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Guidelines for Integrating Safety and Cost-Effectiveness into Resurfacing, Restoration, and Rehabilitation (3R) Projects (2018)

Chapter: Chapter 6. 3R Project Design Guidelines for Specific Roadway Types

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Suggested Citation:"Chapter 6. 3R Project Design Guidelines for Specific Roadway Types." National Academies of Sciences, Engineering, and Medicine. 2018. Guidelines for Integrating Safety and Cost-Effectiveness into Resurfacing, Restoration, and Rehabilitation (3R) Projects. Washington, DC: The National Academies Press. doi: 10.17226/25206.
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Suggested Citation:"Chapter 6. 3R Project Design Guidelines for Specific Roadway Types." National Academies of Sciences, Engineering, and Medicine. 2018. Guidelines for Integrating Safety and Cost-Effectiveness into Resurfacing, Restoration, and Rehabilitation (3R) Projects. Washington, DC: The National Academies Press. doi: 10.17226/25206.
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Suggested Citation:"Chapter 6. 3R Project Design Guidelines for Specific Roadway Types." National Academies of Sciences, Engineering, and Medicine. 2018. Guidelines for Integrating Safety and Cost-Effectiveness into Resurfacing, Restoration, and Rehabilitation (3R) Projects. Washington, DC: The National Academies Press. doi: 10.17226/25206.
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Suggested Citation:"Chapter 6. 3R Project Design Guidelines for Specific Roadway Types." National Academies of Sciences, Engineering, and Medicine. 2018. Guidelines for Integrating Safety and Cost-Effectiveness into Resurfacing, Restoration, and Rehabilitation (3R) Projects. Washington, DC: The National Academies Press. doi: 10.17226/25206.
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Suggested Citation:"Chapter 6. 3R Project Design Guidelines for Specific Roadway Types." National Academies of Sciences, Engineering, and Medicine. 2018. Guidelines for Integrating Safety and Cost-Effectiveness into Resurfacing, Restoration, and Rehabilitation (3R) Projects. Washington, DC: The National Academies Press. doi: 10.17226/25206.
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Suggested Citation:"Chapter 6. 3R Project Design Guidelines for Specific Roadway Types." National Academies of Sciences, Engineering, and Medicine. 2018. Guidelines for Integrating Safety and Cost-Effectiveness into Resurfacing, Restoration, and Rehabilitation (3R) Projects. Washington, DC: The National Academies Press. doi: 10.17226/25206.
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Suggested Citation:"Chapter 6. 3R Project Design Guidelines for Specific Roadway Types." National Academies of Sciences, Engineering, and Medicine. 2018. Guidelines for Integrating Safety and Cost-Effectiveness into Resurfacing, Restoration, and Rehabilitation (3R) Projects. Washington, DC: The National Academies Press. doi: 10.17226/25206.
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Suggested Citation:"Chapter 6. 3R Project Design Guidelines for Specific Roadway Types." National Academies of Sciences, Engineering, and Medicine. 2018. Guidelines for Integrating Safety and Cost-Effectiveness into Resurfacing, Restoration, and Rehabilitation (3R) Projects. Washington, DC: The National Academies Press. doi: 10.17226/25206.
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Suggested Citation:"Chapter 6. 3R Project Design Guidelines for Specific Roadway Types." National Academies of Sciences, Engineering, and Medicine. 2018. Guidelines for Integrating Safety and Cost-Effectiveness into Resurfacing, Restoration, and Rehabilitation (3R) Projects. Washington, DC: The National Academies Press. doi: 10.17226/25206.
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Suggested Citation:"Chapter 6. 3R Project Design Guidelines for Specific Roadway Types." National Academies of Sciences, Engineering, and Medicine. 2018. Guidelines for Integrating Safety and Cost-Effectiveness into Resurfacing, Restoration, and Rehabilitation (3R) Projects. Washington, DC: The National Academies Press. doi: 10.17226/25206.
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Suggested Citation:"Chapter 6. 3R Project Design Guidelines for Specific Roadway Types." National Academies of Sciences, Engineering, and Medicine. 2018. Guidelines for Integrating Safety and Cost-Effectiveness into Resurfacing, Restoration, and Rehabilitation (3R) Projects. Washington, DC: The National Academies Press. doi: 10.17226/25206.
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Suggested Citation:"Chapter 6. 3R Project Design Guidelines for Specific Roadway Types." National Academies of Sciences, Engineering, and Medicine. 2018. Guidelines for Integrating Safety and Cost-Effectiveness into Resurfacing, Restoration, and Rehabilitation (3R) Projects. Washington, DC: The National Academies Press. doi: 10.17226/25206.
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Suggested Citation:"Chapter 6. 3R Project Design Guidelines for Specific Roadway Types." National Academies of Sciences, Engineering, and Medicine. 2018. Guidelines for Integrating Safety and Cost-Effectiveness into Resurfacing, Restoration, and Rehabilitation (3R) Projects. Washington, DC: The National Academies Press. doi: 10.17226/25206.
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Suggested Citation:"Chapter 6. 3R Project Design Guidelines for Specific Roadway Types." National Academies of Sciences, Engineering, and Medicine. 2018. Guidelines for Integrating Safety and Cost-Effectiveness into Resurfacing, Restoration, and Rehabilitation (3R) Projects. Washington, DC: The National Academies Press. doi: 10.17226/25206.
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Suggested Citation:"Chapter 6. 3R Project Design Guidelines for Specific Roadway Types." National Academies of Sciences, Engineering, and Medicine. 2018. Guidelines for Integrating Safety and Cost-Effectiveness into Resurfacing, Restoration, and Rehabilitation (3R) Projects. Washington, DC: The National Academies Press. doi: 10.17226/25206.
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Suggested Citation:"Chapter 6. 3R Project Design Guidelines for Specific Roadway Types." National Academies of Sciences, Engineering, and Medicine. 2018. Guidelines for Integrating Safety and Cost-Effectiveness into Resurfacing, Restoration, and Rehabilitation (3R) Projects. Washington, DC: The National Academies Press. doi: 10.17226/25206.
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Suggested Citation:"Chapter 6. 3R Project Design Guidelines for Specific Roadway Types." National Academies of Sciences, Engineering, and Medicine. 2018. Guidelines for Integrating Safety and Cost-Effectiveness into Resurfacing, Restoration, and Rehabilitation (3R) Projects. Washington, DC: The National Academies Press. doi: 10.17226/25206.
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Suggested Citation:"Chapter 6. 3R Project Design Guidelines for Specific Roadway Types." National Academies of Sciences, Engineering, and Medicine. 2018. Guidelines for Integrating Safety and Cost-Effectiveness into Resurfacing, Restoration, and Rehabilitation (3R) Projects. Washington, DC: The National Academies Press. doi: 10.17226/25206.
