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1 Chapter 1. Introduction 1.1 Purpose of Guidelines The design guidelines presented in this document have been developed to assist highway agencies in making geometric design decisions as part of the project development process for resurfacing, restoration, and rehabilitation (3R) projects. The guidelines address the role of safety considerations in the design of 3R projects and the implementation of a risk-based approach to design based on cost-effectiveness analysis. 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 recommended in these 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. These 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 documented 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. These guidelines 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 presented here 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) (2,3) and other recent safety research. 1.2 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. Section 2.1 discusses the distinctions between new construction, reconstruction, and 3R projects.
2 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 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 crash history review and cost-effectiveness approaches utilized in these guidelines should provide justification of design decisions within any administrative framework for design approval procedures that may be in place. 1.3 History of Guidelines Geometric design criteria have historically been established by AASHTO policies, updated most recently in the 2011 Policy on Geometric Design of Highways and Streets, commonly known as the Green Book (4), which apply to new construction and reconstruction projects. After each updated AASHTO policy is published, FHWA typically adopts the AASHTO geometric design criteria by regulation for application to the National Highway System (NHS) (Code of Federal Regulations, 23 CFR Part 625). In 1985, FHWA regulations identified 13 controlling criteria for geometric design; new construction and reconstruction projects on the NHS required a formal design exception to be initiated by the state or local highway agency and approved by FHWA if any of the 13 controlling criteria are not met. Based on research presented in NCHRP Report 783 (5), FHWA recently reduced the number of controlling criteria from 13 to 10 and no longer requires design exceptions for projects with design speeds of 45 mph or less for 8 of the 10
3 controlling criteria. Design exceptions for structural capacity and design speed are still required for NHS roads at all levels of design speed. Until 1976, Federal highway funds could be used only for new construction or reconstruction projects. The Federal-Aid Highway Act of 1976 first permitted state and local highway agencies to use Federal funds for 3R projects on existing federal-aid highways. Congress specified safety as one of the criteria to be considered in designing 3R projects, but did not specify any particular set of geometric design criteria or any particular safety analysis procedures. In 1977, AASHTO proposed a set of geometric design criteria for 3R projects that were less restrictive than the geometric design criteria in use for new construction and reconstruction (6). This proposal brought criticism from safety advocates who wanted all geometric elements on 3R projects to be upgraded to full new construction criteria to improve safety. Congress held hearings on this issue in 1981 and, as a result, the Surface Transportation Assistance Act of 1982 mandated a study of the cost-effectiveness of geometric design standards and the development of minimum standards for 3R projects on roads other than freeways. The result of this Congressional mandate was the formation of a study committee and the publication of TRB Special Report 214 (1), which proposed geometric criteria for 3R projects that have become the basis for the 3R design policies of many highway agencies. The AASHTO Green Book (4) does not present design criteria for 3R projects, but rather refers users to TRB Special Report 214. There have been many changes in both the state of knowledge and highway agency policies since the publication of TRB Special Report 214 in 1987. Much of this new knowledge is organized in the HSM (2,3). The guidelines presented in this document have been developed to update the guidelines in TRB Special Report 214 based on the new knowledge that is available. 1.4 Organization of Guidelines The remainder of the guidelines for 3R projects are organized as follows. Chapter 2 defines 3R projects and distinguishes them from new construction and reconstruction. Chapter 3 presents the process for 3R project development. Chapter 4 discusses the management of a 3R program to reduce crash frequency and severity, one of several objectives of 3R programs. Chapter 5 presents the application of benefit-cost analysis in 3R programs, including a description of two spreadsheet-based tools developed to supplement these guidelines that can be used to perform benefit-cost analyses. Chapter 6 presents specific design guidelines for 3R projects, incorporating a benefit-cost approach. Chapter 7 presents a summary of the 3R project design guidelines. Appendices A and B present user guides for the two spreadsheet-based geometric design tools. Appendix C presents updated crash cost estimates that may be used as default values in the spreadsheet tools.