Environmental Review Toolkit
NEPA and Project Development

Integrating Road Safety into NEPA Analysis:
A Primer for Safety and Environmental Professionals

5.0 Purpose and Need Statements

5.1 Introduction

The statement of the project purpose and need is the core component of the NEPA document. It describes the impetus for the project and serves as the benchmark against which project alternatives are evaluated.

Purpose and Need

The Council on Environmental Quality (CEQ), the agency responsible for coordinating Federal environmental efforts, provides a brief description of the Purpose-and-Need: “The statement shall briefly specify the underlying Purpose-and-Need to which the agency is responding in proposing the alternatives, including the proposed action.” (40 CFR 1502.13).

The FHWA technical advisory T 6640.8A states that the Purpose-and-Need statement will: “Identify and describe the proposed action and the transportation problem(s) or other needs which it is intended to address (40 CFR 1502.13). This section should clearly demonstrate that a “need” exists and should define the “need” in terms understandable to the general public. This discussion should clearly describe the problems which the proposed action is to correct. It will form the basis for the “no action” discussion in the “Alternatives” section, and assist with the identification of reasonable alternatives and the selection of the preferred alternative.”

Incorporation of safety into the project purpose and need statement involves several considerations, including:

  • Linking the purpose and need statement to safety planning processes and documents. The process of defining the purpose and need for a project should flow from earlier planning activities, such as the development of metropolitan and state transportation plans and safety plans (discussed in Section 3.0).
  • Linking the purpose and need to concerns and issues raised during public outreach (discussed in Section 4.0).
  • Incorporating explicit justification of the extent and nature of the safety problem, if one exists.
  • Incorporating safety issues for all modes of travel and vulnerable road users as appropriate, given the project context.

The latter two topics are discussed in more detail below.

5.2 Defining the Safety Problem

Safety is often included in the purpose and need statement for a project without sufficient analysis to define the problem. For example, the statement may cite the fact that road features are not up to the most recent design standards as justification that a safety problem exists. Defining the true safety performance of the roadway requires understanding the difference between substantive and nominal safety.


Substantive Safety versus Nominal Safety

Design standards provide a consistent, predictable roadway environment, but do not necessarily result in a safer roadway environment. Although uniform roadway designs may confer some safety benefit, few design standards have been rigorously evaluated to quantify their safety impact.

The concepts of “substantive” and “nominal” safety have been developed to help differentiate between design changes that improve safety and those that simply comply with standards. The National Cooperative Highway Research Program (NCHRP) 480, A Guide to Best Practices for Achieving Context Sensitive Solutions, explains that nominal safety refers to a design or alternative’s adherence to design criteria and/or standards; whereas, substantive safety refers to the actual performance of a highway or facility as measured by its crash experience (number of crashes per mile per year, consequences of those crashes as specified by injuries, fatalities, or property damage). It notes that a road can meet all design standards and still have poor safety performance (substantive safety); conversely, a roadway can have design exceptions and still show good safety performance relative to similar roadways of its class. Tort liability concerns frequently lead designers to comply with nominal safety standards, unless substantial documentation is provided to support a deviation from those standards.

The FHWA’s report “Mitigation Strategies for Design Exceptions” illustrates the difference between nominal and substantive safety (Figure 5.1). Nominal safety (blue line) is an “either-or” – a design feature or roadway either meets minimum criteria or it does not. On the other hand, substantive safety (red line) is the actual long-term or expected safety performance of a roadway; determined by its crash experience measured over a long enough time period to provide a high level of confidence that the observed crash experience is a true representation of the expected safety characteristics of that location or highway. Figure 5.1 states that current understanding of the relationships among roadway elements, traffic, drivers, and other factors suggests the true safety risk is better represented by the red line (substantive safety). Incremental changes in design dimensions (typical of design exception decisions) may result in incremental changes in substantive safety. Designers should seek knowledge and data to establish the substantive safety of a contemplated design decision. In many cases, substantive safety can be maximized within the constraints of design standards, since many are written so as to permit a great deal of flexibility. Design exceptions can be pursued in cases where a substantive safety improvement would violate a design standard.

Figure 5.1 Nominal and Substantive Safety

Difference between Nominal and Substantive safety (long description avaiblable)   L

Source: FHWA Technical Report, Mitigation Strategies for Design Exceptions.