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Suggested Citation:"Chapter 6. 3R Project Design Guidelines for Specific Roadway Types." National Academies of Sciences, Engineering, and Medicine. 2018. Guidelines for Integrating Safety and Cost-Effectiveness into Resurfacing, Restoration, and Rehabilitation (3R) Projects. Washington, DC: The National Academies Press. doi: 10.17226/25206.
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Suggested Citation:"Chapter 6. 3R Project Design Guidelines for Specific Roadway Types." National Academies of Sciences, Engineering, and Medicine. 2018. Guidelines for Integrating Safety and Cost-Effectiveness into Resurfacing, Restoration, and Rehabilitation (3R) Projects. Washington, DC: The National Academies Press. doi: 10.17226/25206.
×
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Suggested Citation:"Chapter 6. 3R Project Design Guidelines for Specific Roadway Types." National Academies of Sciences, Engineering, and Medicine. 2018. Guidelines for Integrating Safety and Cost-Effectiveness into Resurfacing, Restoration, and Rehabilitation (3R) Projects. Washington, DC: The National Academies Press. doi: 10.17226/25206.
×
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Suggested Citation:"Chapter 6. 3R Project Design Guidelines for Specific Roadway Types." National Academies of Sciences, Engineering, and Medicine. 2018. Guidelines for Integrating Safety and Cost-Effectiveness into Resurfacing, Restoration, and Rehabilitation (3R) Projects. Washington, DC: The National Academies Press. doi: 10.17226/25206.
×
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Suggested Citation:"Chapter 6. 3R Project Design Guidelines for Specific Roadway Types." National Academies of Sciences, Engineering, and Medicine. 2018. Guidelines for Integrating Safety and Cost-Effectiveness into Resurfacing, Restoration, and Rehabilitation (3R) Projects. Washington, DC: The National Academies Press. doi: 10.17226/25206.
×
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Suggested Citation:"Chapter 6. 3R Project Design Guidelines for Specific Roadway Types." National Academies of Sciences, Engineering, and Medicine. 2018. Guidelines for Integrating Safety and Cost-Effectiveness into Resurfacing, Restoration, and Rehabilitation (3R) Projects. Washington, DC: The National Academies Press. doi: 10.17226/25206.
×
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Suggested Citation:"Chapter 6. 3R Project Design Guidelines for Specific Roadway Types." National Academies of Sciences, Engineering, and Medicine. 2018. Guidelines for Integrating Safety and Cost-Effectiveness into Resurfacing, Restoration, and Rehabilitation (3R) Projects. Washington, DC: The National Academies Press. doi: 10.17226/25206.
×
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Suggested Citation:"Chapter 6. 3R Project Design Guidelines for Specific Roadway Types." National Academies of Sciences, Engineering, and Medicine. 2018. Guidelines for Integrating Safety and Cost-Effectiveness into Resurfacing, Restoration, and Rehabilitation (3R) Projects. Washington, DC: The National Academies Press. doi: 10.17226/25206.
×
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Suggested Citation:"Chapter 6. 3R Project Design Guidelines for Specific Roadway Types." National Academies of Sciences, Engineering, and Medicine. 2018. Guidelines for Integrating Safety and Cost-Effectiveness into Resurfacing, Restoration, and Rehabilitation (3R) Projects. Washington, DC: The National Academies Press. doi: 10.17226/25206.
×
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Suggested Citation:"Chapter 6. 3R Project Design Guidelines for Specific Roadway Types." National Academies of Sciences, Engineering, and Medicine. 2018. Guidelines for Integrating Safety and Cost-Effectiveness into Resurfacing, Restoration, and Rehabilitation (3R) Projects. Washington, DC: The National Academies Press. doi: 10.17226/25206.
×
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Suggested Citation:"Chapter 6. 3R Project Design Guidelines for Specific Roadway Types." National Academies of Sciences, Engineering, and Medicine. 2018. Guidelines for Integrating Safety and Cost-Effectiveness into Resurfacing, Restoration, and Rehabilitation (3R) Projects. Washington, DC: The National Academies Press. doi: 10.17226/25206.
×
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Suggested Citation:"Chapter 6. 3R Project Design Guidelines for Specific Roadway Types." National Academies of Sciences, Engineering, and Medicine. 2018. Guidelines for Integrating Safety and Cost-Effectiveness into Resurfacing, Restoration, and Rehabilitation (3R) Projects. Washington, DC: The National Academies Press. doi: 10.17226/25206.
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105 Chapter 6. 3R Project Design Guidelines for Specific Roadway Types This chapter presents design guidelines for 3R projects. The design guidelines are based on explicit consideration of crash reduction effectiveness estimates for design improvements, where available, and on the use of before-after benefit-cost analysis tools. The design guidelines are organized by roadway type and, within roadway type, by design element. 6.1 Rural Two-Lane Highways 6.1.1 Lane Widening Lane widening should be considered for each 3R project on a rural two-lane highway with existing lane widths less than 12 ft. Decisions about lane widening for 3R projects should be based on benefit-cost analysis. Lane widening is a desirable investment only where the analysis indicates that the expected crash reduction benefits from lane widening will exceed the improvement costs or a crash analysis finds existing crash patterns that can potentially be reduced by lane widening. Where there are no existing crash patterns that can potentially be reduced by lane widening and the expected crash reduction benefits from lane widening are less than the improvement cost, lane widening would be a poor investment and available funds would be better invested at another location where the crash reduction benefits would be larger. Two benefit-cost analysis approaches are applicable to lane widening. The most desirable approach (Option 1) for cost-effective lane widening decisions is to conduct a site-specific benefit-cost analysis for each individual 3R project. Site-specific benefit-cost analyses are desirable because even nominally similar sites may differ in roadway characteristics, traffic volumes, crash history, and improvement costs, such that lane widening may be cost-effective at one site and not at another. The crash reduction effectiveness of lane widening on rural two-lane highways is documented in Section 4.3.1.1. Procedures for site-specific benefit-cost analysis are illustrated in Section 5.2.2. The benefit-cost analysis tool provided with these guidelines enables site-specific benefit-cost analyses to be performed efficiently. The example presented below illustrates the application of Spreadsheet Tools 1 and 2 for site- specific benefit-cost analysis of lane widening. The example shows a rural two-lane highway with existing 9-ft lanes for which the alternative with the maximum net benefit is to widen the lanes to 11 ft. It should be noted that the HSM Chapter 10 (2) crash prediction procedures show that the benefits of lane widening from 11 to 12 ft on rural two-lane highways is relatively small. Therefore, widening narrower lanes to 11 ft will often be the most cost-effective improvement for rural two-lane highways. Widening to 12 ft lanes may only be the most cost-effective improvement for roads with relatively high traffic volumes.

