Highway Safety Manual
The Highway Safety Manual (HSM) is an influential publication developed by the American Association of State Highway Transportation Officials (AASHTO). The manual offers a comprehensive, science-based approach to enhancing highway safety through specific guidelines and methodologies. It is a critical resource for transportation professionals involved in engineering, roadway design, operations, and safety management.
Purpose and Scope
The Highway Safety Manual provides a unified framework for analyzing highway safety and making data-driven safety decisions. The manual's primary objective is to reduce traffic accidents and improve road safety by providing methodologies that predict crash frequency, severity, and types of crashes on various roadway facilities.
Key Components
The HSM incorporates several key components that form the basis of safety analysis:
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Predictive Methods: It utilizes predictive models to estimate the expected number of crashes for specific roadway conditions and configurations. These models help in understanding how changes in highway design or operations can impact safety.
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Crash Modification Factors (CMFs): The Crash Modification Factors Clearinghouse is an essential tool within the HSM that provides data on the expected safety impacts of different highway treatments or design modifications.
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Safety Performance Functions (SPFs): These are mathematical functions used to estimate crash frequency based on traffic volume and roadway characteristics. SPFs are crucial for benchmarking and assessing the safety performance of existing roadways.
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Design Model: The Interactive Highway Safety Design Model (IHSDM) is a software tool that integrates with the HSM to provide detailed analysis and design assistance for highway safety improvements.
Implementation and Usage
The HSM is used by state and local agencies to inform safety-related decisions. It guides the entire process from transportation planning to safety evaluation, identifying the most effective measures to reduce crashes and improve safety. The Federal Highway Administration (FHWA) supports the implementation of the HSM by providing resources and tools such as the Systemic Safety Project Selection Tool.
Impact and Influence
The methodology and guidelines presented in the Highway Safety Manual have significantly influenced modern roadway safety practices. By replacing subjective safety assessments with data-driven analysis, the HSM has empowered engineers and planners to make informed decisions that enhance the safety of transportation infrastructure.