Geometric Design Practices for Resurfacing, Restoration, and Rehabilitation (2011)

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20 CHAPTER FOUR GEOMETRIC DESIGN CRITERIA FOLLOWED BY STATES As stipulated in FHWA Technical Advisory T 5040.28, 13 geometric elements were established as the controlling criteria for geometric design. The survey did not ask what each state used for these design elements for 3R projects; this information was gleaned from the 3R policy documents. Design guidelines for 32 states were reviewed. It would be difficult and impractical to describe what each state follows for the geometric elements because the standards vary widely. Many states have different standards for their class of roads, volume levels, rural vs. urban, and other categories. The design standards for each state can be seen from viewing their documents, which can be accessed at http://www.trb.org/SynthesisPrograms/Public/Compila- tionofStateDesignManuals.aspx. Some state practices will be summarized in this chapter. Throughout the discussion, examples from various states will be provided; they are not necessarily meant to be exam- ples of best practice, but an indication of the variation in how the states treat the various design elements. Several states discuss their geometric design approach; that of Mississippi is highlighted here (from Chapter 11 of the Mississippi design manual): 11-2.01.03 Approach The Department’s approach to the geometric design of 3R projects is to adopt, where justifiable, a revised set of numerical criteria. The design criteria throughout the other Manual chapters proved the frame of reference for the 3R criteria. The following summarizes the approach which has been adopted: 1. Design Speed. The tables in Section 11-2.09 present the 3R design speeds for rural arterials and rural collectors on the State highway system. Note that these speeds are lower than those for new construction/reconstruction projects, subject to the posted/regulatory speed limit. 2. Speed-Related Criteria. Many geometric design values are calculated directly from the design speed (e.g., vertical curves, horizontal degree of curvature). The 3R design speed is used to determine these speed-related criteria. For many speed-related elements, Chapter 11 presents an acceptable threshold value for the element which is considerably below the 3R design speed. For example, if the calculated design speed of an existing crest vertical curve is within 15 mph of the 3R project design speed and there is not an adverse accident history, the existing crest vertical curve may be retained in the project design without a design exception. 3. Cross-Section Widths. The criteria in Chapter 2 have been evaluated relative to the typical constraints of the 3R projects. Where justifiable, the values of the cross section width criteria have been reduced. 4. Other Design Criteria. The Department’s Design Manual contains many other details on proper geometric design techniques. These criteria are obviously applicable to new construction and reconstruction. For 3R projects, these criteria have been evaluated and a judgment has been made on their proper application to 3R projects. Unless, stated otherwise in this Chapter, the criteria in other chapters apply to 3R projects and should be incorporated if practical. 5. NHS Projects. For 3R projects on NHS facilities, it is not acceptable to propose a design value which is less than the value for the existing facility. For example, the proposed roadway width must equal or exceed the existing roadway width. This is just one state’s approach to geometric design of 3R projects, although in many respects it is similar to those used by other states. THIRTEEN CONTROLLING DESIGN CRITERIA FHWA has identified 13 controlling criteria as having such substantial importance to the operational and safety perfor- mance of any highway that special attention should be paid to them in design decisions. FHWA requires a formal writ- ten design exception if design criteria on the NHS are not met for any of the following 13 criteria: 1. Design speed 2. Lane width 3. Shoulder width 4. Bridge width 5. Horizontal alignment 6. Superelevation 7. Vertical alignment 8. Grade