Existing Section L AADT Terrain Pavemen Lane Wid Shoulder Shoulder Roadside Centerlin Shoulder Crash Hi Number Maximum Design S Horizon Curve 1 2 Benefit-C Widening roadway roadway Evaluati Tool 2 ca shown be Improv Wid 1 1 1 1 1 Conditions ength t Type th Width Type Slope e Rumble Strip Rumble Strip story of Curves in Ro Superelevatio peed tal Curve (m 0.1 0.1 ost Evaluatio the existing 9 characteristics section, the la on of a Full Ra n be used to e low, indicate t ed Lane th (ft) 1.0 1.5 2.0 0.5 0.0 9.5 Lane Wi adway Sectio n Rate Length i) Rad 56 4 25 n Results for -ft lanes to 11 . Thus, if lane ne width to be nge of Lane valuate all lan hat widening to Net Benefit ( $97,701 $92,159 $86,617 $62,114 $26,527 $1,305 dening on R n ius (ft) Pres 00 600 Widening to ft produces the widening was widened to sho Widening Sce e widening pos 11-ft lanes pr $) B/ 106 ural Two-L 1.000 mi 2,000 veh/ Level Flexible 9.0 ft 2 ft Unpaved 1V:2H No No No 2 8% 55 mph ence of Spiral No No 11-ft lanes fro highest net b being consider uld be 11 ft to narios with T sibilities at one ovides the larg C Ratio 2.120 1.894 1.729 1.870 1.477 1.033 ane Highw day Transitions m Tool 1 enefit for a rura ed for inclusio get the highes ool 2 time. The res est net benefi Total Benef $184,91 $195,20 $205,48 $133,50 $82,09 $41,04 ays Existing Su Rate 2 3 l two-lane hig n in a 3R proje t return on inv ults of the Too t. it ($) To 7 0 2 6 4 7 perelevation (%) .4 .8 hway with thes ct on this estment. l 2 analysis, tal Cost ($) $87,216 $103,041 $118,865 $71,391 $55,567 $39,742 e

107 A less desirable, but still acceptable, approach (Option 2) for cost-effective lane widening decisions in 3R projects is to develop agency-specific guidelines for minimum traffic volumes that justify lane widening, analogous to the example shown in Table 37. Minimum traffic volume guidelines analogous to Table 37 can be developed by each highway agency (or in some cases by individual districts or regions within a highway agency) as a basis for lane widening decisions. Section 5.4 illustrates procedures for developing minimum traffic volume guidelines like Table 37. The example benefit-cost analysis to develop minimum AADT guidelines, whose results presented in Table 37, shows that lane widening to 12 ft is likely to be cost-effective for 3R projects on rural two-lane highways with existing lane widths of 10 ft or less with traffic volumes greater than approximately 3,000 to 4,000 veh/day, even for projects in level terrain that generally cost less to implement than projects in rolling or mountainous terrain. On rural two- lane highways with lower traffic volumes, lane widening would not be cost-effective and, therefore, should not be considered unless a site-specific crash pattern that indicates a need for lane widening is present. Lane widening to 12 ft is likely to be cost-effective for 3R projects on rural two-lane highways with existing lane widths of 11 ft only for traffic volumes of approximately 16,000 veh/day or more, even in level terrain. Higher traffic volumes are needed to justify widening of existing 11-ft lanes because HSM Chapter 10 (2) indicates that the differences in crash frequency between rural two-lane highways with 11- and 12-ft lanes are relatively small. The traffic volumes thresholds presented above are merely examples, since the results of benefit-cost analyses can vary from site to site and from agency to agency based on roadway characteristics, crash history, and improvement cost levels. Highway agencies also differ in the crash cost values used in benefit-cost analyses. For this reason, Table 37 is not intended for direct application, but tables analogous to Table 37 can be developed by individual highway agencies, following the procedures in Section 5.4. 6.1.2 Shoulder Widening and Paving Shoulder widening should be considered for each 3R project on a rural two-lane highway with existing shoulder widths less than 6 ft. Decisions about shoulder widening for 3R projects should be based on benefit-cost analysis, and shoulder widening is a desirable investment only where the analysis indicates that the expected crash reduction benefits from shoulder widening will exceed the improvement costs or a crash analysis finds existing crash patterns that can potentially be reduced by shoulder widening. Where there are no existing crash patterns that can potentially be reduced by shoulder widening and the expected crash reduction benefits from shoulder widening are less than the improvement cost, shoulder widening would be a poor investment and available funds would be better invested at another location where the crash reduction benefits would be larger. Two benefit-cost analysis approaches are applicable to shoulder widening analysis. The most desirable approach (Option 1) for cost-effective shoulder widening decisions is to conduct a site- specific benefit-cost analysis for each individual 3R project. Site-specific benefit-cost analyses are desirable because even nominally similar sites may differ in roadway characteristics, traffic volumes, crash history, and improvement costs, such that shoulder widening may be cost-