Analysis Techniques

The challenge of evaluating substantive safety is that it requires detailed analysis; whereas, nominal safety involves a straightforward design check. Fortunately, many techniques and tools are available to assist in the identification of the magnitude and nature of a safety problem, ranging from simple to very sophisticated. Appendix A.4 lists these resources and tools, such as the HSM, the Safety Analyst Software tool, and the Interactive Highway Safety Design Model software tool. The HSM, for example, provides a detailed analysis procedure and tools for identifying “sites with promise” or areas with potential for crash reduction. One tool identified in the HSM is the Levels of Service of Safety (LOSS) methodology (see box below).

For example, to review the substantive safety of a two-lane rural highway, an analyst could compare its safety performance with that of similar two-lane rural highways in the state (not to all highways or other highway types). It is important to compare a road to similar roads in its class, because the expected safety performance of the road is strongly related to its context (e.g., traffic volume, location, functional classification, terrain, etc.). If the roadway in question has a significantly higher incidence or severity of crashes than other roads of its kind, it may have a substantive safety problem.

The accuracy of safety analysis depends on the availability and quality of underlying crash and associated road network and exposure data (e.g., traffic volumes). Crash records databases are frequently incomplete (for example, lacking complete crash records for nonfatal crashes or those occurring in rural areas) and are subject to error. Even if data is available, it can be inconclusive due to the strong influence of random chance on the incidence and location of crashes. A recent FHWA report (FHWA, 2010, Interstate System Access Information Guide, http://www.fhwa.dot.gov/design/interstate/pubs/access/access.pdf) suggests addressing these issues:

  • Is the data reasonable?
  • Was the data collected consistently?
  • Was quality control/quality assurance in place to verify the data?
  • RSAs (discussed below) also can be used to incorporate the observations of skilled safety practitioners as a means to supplement safety analysis, particularly if safety data is inconclusive or of poor quality.
  • The HSM provides a more complete discussion of data quality issues in road safety analysis.

Case Study – Safety Analysis Techniques

The Colorado DOT is studying a new six-lane bridge and highway interchange to connect the Stapleton Redevelopment Area and major interstates I-70 and I-270. For the original Draft EIS, the Colorado DOT used an LOSS approach to compare traffic safety under existing conditions and for future design alternatives. The LOSS uses qualitative measures to characterize the actual safety performance of a road segment compared to the expected safety performance. The LOSS analysis identified the need for safety improvements and informed the selection of appropriate countermeasures to remedy the issues. Appendix B.2 provides additional detail on this case study.


Road Safety Audits

Photograph of experts conducting a road safety audit

Road Safety Audits (RSA) are another tool used to identify and describe a safety problem to support development of a NEPA purpose and need statement. An RSA is a formal safety performance examination of an existing or planned road or intersection by an independent, multidisciplinary team. It estimates and reports qualitatively on potential road safety issues, and identifies opportunities for safety improvements for all road users.

RSAs help answer the following questions: 1) What elements of the road may present a safety concern – to what extent, to which road users, and under what circumstances? 2) What opportunities exist to eliminate or mitigate identified safety concerns?

RSAs can be helpful at multiple stages in the project development process, including planning, preliminary design, and final design. RSAs also can be conducted during construction to minimize the safety consequences of road construction. Given this flexibility, RSAs may be used at many stages of the NEPA process, including as a tool to define the purpose and need statement (see example below); to evaluate the safety performance of project alternatives while still in the design stage; and to identify opportunities to reduce construction-related safety impacts. RSAs can be particularly helpful in diagnosing safety problems or opportunities to improve safety when crash data is limited or requires careful interpretation. For example, an RSA team could identify cases where lack of pedestrian crossings inhibits pedestrian use resulting in low numbers of crashes.

Case Study: Expediting Safety Improvements from RSAs

The Tennessee DOT has an extensive program to conduct Road Safety Audit Reviews (RSAR) that examine the need for safety improvements for existing road segments, intersections, corridors, and ramp queues. These types of activities include, but are not limited to, pavement markings, rumble strips, traffic lights and/or signs, guard rails, and concrete barrier end treatments. Tennessee DOT has prepared a Programmatic Categorical Exclusion (PCE) for most of these types of projects, presuming they stay within existing right of way. In this manner, Tennessee DOT is able to expeditiously address safety problems as soon as they are evident. See Appendix B.6 for details.