21 According to AASHTO (7), design speed is “a selected speed used to determine the various geometric design fea- tures of the roadway.… Once … selected, all of the pertinent highway features should be related to it to obtain a balanced design.” The current edition of the Green Book devotes four and a half pages of discussion to design speed. In discussing design speed, references are often made to operating speed, posted speed limit, and 85th percentile speed. See Donnell (14) for a good discussion of alternative speed concepts and the explanation of a new speed concept. As presented in chapter three, respondents ranked design speed as the most critical of the 13 controlling design ele- ments, more often than any of the other elements. In the state design documents, most states mention design speed, but they differ as to which speed should be referenced, includ- ing speed limit, 85th percentile speed, and average running speed. Texas is one of a few states that have design speeds that vary by road type. Florida DOT has the most extensive discussion of design speed in its 3R guidelines. Chapter 25 of Florida’s Plans Preparation Manual provides Florida’s design criteria for 3R projects. In general, Florida’s design speed criterion is that the design speed used in the original design of the high- way should be used in 3R projects and that it should not be less than the legal posted speed. (It is recognized that many 3R projects are for roads that did not have an original design speed and that the speed limit is all that is available.) Florida provides the guidance found in Table 11 for determining the appropriate design speed for three different cases. CASE 1: The existing posted speed falls within an acceptable range of the original design speed [i.e., PS ≤ DSo ≤ (PS + 10 mph). Example DSo = 65 mph and PS = 55 mph]. CASE 2: The existing posted speed falls below an acceptable range of the original design speed. In a case like this, the posted speed was reduced, and the operational con- ditions have changed [i.e., DSo > (PS + 10 mph). Example DSo = 65 mph and PS = 35 mph]. CASE 3: The existing posted speed falls above an acceptable range of the original design speed. In a case like this, the posted speed was increased, and the operational conditions have changed [i.e., PS > DSo). Example DSo = 50 mph and PS = 60 mph]. Legend: DSo = Design speed used in the original project, DSp = Proposed design speed for project, and PS = Existing (or proposed if different) posted speed. 9. Stopping sight distance 10. Cross slope 11. Vertical clearance 12. Horizontal clearance (also known as lateral offset to obstruction) 13. Structural capacity. Table 9 shows the number of states that had design val- ues or at least mentioned each of the 13 design elements in their 3R guidance. As shown, 31 of the 32 states have design values for lane width and shoulder width. At the other end of the distribution, only 20 of the 32 states had values for, or at least discussed, vertical clearance and grade within their 3R design policy. TABLE 9 NUMBER OF STATES WITH DESIGN ELEMENT INCLUDED IN 3R POLICY Design Element No. of States Lane Width 31 Shoulder Width 31 Bridge Width 28 Horizontal Alignment 28 Vertical Alignment 28 Design Speed 28 Cross Slope 26 Superelevation 24 Structural Capacity 24 Stopping Sight Distance 23 Horizontal Clearance 23 Vertical Clearance 20 Grade 20 Although most states discuss each of these design ele- ments to varying degrees, a few simply present the guidelines in a table without further explanation. For example, Table 10, extracted from Michigan’s road design manual, shows 3R minimum guidelines for the 13 controlling criteria applicable to non-NHS roads. A similar table is provided for NHS roads. The following sections present examples of how the states discuss the 13 controlling criteria. Design Speed This criterion is typically the first mentioned, understand- ably so as several other design criteria are based on it.

22 ing either or both for a 3R project can be problematic, especially if additional ROW is needed. Aside from the costs for the improvement to the road, obtaining ROW can be costly and requires additional studies and approvals. Hence, it is critical for 3R projects to set design criteria for these two elements. Table 12 shows the minimum lane and shoulder widths for two-lane rural highways recommended in TRB SR 214. The table in that report has been revised to show shoulder B. Non-Freeway, Non-NHS TABLE 10 MINIMUM GUIDELINES FOR 13 CONTROLLING CRITERIA FOR NON-NHS 3R PROJECTS (Michigan) Lane and Shoulder Width Wider travel lanes and wider shoulders are associated with higher capacity, higher operating speeds, and increased safety. For 3R projects, these two cross-section elements are discussed together, especially for two-lane facilities. They were also highly rated by the survey responders as critical criteria for 3R projects. In many cases, the 3R projects involve roads with lane (pavement) and shoul- der widths that are less than desirable. However, widen-

