wide edgeline, the search would return CMFs for countermeasures containing the word wide AND the word edgeline. More search terms means a more specific search and thus fewer results.

Solutions for Too Few or Too Many Results
There may be several reasons that a search is producing too few or no CMFs. The following options may help expand the search to relevant CMFs:

• Use fewer search terms (e.g. rumble instead of centerline and edgeline rumble strips).
• Use search terms that refer to a countermeasure name instead of the setting or the crash problem (e.g., roundabout instead of urban intersection or angle crash).
• Search in all fields instead of just the countermeasure name.

If these options have been tried and the search is still not producing any results, it is likely that the CMF Clearinghouse does not contain any CMFs for that search term. This reflects the fact that the safety research field still has many topics and countermeasures in need of good quality, crash-based research.

If a search produces too many results, using additional search terms will reduce the number of results. For example, if the initial search used the term lane, the user should try something more specific, such as lane width. Alternatively, the user can also use the “Filter” tool on the search results page to narrow results based on the star quality rating, country, crash type, crash severity, roadway type, area type, intersections type, intersection geometry, traffic control, and presence of CMF in HSM.

Blank Searches to See All CMFs in the Clearinghouse
Some users prefer to peruse the Clearinghouse contents rather than searching for a specific countermeasure. The Clearinghouse search tool is designed so that a blank search (i.e., no search term) will return all CMFs in the Clearinghouse. On the search results page, the expandable search results allows users to explore CMFs in the various categories and subcategories of the Clearinghouse data, as described below.

How are search results presented in the CMF Clearinghouse?

After a search is initiated on the front page of the Clearinghouse, the user will be brought to the search results page where all CMFs meeting the search criteria are displayed. The CMFs are organized into an expanding/collapsing structure beginning with a broad countermeasure category (e.g., roadway) followed by subcategories (e.g., number of lanes, lane width, etc.) and then specific countermeasures (e.g., widen lanes from 10 to 12 feet). Expanding any countermeasure shows the CMFs available for that countermeasure. Each CMF is displayed with certain summary details, including the CMF value, star quality rating, crash type, crash severity, area type, a link to the study reference page, and comments, which display special notes for CMFs as needed.

See the video below for an example of a search results page and learn how the Clearinghouse presents the results of a search.

Categories and Subcategories
In order to organize numerous CMFs into a manageable set of results, the Clearinghouse places each countermeasure into a category that best describes the overall topic of the countermeasure, such as Alignment or Intersection Geometry. Users can expand a category and subcategory to view all the countermeasures, and then expand any particular countermeasure to view all the CMFs related to that countermeasure.

Only one category is assigned to each countermeasure; countermeasures are not placed into two different categories. Table 2 provides a list of the categories used by the Clearinghouse with a description of each category.

Table 2. Countermeasure Category Descriptions

Category	Description
Access management	Relates to managing access to the roadway, including median presence, left turn restricting designs such as left-overs, access point density, and driveway reduction
Advanced technology and ITS	Relates to technology-driven strategies, including such things as red light cameras, speed cameras, and dynamic warning signs
Alignment	Relates to vertical or horizontal alignment of the roadway, including such things as grade, curve radius, and spirals
Bicyclists	Relates to bicycle safety
Delineation	Relates to delineation of the travelway
Highway lighting	Relates to lighting along the roadway
Interchange design	Relates to interchange design, including such things as conversion to another type of interchange, ramp design, and acceleration/deceleration lanes
Intersection geometry	Relates to geometric and physical design of an intersection
Intersection traffic control	Relates to traffic control at intersections
On-street parking	Relates to parking on the street, including such things as prohibitions, time of day restrictions, and parking design
Pedestrians	Relates to pedestrian safety
Railroad grade crossings	Relates to railroad grade crossings, including such things as signals, gate arms, and warning devices
Roadside	Relates to anything beyond the shoulder on either side of the road, including median area. This includes such things as slopes, ditches, culverts, abutments, guardrails, and sight distance
Roadway	Relates to the traveled surface of the roadway, including all types of lanes (through, turning, passing), and the roadway surface
Shoulder treatments	Relates to anything on the paved or unpaved shoulder of the roadway
Signs	Relates to signing
Speed management	Relates to the management of vehicle speeds
Transit	Relates to transit issues involving buses, light rail, and other transit vehicles
Work zone	Relates to work zones, including such things as lane closures, times of activity, and traffic operations

Some categories, such as Roadway and Intersection Traffic Control, include a broad range of countermeasures. This can make it difficult for a user to sort through a large number of search results. In order to place these countermeasures into logical groups, the Clearinghouse also provides subcategories in the search results. Table 3 provides an overview of each subcategory and an example of the type of countermeasure which would be found in that subcategory. Some categories, such as Pedestrian, have few CMFs and therefore have no subcategories. The search results will display these as “Subcategory: None”.

