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Publication Number:  FHWA-HRT-11-004    Date:  May/June 2011
Publication Number: FHWA-HRT-11-004
Issue No: Vol. 74 No. 6
Date: May/June 2011


Training Update

by Lilly Pinto

Reducing Crash Frequency and Severity

More than 33,000 traffic fatalities occurred on U.S. roadways nationwide in 2009 according to the National Highway Traffic Safety Administration. The sheer number of fatalities underscores the need for effective tools to help the transportation community predict crash frequency and severity, and then make appropriate decisions about how to improve safety. To fill this need, the American Association of State Highway and Transportation Officials (AASHTO) helped develop the Highway Safety Manual (HSM). The HSM is the first nationally recognized resource for quantitative information on predicted crash frequency of elements considered in road planning, design, construction, operation, and maintenance. In short, the manual helps take the guesswork out of safety analysis.

The National Highway Institute (NHI) offers a suite of courses to help transportation professionals at every level and function, from planners and designers to engineers and project managers, use the HSM to improve transportation systems and to help prevent traffic injuries and fatalities. HSM's application also can lead to more effective planning for safety investments.

"The Highway Safety Manual introduces an opportunity for safety impacts to be evaluated alongside environmental and operational impacts, which wasn't possible before," says Esther Strawder, safety specialist with the Federal Highway Administration's (FHWA) Office of Safety. "By putting the HSM's safety analysis tools into practice, transportation professionals can have a substantial impact on reducing crashes and saving lives."

Tools, Techniques, and Benefits

Prior to the HSM, safety considerations often carried little weight in the project development process. The HSM aims to provide transportation professionals with current knowledge, techniques, and methodologies to quantify safety impacts and conduct safety analyses in a technically sound and consistent manner.

The HSM is divided into four parts that outline the tools and techniques for quantifying safety impacts within a locality. Part A describes the purpose and scope of the HSM, explaining the relationship of the manual to planning, design, operations, and maintenance activities. Part B includes steps for identification of improvement sites, diagnosis, countermeasure selection, economic appraisal, project prioritization, and effectiveness evaluation. The predictive method for estimating the expected average crash frequency of a network, facility, or individual site is highlighted in Part C. The final component, Part D, includes a catalog of crash modification factors (CMFs), which estimate the change in the expected average crash frequency resulting from modifications to a given site compared to baseline conditions.

Training participants in Ames, IA, complete an exercise during a recent session of the course HSM Practitioner's Guide for Two-Lane Rural Highways.
Training participants in Ames, IA, complete an exercise during a recent session of the course HSM Practitioner's Guide for Two-Lane Rural Highways.

The HSM gives safety engineers the tools to identify locations that are most likely to respond to safety improvements, better evaluate the economic validity of individual projects, and prioritize projects across a system. The HSM also can assist project managers in assessing the safety performance of design alternatives based on their geometric and operational characteristics.

HSM Practitioner's Guide Courses

NHI revised five training courses to specifically highlight the practical application of the HSM.

The HSM Practitioner's Guide for Intersections course, for example, provides an indepth and comprehensive review of the HSM as it relates to intersections. The course introduces practitioners at the State, county, and local levels to the new techniques and knowledge contained in the manual. During the training, participants complete a series of exercises, such as calculating the number of predicted crashes for a given set of conditions at an intersection based upon the intersection's design and then comparing the predicted crashes to the number of observed crashes.

"This course helps practitioners apply HSM methodology to evaluate intersection operational and safety performance," says Tom Elliott, NHI's training program manager for highway safety. "It also teaches practitioners how to better use scarce resources more efficiently."

For course descriptions, visit NHI's Web site at www.nhi.fhwa.dot.gov.




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