23 TABLE 13 MINIMUM LANE/SHOULDER WIDTHS FOR VERMONT 3R PROJECTS Design ADT NHS Non-NHS Rural Urban Rural Urban <10,000 11/3 12/2 9/1 12/2 ≥10,000 11/4 12/2 11/3 12/2 A relevant question for 3R projects is, “Given a fixed roadway width for two-lane, undivided, rural roads, which is safer—wider shoulders or wider lanes?” This question is particularly relevant to 3R projects because these projects are typically constrained to be within the existing ROW. If any geometric improvements are to be made for a specific project, one question to consider is whether it is more cost- effective to widen the lanes, with a corresponding reduction in shoulder width, or widen the shoulder, with a correspond- ing reduction in lane width. This question was the subject of a study by Gross et al. (15), who used geometric, traffic, and crash data for more than 44,500 miles of roadway seg- ments in Pennsylvania and 8,300 miles in Washington State to evaluate the safety effectiveness of lane-shoulder configu- rations for fixed total paved widths. The results from these two states were combined with two other relevant informa- tion sources on this topic: (1) the chapter on two-lane rural roads from the Highway Safety Manual (12), and (2) a report by Texas DOT (16). From these three sources, Gross et al. developed the Crash Modification Factors (CMF), which are graphically presented in Figure 3 in relation to a 36-ft base- line with 12-ft lanes and 6-ft shoulders. The general finding is that, given a fixed paved width, configurations with wide lanes and narrow shoulders are associated with a reduction in crashes. This finding supports the notion that, all things being equal, it is more important to keep the motorist on the travel lane than to provide more space for recovery at the expense of travel lane width. It also demonstrates that wider pavement widths (32 ft to 36 ft) are associated with fewer crashes than narrow pavement widths (26 ft to 30 ft). width. In TRB SR 214, there are two columns labeled “Com- bined Lane and Shoulder Width.” In preparing Table 12, it is assumed that the shoulder width is the combined lane and shoulder width minus the lane width. TABLE 11 3R DESIGN SPEED VERSUS POSTED SPEED (Florida DOT) Condition Establishing Proposed Project Design Speed (DSp) Case 1 Use the design speed used in original design of highway. DSp = DSo Case 2 Use the design speed used in original design of high- way unless a reduced design speed (not less than posted speed) is approved by the District Design Engineer and District Traffic Operations Engineer. DSp = DSo Case 3 Use the design speed used in original design of high- way unless there is a significant crash history associ- ated with a specific highway feature. If so, then the design speed used in correcting the feature shall be equal to or greater than the posted speed. The posted speed shall also be used as the design speed for any other new highway features (not replacements). DSp = DSo and DSp = PS (for design of features that are new or have a significant crash history) The review of the states’ design manuals on 3R revealed considerable variation for these two cross-section elements, not so much in the actual widths but in the conditions. Some states have one value for all road types and conditions, whereas several others have values that vary by ADT, speed, urban vs. rural, and road type. Vermont is an example of a state that has minimum values for lane and shoulder width that vary by ADT, rural vs. urban location, and NHS vs. non-NHS facility. Table 13 shows their values. In addition, Vermont’s guidelines state that all shoulder widths should be reviewed for accommo- dation of bicycle and pedestrian traffic according to its Pedes- trian and Bicycle Facility Planning and Design Manual. TABLE 12 MINIMUM LANE AND SHOULDER WIDTHS RECOMMENDED IN TRB SR 214 Volume/Speed 10 Percent or More Trucksa Less Than 10 Percent Trucks Design Year Volume (ADT) Running Speed (mph) Lane Width (ft) Shoulder Width (ft) Lane Width (ft) Shoulder Widthb (ft) 1–750 Under 50 10 2 9 2 50 and over 10 2 10 2 751–2,000 Under 50 11 2 10 2 50 and over 12 3 10 3 More than 2,000 All 12 6 11 6 a Trucks are defined as heavy vehicles with six or more tires. b One ft less for highways on mountainous terrain.

