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FHWA Highway Safety Programs

III. Applying the HSM in Alternatives Development and Analysis

1. Project Scoping and “Purpose and Need”

Planning agencies develop multiyear programs outlining system wide and corridor needs. From these efforts, an agency’s project development process initiates actual implementation of elements of the program. A project will be identified to move forward within a set project scope. The project scope includes defined limits, resource budget and a schedule for eventual completion including construction.

Every project has a fundamental purpose or objective, typically reflecting the identified planning needs, such as providing improvements to mobility for a corridor or subarea, addressing infrastructure repair or rehabilitation based on input from asset management data, enabling expansion of modal choice (e.g., bus, bicycle, etc.), or improvements to address a public safety concern. Any of these objectives may be expressed as a project’s purpose and need in an environmental evaluation document, also referred to as a NEPA document.

Once a project’s scope and “purpose and need” are established, the project can move to the critical step of Alternatives Development and Analysis. Best project development practices emphasize development of multiple alternatives within the project scope, one of which is typically a “no-build” alternative.

NEPA analysis frequently assumes safety will be maximized solely through adherence to roadway design standards. Yet traffic crashes continue to be a frequent occurrence, even on newly constructed roadways; and nationally, tens of thousands die each year in traffic crashes. Addressing this problem requires considering more than standards to maximize the safety of new transportation projects.”

– Integrating Road Safety into NEPA Analysis: A Primer for Safety and Environmental Professionals (FHWA 2011).

As alternatives are proposed, they are first evaluated against the stated purpose and need. Multiple alternatives may be viable but may differ in meaningful ways that relate to their footprint, impacts to adjacent land use, design characteristics, traffic operational quality, and safety performance.

Within this typical project development process, agencies can apply the HSM to support explicit consideration of quantitative safety during alternatives development and analysis. In this stage of the project development process, agencies proceed with a detailed engineering and environmental analyses of each alternative, in an effort to understand the specific costs, impacts and attributes. This analysis will provide decision-makers with objective data to inform the decision on a preferred alternative, which is typically documented in a Categorical Exclusion (CE), or an Environmental Impact Statement (EIS).

In the past, agencies and technical professionals were readily able to assess project impacts by applying quantitative tools and methods to estimate measures of noise and air quality, wetlands, threatened and endangered species, and an array of other features important to society. Similarly, through the methodologies established in the Highway Capacity Manual (HCM), transportation professionals have access to sophisticated traffic operational tools to estimate speeds, delay, hours of congestion, etc. Databases and tools were also available to develop quantitative dollar cost estimates for construction and right-of-way. What has been lacking until the HSM was a science-based method for estimating safety performance in meaningful quantitative terms. In the absence of such methods, safety has typically not been a distinguishing factor among alternatives and hence has not typically influenced the ultimate decision.

This section discusses applying the HSM to incorporate safety into decisions made during alternatives development and analysis stage of the project development process. While the section focuses in particular on the use of the HSM in the NEPA process, the HSM can be used in a similar way for any project, regardless of whether a formal environmental process is required or not.

2. Applying the HSM in Environmental Analysis

Projects requiring environmental analysis, as directed by the National Environmental Policy Act (NEPA), can particularly benefit from the use of the HSM in the following activities:

  • Define purpose and need for the project.
  • Define and refine the range of project alternatives.
  • Analyze alternatives.
  • Evaluate alternatives.
  • Select alternative for implementation.

Exhibit 4, from the FHWA Practitioners’ Primer: Integrating Road Safety into NEPA Analysis (2011), demonstrates the opportunities for integration of safety into NEPA analysis.

Define purpose and need for the project. Purpose and need statements can refer to providing or enhancing mobility, repairing or replacing infrastructure in poor condition, addressing modal choice, or improving safety. While most projects do not identify safety as a primary purpose and need, the HSM provides methods for agencies to objectively define locations or projects for which the potential for safety improvement is indeed significant. For projects with safety as a primary driver, the tools and methods in the HSM allow agencies to identify historic crash characteristics and probable contributing factors to crashes, particularly fatal and serious injury crashes. An agency can use the predicted method in the HSM to calculate the historic and anticipated future safety performance (calculated using the predictive methods in the HSM) and the fundamentals of human factors in the HSM to identify safety-specific needs for a project and estimate the potential for safety improvement. Such an approach increases the likelihood that safety investments will be cost-effective. For other projects with different purpose and need statements, the HSM still has value as discussed below.

Exhibit 4. Integrating Safety into NEPA Analysis

Graphic: Flowchart illustrating how safety can be integrated into NEPA analysis.

Source: FHWA, Integrating Road Safety into NEPA Analysis, 2011.

Determine project scope. An important part of a project’s scope is the designation of the type of project. This designation translates to applicable design criteria. For projects involving an existing road in need of some improvement, there are two fundamental project types, reconstruction and rehabilitation. Reconstruction is associated with major change to the road cross-section, alignment, or both. Applicable design criteria often exceed that of the older road, necessitating significant and costly reconstruction. Most agencies have adopted alternative design criteria for road projects primarily driven by infrastructure repair, referred to by some as “3R” criteria (resurfacing, restoration, and rehabilitation). However, the use of full reconstruction criteria is often promoted as necessary or desirable to enhance safety. With adoption of tools and methods in the HSM, agencies can incorporate the historic safety performance of the existing road into their decision on the designation of project type. By designating a project as “3R” based on a review of its historic safety performance compared with expected performance per HSM information, agencies can reduce project costs and impacts by avoiding more costly reconstruction aimed at improving safety, when no such improvement is expected.