effective on rural t benefit-c these gui A less de decisions that justif volume g cases by widening guideline Benefit-c to consid shoulder still acce Benefit-C Using the to find wh shoulder Evaluati Tool 2 ca shown be Improved Wid at one site a wo-lane hig ost analysis delines enab sirable, but in 3R proje y shoulder w uidelines an individual d decisions. S s like Table ost analyses er whether t paving alter ptable appro ost Evaluatio same rural tw at width to wid s to 8 ft produc on of a Full Ra n be employed low, indicate t Shoulder th (ft) 8 7 6 5 4 3 nd not at an hways is do are illustrate les site-spec still accepta cts is to dev idening, an alogous to T istricts or re ection 5.4 i 38. can also be he shoulder natives for e ach is to det Shoulder W n Results for o-lane highwa en the should es the highest nge of Shoul to analyze al hat widening to Net Benefit ( $88,882 $68,943 $49,004 $26,899 $5,130 -$18,779 other. The c cumented in d in Section ific benefit- ble, approac elop agency alogous to t able 38 can gions within llustrates pr applied to r should be p ach shoulde ermine the o idening o Widening to y section used ers to in order net benefit, sh der Widening l shoulder wide 8-ft shoulders $) B/C 1 1 1 1 1 0 108 rash reducti Section 4.3 5.2.2. The cost analyse h (Option 2 -specific gu he example be develop a highway ocedures for ural two-lan aved. The m r width alte ptimal shou n Rural Tw 8-ft Shoulders in the previou to produce the own in the foll Scenarios w ning scenarios provides the Ratio T .875 .751 .598 .373 .082 .642 on effective .1.2. Proced benefit-cost s to be perf ) for cost-ef idelines for shown in T ed by each h agency) as developing e highway s ost desirabl rnative eval lder width o-Lane Hig from Tool 1 s lane widenin highest net be owing results. ith Tool 2 at one time. T largest net ben otal Benefit ($ $190,508 $160,746 $130,984 $99,056 $67,465 $33,732 ness of shou ures for site analysis too ormed effic fective shou minimum tr able 38. Min ighway age a basis for sh minimum t ites with un e approach uated. A les for the proje hways g example, To nefit. Widenin he result of th efit. ) Total $10 $9 $8 $7 $6 $5 lder wideni -specific l provided w iently. lder widenin affic volum imum traffi ncy (or in s oulder raffic volum paved shou is to conside s desirable, ct and then ol 1 can be us g the unpaved e Tool 2 analy Cost ($) 1,627 1,804 1,981 2,157 2,334 2,511 ng ith g es c ome e lders r but ed sis,

evaluate that utiliz levels. N projects w 6.1.3 H Horizont some cas value in t that there Spreadsh improvem Tool 1 is Realignm as part of therefore so their s Realignm as recons 6.1.4 Si Stopping respondin distance This exam Section 6 superelev determin as if the 8.0%. Th exceedin whether the e paved sho othing in the here the ag orizontal C al curve imp es. Where th he AASHTO will be a sa eet Tool 1 c ents. An ex presented b ent of an is a 3R projec , lengthenin afety benefi ent of mult truction and ght Distan sight distan g to situatio limitations m Sup ple considers .1.1. This exa ation rates tha e if improving s benefit outweig e Tool 1 result g 8 and a net b shoulder sh ulders only se guideline ency’s desig urve Impr rovements o e superelev Green Bo fety benefit an be used t ample of be elow. olated horiz t. Typically g the curve. ts would nee iple horizon , therefore, ce Improv ce (SSD) is ns on the ro ay include erelevation the same rura mple segment t are less than uperelevation hs the implem s indicate that enefit of $32,5 ould be pave for specific s requires a n policy ca ovements n rural two ation of an e ok (4) by mo from restor o assess the nefit-cost a ontal curve o , such an im The spreads d to be asse tal curves on out of the sc ements provided alo adway ahea crest vertica Improvem l two-lane high contains two h superelevatio rates to Green entation cost. the supereleva 38. 109 d. Many hig roadway typ highway ag lls for unpav -lane highw xisting curv re than 1 pe ing the supe cost-effectiv nalysis for a n a rural tw provement w heet tools d ssed with th a roadway ope of 3R im ng roadway d that may r l curves or o ent on Rur way segment orizontal curve n rates recom Book recomm For both curve tion improvem hway agen es or above ency to pro ed shoulder ays may be e is less tha rcent, HSM relevation to eness of su superelevat o-lane high ould invol o not addres e HSM Cha section wou provement s to assist d equire drive bjects on th al Two-Lan considered in s. These two c mended in the ended rates p s, the improve ent is cost effe cies have de specific tra vide paved s s. considered 3 n the design Chapter 10 the Green ch superelev ion improve way can also ve flattening s improvem pter 10 proc ld generally s. rivers in det rs to slow o e inside of h e Highway the land widen urves have ex Green Book. T roduces a safe d superelevatio ctive with a be sign policie ffic volume houlders on R projects i supereleva (2) indicate Book value. ation ment using be conside the radius a ents of this edures. be conside ecting and r stop. Sigh orizontal ing example in isting ool 1 is used ty benefit as w n rate will be nefit-cost ratio s n tion s red nd, type, red t to ell

