The Highway Safety Manual (HSM)
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.