Define and refine the range of project alternatives. The HSM can support the identification of likely reasonable alternatives. Documentation for NEPA requires a discussion of the approach and rationale for selecting the reasonable alternatives for detailed analysis and an explanation for eliminating alternatives (FHWA Technical Advisory T6640.8A: Guidance for Preparing and Processing Environmental and Section 4(F) Documents). Agencies can use the predictive method in the HSM or use CMFs to quantify the anticipated change in crash frequency and/or severity across alternatives. This process can be iterative, allowing agencies to select feasible alternatives during the identification and screening of the alternatives. For example, an agency may consider reconstructing a two-lane rural highway. Using the HSM, the agency can perform a quick initial assessment of the order of magnitude of change in crashes for different combinations of lane and shoulder widths for given geometric and environmental conditions. If the assessment is conducted for a safety-specific project and the assessment indicates the likely benefit of some alternatives may be negligible or even adversely affect safety performance, the agency can eliminate some alternatives initially considered. The information derived from the HSM could then be part of the documentation needed to support the elimination of these alternatives.

Analyze alternatives. Tools and methods in the HSM support quantifying safety performance during alternative analysis. For urban and suburban arterials, the predictive method in the HSM offers the ability to assess the impacts of changes in geometric features or traffic volume on pedestrian and bicycle crashes.

Evaluate alternatives. The predictive methods in the HSM Part C provide the ability to quantify the anticipated safety performance for each alternative in terms of its anticipated crash frequency and severity. This evaluation can also include comparison with a no-build alternative and, if desired, translation of crash reductions into economic benefits based on guidance in Part B of the HSM.

Select alternative for implementation. For the first time, agencies are now able to make relative comparisons between alternatives based on the number of crashes or combinations of particular crash severities by using the predictive methods of Part C of the HSM. In the event that agencies select an alternative that does not have the highest predicted safety performance (e.g., because environmental or other impacts were greater for the particular geometric configuration), agencies can use the HSM to identify safety mitigation strategies to increase safety performance for the selected alternative.

Project decision-making can be complex. It inherently involves tradeoffs among alternatives with differing performance attributes. Using the HSM to inform the decision-making process does not place any requirements on an agency to select the alternative with the best safety performance any more than would making a decision solely based on capital cost. Furthermore, absent application of HSM and quantification of safety, the decision-maker has no way of knowing what if any safety tradeoffs exist.

The HSM is neither intended to be, nor does it establish, a legal standard of care for users or professionals. No standard of conduct or any duty toward the public or any person shall be created or imposed by the publication and use or nonuse of the HSM. Documentation used, developed, compiled or collected for analyses conducted in connection with the HSM may be protected under Federal law (23 USC 409).

3. Tools to Support Application of the HSM in Alternatives Development and Analysis

Applying the HSM in alternatives development and analysis primarily relies on using the HSM predictive method and CMFs.

Florida DOT District 6 (Tampa) analyzed a corridor-widening project on SR 574. As part of the analysis the DOT used the HSM to evaluate a design variation. The analysis quantified the anticipated impact of the design variation, resulting in a $1.6 million reduction in overall project right-of-way costs.

More information about this case study is available in the Highway Safety Manual Case Study 3. (FHWA 2012).

Agencies can select from a variety of tools to perform a predictive analysis using the HSMFHWA developed the IHSDM software tool that can perform several other analyses that are of value during the alternatives analysis process. More information is available at the Interactive Highway Safety Design Model software download web site. Agencies can also use spreadsheets to perform basic HSM predictive analysis. The NCHRP 17 38 spreadsheets and those from ALDOT and VDOT are available on-line from the TRB Highway Safety Performance Committee web site. Other states, such as Illinois and Washington have developed state-specific spreadsheet tools that these agencies use during alternatives development and analysis.

The FHWA CMF Clearinghouse is an on-line, free database of CMFs to quantify the impact of treatments. Agencies can query the database on-line. FHWA updates the Clearinghouse regularly.

4. Example Application: Alternative Analysis

This example application continues the hypothetical example presented in Section II.

The MPO is now conducting a corridor study, consistent with NEPA requirements, on the corridor selected (Route A) with potential for safety improvement. The following demonstrates how such a study might be conducted and how the results might be summarized in a NEPA document.

Exhibit 5 illustrates and describes the three project alternatives: a no-build scenario, Alternative 1 and Alternative 2.

Exhibit 5. Project Alternatives for the Example Application

Graphic: Provides graphical illustrations and descriptions of three project investment alternatives: a no-build scenario, Alternative 1, and Alternative 2.

Source: (Graphics: CH2M HILL).