110 curves. The SSD design criteria used by most states are based on the SSD values in the AASHTO Green Book (4). Recent research (5) has shown that limited SSD on rural two-lane highways is unlikely to lead to crashes unless the portion of the roadway hidden from the driver’s view by the sight distance limitation includes a roadway feature where drivers need to take steering or braking action, such as an intersection, a driveway, or a horizontal curve. Where an area with SSD less than the Green Book SSD design criteria is present on a rural two-lane highway, but there are no hidden features such as intersections, driveways, or horizontal curves and no history of crashes related to limited SSD, sight distance improvements are unlikely to have any effect on crash frequency or severity, are, therefore, unlikely to be cost-effective, and need not be considered in 3R projects. By contrast, where a portion of the highway has SSD less than the Green Book SSD design criteria, and an intersection, driveway, or horizontal curve is present in the area with limited SSD, or the crash history shows a pattern of crashes potentially related to limited SSD, an SSD improvement is desirable. SSD improvements can include realigning a crest vertical curve or removing or relocating objects on the inside of a horizontal curve. Where the cost of the SSD improvement is substantial, consideration may be given to mitigation measures such as providing wider shoulders and/or advance warning signs. 6.1.5 Bridge Width Recent research (5) has shown that narrow bridges on rural two-lane highways, defined as bridges where the curb-to-curb bridge roadway width is less than the approach roadway width (lanes and shoulders combined) are not typically associated with increases in crash frequency. Crash reductions are not likely to result from bridge widening or replacement for bridges on rural two-lane highways, even narrow bridges. Bridges on two-lane highways should remain in place in 3R projects unless (a) there is either a structural need to strengthen or replace the bridge or (b) there is a documented pattern of crashes at the bridge that can potentially be reduced by widening or replacing the bridge. 6.1.6 Normal Pavement Cross Slope Pavement cross slope is needed for drainage so that water flows off the pavement during and after precipitation. Each highway agency has their own design criteria for normal pavement cross slope; these criteria are typically selected as suitable for local climate conditions. Where the pavement cross section within a 3R project does not have sufficient cross slope for drainage, the pavement cross slope should be restored to meet the highway agency’s applicable design criteria for pavement cross slope. Given the importance of pavement cross slope to drainage, no benefit- cost analysis is needed to justify restoration of normal pavement cross slope in a 3R project on a rural two-lane highway.

6.1.7 R Centerlin highways intended are provi to provid and begin —steerin The crash documen installatio become c threshold develope that insta highways Benefit-c strips can level of 2 This exam Section 6 segment installatio will almo umble Stri e rumble str to provide travel lane a ded on a pav e an audible s to encroac g and, wher reduction e ted in Sectio n of centerl ost-effectiv is merely a d with Sprea llation of ce , other than ost analysis be highly c ,000 veh/da Insta ple considers .1.1. The econ is analyzed wi n is $52,438. st always be ec p Improve ips are prov an audible a nd begins to ed shoulder and tactile h on the sh e appropriat ffectivenes ns 4.3.1.5 a ine or shoul e on rural tw n example, a dsheet Too nterline or s very low-vo examples p ost-effectiv y. ll Centerlin the same rura omic impact o th Tool 1. The Due to the low onomically jus ments ided betwee nd tactile w cross the r or at the ed warning to d oulder. Thes e, braking— s of rumble nd 4.3.1.6. A der rumble o-lane high nd agency- l 1. Howeve houlder rum lume roads resented bel e on rural tw e Rumble S l two-lane high f installing a ce benefit-cost ra installation cos tified. 111 n the two di arning to dri oadway cent ge of the tra rivers when e warnings to return to strip installa n example strips in con ways at AA specific min r, such agen ble strips is . ow show tha o-lane high trip on Ru way segment nterline rumbl tio is exception t and high saf rections of t vers when t erline. Simi veled way o their vehic alert the driv their intend tion on rura benefit-cost junction wit DTs as low imum AAD cy-specific cost-effecti t both cente ways, even ral Two-La considered in e strip on the r ally high and ety benefit, ce ravel on rur heir vehicle larly, should n rural two- le is leaving er to take c ed travel lan l two-lane h analysis (6 h a resurfac as 400 veh/d T guideline guidelines a ve for most rline and sh at a modest ne Highwa the lane widen ural two-lane h the net benefit nterline rumble al two-lane leaves its er rumble s lane highwa the roadwa orrective ac e. ighways is ) has shown ing project c ay. This AA s can be re likely to s rural two-la oulder rumb traffic volum y ing example in ighway examp of the treatme strip installati trips ys y tion that an DT how ne le e le nt on

