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Suggested Citation:"Chapter 9. Development of Design Guidelines for 3R Projects." National Academies of Sciences, Engineering, and Medicine. 2021. Developing Guidelines for Integrating Safety and Cost-Effectiveness into Resurfacing, Restoration, and Rehabilitation (3R) Projects. Washington, DC: The National Academies Press. doi: 10.17226/26199.
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Suggested Citation:"Chapter 9. Development of Design Guidelines for 3R Projects." National Academies of Sciences, Engineering, and Medicine. 2021. Developing Guidelines for Integrating Safety and Cost-Effectiveness into Resurfacing, Restoration, and Rehabilitation (3R) Projects. Washington, DC: The National Academies Press. doi: 10.17226/26199.
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Suggested Citation:"Chapter 9. Development of Design Guidelines for 3R Projects." National Academies of Sciences, Engineering, and Medicine. 2021. Developing Guidelines for Integrating Safety and Cost-Effectiveness into Resurfacing, Restoration, and Rehabilitation (3R) Projects. Washington, DC: The National Academies Press. doi: 10.17226/26199.
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Suggested Citation:"Chapter 9. Development of Design Guidelines for 3R Projects." National Academies of Sciences, Engineering, and Medicine. 2021. Developing Guidelines for Integrating Safety and Cost-Effectiveness into Resurfacing, Restoration, and Rehabilitation (3R) Projects. Washington, DC: The National Academies Press. doi: 10.17226/26199.
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Suggested Citation:"Chapter 9. Development of Design Guidelines for 3R Projects." National Academies of Sciences, Engineering, and Medicine. 2021. Developing Guidelines for Integrating Safety and Cost-Effectiveness into Resurfacing, Restoration, and Rehabilitation (3R) Projects. Washington, DC: The National Academies Press. doi: 10.17226/26199.
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Suggested Citation:"Chapter 9. Development of Design Guidelines for 3R Projects." National Academies of Sciences, Engineering, and Medicine. 2021. Developing Guidelines for Integrating Safety and Cost-Effectiveness into Resurfacing, Restoration, and Rehabilitation (3R) Projects. Washington, DC: The National Academies Press. doi: 10.17226/26199.
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99 Chapter 9. Development of Design Guidelines for 3R Projects This chapter describes the development of design guidelines for 3R projects, which was a key objective of the current research. The design guidelines that were developed are presented in a separate, stand-alone guidelines document (9). 9.1 Overview The design guidelines developed in this research propose a performance-based approach to design decisions for 3R projects. Section 7.6 of this report has demonstrated that dimensional design criteria such as those presented in TRB Special Report 214 (4) by their nature provide smaller crash reduction benefits than an approach based on benefit–cost analysis. The guidelines feature benefit–cost analysis tools that can assist designers in making 3R design decisions. However, as explained below, crash history reviews and traffic operational analyses also have an important role in 3R project design decisions. 3R projects are typically initiated based on current or anticipated pavement conditions that indicate the need for pavement resurfacing. In designing 3R projects, highway agencies need to decide whether to simply resurface the pavement or whether to utilize the 3R project as an opportunity to implement other desirable improvements, such as geometric design changes, to reduce crash frequency and severity and/or improve traffic operations. The approach to such decisions proposed in the guidelines for application to specific 3R projects considers current roadway and roadside design, current and anticipated future traffic volumes, crash history and anticipated future crash frequency and severity, improvement implementation costs, and other economic, environmental, and community factors that highway agencies consider in the project development process. The guidelines provide a framework for considering these factors in 3R project design decisions, so that funds are invested in geometric design improvements as part of 3R projects primarily where documented crash patterns exist or where, in the absence of a docu- mented crash pattern, the anticipated crash reduction benefits over the service life of the project exceed the improvement implementation costs. The guidelines advise highway agencies to avoid investing funds in geometric design improvements where the improvement implementation costs exceed the anticipated crash reduction benefits, unless there is either a documented crash pattern that can be mitigated by the improvements or a documented traffic operational improvement need. The guidelines developed in this research are intended to replace the design guidelines for 3R projects presented in TRB Special Report 214, Designing Safer Roads: Practices for Resurfacing, Restoration, and Rehabilitation (4). The guidelines presented in this document are based on substantial advances in knowledge about the effects of geometric design features on crash frequency and severity since TRB Special Report 214 was published in 1987. Most specifically, the guidelines implement the safety knowledge presented in the American Association of State Highway and Transportation Officials (AASHTO) Highway Safety Manual (HSM) (6,7) and other recent safety research.