5.3 Considering Multimodal Safety

When incorporating safety analysis into the project purpose and need, consideration should be given to all affected road users, including drivers, rail, transit, and particularly those likely to be more vulnerable in crashes, such as the elderly, children, disabled, pedestrians, and bicyclists. Specialized tools and resources are available to evaluate safety problems for a range of user groups. See Section 7.0, Defining the Affected Environment, for suggestions.

Case Study: Addressing Multimodal Safety

The Washington, D.C. DOT developed a streetscape plan for redesigning South Capitol Street as part of a redevelopment project along the Anacostia River waterfront. As part of the assessment, D.C. DOT investigated and analyzed existing and future multimodal patterns and crash rates in the South Capitol corridor. The findings from this analysis were included in the Draft EIS detailing the safety issues that needed to be addressed. It was determined that transforming South Capitol Street from an expressway to an urban boulevard design and including numerous pedestrian and bicycle safety features would address these issues and contribute to the safety, accessibility, multimodal mobility, and economic development of the corridor. See Appendix B.3 for details.

Identifying the safety problems experienced by a range of users is part of sensitivity to the project’s context and is consistent with the philosophy of Context Sensitive Solutions (CSS). However, a perception may exist that deviating from project design standards to adapt to the community context and the needs of multiple users may result in negative safety consequences (see box below).

Context Sensitive Solutions and Safety

Context Sensitive Solutions (CSS) is a collaborative, interdisciplinary approach that involves all stakeholders in providing a transportation facility that fits its setting. CSS grew out of landmark Federal transportation policies (Intermodal Surface Transportation Efficiency Act and the National Highway System Designation Act) emphasizing the importance of flexible highway design.

A core principle of CSS is “exercise flexibility and creativity to shape effective transportation solutions, while preserving and enhancing community and natural environments.” Applying this principle often means adapting road design standards, such as lane widths, turning radii, and design speeds, to match the community context.

Because of the belief that road design standards ensure safety, some assume that changing design standards to apply the philosophy of CSS will result in negative safety outcomes, and therefore, CSS and safety are incompatible. This is not the case, as design standards do not equate to safety, and many design standards have not been tested for their safety effects. To determine the true or “substantive” safety of design features, safety practitioners should apply the latest available analytical tools, and make use of research identifying proven safety countermeasures.

Safety is considered a cornerstone of sustainability and livability, and CSS is a tool by which to achieve these goals. Safety is also an important stakeholder value that communities want to achieve in addition to, rather than instead of, other stated goals.

5.4 If Safety is Not Part of the Purpose and Need

If no substantive safety problem exists or safety is not a part of the project purpose and need, safety analysis does not necessarily need to be included in the purpose and need statement. However, it may still be appropriate and beneficial to identify possible safety enhancements to the project’s safety. Every modification to a roadway presents a potential opportunity to improve design, and some agencies, including FHWA, specifically encourage or mandate consideration of safety as part of every project. Transportation agencies can use discretion in determining whether to address safety as part of every project. Agencies should avoid using generic statements regarding project impacts to meet the goal of addressing safety in all projects, and should instead strive to use objective analysis and proven countermeasures to demonstrate substantive safety benefits.

5.5 Summary

If safety is part of the project purpose and need, the purpose and need statement should include analysis to define the problem, reference applicable safety plans, incorporate the results of public outreach, and address the safety of all road users.

Table 5.1 provides information and data that may be included in purpose and need statements.

Table 5.1 Information and Data to Include in Purpose and Need Statements for Safety Focused Projects
Type of Information Example Information to Consider for Inclusion
Roadway performance Comparison of roadway crash rates to expected crashes for similar facility types given traffic volumes to identify the existence of a safety problem (see HSM for analysis techniques).
Crash rates for multiple types of road users.
Contributing crash factors Analysis of crash history to indicate predominance of certain crash types.
Multimodal safety issues Safety issues for specific types of road users, including pedestrians, bicyclists, freight vehicles, and transit vehicles.
Public perceptions Safety issues raised by the public as being of concern.
Results of RSA RSA results indicating any findings regarding deficiencies/‌opportunities for improving safety performance.

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