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

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4 Chapter 2. Literature and Current Practice Review This section of the report summarizes the literature review conducted for research including safety effects of geometric design features, traffic operational effects of geometric design features, pavement resurfacing effects, and cost-effectiveness/benefit–cost tools. A discussion of the issue of tort liability related to 3R projects is also presented. The review of current practices is continued in Section 3 with a summary of highway agency survey results and in Section 4 with a review of 3R design criteria. 2.1 Safety Effects of Geometric Design Features TRB Special Report 214, Designing Safer Roads: Practice for Resurfacing, Restoration and Rehabilitation (4), presented guidelines for 3R design criteria based on safety relationships available when the report was published in 1987. TRB Special Report 214 (4) cited the following sources as providing the best information available in 1987 on safety effects of geometric design features:  safety effects of lane and shoulder width and shoulder type were based on work by Zegeer et al. (10)  safety effects of roadside slopes and clear zones were based on a much simpler predecessor (11) of the current RSAP model (12,13,14)  safety effects of bridge width were based on research by Turner (15)  safety effects of horizontal curvature were based on research by Glennon et al. (16)  safety effects of stopping sight distance were based on research by Olson et al. (17)  safety effects of intersection improvements were based on a variety of sources  safety effects of pavement resurfacing were based on a variety of sources synthesized by Cleveland (18)  safety effects of pavement shoulder drop-offs were based on experimental track testing (19) and a critical review of previous research (20) All of these sources on which TRB Special Report 214 was based are now outdated and have been superseded by more recent research, with the exception of the lane width, shoulder width, and shoulder type study by Zegeer et al. (10). The crash modification factors for lane width, shoulder width, and shoulder type in the current edition of the Highway Safety Manual (HSM) (6) are based, in part, on the Zegeer et al. study. Chapter 5 of this report summarizes current knowledge on the crash reduction effectiveness of specific 3R improvement types. Table 1 summarizes the geometric design criteria and roadway types for which safety effects have and have not been quantified. This table addresses each of

5 FHWA’s 10 controlling criteria for geometric design (21), with the exception of design loading structural capacity, which is not a geometric design element. Cells in the table that contain a bullet identify combinations of a geometric design element and a roadway type for which a safety effect is documented in Chapter 5 of this report; blank cells indicate combinations of a geometric design element and a roadway type for which there is no known, quantitative safety effect. Table 1. Summary of Safety Effects of Key Geometric Design Features [adapted from (22)] Rural two-lane highways Rural multilane highways Urban and suburban arterials Freeways Design speed a a a a Lane width     Shoulder width    Bridge width  Horizontal curve radius    Superelevation rate  Stopping sight distance  Grade  Cross slope Vertical clearance N/A N/A N/A N/A a There are no direct safety effects of design speed; however, design speed may influence safety indirectly through the criteria for lane width, horizontal alignment, vertical alignment, and stopping sight distance. Roadside design for rural two-lane highways is addressed in HSM Chapter 10 (6) with a CMF for a roadside rating on a scale from 1 (a poor roadside design) to 7 (a good roadside design). For rural multilane highways, HSM Chapter 11 (6) does not include a CMF for roadside design. For urban and suburban arterials, HSM Chapter 12 (6) includes a CMF for roadside fixed objects based on object density per mile and offset from the traveled way. HSM Chapter 18 (7) includes CMFs that address roadside design in terms of roadside barrier presence and offset from the traveled way. More detailed analyses of roadside design features can be conducted with a model known as the Roadside Safety Analysis Program (RSAP) (12,13,14). 2.2 Traffic Operational Effects of Geometric Design Features The traffic operational effects of geometric design features are documented in the HCM (16). Additional sources of traffic operational relationships include the design consistency module of the FHWA Interactive Highway Safety Design Model (IHSDM) (23,24), and NCHRP Project 783 (22). Table 2 summarizes the geometric design criteria and roadway types for which traffic operational effects have and have not been quantified. This table addresses each of FHWA’s 10 controlling criteria for geometric design, with the exception of structural capacity, which is not a geometric design element. Cells in the table that contain a bullet identify combinations of a geometric design element and a roadway type for which an operational effect has been documented; blank cells indicate combinations of a geometric design element and a roadway type for which there is no known, quantitative operational effect.

