scope:

SCOPE AND ORGANIZATION

The emphasis of the HSM is on quantifying the safety effects of decisions in planning, design, operations, and maintenance through the use of analytical methods. The first edition does not address issues such as driver education, law enforcement, and vehicle safety, although it is recognized that these are important considerations within the broad topic of improving highway safety.

■ The HSM is organized into the following four parts:

■ Part A-Introduction, Human Factors, and Fundamentals

■ Part B-Roadway Safety Management Process

■ Part C-Predictive Method

■ Part D-Crash Modification Factors

Part A-Introduction, Human Factors, and Fundamentals

Part A describes the purpose and scope of the HSM and explains the relationship of the HSM to planning, design, operations, and maintenance activities. Part A also presents an overview of human factor principles for road safety and fundamentals of the processes and tools described in the HSM. Content in Chapter 3, "Fundamentals," provides background information needed prior to applying the predictive method, crash modification factors, or evaluation methods provided in the HSM. This content is the basis for the material in Parts B, C, and D. The chapters in Part A include

■ Chapter 1, Introduction and Overview

■ Chapter 2, Human Factors

■ Chapter 3, Fundamentals

Part B-Roadway Safety Management Process

Part B presents the steps that can be used to monitor and reduce crash frequency and severity on existing roadway networks. This section includes methods useful for identifying improvement sites, diagnosis, countermeasure selection, economic appraisal, project prioritization, and effectiveness evaluation. The chapters in Part B include

■ Chapter 4, Network Screening

■ Chapter 5, Diagnosis

■ Chapter 6, Select Countermeasures

■ Chapter 7, Economic Appraisal

■ Chapter 8, Prioritize Projects

■ Chapter 9, Safety Effectiveness Evaluation

Part C-Predictive Method

Part C of the HSM provides a predictive method for estimating expected average crash frequency of a network, facility, or individual site. The estimate can be made for existing conditions, alternative conditions, or proposed new roadways. The predictive method is applied to a given time period, traffic volume, and constant geometric design characteristics of the roadway. The Part C predictive method is most applicable when developing and assessing multiple solutions for a specific location. For example, a roadway project that considers various cross-section alternatives could use Part C to assess the expected average crash frequency of each alternative. Part C can also be used as a source for safety performance functions (SPFs).

The chapters in Part C provide the prediction method for the following facility types:

■ Chapter 10, Rural Two-Lane Roads (Segments and Intersections)

■ Chapter 11, Rural Multilane Highways (Segments and Intersections)

■ Chapter 12, Urban and Suburban Arterials (Segments and Intersections)

Future editions of the HSM will expand the material included in Part C to include information applicable to additional types of roadway facilities.

Part D-Crash Modification Factors

Part D summarizes the effects of various treatments such as geometric and operational modifications at a site. Some of the effects are quantified as crash modification factors (CMFs). CMFs quantify the change in expected average crash frequency as a result of modifications to a site.

The CMFs in Part D-Crash Modification Factors can be used as a resource for methods and calculations presented in Chapter 6, "Select Countermeasures," Chapter 7, "Economic Appraisal," and chapters in Part C-Predictive Method. Some Part D CMFs are used in the Part C-Predictive Method. However, not all CMFs presented in Part D apply to the predictive models in Part C. CMFs in general can be used to test alternative design options.

The chapters in Part D are organized by site type as follows:

■ Chapter 13, Roadway Segments

■ Chapter 14, Intersections

■ Chapter 15, Interchanges

■ Chapter 16, Special Facilities

■ Chapter 17, Road Networks

Each chapter includes exhibits summarizing the treatments and available CMFs. The appendix to each chapter contains the treatments for which CMFs are not available but general trends are known (e.g., increase or decrease in crash occurrence), and the treatments whose crash effects are unknown. Similar to Part C, it is envisioned that the material included in Part D will be expanded in future editions of the HSM.