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U.S. Department of Transportation U.S. Department of Transportation Icon United States Department of Transportation United States Department of Transportation
FHWA Highway Safety Programs

I. Introduction

The AASHTO Highway Safety Manual (HSM), published in 2010, represents the culmination of 10 years of research and development by an international team of safety experts, academics, and practitioners. Under leadership from the American Association of State Highway Officials (AASHTO), the National Cooperative Highway Research Program (NCHRP) and the Federal Highway Administration (FHWA), and with direction from a Task Force of the Transportation Research Board (TRB), a major research program provided the technical contents of the HSM and funded its development into a practitioner-friendly document.

The HSM provides a set of tools and knowledge to support a science-based approach to quantifying safety. As a tool, the HSM provides the ability to incorporate meaningful safety metrics – crash frequency and severity – into an agency’s program planning and project development processes, whether the project’s purpose is driven by a particular safety concern or not.

For the first time, there is standardized guidance for incorporating safety performance-based decision-making into project development. Planners, designers and traffic engineers are now able to evaluate the impacts of decisions about the roadway environment (e.g., roadway design or changes in traffic volume) on crash frequency and crash severity.

This guide provides information for state and local practitioners on how to integrate the HSM into their project development processes. Each section provides an overview of possible implementation opportunities for the HSM during each stage of the project development process.

1. How to Use the Guide

Exhibit 1 illustrates the major steps of the project development process and provides a simplified explanation of activities in each step. Each section in this guide provides discussion of how the HSM could be applied in this process. Practitioners who work on each step of this process will find specific chapters useful as they apply to their areas. Safety practitioners can use this guide to communicate these applications to their colleagues in other areas of the development process. To this end:

  • Section II discusses how agencies can use the HSM in planning;
  • Section III discusses the use of the HSM in alternative development and analysis;
  • Section IV focuses on how agencies can apply the HSM in design;
  • Section V presents the application of the HSM in the operation and maintenance of the roadway system; and
  • Section VI provides a summary of this guide.

2. Overview of Applying HSM in the Project Development Process

The HSM provides methods to allow agencies to incorporate safety throughout the project development process.

In the Planning phase, agencies (e.g., state departments of transportation or metropolitan planning organizations) assess existing conditions, establish goals and objectives, identify future travel characteristics, and evaluate the multimodal transportation network to develop programs, identify and prioritize projects, and institute policies to address long-term (i.e., 20 years) transportation system and community needs. During Planning, agencies may identify locations on the system that have potential for safety improvement or sites most likely to respond to particular treatments.

Agencies may also be interested in adopting policies across the jurisdiction or understanding the quantitative safety implication of one network versus another. When agencies include safety performance in planning, they are promoting longer-term approaches to support the reduction in the number and severity of crashes.

Agencies may also be interested in adopting policies across the jurisdiction or understanding the quantitative safety implication of one network versus another. When agencies include safety performance in planning, they are promoting longer-term approaches to support the reduction in the number and severity of crashes.

Exhibit 1. Typical Highway Project Development Process

Graphic: Illustrates the typical steps in the highway project development process, including planning studies, alternative identification and evaluation, preliminary design, final design, and construction.

Note: The process outlined above is generic and for the purpose of discussions in this document only. The process may differ in terminology and process across project types and across agency-specific processes and procedures.
* Include mitigating impacts and the Draft EIS when an EIS is required.
** Include the Final EIS and Record of Decision when an EIS is required.

The inclusion of safety performance in planning supports strategic investments where the impact is likely to be the highest. When agencies use data-driven processes that include consideration of safety performance, the likelihood of cost-effective expenditure of resources is more likely. Section II discusses the application of the HSM in planning in further detail.

Individual projects are derived from agency planning efforts. Projects have defined limits, budgets, and schedules for completion, which constitute the project’s scope. Every project has a fundamental purpose or objective, typically reflecting needs such as providing improvements to mobility, infrastructure repair or rehabilitation, expansion of modal choice, or improvements to public safety. Any of these may be expressed as a project’s “purpose and need.”

Once a project’s scope and purpose and need are established, the project moves to the critical step of Alternatives Development and Analysis. Multiple alternatives within the project scope are developed based on addressing the stated purpose and need.

Whether the “purpose and need” is safety-related or not, every project can benefit from applying the HSM in the development and evaluation of alternatives. Project decisions are based on full evaluation of costs, right-of-way, traffic operations, environmental factors and safety. Prior to publication of the HSM, there was no common, science-based and reliable means of safety quantification within this process.

The HSM allows agencies to consider the existing potential for safety improvement for a particular project alongside other project-specific issues (e.g., queuing, capacity constraints). The HSM predictive method can be used to compare the safety performance of two distinctly different alternatives (e.g., an arterial with or without a raised median). As agencies develop concepts and proceed with a detailed engineering and environmental analyses of each alternative, results from safety diagnostic analyses (HSM Chapter 5) can be used to inform the development of concepts, and the predictive method can be used to estimate changes in crash frequency or severity between different options.

Safety Return on Investment

A return-on-investment evaluation provides information about whether the proposed action maximizes system benefit. With the HSM, safety can be considered as a benefit (alongside mobility, environment, etc.) included in the return on investment evaluation.

The predictive method can also be used as part of an alternatives evaluation process to estimate the changes in crash frequency or severity associated with a change in traffic volume or traffic control. Finally, the safety benefits of a preferred alternative compared with a no-build alternative can be readily estimated and incorporated into project documentation. Section III presents examples of opportunities for the application of the HSM in alternatives development and analysis and selection of a preferred alternative.

Once a preferred alternative is selected, the project typically moves into Preliminary and Final Design. A designer can use the knowledge and tools in the HSM to inform design decisions throughout Final Design and Construction. For example, designers can incorporate human factor considerations into designs (using Chapter 2 of the HSM). The need for design exceptions (use of a design element or dimension outside of the established criteria) is common on urban projects and reconstruction projects with extensive constraints. Analysis, decision-making and documentation of the quantitative safety effects of a proposed design exception are among the most significant enhancements the HSM brings to project development.

In the daily operation of the roadway network, agencies can use the HSM in Operations and Maintenance. Agencies can incorporate safety into existing processes that monitor system performance, allowing for consideration of safety performance improvements along with competing needs. This approach supports strategic investment and improvement of the roadway system. For example, agencies can consider the impact of changes or upgrades in mobility, decisions related to access, setting maintenance policies and priorities, and other operational considerations on safety performance. When agencies apply the evaluation methods in the HSM to implemented projects and policies, they can identify opportunities to improve policies and future decision-making based on the changes in crash frequency or severity.

In reviewing this guide, agencies will find the HSM provides opportunities to extend safety performance as a consideration into all decisions about the roadway environment (e.g., with maintenance, mobility, or preservation programs), rather than only considering safety in projects driven by safety needs.

3. Resources for Application of the HSM

Several tools and resources exist to support the application of the HSM. Tools for implementing the HSM include:

Each HSM application example provided in this guide includes references to applicable tools.

Exhibit 2 lists and briefly describes different resources that support HSM implementation. Several web sites offer HSM guidance, technical assistance, case studies and training opportunities:

Exhibit 2. Resources to Support the Implementation and Institutionalization of the HSM


Technical Support

Software Tools

General Information