6 Table 2. Summary of Traffic Operational Effects of Key Geometric Design Elements [adapted from (22)] Rural two-lane highways Rural multilane highways Urban and suburban arterials Freeways Design speed a a a a Lane width     Shoulder width    Bridge width Horizontal curve radius     Superelevation rate  Stopping sight distance Grade    Cross slope Vertical clearance N/A N/A N/A N/A a There are no direct operational effects of design speed; however, design speed may influence operations indirectly through the criteria for lane width, horizontal alignment, vertical alignment, and stopping sight distance. 2.3 Pavement Resurfacing Effects In the 1970s and 1980s, leading up to the publication of TRB Special Report 214 (4), there was quite an extensive debate on the effect of pavement resurfacing on safety. Highway agencies maintained that resurfacing (without geometric improvements) enhances safety, while safety organizations argued the opposite. TRB Special Report 214 noted that the potential effect of resurfacing on safety is a result of two factors working in opposite directions. First, resurfacing reduces surface roughness and improves ride quality, generally increasing average traffic speeds. Second, resurfacing often increases pavement skid resistance, which reduces stopping distance and improves vehicle controllability when the pavement surface is wet (4). Research reported in NCHRP Report 486 (25), published after TRB Special Report 214, found an average increase in traffic speed of 1 mph from before to after resurfacing, although this effect was also found to vary substantially from site to site. Research by Hauer et al (26) suggests that this increase in speed is a short-term effect since elevated crash frequencies after resurfacing remained higher for only 12 to 30 months. Pavement management systems maintained by highway agencies include capabilities for forecasting time-until-resurfacing and time-until-replacement for pavements. Many highway agencies use such information as part of their decision-making process to initiate 3R projects. 2.4 Cost-Effectiveness/Benefit–cost Tools This section reviews two existing cost-effectiveness/benefit–cost tools that can be used to support design decisions concerning 3R projects: Resurfacing Safety Resource Allocation

7 Program (RSRAP) and AASHTOWare Safety Analyst. These tools have not been used directly in the development of the guidelines in the current research, but they serve as examples of past work that has been considered in the research. 2.4.1 Resurfacing Safety Resource Allocation Program Resurfacing Safety Resource Allocation Program (RSRAP) is a benefit–cost decision support tool for application in the design of 3R projects. It was completed in 2003 and released as part of NCHRP Report 486 (25). A brief summary of the key features of RSRAP is presented here. RSRAP was conceived as a simple stand-alone spreadsheet tool. It does not link directly to highway agency roadway inventory or crash data bases. Rather, the user manually enters simple site characteristics and crash totals and the spreadsheet tool performs appropriate benefit–cost computations. Highway agency input received during the research indicated that the number of resurfacing projects considered by a highway agency or a district office, and the fact that this analysis would generally be performed only once per year, made this approach feasible. RSRAP can operate in either of two modes:  Consider a set of roadway sections for which the decision to resurface the pavement has already been made and assess which projects should also incorporate specific safety improvements, or  Consider a set of roadway sections that are candidates for resurfacing and assess which roadway sections should be resurfaced now and, among the roadway segments to be resurfaced now, assess which projects should also incorporate safety improvements. RSRAP is capable of assessing the following types of improvements.  Pavement resurfacing  Lane widening  Shoulder widening  Shoulder paving  Horizontal curve improvements  Roadside improvements  Intersection left- and right-turn improvements  Other user-defined alternatives (any alternative for which the user can provide both a cost and a crash modification factor)

