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

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105 Chapter 10. Conclusions The primary conclusion of the research is that the state of knowledge concerning the crash reduction effectiveness of improvements typically made in 3R projects has advanced to the point that a performance-based design process is feasible. Crash reduction effectiveness measures are not yet available for every potential improvement type of interest for every roadway type, but enough is known that a performance-based approach that uses benefit–cost analysis to assist in design decisions is feasible for rural two-lane highways, rural multilane undivided and divided highways, and rural and urban freeways. The performance-based approach can provide greater overall benefits that a design approach based on dimensional geometric design criteria. The findings of the research are as follows: 1. A performance-based design process for 3R projects that uses benefit–cost analysis is proposed to assist in design decisions. In the performance-based approach design improvements should be made as part of 3R projects in any of 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, • 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 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. 2. A crash history analysis or a traffic operational analysis, 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. 3. 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. 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 report 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

106 prediction methods from Part C of the Highway Safety Manual (6,7). The assessment of the appropriateness and the affordability of the improvement should be made by the highway agency. 4. The spreadsheet tools discussed in Item 3 can be used to conduct three types of benefit–cost analyses: • benefit–cost analysis for a single design alternative at a single site • benefit–cost analysis to choose among several design alternatives for a single site • 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. 5. A few design improvements, such as normal cross slope restoration, are indicated 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 suggested to assess the need for specific design improvements and situations where specific restoration or rehabilitation work may be appropriate even where benefit–cost analyses are not currently feasible. 6. Where none of the three criteria in Item 1 are met and no design improvements of the type discussed in Item 5 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, highway agencies are encouraged 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 approach—focusing 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 limited—the total crash reduction expected from each year’s 3R projects can be increased. 7. The design guidelines for 3R projects developed in this research are published in NCHRP Research Report 876: Guidelines for Integrating Safety and Cost-Effectiveness into Resurfacing, Restoration, and Rehabilitation (3R) Projects (9) and are presented for application by highway agencies. These design guidelines are intended to replace the older guidance presented in TRB Special Report 214 (4). 8. No substantive changes to existing AASHTO documents are needed to implement the proposed design guidelines for 3R projects. However, AASHTO should consider

107 referencing the design guidelines (9) developed in the current research rather than TRB Special Report 214 (4) in the Green Book (1) and in the design guidelines for low- volume roads (5). 9. Since the guidelines and the spreadsheet tools developed in this research represent a new approach to making design decisions for 3R projects, a project to assist highway agencies in implementing the guidelines and the spreadsheet tools would be desirable.