Guidelines for Integrating Safety and Cost-Effectiveness into Resurfacing, Restoration, and Rehabilitation (3R) Projects (2021)

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1   Resurfacing, restoration, and rehabilitation (3R) projects are typically initiated on the basis of 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 to utilize the 3R project as an opportunity to implement other desirable improvements, such as geometric design changes, to reduce crash frequency and severity or improve traffic operations. The approach to such decisions presented in this report’s guidelines for application to specific 3R projects considers current roadway and roadside design; current and anticipated future traffic volumes; crash history and antici- pated future crash frequency and severity; the costs of implementing improvements; and other economic, environmental, and community factors that highway agencies consider in the project development process. These guidelines provide a framework for considering these factors in design decisions for 3R projects, so that investment of funds in geometric improvements as part of 3R projects is made primarily in cases where documented crash patterns exist or where, in the absence of a documented crash pattern, the anticipated crash reduction benefits over the service life of the project exceed the costs of imple- menting improvements. The guidelines advise highway agencies to avoid investing funds in geometric improvements where the costs of implementing improvements exceed the anticipated benefits in crash reduction, unless there is either a documented crash pattern that can be mitigated by the improvements or a documented need for traffic operational improvement. The guidelines presented in this report 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 (1). The guidelines are based on substantial advances in knowledge about the effects of geometric design features on crash frequency and severity since 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) (2, 3) and other recent safety research. Scope of Guidelines The scope of the guidelines is limited to projects involving only resurfacing, restoration, or rehabilitation. New construction and reconstruction projects are not addressed in this report. 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 S U M M A R Y Guidelines for Integrating Safety and Cost-Effectiveness into Resurfacing, Restoration, and Rehabilitation (3R) Projects

2 Guidelines for Integrating Safety and Cost-Effectiveness into Resurfacing, Restoration, and Rehabilitation (3R) Projects 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 the design of 3R projects on rural two-lane highways, rural multi- lane 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 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 improvements or whether (and what) geometric design changes should be made as part of the project. The goal of the guidelines is entirely to determine the appropriate geometric design for the roadway after project implementation (either the same as the existing roadway or incor- porating cost-effective 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. 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 AASHTO’s A Policy on Geometric Design of Highways and Streets (commonly known as the “Green Book”) (4) and on 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 the 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 affect adjacent development, established communities, or sensitive environments; in these situations, highway agencies typically seek a design exception to minimize such impacts. Resurfacing, restoration, and rehabilitation projects are usually initiated on the basis of the need for pavement resurfacing and are most appropriately considered as mainte- nance activities. A performance-based design process provides the basis for the design of 3R projects focusing on the decision about which projects should be resurfaced without accompanying design improvements and which projects should incorporate design improvements. 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

Summary 3   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 (4), the guidelines in this report 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 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 geometric improvement; • 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 lower than the target LOS within the service life of the planned pavement resurfacing (typically 7 to 12 years); or • A geometric improvement would reduce sufficient crashes over its service life to be cost-effective; that is, the anticipated crash reduction benefits over the service life of the project should exceed the cost of implementing the improvement. 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 when the existing roadway is performing well and potential design improvements would not be cost-effective. The funds needed for such a project can be better invested in projects that do have docu- mented performance concerns or those in which 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 for which 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 focuses 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 improve- ments 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 in this report 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.

4 Guidelines for Integrating Safety and Cost-Effectiveness into Resurfacing, Restoration, and Rehabilitation (3R) Projects 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 on the basis of crash modification factors (CMFs), as presented in the AASHTO Highway Safety Manual (2, 3) and recent research. Benefit–Cost Analysis Procedures The guidelines present a set of procedures for benefit–cost analysis that can be applied to alternative geometric improvements for 3R projects to determine which improvements would be cost-effective and which would not be. Three specific applications of benefit–cost analysis have a role in design decisions for 3R projects: • Benefit–cost analysis for a single design alternative for a specific site, • Benefit–cost analysis to choose between several design alternatives for a specific site, and • Benefit–cost analysis to develop agency-specific minimum guidelines for annual average daily traffic (AADT) for application in design decisions. Procedures for each of these applications are presented in Section 5.5 of these guidelines. Benefit–Cost Analysis Tools Two spreadsheet tools for benefit–cost analysis in support of design decisions for 3R projects are presented in these guidelines. These include a tool for analysis of a single design alternative or combination of alternatives (Spreadsheet Tool 1) and a tool for com- parison of several design alternatives or combinations of alternatives (Spreadsheet Tool 2). Both spreadsheet tools may be downloaded from the TRB website (trb.org) by searching for “NCHRP Research Report 876”. 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 estimates of crash reduction effectiveness are available for most project types on arterials. Examples of the application of each spreadsheet tool are presented in Section 5.7 of these guidelines. User guides for the spreadsheet tools are presented in Appendices A and B. 3R Project Design Guidelines for Specific Roadway Types General design guidelines applicable to all 3R projects are presented in Chapters 2 through 5, including an introduction to the spreadsheet benefit–cost analysis tools in Chapter 5. Chapter 5 includes examples of how benefit–cost analyses can be used, including applica- tion to rural two-lane highways, rural multilane highways, and freeways; also included is an example of how benefit–cost analysis can be used to derive AADT-based guidelines for specific types of improvements. Chapter 6 presents specific design guidelines for 3R projects on the roadway types to which the spreadsheet benefit–cost analysis tools apply as well as for urban and suburban arterials. 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, removal of roadside objects, installation/rehabili- tation of guardrail and other traffic barriers, intersection turn lane improvements, and other intersection improvements. A summary of the guidelines is presented in Chapter 7.