Table 3. Countermeasure Categories and Subcategories with Examples

Category	Subcategory	Example Types of Countermeasures
Access management	None	Create directional median openings to allow left-turns and u-turns
Advanced technology and ITS	None	Install red-light camera
Alignment	None	Flatten horizontal curve
Bicyclists	None	Install bicycle lanes
Delineation	On-pavement markings	Install centerlines, edgelines, stop ahead markings
	Supplemental delineation	Add pavement reflective markers, post mounted delineators
	Visibility of existing markings	Widen lines, change marking material, increase reflectivity
	Other	Distance markers (angle symbols) on roadway segments
Highway lighting	None	Install intersection lighting
Interchange design	None	Extend deceleration lane
Intersection geometry	Turn lanes	Add turn lane, extend turn lane, channelize turn lane
	Number of intersection legs	Presence of three leg intersection vs. four leg intersection
	Intersection geometry reconfiguration	Convert intersection to superstreet, convert intersection to roundabout, align a skewed intersection, implement other alternative or nonconventional designs
	Other	Change roundabout intersection sight distance from X to Y
Intersection traffic control	Traffic control type	Installation or removal of signals
	Traffic control visibility	Install dual red head, double stop sign, flashing beacon, backplate, larger stop sign
	Signal phasing or timing	Convert permissive to protected left turn signal
	Turn prohibitions/permissions	Prohibit RTOR, allow RTOR, prohibit left turns, prohibit U-turns
	Other	Convert signal from pedestal-mounted to mast arm
On-street parking	None	Convert angle parking to parallel parking
Pedestrians	None	Install high-visibility crosswalk
Railroad grade crossings	None	Install flashing lights and sound signals
Roadside	Roadside barriers	Install barrier, install guardrail, change barrier type
	Median barriers	Install barrier, install guardrail, change barrier type
	Clear zone	Flatten side slope, modify ditches
	Fixed object	Remove fixed object, change fixed object density
	Other	Modify roadside hazard rating
Roadway	Lane width	Widen lanes, decrease lane width
	Number of lanes	Add TWLTL, add passing lane, convert 4-lane to 6-lane
	Lane restrictions	HOV, HOT, truck lane restrictions, one-way vs. two-way
	Pavement condition and friction	Resurface, add high friction treatment, change type of pavement material
	Winter weather treatment	Use of salt or chemicals, improve winter maintenance
	Roadway rumble strips	Install centerline rumble strips
	Other	Removing mainline barrier toll plazas on highways
Shoulder treatments	Shoulder rumble strips	Install shoulder rumble strips
	Shoulder type	Pave an unpaved shoulder
	Shoulder width	Widen shoulder by paving, widen or narrow shoulder by restriping
	Other	Installation of safetyedge treatment
Signs	None	Advance static curve warning signs
Speed management	None	Lower posted speed by 10 mph
Transit	None	Install transit signal priority (TSP) technology
Work zone	None	Modify work zone length

Non star rated secondary results
The CMF Clearinghouse contains some CMFs that are not star rated. This is because these CMFs were derived from a survey of one or more state transportation agencies to determine what CMF values were being used by states for particular countermeasures at that time. The resulting responses were averaged or summarized to arrive at a "most commonly used" value. The Clearinghouse star rating review process could not be applied to these CMFs since the estimates were not the results of crash-based research.

These non-star rated CMFs are provided in a secondary results page. The link to the secondary results is found at the bottom of the initial search results page, under the heading “Search Results Without Star Ratings”. These CMFs should only be used if there are no star rated CMFs available for the countermeasure of interest. If they are used, the user should be cautious and use engineering judgement when applying the CMF to a particular situation.

CMF Details Page
Because of limited screen space, the initial search results page can only display a limited amount of detail for each CMF, such as the crash type and severity. Occasionally, CMFs in the search results can look identical if a user is judging solely on the few fields displayed. However, the Clearinghouse contains much more information for most CMFs. Clicking on the CMF value on the search results will bring up the details page for that CMF. The information on the CMF details page informs the user about:

• Star rating – many CMFs have a link called “View score details” which will provide a pop-up window with the breakdown of the scores for the various rating criteria
• CMF and CRF – the values of the CMF and CRF are provided along with a standard error, if provided by the authors. CMFunctions will appear as images.
• Applicability – this section provides details about the sites that were used to develop the CMF. These details are particularly important to ensure that a selected CMF will be applied to a site that matches the same conditions under which it was developed.
• Development details – the details about the study are provided, including the years of data and the geographic area where the CMF was developed.
• Other details – this section provides other relevant details about the CMF, particularly the comments field, where information about special notes on the CMF is occasionally provided.

Next Chapter: Identifying Appropriate CMFs -->

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For more information, contact Sarah Weissman Pascual at sarah.pascual@dot.gov