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

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28 Chapter 4. Current Highway Agency 3R Design Guidelines This chapter reviews 3R design guidelines. The discussion begins with a summary of the 3R design guidelines presented in TRB Special Report 214 (4). Then, the review of state 3R design guidelines conducted in the research is summarized. Finally, the new design approaches of highway agencies that no longer have 3R design guidelines are described. 4.1 3R Design Guidelines in TRB Special Report 214 TRB Special Report 214 (4) presents the following design guidance for 3R projects. This guidance is based on a synthesis of literature and cost-effectiveness analyses conducted for TRB Special Report 214. 4.1.1 Minimum Lane and Shoulder Widths Table 19 presents the minimum lane and shoulder widths for two-lane highways presented in TRB Special Report 214 (4). These values are, in some cases, less than the comparable values used in the AASHTO Green Book (1) for new construction or reconstruction of local rural roads shown in Table 20. Table 21 shows the comparable Green Book design criteria, for rural collector roads and Table 22 shows the comparable Green Book design criteria for rural two- lane arterials. Table 19. Minimum Lane and Shoulder Widths for Rural Two-Lane Highways That Were Presented in TRB Special Report 214 (4) 10 percent or more trucksc Less than 10 percent trucks Design year volume (ADT)a Running speedb (mph) Lane width (ft) Combined lane and shoulder widthd Lane width (ft) Combined lane and shoulder width (ft)d 1-750 Under 50 10 12 9 1150 and over 10 12 10 12 751-2,000 Under 50 11 13 10 1250 and over 12 15 11 14 Over 2,500 All 12 18 11 17 a Design volume for a given highway feature should match average traffic anticipated over the expected performance of that feature. b Highway segments should be classified as “under 50” only if most vehicles have an average speed of less than 50 mph over the length of the segment. c For this comparison, trucks are defined as heavy vehicles with six or more tires. d One foot less for highways in mountainous terrain.

29 Table 20. Green Book Design Criteria for Minimum Width of Traveled Way on Rural Two-Lane Local Roads (1) Design speed (mph) Minimum width of traveled way (ft)a for specified design volume (veh/day) Under 400 400 to 1,500 1,500 to 2,000 Over 2,000 15 18 20a 20 22 20 18 20a 22 24c 25 18 20a 22 24c 30 18 20a 22 24c 40 18 20a 22 24c 45 20 22 22 24c 50 20 22 22 24c 55 22 22 24c 24c 60 22 22 24c 24c All speeds Width of graded shoulder on each side of the road (ft) 2 5a,b 6 8 a For roads in mountainous terrain with design volume of 400 to 600 veh/day, use 18-ft traveled way width and 2- ft shoulder width. b May be adjusted to achieve a minimum roadway width of 30 ft for design speeds greater than 40 mph. c Where the width of the traveled way is shown as 24 ft, the width may remain at 22 ft on reconstructed highways where alignment and safety records are satisfactory. Table 21. Green Book Design Criteria for Minimum Width of Traveled Way on Rural Two-Lane Collector Roads (1) Design speed (mph) Minimum width of traveled way (ft)a for specified design volume (veh/day) Under 400 400 to 1,500 1,500 to 2,000 Over 2,000 20 20b 20 22 24 25 20b 20 22 24 30 20b 20 22 24 35 20b 22 22 24 40 20b 22 22 24 45 20 22 22 24 50 20 22 22 24 55 22 22 24 24 60 22 22 24 24 All speeds Width of shoulder on each side of road (ft) 2.0 5.0c 6.0 8.0 a On roadways to be reconstructed, a 22-ft traveled way may be retained where the alignment and safety records are satisfactory. b An 18-ft minimum width may be used for roadways with design volumes under 250 veh/day. c Shoulder width may be reduced for design speeds greater than 30 mph as long as a minimum roadway width of 30 ft is maintained.

30 Table 22. Green Book Design Criteria for Minimum Width of Traveled Way on Rural Two-Lane Arterial Roads (1) Design speed (mph) Minimum width of traveled way (ft)a for specified design volume (veh/day) Under 400 400 to 1,500 1,500 to 2,000 Over 2,000 40 22 22 22 24 45 22 22 22 24 50 22 22 24 24 55 22 22 24 24 60 24 24 24 24 65 24 24 24 24 70 24 24 24 24 75 24 24 24 24 All speeds Width of usable shoulder (ft)b 4 6 6 8 a On roadways to be reconstructed, an existing 22-ft traveled way may be retained where alignment and safety records are satisfactory. b Usable shoulders on arterials should be paved; however, where volumes are low or a narrow section is needed to reduce construction impacts, the paved shoulder may be reduced to 2 ft. 4.1.2 Horizontal Curvature and Superelevation TRB Special Report 214 (4) indicates that highway agencies should increase the superelevation of horizontal curves when the design speed of an existing curve is below the 85th percentile speed of traffic and the existing superelevation is below the minimum specified by AASHTO new construction policies. Highway agencies should evaluate reconstruction of horizontal curves when the design speed of the existing curve is more than 15 mph below the 85th percentile speed of traffic (assuming improved superelevation cannot reduce this difference below 15 mph) and the average daily traffic volume is greater than 750 veh/day. TRB Special Report 214 also suggests that at horizontal curves where reconstruction is unwarranted, highway agencies should evaluate less costly safety measures. 4.1.3 Vertical Curvature and Stopping Sight Distance TRB Special Report 214 (4) suggests that highway agencies should evaluate the reconstruction of hill crests when (a) the hill crest hides from view major hazards such as intersections, sharp horizontal curves, or narrow bridges; (b) the average daily traffic is greater than 1,500 veh/day; and (c) the design speed of the hill crest (based on the minimum stopping sight distance provided) is more than 20 mph below the 85th percentile speed of vehicles on the crest.

