Highway Safety Manual (HSM)

The Highway Safety Manual (HSM), developed by the American Association of State Highway and Transportation Officials (AASHTO), is used to incorporate a quantitative safety analysis during the highway transportation project development processes.  The HSM, first published by AASHTO in 2010 with a supplement for freeways published in 2014, presents contemporary scientific methodologies for estimating safety performance of highways and roads to further inform the highway transportation decision-making processes.

The HSM provides a science-based, technical approach to facilitate consideration of safety in roadway planning, design, operations, and maintenance decisions. This allows safety to be quantitatively evaluated alongside other transportation performance measures such as traffic operations, environmental impacts, pavement durability, and construction costs.

More information about the HSM and the available HSM tools can be found on AASHTO’s Highway Safety Manual webpage at https://www.highwaysafetymanual.org

The Federal Highway Administration's (FHWA)'s HSM webpage serves as the official HSM website where you can find the most up-to-date information and new HSM developments.  It includes HSM outreach, materials, technical support, informational resources, training, case studies, tools, and supplemental resources. Visit the FHWA’s HSM webpage at https://highways.dot.gov/safety/data-analysis-tools/highway-safety-manual

The FHWA’s Crash Modification Factors (CMF) Clearinghouse is a frequently updated and searchable repository where you can find "Part D" CMFs based on the latest transportation safety research, and other educational CMF resources.  Visit the CMF Clearinghouse at https://www.cmfclearinghouse.org/

Caltrans’ Application of the HSM

Caltrans has established a policy for use of the HSM during project development.  It includes information related to project application requirements, roles and responsibilities, analysis, and limitations.  The policy can be found on the Design Memoranda website at https://dot.ca.gov/programs/design/design-memoranda

Supplemental HSM Guidance

Additional guidance to incorporate the HSM methodologies into Caltrans’ project development processes has been developed as follows:

03/30/2023 – Application of the HSM Methodology for Project Development – 36 pages (PDF)