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The Highway Safety Manual (HSM) is the premier guidance document for incorporating quantitative safety analysis in the highway transportation project planning and development processes. The HSM, developed by AASHTO and first published in 2010 with a supplement for freeways published in 2014, presents contemporary scientific methodologies for estimating safety performance of highways and streets to inform the highway transportation decision-making process.

The HSM includes guidance on:

  • Human factors and the fundamentals of traffic safety;
  • The roadway safety management process (including information relevant to FHWA’s Highway Safety Improvement Program requirements and project planning), including:
    • Network screening (identify sites with potential for crash or severity reduction);
    • Site assessment (diagnosis, countermeasure selection, economic appraisal);
    • Project prioritization;
    • Safety effectiveness evaluation;
  • Predictive methods for infrastructure improvement project alternative analysis and development/design, including:
    • Use of national safety performance functions (models) developed to predict crashes by severity specific facility types and base conditions; and
    • Associated crash modification factors (CMFs) to estimate the potential effects of design alternatives or changes from base conditions.

The HSM was developed over a 15 year period and is intended to be used in conjunction with related publications from AASHTO, TRB, and FHWA. Examples of such publications include the Roadside Design Guide, the Human Factors Guide (NCHRP Report 600), the Highway Capacity Manual, the Policy on Geometric Design of Highways and Streets, and the MUTCD among others.

MMore information about the application of the four parts, background, and benefits of the HSM can be found in AASHTO’s Introduction to the Highway Safety Manual. Additionally, tools, training materials, frequently asked questions (FAQ), and more can be found on this website. To purchase the HSM, visit AASHTO’s online store.

Highway Safety Manual First Edition 2010

Errata for the HSM

Technical corrections and minor fixes to models and texts within the HSM have been summarized in the HSM errata. The latest version of the HSM errata (March, 2016) can be downloaded here.

The Second Edition is Coming Soon

Much research has been completed and practical experience gained since the first HSM was published in 2010. National Cooperative on Highway Research Program (NCHRP) Project Number 17-71 is presently updating the manual and incorporating state of the art research, lessons learned, and more. The second edition of the HSM is expected to be completed in 2021, being published by AASHTO in 2022.