Note: The project information and analysis results in these examples are hypothetical and for illustration purposes only. It does not reflect results from an actual analysis nor does it intends to serve as an example of the relative anticipated safety performance of these three alternatives for an actual project.

The agency used the HSM Part C to assess the current and future anticipated safety performance for the no-build conditions, Alternative 1, and Alternative 2.

Exhibit 6 presents the different components evaluated in the corridor safety study.

Exhibit 6. Safety Analysis Approach for Alternatives in the Example Application

Alternative

Description of Alternative-Specific Features and Analysis Approach Using the HSM

No-Build

The Purpose and Need Statement was developed in part by evaluating existing crash data including identifying an overrepresentation of fatal and serious injury crashes involving parked vehicles and vehicles turning left into driveways along the most southern section of the corridor.

The agency used the predictive method in Chapter 12 of the HSM Part C to quantify the safety performance (expressed in crashes in this example) for the existing and future traffic volumes for the current corridor configuration. This method accounts for the presence of on-street parking, the particular driveway density of the project, and the presence of the two-way left-turn lane. The agency used the analysis results and updated the Purpose and Need Statement, so that it specifically refers to the need to reduce the fatal and serious injury crashes involving parked vehicles and left-turning vehicles on the southernmost section of the corridor.

Alternative 1

The agency used the predictive method in Chapter 12 of the HSM Part C to identify the crash frequency associated with Alternative 1 compared to the no-build option. Alternative 1 represents the following changes from the no-build:

  • Removal of on-street parallel parking;
  • Use of street-trees;
  • Consolidation of a subset of driveways on a particular part of the corridor; and
  • Installation of a median where left-turning driveway-related crashes are overrepresented.

The FHWA CMF Clearinghouse provides insight into the likely impact of dedicated bus pullout locations along the corridor.

Alternative 2

The agency used the predictive method in Chapter 12 of the HSM Part C to estimate the change in crash frequency associated with Alternative 2 compared to the no-build option. Alternative 2 represents the following changes from the no-build: more comprehensive consolidation of driveways (as compared to Alternative 1) and a raised median throughout the corridor with left-turn pockets at predetermined locations.

Note: The agency did not consider the HOV as a lane that adds capacity (additional general-purpose volume).

Exhibit 7 summarizes the analysis results for the evaluation of the 2025 anticipated safety performance for the no-build option, Alternative 1, and Alternative 2.

Exhibit 7. Safety Analysis Results for Future Safety Performance for Alternatives in the Example Application

Alternative

Results of Safety Analysis (2025)

No-Build

Nexpected = 110 fatal and injury crashes per year

Discussion of results: It is anticipated that the existing facility will experience, on average, 110 fatal and injury crashes per year in 2025. A corridor with similar volumes and characteristics is anticipated to experience, on average, 62 crashes per year. The no-build option has an average potential for improvement of 48 fatal and injury crashes per year.

Alternative 1

Nexpected = 65 fatal and injury crashes per year

Discussion of results: It is anticipated that the existing facility will experience, on average, 65 fatal and injury crashes per year in 2025. A corridor with similar volumes and characteristics is anticipated to experience, on average, 45 fatal and injury crashes per year, indicating an anticipated average potential for improvement of 20 fatal and injury crashes per year. Alternative 1 is anticipated to experience 45 fewer fatal and injury crashes on average per year than the no-build option.

Alternative 2

Nexpected = 45 fatal and injury crashes per year

Discussion of results: It is anticipated that the existing facility will experience, on average, 45 fatal and injury crashes per year in 2025. A corridor with similar volumes and characteristics is anticipated to experience, on average, 34 crashes per year, indicating an anticipated average potential for safety improvement of 20 fatal and injury crashes per year. Alternative 2 is anticipated to experience 65 fewer fatal and injury crashes on average per year than the no-build option, and 20 fewer fatal and injury crashes on average per year when compared to Alternative 1.

Note: Nexpected represents the anticipated expected average crash frequency. The HSM defines the expected average crash frequency as the number of crashes anticipated per year, if the long-term average number of crashes at a site could be determined for a particular site (a segment or intersection) with a given set site conditions.

Based on Exhibit 7 the agency concludes that:

  • It is anticipated that without improvement, the no-build alternative will experience, on average, 110 fatal and injury crashes per year in 2025.
  • If the agency implements Alternative 1, it is anticipated that there will be, on average, 65 fatal and injury crashes per year in 2025.
  • If the agency implements Alternative 2, it is anticipated that there will be, on average, 45 fatal and injury crashes per year in 2025.
  • The difference in safety performance between the no-build and Alternative 1 is 45 average fatal and injury crashes on the corridor per year in 2025.
  • The difference in safety performance between Alternative 1 and Alternative 2 is 20 average fatal and injury crashes on the corridor per year in 2025.

Note: The analysis summary only reports on the analytical results for the anticipated future safety performance of the different options. The agency did not make any recommendations for the implementation of one particular alternative based solely on results from the safety performance analysis. The HSM does not require an agency to implement a particular alternative based solely on the safety performance evaluation, and is not intended to be a substitute for the exercise of sound engineering judgment (AASHTO 2010; page 2 of the Preface to the Highway Safety Manual).