24 widened. This recommendation is included in FHWA Technical Advisory T 5040.28. Florida is one state that has a slightly higher guideline. Table 14 shows the clear width criteria for bridges to remain in place. TABLE 14 CLEAR WIDTH CRITERIA FOR BRIDGES (Florida) Design Year (ADT) Minimum Usable Bridge Width (ft) Undivided 0–750 Total width of approach lanes + 4 750+ Total width of approach lanes + 8 Divided ALL Total width of approach lanes + 5.5 (median separator)* Total width of approach lanes + 6.5 (median barrier wall)** One-Way Bridges ALL Total width of approach lanes + 6.5 (2.5 Lt. and 4.0 Rt.) *1.5 ft median and 4 ft outside shoulder. **2.5 ft median and 4 ft outside shoulder. Structural Capacity This design element refers to bridge structural capacity. Bridges are usually designed to accommodate either an H-15 or HS-20 loading. An H-15 loading is represented by a two- FIGURE 3 Selected CMFs from research and literature in relation to 36-ft baseline with 12-ft lanes and 6-ft shoulders [Source: Mahoney et al. 2006 (13)]. Bridge Width Quite often, especially for rural roads, the width of the bridge is less than the width of the approach roadway. The shoulders are often eliminated and the total travel lane width may be less than that of the approach roadway. This can be a safety hazard even if the bridge has adequate bridge rails and barriers. TRB SR 214 recommended that highway agen- cies evaluate bridge replacement or widening if the bridge is less than 100 ft long and the clear width of the bridge is less than the following values: Design Year Volume (ADT) Clear Bridge Width (ft) 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 More than 4,000 Width of approach lanes plus 6 ft The recommendation also stated that if lane widening is planned as part of the 3R project, the clear (the term used in TRB SR 214 is “usable,” which is the same as “clear,” the term used by AASHTO) bridge width should be compared with the planned width of the approaches after they are

25 Nearly every state’s design guidelines discuss their policy with regard to horizontal alignment, or specifically, hori- zontal curves. Some refer to the FHWA Technical Advisory and/or TRB SR 214, or have essentially the same information as contained in Recommendation No. 6. Georgia’s policy, shown in Table 15, is tied to the accident history of the exist- ing curve and the speed (presumably running speed, because not mentioned). TABLE 15 POLICY FOR HORIZONTAL ALIGNMENT FOR EXISTING FEATURES (Georgia) Condition Accident History Policy ≤10 mph below AASHTO guidelines Low, compared with statewide average Retain. The designer shall address and justify exist- ing features to be retained which do not meet 3R guidelines ≤10 mph below AASHTO guidelines Directly related accident history compared with statewide average Correct to AASHTO guidelines or to the high- est design speed practical >10 mph below AASHTO guidelines Not applicable Correct to AASHTO guideline if practicable. If not, correct to highest design practicable and request a design exception. Wisconsin’s Facility Development Manual provides the following for horizontal curves and superelevation: 1.5.3 Horizontal Curves and Superelevation Identify potentially hazardous curves through crash analysis and safety reviews. (See Attachment 1.7 [Figure 4] for a decision tree flow chart on the treatment of existing horizontal curves.) Evaluate these for reconstruction or application of other safety measures. Even if a location doesn’t have a high crash rate, improvements may still be desirable. Superelevation rates in excess of 8% shall be reduced to 8%, or less (see FDM 11-10-5). High hazard locations, regardless of AADT, need to be identified and corrected, as noted above. In addition, deficient horizontal curves or superelevation shall be upgraded on highways where the design traffic volume exceeds 750 AADT and where any of the following conditions exist: 1. If the existing curve radius equals or exceeds that required for the project design speed, but the superelevation is less than required, then increase the superelevation to the required rate. 2. If the existing curve radius is less than, but within 15 mph of, that required for the project design speed, but the superelevation is less than e max, then increase the superelevation to the e max rate (see FDM 11-10-5). axle single-unit truck weighing 15 tons with 2 tons on its steering axle and 12 tons on its drive axle. An HS-20 loading is represented by a three-axle semitrailer combination weigh- ing 36 tons with 4 tons on its steering axle, 16 tons on its drive axle, and 16 tons on the semitrailer axle. The “20” is 20 tons for the 4 tons on steering axle and 16 tons on the drive axle. The “S” stands for semitrailer combination, which adds in the additional 16 tons for the third axle to give a total of 36 tons. Many states do not mention structural capacity in their 3R guidelines. Examples of states that do have a structural capacity requirement include the following: • Alaska—If structural capacity is less than HS-15, replace member. • Georgia—Retained bridges must have HS-15 capacity. • Florida—Bridges on collector facilities are to have an HS-15 capacity and HS-20 on arterial facilities. • Ohio—Bridges on expressways and arterials are to have minimum design capacity of HS-20; all other roads are to be HS-15, except that local roads with ADTs of 50 or less can have an HS-10 capacity. Horizontal Alignment and Superelevation In terms of the 13 controlling criteria, horizontal alignment refers only to the horizontal curvature of the roadway. The adopted design criteria specify a minimum radius for the selected design speed, which is calculated from the maxi- mum rate of superelevation (set by policy from a range of options) and the side friction factor (established by policy through research). Although superelevation is considered a separate criterion, it is often discussed in relation to hori- zontal curvature. Horizontal alignment influences stopping sight distance, another primary controlling criterion. TRB SR 214 has two recommendations regarding hori- zontal curvature (and superelevation): • Recommendation No. 6. Highway agencies should increase the superelevation of horizontal curves when the design speed of an existing curve is below the running speeds (85th percentile speed is to be used for this comparison) of approaching vehicles and the existing superelevation is below the allowable maximum 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 running speeds of approaching vehicles (assuming improved superelevation cannot reduce this difference below 15 mph) and the average daily traffic volume is greater than 750 vehicles per day. • Recommendation No. 7. At horizontal curves where reconstruction is unwarranted, highway agencies should evaluate less costly safety measures such as widening lanes, widening and paving shoulders, flattening steep sideslopes, removing or relocating roadside obstacles, and installing traffic control devices.