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effectiven Section 4 The follo delineatio 6.1.9 R Roadside with road available propertie roadside slope flat crash red crash ana reduced b effective patterns t reduction slope flat another l Roadside specific b indicates A Using the used to e additiona Percent o Percent o Percent o Total Len The net b ess of impr .3.1.7. wing examp n on a rural oadside S slope flatte side slopes (or could be s, structures slope flatten tening is a d uction bene lysis finds e y roadside because of h hat can pote benefits fro tening woul ocation whe slope flatte enefit-cost that the pre dding Enh same rural tw xamine the ec l inputs neede f Roadway Se f Roadway Se f Roadway Se gth of Roadwa enefit of addin oved stripin le presents two-lane hi lope Flatte ning should steeper than acquired) a , or environm ing for 3R p esirable inv fits from roa xisting cras slope flatten igh project ntially be re m roadside d be a poor re the crash ning should analysis too sent value o anced Stri o-lane highwa onomic impact d about the ex ction with Das ction with Soli ction with Dou y Section with g this treatme g and deline benefit-cost ghway. ning be consider 1V:4H whe nd where sl entally sen rojects shou estment only dside slope h patterns (e ing. In many implementa duced by ro slope flatten investment reduction be be consider l (Spreadshe f the benefit ping and De y example seg of adding enh ample roadway hed Centerline d-Dash Center ble Solid Cent Delineator Po nt is $130,410 113 ation on rur analysis res ed for each re sufficien ope flattenin sitive areas ld be based where the flattening w .g., run-off- cases, road tion costs. W adside slope ing are less and availabl nefits woul ed only whe et Tool 1) o s of the slop lineation o ment consider anced striping for Tool 1 to Striping line Striping erline Striping sts (Includes e with a benefit- al two-lane ults for addi 3R project o t right-of-wa g would no , such as we on benefit- analysis ind ill exceed th road crashe side slope f here there flattening a than the im e funds wou d be larger. re a benefit- r with the R e flattening n a Rural T ed for lane wid and delineatio perform the an ach side sepa cost ratio of 2. highways is ng enhance n a rural tw y for slope t adversely tlands. Deci cost analysis icates that th e improvem s) that can p lattening wi are no exist nd the expe provement c ld be better cost analysi SAP model project wou wo-Lane H ening in Secti n. The followin alysis. rately) 435, based on documente d striping an o-lane highw flattening is affect adjace sions about , and roadsi e expected ent costs or otentially be ll not be cos ing crash cted crash ost, roadsid invested at s with the s (23, 24, 25) ld exceed th ighway on 6.1.1, Tool g table presen 20.00% 25.00% 55.00% 2.000 mi the Tool 1 res d in d ay nt de a t- e ite- e 1 is ts ults.

cost (i.e., slope flat site-spec provided efficientl There is n projects b estimates Where ro considera Section 6 found to 6.1.10 R Where ro removal model (2 breakawa regular in not likely Using the used to d scenario The resu benefit. Tool 2 ca analysis Improv 1 1 1 the net ben tening on ru ific benefit-c with these g y. o option fo ecause the are needed adside slope tion may al .1.10) or pro be cost-effe emoval o adside obje should be co 3, 24, 25). G y design ne tervals thro to be cost-e Ro same two-lan etermine if roa one at a time, lts shown belo n be used to e are shown belo ed Slope V:6H V:4H V:3H efits would e ral two-lane ost analysis uidelines en r developing costs of such . flattening i so be given viding traff ctive using t f Roadside cts are prese nsidered on enerally, on ed to be con ughout all o ffective and adside Slop e highway exa dside slope fla it can be deter w are for flatte xamine all pos w. Net Benefit ( $45,483 $12,064 -$22,903 xceed zero) highways i are illustrat ables site-s minimum A projects ca s considered to mitigation ic barriers ( he RSAP m Objects nt within th the basis of ly objects g sidered. Wh r part of the a formal R e Flattening mple segment ttening is cost mined which im ning the roads sible slope flat $) B/ 114 . The crash s documente ed in Sectio pecific bene ADT guid n vary wide , but not im measures s see Section odel. e clear zone a cost-effec reater than 4 ere roadside length of a SAP analysi on a Rura considered fo effective. By a proved roads ide slopes to a tening scenari C Ratio 1.710 1.282 0.285 reduction ef d in Section n 5.4. The b fit-cost anal elines for ro ly from site plemented, uch as remo 6.1.11), whe width on a r tiveness an inches in d objects are 3R project, r s is not nee l Two-Lane r lane widening nalyzing each ide slope gene 1V:6H slope, os at one time Total Benef $109,54 $54,77 $9,12 fectiveness 4.3.1.8. Pr enefit-cost a yses to be p adside slope to site, so si in a 3R proj ving roadsi re such imp ural two-lan alysis, using iameter and present con emoval of t ded. Highway in Section 6. possible slope rates the high which produce . The results o it ($) To 7 4 9 of roadside ocedures for nalysis tool erformed flattening te-specific c ect, de objects (s rovements a e highway, the RSAP not of tinuously or hose objects 1.1, Tool 1 can flattening est net benefit s the highest n f the Tool 2 tal Cost ($) $64,064 $42,709 $32,032 ost ee re their at is be . et

