Transportation professionals continually strive to determine more effective ways to identify, implement, and evaluate cost-effective solutions to improve roadway safety. One question that often arises is, "What is the best countermeasure to apply at this intersection?" A crash modification factor (CMF), which is used to estimate change in the number of crashes expected after implementing a countermeasure, can help engineers answer such questions. But until recently, CMFs were not available in a centralized location. Recognizing the need for up-to-date and easily accessible CMF information, the Federal Highway Administration (FHWA) established the Crash Modification Factors Clearinghouse.

The clearinghouse (at www.CMFClearinghouse.org) offers transportation professionals a Web-based repository of CMFs and related resources.

"The new clearinghouse provides an excellent tool for use in the development of safety projects around [our] State," says Kelly Becker, regional traffic engineer with the North Carolina Department of Transportation. "It is my hope that it will be a central location for our traffic engineers to reference modification factors."

CMFs at Work

CMFs help transportation professionals make evidence-based decisions with the goal of improving roadway safety and reducing motor vehicle crashes. For example, imagine that an intersection is experiencing 100 angle crashes and 500 rear-end crashes per year. If you apply a countermeasure that has a CMF of 0.80 for angle crashes, then you can expect the number of angle crashes to drop to 80 per year following the implementation of the countermeasure (100 x 0.80 = 80). If the same countermeasure also has a CMF of 1.10 for rear-end crashes, then you would expect to see an increase to 550 rear-end crashes per year after installation (500 3 1.10 5 550). Engineers can perform similar calculations to determine a countermeasure that offers the optimum overall improvement in safety. In this way, CMFs enable engineers to compare the safety effectiveness of alternative treatments and help them conduct benefit-cost analyses to prioritize treatment locations.

Crash reduction factors (CRFs) too are represented in the clearinghouse because of their widespread use. Both CMFs and CRFs are displayed side-by-side on the basic search results page as well as on each CMF details page. A CRF reflects an estimate of the percentage reduction in crashes after implementing a given improvement. A CRF of 46, for example, represents a 46 percent reduction in crashes at a particular site.

Using the Web Site

At the clearinghouse's launch in late 2009, it contained more than 1,800 CMFs for more than 400 countermeasures. To find CMF information, Web site users can conduct a quick keyword search from the home page or narrow their search by countermeasure, crash type, crash severity, and roadway type. The site also has an advanced search feature that enables users to search by more detailed parameters, such as intersection type, traffic control, area type, and more. Users then can export their search results into a Microsoft^® Excel^® spreadsheet or an Adobe^® Acrobat^® PDF document for easy reference and dissemination.

Another purpose of the Web site is to educate transportation professionals about the application of CMFs. The site includes an overview of CMFs and a glossary of terms related to their use. Frequently asked questions address issues such as the difference between CMFs and CRFs and how to apply multiple CMFs to one location. The clearinghouse also includes a comprehensive resources section with links to information on training, publications, and other resources.

Transportation professionals also can submit their own CMF studies for inclusion in the clearinghouse. CMF studies sent to the database will undergo a review process, which evaluates each study according to its design, sample size, standard error, potential bias, and data source to determine whether it meets the minimum requirements for inclusion.

"The Web site is very user friendly and most, if not all, traffic/safety engineers will use this site quite often," says Tom Hammonds, Highway Safety Improvement Program (HSIP) coordinator with the West Virginia Department of Transportation. "I will bookmark this site on my computer at work."

For more information, visit www.CMFClearinghouse.org or contact Karen Yunk at 609-637-4207 or karen.yunk@dot.gov.

Katy Jones is the manager for research information and education programs at the University of North Carolina Highway Safety Research Center.

Karen Yunk, P.E., is the HSIP implementation manager with FHWA's Office of Safety Programs.