26 TRB SR 214 makes the following recommendation with regard to vertical curvature and stopping sight distance: Recommendation No. 8: 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 vehicles per day; and (c) the design speed of the hill crest (based on minimum stopping sight distance) is more than 20 mph below the running speeds (85th percentile) of vehicles on the crest. The review of the states’ design policies for this feature shows that most states have stated guidelines, with several following TRB SR 214. Several states note that improvement to a vertical curve is determined by its safety record. Utah includes the TRB SR 214 recommendation, and summarizes its policy as shown Table 16. Georgia DOT uses the same guideline used for horizontal alignment, which was shown in Table 15. Stopping Sight Distance Stopping sight distance is an important design criterion for safety. The longitudinal sight distance provided along the road will determine a driver’s ability to stop to avoid an object in the road given the vehicle speed. AASHTO’s Green Book provides minimum stopping sight distance based on design speed and grade. 3. If the existing curve radius is less than, and not within 15 mph of that required for the project design speed, then realign the curve. Curve realignment, when warranted, is desirably to new construction standards, but as a minimum shall provide a design speed through the curve that is within 10 mph of the overall project design speed. Proposed curve or superelevation modifications that aren’t warranted, as described above, will desirably be consistent with adjacent sections of road, and will minimally not reduce the existing curve speed rating. If a deficient curve is either not reconstructed or is reconstructed to less than new construction standards, then apply appropriate safety mitigation measures. Vertical Alignment In terms of the 13 controlling criteria, vertical alignment includes only vertical curvature (both crest and sag). Grade is considered separately and discussed below. As horizon- tal curves are to horizontal alignment, vertical curves are to vertical alignment. Vertical curvature influences stop- ping sight distance, another primary controlling criterion. The geometric design basis for minimum length of crest vertical curvature is to provide the minimum stopping sight distance for the combination of grades and design speed. Sag vertical curves are normally designed so that the curve does not restrict the distance of roadway illumi- nated by vehicle headlights, which would reduce stopping sight distance at night. *Accelerated Design Process Can Be Used for **e.g., -Curve Hidden From View by Crest of Hill - Sharp Curve in a Series of Gentle Curves - Compound Curve - Sight Distance Deficiency Due to Horizontal. ***This Needs to Be Done Unless There Is an Approved Exception to Standards or a Programmatic Exception to Standards (PESR) (see Accelerated Design Process).