115 As alternatives to removing roadside objects, consideration may also be given to replacing the object with a similar object of breakaway design, relocating the object behind an existing guardrail or traffic barrier, or installing a new guardrail or traffic barrier. Decisions concerning the cost-effectiveness of new guardrail or other traffic barriers should be made with the RSAP model (see Section 6.1.11) 6.1.11 Installation/Rehabilitation of Guardrail and Other Traffic Barriers Existing guardrail or other traffic barriers that have reached the end of their useful life or are of obsolete design should generally be rehabilitated or replaced as part of a 3R project. The decision to rehabilitate or replace a guardrail or traffic barrier does not require a formal economic analysis, as long as the highway agency believes that the guardrail or traffic barrier is needed and warranted at its location. If the highway agency has reason to believe that the existing guardrail or traffic barrier may not be warranted, the warrants and length of need for the barrier can be assessed with the AASHTO Roadside Design Guide (30). Installation of new guardrail or other traffic barriers may be considered by highway agencies as part of 3R projects on rural two-lane highways. The RSAP model should be used to evaluate the cost-effectiveness of any new guardrail or traffic barrier installations that are considered. 6.1.12 Passing Lanes Passing Lanes may be added as part of 3R projects on rural two-lane highways to increase passing opportunities. Passing lanes can be added in one or both directions of travel. Where a passing lane is added on an upgrade to allow vehicles to pass trucks or other heavy vehicles slowed by the upgrade, the added lane is known as a climbing lane. The traffic operational analysis procedures in the Highway Capacity Manual (11) can be used to assess the effect of added passing or climbing lanes on the traffic operational level of service for a rural two-lane highway. The AASHTO Green Book (4) presents criteria for where climbing lanes should be considered on rural two-lane highways. Passing and climbing lanes should generally be installed only where a Highway Capacity Manual analysis established that there is a traffic operational need for the added lane. For climbing lanes, the traffic operational criteria in the AASHTO Green Book should also be met. In most cases for which an added passing or climbing lane is needed for traffic operational reasons, it will also have sufficient safety benefit to be cost-effective as a safety improvement. This can be verified with Spreadsheet Tool 1.

116 6.1.13 Intersection Turn Lane Improvements The crash reduction effectiveness of intersection turn lane improvements on rural two-lane highways is documented in Section 4.3.1.10. Benefit-cost analyses (7) have shown that intersection turn-lane improvements, including installation of left- and right-turn lanes, are likely to be cost-effective at any intersection where installation to the turn lane makes traffic operational sense. Highway agencies should, therefore, assess the traffic operational need to intersection turn lanes using established access management policies or traffic operational analysis tools. If the highway agency concludes that installation of the turn lane is justified on a traffic operational basis, there is little doubt that the turn lane will be cost-effective on a safety basis as well. 6.1.14 Other Intersection Improvements A 3R project may provide an opportunity for implementing other intersection improvements, involving traffic control, signing, delineation, marking, or sight distance. Highway agencies should implement such improvements if a need is identified based on a crash history review. 6.2 Rural Multilane Undivided Highways 6.2.1 Lane Widening Lane widening should be considered for each 3R project on a rural multilane undivided highway with existing lane widths less than 12 ft. Decisions about lane widening for 3R projects should be based on benefit-cost analysis. Lane widening is a desirable investment only where the analysis indicates that the expected crash reduction benefits from lane widening will exceed the improvement costs or a crash analysis finds existing crash patterns that can potentially be reduced by lane widening. Where there are no existing crash patterns that can potentially be reduced by lane widening and the expected crash reduction benefits from lane widening are less than the improvement cost, lane widening would be a poor investment and available funds would be better invested at another location where the crash reduction benefits would be larger. Two benefit-cost analysis approaches applicable to lane widening analysis are discussed below. The most desirable approach (Option 1) for cost-effective lane widening decisions is to conduct a site-specific benefit-cost analysis for each individual 3R project. Site-specific benefit-cost analyses are desirable because even nominally similar sites may differ in roadway characteristics, traffic volumes, crash history, and improvement costs, such that lane widening may be cost-effective at one site and not at another. The crash reduction effectiveness of lane widening on rural multilane undivided highways is documented in Section 4.3.2.1. Procedures for site-specific benefit-cost analysis are illustrated in Section 5.2.2. The benefit-cost analysis tool provided with these guidelines enables site-specific benefit-cost analyses to be performed efficiently.

117 An example of the application of Spreadsheet Tool 1 to a lane widening improvement on a rural two-lane highway has been presented above in Section 6.1.1. Analysis of lane widening for rural multilane undivided highways can be performed in the same manner, with the only difference in input data being the roadway type. A less desirable, but still acceptable, approach (Option 2) for cost-effective lane widening decisions in 3R projects is to develop agency-specific guidelines for minimum traffic volumes that justify lane widening, analogous to the example shown in Table 37. Minimum traffic volume guidelines analogous to Table 37 can be developed by each highway agency (or in some cases by individual districts or regions within a highway agency) as a basis for lane widening decisions. Section 5.4 illustrates procedures for developing minimum traffic volume guidelines like Table 37. An example benefit-cost analysis to develop minimum AADT guidelines for rural two-lane highways has been presented in Table 37. The same analysis approach can be applied to lane widening on rural multilane undivided highways. 6.2.2 Shoulder Widening and Paving Shoulder widening should be considered for each 3R project on a rural multilane undivided highway with existing shoulder widths less than 6 ft. Decisions about shoulder widening for 3R projects should be based on benefit-cost analysis, and shoulder widening is a desirable investment only where the analysis indicates that the expected crash reduction benefits from shoulder widening will exceed the improvement costs or a crash analysis finds existing crash patterns that can potentially be reduced by shoulder widening. Where there are no existing crash patterns that can potentially be reduced by shoulder widening and the expected crash reduction benefits from shoulder widening are less than the improvement cost, shoulder widening would be a poor investment and available funds would be better invested at another location where the crash reduction benefits would be larger. Two benefit-cost analysis approaches applicable to shoulder widening analysis are discussed below. The most desirable approach (Option 1) for cost-effective shoulder widening decisions is to conduct a site-specific benefit-cost analysis for each individual 3R project. Site-specific benefit-cost analyses are desirable because even nominally similar sites may differ in roadway characteristics, traffic volumes, crash history, and improvement costs, such that shoulder widening may be cost-effective at one site and not at another. The crash reduction effectiveness of shoulder widening on rural multilane undivided highways is documented in Section 4.3.2.2. Procedures for site-specific benefit-cost analysis are illustrated in Section 5.2.2. The benefit-cost analysis tool provided with these guidelines enables site-specific benefit-cost analyses to be performed efficiently. An example of the application of Spreadsheet Tool 1 to a shoulder widening improvement on a rural two-lane highway has been presented above in Section 6.1.2. Analysis of shoulder widening for rural multilane undivided highways can be performed in the same manner, with the only difference in input data being the roadway type.