8 RSRAP automatically considers all feasible combinations of lane widening, shoulder widening, and shoulder paving for every project. The other improvement types are considered if and when the user chooses to consider them. RSRAP does not use safety performance functions (SPFs). Rather, a crash modification factor (CMF) is applied to the estimated crash frequency per year by severity level for the road section. This is equivalent to one of the four HSM methods for estimating the safety benefit of a proposed project. The CMFs used in RSRAP are the same CMFs used in HSM Chapter 10. RSRAP also gives the user the option to consider a short-term increase in crash frequency due to pavement resurfacing [based on the results of Hauer et al. (26)], if the pavement is resurfaced without potentially needed accompanying geometric improvements, and the short-term traffic operational effect of resurfacing [a 1-mph increase in speed based on research in NCHRP Report 486 (25)]. These effects, when considered, last for the first 30 months after resurfacing for nonintersection crashes and the first 12 months after resurfacing for intersection crashes. RSRAP performs an optimization computation to prioritize the safety improvements. The user specifies the available budget to implement improvements and RSRAP determines the set of potential improvements, across all candidate sites, that provide the maximum benefits. Depending on the available budget, the maximum-benefit solution may include implementation of geometric improvements at some sites, but not at others. 2.4.2 Safety Analyst AASHTOWare Safety Analyst is a set of software tools for safety management of specific highway sites (27,28). Safety Analyst is capable of conducting optimization analyses comparable to RSRAP as part of a more sophisticated tool that links directly to highway agency roadway inventory, intersection inventory, and crash data bases. Safety Analyst was developed to use exactly the same optimization engine and exactly the same optimization approach as RSRAP. Both Safety Analyst and RSRAP can provide systemwide optimum solutions that maximize benefits for a given budget. Key differences between Safety Analyst and RSRAP include:  Safety Analyst can address the need for geometric improvements, but does not include logic to assess whether the pavement on specific projects should be resurfaced or not.  Unlike RSRAP, Safety Analyst does not automatically select certain feasible lane width, shoulder width, and shoulder paving improvements to be assessed; all countermeasures evaluated by Safety Analyst must be individually selected by the user.  Safety Analyst does not consider traffic operational differences between improvement alternatives and does not consider short-term resurfacing effects on crash frequency and speed.  Safety Analyst requires the use of large, systemwide databases that address the entire road network, not just the sites under consideration for resurfacing or 3R projects. While

9 Safety Analyst requires more data than RSRAP, its data requirements are less than those for HSM Part C.  Safety Analyst includes built-in default SPFs for specific roadway segment and intersection types and can also utilize user-supplied SPFs. Safety Analyst is made available to highway agencies through the AASHTOWare program and is currently being used by 17 states. 2.5 Tort Liability Considerations NCHRP Report 486 (25) includes a review of tort liability considerations related to 3R projects. To obtain a more recent perspective, members of the research team participated in an interview with three experienced defense attorneys and risk managers as part of NCHRP Project 15-47, “Developing an Improved Highway Design Process” (29). Research team members also attended Session 733, “Legal and Policy Implications of Using Quantitative Safety Analysis,” at the TRB annual meeting on January 15, 2014, which addressed similar issues. The key guidance from defense attorneys and risk managers relevant to design of 3R projects includes:  Laws and legal procedures vary from jurisdiction to jurisdiction; tort actions are more likely to be successful or to result in larger awards in some jurisdictions than in others.  Do not let tort liability concerns get in the way of making sound engineering decisions. Engineers should make rational and technically sound decisions that best serve the public good and trust that the agency’s lawyers and risk managers will defend any tort actions effectively.  Document engineering decisions thoroughly to create a record on which the agency can rely in court. Making good decisions by itself is not enough; documentation is important to show why the decisions were made.  Establishing policies and following a well-documented process for exceptions to those policies, where appropriate, is useful in defending against tort actions.  Priorities based on cost-effectiveness or benefit–cost analysis that suggest a smaller safety investment at Site A and a larger safety investment at Site B, will not necessarily help defend a tort action involving a crash that occurs at Site A. However, if the analysis results indicate that an investment at Site B will reduce more crashes than a similar investment at Site A, the investment at Site B is still the right course of action from an engineering standpoint. This guidance suggests that new approaches to the 3R design process are unlikely to raise significant tort liability issues for highway agencies as long as those new approaches are based on substantive engineering analyses.