27 Crest vertical curves should be evaluated for reconstruc- tion when: • The design speed of the curve (based on stopping sight distance) is more than 20 mph below the project design speed, and • The design year ADT is greater than 1,500 vehicles per day. Florida simply provides a table showing its requirements for stopping sight distance (see Table 17). FIGURE 4 Decision tree for treatment of existing horizontal curves. Because stopping sight distance is integral to horizontal and vertical alignment, many states discuss it within these two alignment features. For example, Wisconsin has the fol- lowing guideline for crest vertical curves that is based on stopping sight distance: All crest vertical curves with an existing design speed based on stopping sight distance provided, not within 15 mph of the overall project design speed shall be upgraded on highways with a design traffic volume over 1,500 AADT. Alabama has a similar guideline:

28 maximum being 2.5% (e.g., Alabama and Georgia) or 3.0% (e.g., Utah and New York). Wisconsin specifies that when 3R projects include new pavement or pavement resurfacing, a 2% pavement cross slope should be provided. However, a 1.5% cross slope may be provided when resurfacing port- land cement concrete pavements that have a cross slope of 1% or flatter. Some states provide cross slope values for shoulders. For example, New York specifies a minimum of 2% to 8% maxi- mum and even specifies values for parking lanes on urban facilities—1.5% minimum to 5% maximum. Grades The grade of the road can affect operating speed, especially for trucks and other large vehicles. Steep grades can have deleterious effects on safety, especially on downgrades. According to the Green Book, maximum grades of about 5% are considered appropriate for a design speed of 70 mph and 7% to 12% for a design speed of 30 mph. The terrain plays a major factor in the grade provided. Most of the states do not mention grade requirements for 3R projects. It was ranked as the least important design cri- terion. Some states that do mention grades in their 3R policy state that the existing grade should remain unless there is an identified safety problem associated with the section and the improvement can be made cost-effectively. When the grade has to be reduced for safety or operational reasons, it usually requires significant reconstruction, which moves the project out of the 3R program. Horizontal Clearance (Other Than Clear Zone) The requirement for horizontal clearance is sometimes con- fused with clear zone. Horizontal clearance is defined as the lateral distance (offset) from the edge of the travel lane to a roadside feature or object, such as curbs, walls, barri- ers, bridge piers, sign and signal supports, trees, and utility poles. This is not the same as clear zone. Clear zone is a clear recovery area, free of rigid obstacles and steep slopes, that allows vehicles that have run off the road to safely recover or come to a stop. While horizontal clearance can be thought TABLE 16 VERTICAL CURVE IMPROVEMENT GUIDELINE (Utah DOT) Design Speed (D.S.) > AADT > Lower than Project D.S. <1,500 VPD Lower than Project D.S. >1,500 VPD Within 20 mph of Project D.S. < 1,500 VPD Within 20 mph of Project D.S. >1,500 VPD Alignment * MI/R R M MI/R M = Mitigate for existing substandard design elements. MI = Minor design improvements other than reconstruction. R = Reconstruct vertical curve to current UDOT standards based on cost/benefit analysis. * High-accident locations must be analyzed for reconstruction to current UDOT standards. TABLE 17 STOPPING SIGHT DISTANCE REQUIRED FOR 3R PROJECTS IN FLORIDA Design Speed (mph) Stopping Sight Distance (ft) 15 80 20 115 25 155 30 200 35 250 40 305 45 360 50 425 55 495 60 570 65 645 Cross Slope Typically, the pavement surface is sloped slightly to facilitate water drainage. For undivided road on tangents or flat curves, there is a crown or high point at the middle and a cross slope downward toward both edges. On divided multilane roads, the cross slope can be sloped either one way across the travel lanes or two ways. Normal travel way cross slopes range from 1.5% to 2% for paved surfaces (any asphalt or con- crete type surface) and 2% to 6.5% for unpaved surfaces (earth, gravel, or crushed stone). If the slope is too small water will stand on the pavement, but if the slope is too large it can affect vehicle tracking. On curved sections, the cross slope essentially becomes the superelevation and the speed- curvature relationships determine the required slope. For 3R projects, there are two concerns—the existing pavement may have inappropriate cross slopes (or superelevation), and the resurfacing could change the cross slope (superelevation) from adequate to inadequate if not done properly. The review of many state design manuals showed that several did not discuss cross slope. For those that did, several simply stated that the minimum should be 1.5%, with the