31 4.1.4 Bridge Width TRB Special Report 214 (4) suggests that highway agencies should evaluate bridge replacement or widening if the bridge is less than 100 ft long and the usable width of the bridge is less than the values shown in Table 23. Table 23. Usable Bridge Width Criteria for Bridge Replacement from TRB Special Report 214 (4) Design year volume (ADT) Usable bridge width (ft)a 0-750 Width of approach lanes 751-2,000 Width of approach lanes plus 2 ft 2,001-4,000 Width of approach lanes plus 4 ft Over 4,000 Width of approach lanes plus 6 ft a If lane widening is planned as part of a 3R project, the usable bridge width should be compared with the planned width of the approaches after they are widened. 4.1.5 Sideslopes and Clear Zones TRB Special Report 214 (4) suggests that state highway agencies should develop consistent procedures for evaluating and improving roadside features with the following objectives:  Flatten sideslopes of 1V:3H or steeper at locations where run-off-road crashes are likely to occur (e.g., on the outside of sharp horizontal curves.);  Retain current slope widths (without steepening sideslopes) when widening lanes and shoulders unless warranted by special circumstances; and  Remove, relocate, or shield roadside obstacles. 4.1.6 Pavement Edge Drop and Shoulder Type TRB Special Report 214 (4) suggests that, to reduce pavement edge-drop hazards on highways with narrow unpaved shoulders, highway agencies should either:  Selectively pave shoulders at points where out-of-lane vehicle encroachments and pavement edge-drop problems are likely to develop (e.g., at horizontal curves); or  Construct a beveled or tapered pavement edge shape at these points. 4.1.7 Intersections TRB Special Report 214 (4) suggests that state highway agencies should develop consistent procedures and checklists for evaluating intersection improvements on 3R projects.

32 4.1.8 Normal Pavement Crown TRB Special Report 214 (4) suggests that, on resurfacing projects, highway agencies should construct pavement overlays with normal pavement crowns that match new construction standards. 4.1.9 Other Design Procedures and Assumptions TRB Special Report 214 (4) also states that:  The design traffic volume for a given highway feature should match the average traffic anticipated over the expected performance period of that feature.  When evaluating geometric design improvements where vehicle speed is a key factor, highway agencies should estimate running speeds (i.e., 85th percentile speeds) in a manner appropriate for the feature under consideration.  Highway agencies should estimate the incremental safety cost-effectiveness of improvements that exceed the minimum standard. Designers should consider overall highway geometry, design of adjacent segments, and expected trends in traffic growth and truck use when selecting design values.  When a highway agency requests an exception to a standard, the request should explicitly address the expected safety consequences, along with costs and other impacts. 4.2 Highway Agency 3R Design Criteria Review State highway agencies are permitted by Federal policy to develop geometric design criteria for 3R projects that differ from the geometric design criteria used for new construction and reconstruction projects. Once approved by FHWA, these alternative design criteria can be applied in the design of 3R projects. As part of this research effort, a review of various state 3R policies was conducted. The intent of this review was to examine a diverse cross section of state highway agency 3R policies. These states are: Florida, Hawaii, Iowa, Illinois, Louisiana, Massachusetts, Missouri, Texas, Virginia, and Wisconsin. The specific policies of the agencies are too diverse and too detailed to present in this report. Each agency’s 3R design policies include tables of design criteria that are less restrictive than the criteria in the AASHTO Green Book (4) and the criteria used in the agency’s design manual for new construction and reconstruction. Each of these sets of 3R design criteria have been proposed by the highway agency and approved by FHWA, and each is followed by the agency in designing 3R projects unless a design exception is requested and obtained. The individual agency policies differ from one another in their details, even though they serve the same overall purpose. Each of the policies differs from TRB Special Report 214 (4).

33 4.3 Evolving Design Approaches Several state highway agencies have been moving away from formal 3R design policies, not because they reject the concept of 3R design criteria, but rather because they believe that the 3R design concept has broader application than just to projects performed as part of the Federal 3R program. Such states formerly had 3R design policies, but have replaced those policies with new, more broadly based approaches. Such states typically indicated, in the highway agency survey, that they do not have specific geometric design criteria for 3R projects. The policies of the Washington State DOT are presented below as examples of this trend. Minnesota and Ohio are using similar approaches. The Washington State DOT has adopted a series of design matrices to guide the geometric design of specific projects. For projects not on Interstate freeways, there are three levels of design, each with its own matrix of applicable geometric design criteria. The three levels of design are:  Basic design level  Modified design level  Full design level The basic design level is analogous to what previously might have been considered to be 3R design criteria. The full design level is analogous to applying full Green Book geometric design criteria. The modified design level has geometric design criteria between the basic and full levels. In applying the design matrix approach, an early step in the project development process for any project (not just for 3R projects) is to select the design level applicable to that project – basic, modified, or full. This decision establishes the framework for the rest of the geometric design process. Most projects that would previously have been designed using the 3R design criteria would today be designed with the criteria for the basic design level, which is intended to preserve pavement structures, extend pavement service life, and maintain safe highway operations. However, the basic design level need not be used exclusively for 3R projects. Any project can be designed with which design level the agency considers appropriate. The Washington State DOT approach changes the selection of the design level for a project such that this decision is not tied to any specific funding source. The design matrix approach provides a consistent set of criteria for practical design; one of three sets of design criteria is selected for each project, rather than making a decision on design criteria on a case-by-case basis. It should also be noted that, for safety improvement projects, the Washington State DOT makes decisions about geometric improvements based on cost-effectiveness analyses, rather than any specific set of geometric design criteria.