100 9.2 Scope of Guidelines The scope of the guidelines is limited to projects involving only resurfacing, restoration, and/or rehabilitation. New construction and reconstruction projects are not addressed by these guidelines. New construction projects typically consist of projects on new alignment where no highway facility has existed before (e.g., projects on greenfield sites). Some projects on existing roads might be classified as new construction if the existing roadway is completely removed, a new alignment or cross section is developed for the facility, and the new alignment and cross section are not substantially constrained by development adjoining the existing road; this situation is rare, but can occur. Reconstruction projects include projects on existing roads that are not considered new construction and in which:  the entire pavement structure, down to the subgrade, is removed and replaced, for all or most of the project length,  a substantial proportion of the existing alignment is modified, or  the basic roadway cross section is changed (e.g., expanding an existing two-lane highway to four lanes). The guidelines address 3R projects initiated for any reason. Most 3R projects are initiated because of poor pavement condition that indicates a need for pavement resurfacing, but the guidelines can also be applied to projects initiated for other reasons, as long as the project does not involve new construction or reconstruction. The guidelines address design of 3R projects on rural two-lane highways, rural multilane undivided highways, rural multilane divided nonfreeways, urban and suburban arterials, and rural and urban freeways. The guidelines are based on the current state of knowledge concerning crash reduction effectiveness and traffic operational improvements that can result from specific design alternatives for 3R projects. The guidelines should be updated in the future as knowledge of these issues advances. The guidelines are intended for application to 3R projects paid for from any funding source. Thus, the guidelines are not limited just to projects funded as part of the Federal 3R program. The guidelines are also applicable to 3R projects funded from other Federal sources and to projects funded entirely with state or local funds. The guidelines focus on deciding whether any specific project should be resurfaced without accompanying geometric design improvements or whether (and what) geometric design changes should be made as part of the project. The focus of the guidelines is entirely on determining the appropriate geometric design for the roadway after project implementation (either the same as the existing roadway or incorporating cost-effective

101 changes). The guidelines do not address administrative issues such as the appropriate form of design approvals or the need for design exceptions. Such administrative issues are best addressed by the highway agencies involved. The highway community is moving toward more flexible geometric design processes, with reduced need for routine design exceptions, but such administrative issues are outside the scope of these guidelines. In any case, the cost-effectiveness approach utilized in these guidelines should provide the justification needed for design decisions within any administrative framework for design approval procedures that may be in place. 9.3 How Does the Design Process for 3R Projects Differ from the Design Process for New Construction and Reconstruction Projects? The current design process for new construction projects is based primarily on the dimensional design criteria presented in the AASHTO Green Book (1) and in the design policies of individual highway agencies. It is appropriate to use established dimensional design criteria for new construction projects because, in such projects, there is no existing roadway with a safety and traffic operational performance history that can be used to guide the design process. Established dimensional design criteria provide an aspirational goal for design of reconstruction projects. Where a roadway is being fully reconstructed, design improvements may be feasible with limited additional cost, except where such improvements would substantially impact adjacent development, established communities, or sensitive environments; in these situations, highway agencies typically seek a design exception to minimize such impacts. 3R projects are usually initiated based on the need for pavement resurfacing and are most appropriately considered as maintenance activities. A performance-based design process provides the basis for design of 3R projects focusing on the decision about which projects should be resurfaced without accompanying design improvements and which projects should have design improvements incorporated. The design process for 3R projects begins with the recognition that the project will be implemented on an existing road whose past safety and traffic operational performance is known and should serve as a key factor in design decisions. Unlike new construction and reconstruction projects, which are designed in accordance with dimensional design criteria presented in the AASHTO Green Book (1), these guidelines do not establish dimensional design criteria for 3R projects. Rather, 3R design decisions are based on an assessment of the safety and traffic operational performance of the existing road and the cost-effectiveness of potential design improvements. Geometric design improvements should be considered as part of a 3R project in the following situations:  An analysis of the crash history of the existing road identifies one or more crash patterns that are potentially correctable by a specific design improvement, or  An analysis of the traffic operational level of service (LOS) indicates that the LOS is currently lower than the highway agency’s target LOS for the facility or will become

