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:

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.

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:

Next Chapter: Identifying Appropriate CMFs -->

The information contained in the Crash Modification Factors (CMF) Clearinghouse 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 in the CMF Clearinghouse. The information contained in the CMF Clearinghouse does not constitute a standard, specification, or regulation, nor is it a substitute for sound engineering judgment.