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135 Chapter 7. Summary of 3R Design Guidelines This chapter presents a summary of the design guidelines presented in this document. 1. The guidance presented in this document is applicable only to 3R projects; i.e., projects whose scope includes only resurfacing, restoration, or rehabilitation. The guidelines are not applicable to new construction or reconstruction projects. Therefore, 3R projects should not involve a substantial amount of construction on new alignment, removal of the entire pavement structure down to the subgrade, realignment of a substantial portion of the project, or a change in the basic roadway cross section; projects that involve these changes would more properly be classified as new construction or reconstruction. If a limited or isolated portion of a project involves new construction or reconstruction, the remainder of the project can be designed as 3R work. For freeway projects, any change in the existing roadway alignment should be considered as reconstruction. 2. The guidance presented in this document is applicable to projects that fall within the scope of 3R work, as defined above in Guideline 1, regardless of the funding source for the project. These guidelines are intended for application to any project involving 3R work, not just projects funded from the Federal 3R program or the 3R program of any highway agency. 3. The primary objective of most 3R projects is to preserve and extend the life of the pavement by resurfacing. Thus, 3R projects are normally initiated because the need for pavement resurfacing has been identified by a pavement management system or by other means. However, the guidelines presented in this document may be applied to any project that falls within the scope of 3R work (i.e., does not involve new construction or reconstruction) regardless of the means by which the need for the project was identified. 4. While the primary objective of most 3R projects is to preserve and extend the life of the pavement, 3R projects may also provide an opportunity to make additional design improvements that may reduce crash frequency or severity or may improve traffic operations. As part of the design process for 3R projects, an assessment should be made as to whether such design improvements should be incorporated in the 3R project. 5. Design guidance for 3R projects based on dimensional design criteria, such as the 3R design criteria presented in TRB Special Report 214 (1) are no longer recommended. Research has shown that application of any set of fixed dimensional design criteria for 3R projects is likely to produce smaller crash reduction benefits than the performance- based approach recommended in Guideline 6 (7). 6. Design improvements should be incorporated in 3R projects when any of the following three criteria are met: a. 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, b. An analysis of the traffic operational level of service (LOS) indicates that the LOS is currently lower than the highway agencyâs target LOS for the facility or will become
136 lower than the target LOS within the service life of the planned pavement resurfacing (typically 7 to 12 years), or c. A design improvement would be expected to 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. Procedures for applying the types of analyses identified in Guidelines 6a, 6b, and 6c are presented in Chapters 3, 4, and 5 of this document. 7. A crash history analysis or a traffic operational analysis (as described in Guidelines 6a and 6b, respectively), by itself, provides sufficient justification for implementing an appropriate design improvement that addresses the identified need and for which the highway agency has sufficient funding available. The assessment of the appropriateness and affordability of the improvement should be made by the highway agency. 8. If neither the crash history analysis nor the traffic operations analysis identifies a need for a design improvement, implementation of an improvement may still be appropriate if an assessment of the anticipated crash reduction benefits and costs of the design or traffic control improvements indicate that the improvements would be cost-effective (see Guideline 6c). The benefits and costs considered in such an analysis are those above and beyond the anticipated benefits and costs of the pavement resurfacing, which is already planned and which will likely be accomplished whether or not additional improvements are made. Design or traffic control improvements in addition to pavement resurfacing should be considered where their anticipated benefits exceed their anticipated costs. Spreadsheet Tools 1 and 2 presented in Chapter 5 of this document can be used to assess the anticipated benefits and costs, and the cost-effectiveness, of specific design improvements. The benefits of design improvements are assessed in the spreadsheet tools based on the crash prediction methods from Part C of the Highway Safety Manual (2,3). The assessment of the appropriateness and the affordability of the improvement should be made by the highway agency. 9. The spreadsheet tools discussed in Guideline 8 can be used to conduct three types of benefit-cost analyses: ï· benefit-cost analysis for a single design alternative at a single site ï· benefit-cost analysis to choose among several design alternatives for a single site ï· benefit-cost analyses to develop agency-specific minimum AADT guidelines for application in design decisions The first two types of benefit-cost analyses listed above are preferred. The third type of benefit-cost analysis is less desirable than the first two approaches, but should provide acceptable results. The three analysis approaches are discussed in Chapter 5 of this document. 10. A few design improvements, such as normal cross slope restoration, are recommended in 3R projects where a need is identified, even where formal tools to assess the cost- effectiveness of such improvements do not exist. The design guidelines discussion in Chapter 6 of this document identifies situations in which benefit-cost analyses are feasible and are recommended to assess the need for specific design improvements and
137 situations where specific restoration or rehabilitation work may be appropriate even where benefit-cost analyses are not currently feasible. 11. Where none of the three criteria in Guideline 6 are met and no design improvements of the type discussed in Guideline 10 are needed, 3R projects should generally be limited in scope to pavement resurfacing. 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 the potential design improvement would not be cost-effective. Making improvements that are not needed and/or not cost-effective will likely provide only small benefits and the costs may be substantial. The same funds, invested elsewhere where the need for improvement is documented and/or the cost-effectiveness of the improvement is demonstrated, would be expected to provide greater benefits, including more lives saved, more injuries prevented, and more crashes eliminated. Since available funds for 3R projects are limited, Guideline 11 encourages highway agencies to take a systemwide perspective in planning 3R projects, investing available funds where they will provide the greatest crash reduction and avoiding investments that will provide little crash reduction. With this approachâfocusing design improvements on the projects with the best opportunities to reduce crashes and implementing only resurfacing on projects without accompanying design improvements where opportunities to reduce crashes are more limitedâthe total crash reduction expected from each yearâs 3R projects can be increased.