102 lower than the target LOS within the service life of the planned pavement resurfacing (typically 7 to 12 years), or  A design improvement would reduce sufficient crashes over its service life to be cost- effective; i.e., the anticipated crash reduction benefits over the service life of the project should exceed the improvement implementation cost. In the absence of any of the three situations defined above, there is no indication that a design improvement is needed as part of a 3R project, and the existing roadway and roadside geometric features should remain in place. It makes little sense to invest scarce resources in design improvements as part of a 3R project where the existing roadway is performing well and where potential design improvements would not be cost-effective; the funds needed for such a project can be better invested in projects that do have documented performance concerns or where potential design improvements would be cost-effective. In particular, improvement of systemwide safety across the road network is so important that funds invested with the objective of improving safety should be directed toward projects where it can be demonstrated that safety benefits will actually be obtained. The reliance on cost-effectiveness to guide design decisions for 3R projects has several advantages:  Highway agencies can have confidence that funds invested in design improvements intended to reduce crashes as part of 3R projects are, in fact, likely to result in reduced crashes.  Since crash frequency for a road generally increases with increasing traffic volume, the use of cost-effectiveness analysis as a basis for design decisions means that the likelihood of design improvements being included in a 3R project increases with increasing traffic volume. This dependence of design decisions on traffic volume levels is logical and desirable and is not fully reflected in most current dimensional design criteria for new construction and reconstruction.  A cost-effectiveness approach will focus improvement needs on low-cost improvements with documented safety effectiveness, which are most consistent with the limited scope of 3R projects. However, the procedures are flexible enough that higher cost improvements can be considered where benefits are sufficient to justify their implementation. If extensive geometric improvements are found to be cost-effective, consideration may be given to reclassifying the project as a reconstruction project. The guidelines demonstrate that reliance on dimensional design criteria will result in suboptimal results, with some investments made at locations where they are not cost-effective and other investments not made at locations where they would be cost-effective. 9.4 Crash Reduction Effectiveness of 3R Improvements The crash reduction effectiveness of design improvements that are commonly incorporated in 3R projects is documented in these guidelines based on crash modification factors (CMFs) presented

103 in the AASHTO Highway Safety Manual (6,7) and recent research. Chapter 5 of this report presents the crash reduction effectiveness estimates used in the 3R project design guidelines. 9.5 Benefit–cost Analysis Procedures The guidelines present a set of benefit–cost analysis procedures that can be applied to alternative geometric design improvements for 3R projects to determine which improvements would be cost-effective and which improvements would not be cost-effective. Chapter 7 of this report summarizes the benefit–cost analysis procedures used in the 3R project design guidelines. Three specific benefit–cost analysis applications have a role in 3R project design decisions. These are:  benefit–cost analysis for a single design alternative for a specific site  benefit–cost analysis to choose among several design alternatives for a specific site  benefit–cost analysis to develop agency-specific minimum AADT guidelines for application in design decisions Procedures for each of these applications are presented in of the guidelines. 9.6 Benefit–cost Analysis Tools Two spreadsheet tools for benefit–cost analysis in support of 3R project design decisions are discussed in this section. These include a tool for analysis of a single design alternative or combination of alternatives (Spreadsheet Tool 1) and a tool for comparison of several design alternatives or combinations of alternatives (Spreadsheet Tool 2). The spreadsheet tools apply to rural two-lane highways, rural multilane nonfreeways (including both undivided and divided highways), and rural and urban freeways. The tools do not address urban and suburban arterials because no crash reduction effectiveness estimates are available for most project types on arterials. The capabilities and application of each spreadsheet tool are presented in Chapter 8 of this report. User guides for the spreadsheet tools are presented in the stand-alone guidelines document (9). 9.7 3R Project Design Guidelines for Specific Roadway Types Specific 3R project design guidelines for each roadway type of interest are presented in the guidelines document (9). The roadway types of interest include rural two-lane highways, rural multilane undivided and divided highway, urban and suburban arterials, and rural and urban freeways. The specific types of 3R project improvements addressed by the guidelines include lane widening, shoulder widening and paving, horizontal curve improvements, sight distance improvements, bridge widening, passing lanes, restoration of normal pavement cross slope, rumble strip improvements, striping and delineation improvements, roadside slope flattening,

104 removal of roadside objects, installation/rehabilitation of guardrail and other traffic barriers, intersection turn lane improvements, and other intersection improvements. The guidelines incorporate use of the spreadsheet-based benefit–cost analysis tools wherever this is feasible and suggest alternative approaches where the spreadsheet tools are not applicable.

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The aging U.S. highway system, coupled with fiscal constraints, is placing increased pressures on highway agencies to maintain the highway system in a cost-effective manner and is, thus, creating greater needs for 3R projects.

The TRB National Cooperative Highway Research Program's NCHRP Web-Only Document 244: Developing Guidelines for Integrating Safety and Cost-Effectiveness into Resurfacing, Restoration, and Rehabilitation (3R) Projects presents the results of research to develop improved design guidelines for 3R projects. The guidelines were developed to replace the older guidance presented in TRB Special Report 214: Designing Safer Roads: Practices for Resurfacing, Restoration, and Rehabilitation.

Supplementary to the Document is NCHRP Research Report 876: Guidelines for Integrating Safety and Cost-Effectiveness into Resurfacing, Restoration, and Rehabilitation (3R) Projects. Two spreadsheet tools for benefit–cost analysis in support of design decisions for 3R projects also accompany the report. Spreadsheet Tool 1 is a tool for analysis of a single design alternative or combination of alternatives. Spreadsheet Tool 2 is a tool for comparison of several design alternatives or combinations of alternatives.

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