29 of as an operational offset, the clear zone primarily serves a substantive safety function. Few states provide guidance on this design feature for 3R projects. An exception is Florida, which provides guidance for horizontal clearances for traffic control signs, light poles, utility installations, signal poles and trees (see Chapter 25 of the Florida DOT’s Plans Preparation Manual). Vertical Clearance Vertical clearance is the distance from the top of the pave- ment (at the highest elevation) to the bottom of the overhead structure, usually a bridge overpass for another road or rail- road, or possibly a sign truss or pedestrian bridge. If a new layer of pavement surfacing is placed over the existing sur- face, the clearance will decrease by the depth of the resur- facing, which could be an inch or more. This will decrease the vertical clearance accordingly, so it should be taken into consideration for 3R projects. Also, the existing road may already have an overpass structure that does not meet mini- mum vertical clearance standards. Only a few states discuss vertical clearance in their 3R policy. Those that do cite 14 ft as a minimum for keeping a structure as is, and as low as 13.5 ft for non-NHS routes. Oklahoma requires 14 ft 6 in. for existing bridges on state highways and 14 ft for nonstate highways for 3R projects. Indiana requires 17 ft minimum for existing sign trusses or pedestrian bridges. OTHER DESIGN CRITERIA One of the survey questions asked whether the states felt that other design features beyond the 13 controlling criteria should be considered. The responses to that question are presented in Table 8. Many design elements were suggested, with the highest responses related to roadside elements including clear zone, guardrail upgrades, and crashworthy roadside features. Clear Zone and Side Slope The review of the states’ design documents showed that sev- eral states have guidelines for roadside elements, with at least 18 states providing clear zone guidance. The guidelines for clear zone vary from specific values to general statements of the desirability of adequate clear zone. For example, Mis- sissippi’s design manual for 3R projects notes that providing full clear zone for 3R projects can be difficult to achieve, and therefore the designer must exercise considerable judgment when determining the appropriate clear zone. Factors to be considered in that judgment include the following: • Accident data – specifically, clusters of run-off-the- road accidents. • Utilities – relocation is mandatory when the poles physically interfere with construction, but relocations for safety benefits must be evaluated on a project-by- project basis. • Application – selective application of the roadside clear zone criteria may be appropriate, depending upon the nature of the hazards. • Public – the community impact should be considered, especially when it involves tree removal. • Safety appurtenances – installing barriers or impact attenuators is an alternative to providing a clear zone. In addition to this general guidance, Mississippi provides a table for recommended clear zone distances that are based on design speed, design ADT groups, and side slope for both fill and back slopes. Ohio’s guideline states that “on 3R improvements, unless accident history, public complaint or site inspections indi- cate a problem, it may not be cost effective to fully comply with the clear zone requirements for new construction [refer- ence is made to a figure that is in compliance with the guid- ance provided in the Roadside Design Guide]. Therefore, the clear zone criteria shown [in the referenced figure] may be reduced by 50% on 3R improvements.” West Virginia has different design guidance for clear zone for NHS and non-NHS routes. For NHS multilane highways, the minimum clear zone is to be that stipulated in the RDG. Separate values are provided for two-lane rural and urban highways. For non-NHS highways, there are no set clear zone width values. The mountainous terrain of West Vir- ginia makes it difficult to provide a clear zone. It is acknowl- edged that a policy that requires a statewide uniform clear zone distance would be neither practical nor effective. Side slopes are relevant to the provision of clear zone; hence, several states refer to the need for flattening steep side slopes. Florida’s guidance on side slopes is listed below: Front slopes: 1. 1:6 are desirable. 2. 1:4 may be constructed within the clear zone. 3. 1:3 may be constructed outside the clear zone. 4. Existing front slopes 1:3 or flatter may remain within the clear zone. Shielding may be required. 5. Steeper than 1:3 shall be shielded. 6. Consideration should be given to flattening slopes of 1:3 or steeper at locations where run-off-the-road type crashes are likely to occur (e.g. on the outsides of horizontal curves). 7. The proposed construction should not result in slopes steeper than the existing slopes in violation of the above values.

30 of an urban area. Within its Plans Preparation Manual, Florida provides a considerable discussion of providing for pedestrian, bicyclist, and transit needs. As with most states, Florida’s guidelines call for meeting ADA require- ments on detectable warnings and curb ramps. For bicyclist needs, Florida has guidance for providing space within the travel way for bicycles; bicycle lanes at right-turn lanes; and proper treatment of drainage inlets, grates, and utility cov- ers. Under transit needs, it states that a 5-ft-wide sidewalk that connects a transit stop or facility with an existing side- walk or shared use path shall be included to comply with ADA accessibility standards. Other Considerations Many states include guidance for other design features for 3R projects. A partial list of those features includes intersec- tions, drainage, railroad grade crossings, highway lighting, signing and markings, and utilities. Back Slopes: 1. 1:4 are desirable. 2. 1:3 may be constructed in the clear zone. 3. 1:2 may be constructed outside the clear zone without shielding. 4. Existing back slopes 1:2 and flatter may remain. 5. Existing back slopes steeper than 1:3 within the clear zone may require shielding. Pedestrian and Bicycle Accommodations Most states have guidelines for making improvements to accommodate pedestrians and bicycles as part of 3R proj- ects. Florida noted that according to its state statute, it must fully consider pedestrian and bicycle ways in every transportation project, especially those in or within 1 mile