118 A less desirable, but still acceptable, approach (Option 2) for cost-effective shoulder widening decisions in 3R projects is to develop agency-specific guidelines for minimum traffic volumes that justify shoulder widening, analogous to the example shown in Table 38. Minimum traffic volume guidelines analogous to Table 38 can be developed by each highway agency (or in some cases by individual districts or regions within a highway agency) as a basis for shoulder widening decisions. Section 5.4 illustrates procedures for developing minimum traffic volume guidelines like Table 38. Benefit-cost analyses can also be applied to rural multilane undivided highway sites with unpaved shoulders to consider whether the shoulder should be paved. The most desirable approach is to consider shoulder paving alternatives for each shoulder width alternative evaluated. A less desirable, but still acceptable approach is to determine the optimal shoulder width for the project and then evaluate whether the shoulder should be paved. Many highway agencies have design policies that utilize paved shoulders only for specific roadway types or above specific traffic volume levels. Nothing in these guidelines requires a highway agency to provide paved shoulders on projects where the agency’s design policy calls for unpaved shoulders. 6.2.3 Horizontal Curve Improvements Horizontal curve improvements on rural multilane undivided highways may be considered 3R projects in some cases. Superelevation variances greater than 1 percent on horizontal curves on rural multilane undivided highways should be restored in 3R projects. Realignment of an isolated horizontal curve on a rural multilane undivided highway can also be considered as part of a 3R project. Typically, such an improvement would involved flattening the radius and, therefore, lengthening the curve. The spreadsheet tools do not address improvements of this type, so their safety benefits would need to be assessed by other means. The HSM Chapter 11 procedures do not address the effects of horizontal curve radius and length, so some other assessment would need to be made. The HSM Chapter 10 procedures could provide a conservative approach to such an analysis. Realignment of multiple horizontal curves on a roadway section would generally be considered as reconstruction and, therefore, out of the scope of 3R improvements. 6.2.4 Sight Distance Improvements Stopping sight distance (SSD) is provided along roadways to assist drivers in detecting and responding to situations on the roadway ahead that may require drivers to slow or stop. Sight distance limitations may include crest vertical curves or objects on the inside of horizontal curves. The SSD design criteria used by most states are based on the SSD values in the AASHTO Green Book (4).

119 Recent research (5) has shown that limited SSD on rural two-lane highways is unlikely to lead to crashes unless the portion of the roadway hidden from the driver’s view by the sight distance limitation includes a roadway feature that may require drivers to take steering or braking action, such as an intersection, a driveway, or a horizontal curve. There has been no similar research on rural multilane undivided highways, but the research findings for rural two-lane highways can logically be extended to rural multilane highways as well. Where an area with SSD less than the Green Book SSD design criteria is present on a rural multilane undivided highway, but there are no hidden features such as intersections, driveways, or horizontal curves and no history of crashes related to limited SSD, sight distance improvements are unlikely to be cost-effective and need not be considered in 3R projects. By contrast, where a portion of the highway has SSD less than the Green Book SSD design criteria, and an intersection, driveway, or horizontal curve is present in the area with limited SSD, or the crash history shows a pattern of crashes potentially related to limited SSD, an SSD improvement is desirable. SSD improvements can include realigning a crest vertical curve or removing or relocating objects on the inside of a horizontal curve. Where the cost of the SSD improvement is substantial, consideration may be given to mitigation measures such as providing wider shoulders and/or advance warning signs. 6.2.5 Bridge Width Recent research (5) has shown that narrow bridges on rural two-lane highways, defined as bridges where the curb-to-curb bridge roadway width is less than the approach roadway width (lanes and shoulders combined) are not typically associated with increases in crash frequency. Crash reductions are not likely to result from bridge widening or replacement for bridges on two- lane highways, even narrow bridges. There has been no similar research on rural multilane undivided highways, but the research findings for rural two-lane highways can logically be extended to rural multilane highways as well. Bridges on rural multilane undivided highways should remain in place in 3R projects unless (a) there is either a structural need to strengthen or replace the bridge or (b) there is a documented pattern of crashes at the bridge that can potentially be reduced by widening or replacing the bridge. 6.2.6 Normal Pavement Cross Slope Pavement cross slope is needed for drainage so that water flows off the pavement during and after precipitation. Each highway agency has their own design criteria for normal pavement cross slope; these criteria are typically selected as suitable for local climate conditions. Where the pavement cross section within a 3R project does not have sufficient cross slope for drainage, the pavement cross slope should be restored to meet the highway agency’s applicable design criteria for pavement cross slope. Given the importance of pavement cross slope to drainage, no benefit- cost analysis is needed to justify restoration of normal pavement cross slope in a 3R project on a rural multilane undivided highway. 6.2.7 Rumble Strip Improvements

120 Centerline rumble strips are provided between the two directions of travel on rural multilane undivided highways to provide an audible and tactile warning to drivers when their vehicle leaves its intended travel lane and begins to cross the roadway centerline. Similarly, shoulder rumble strips are provided on a paved shoulder or at the edge of the traveled way on rural two- lane highways to provide an audible and tactile warning to drivers when their vehicle is leaving the roadway and begins to encroach on the shoulder. These warnings alert the driver to take corrective action—steering and, where appropriate, braking—to return to their intended travel lane. An example benefit-cost analysis (5) has shown that installation of centerline or shoulder rumble strips in conjunction with a resurfacing project can become cost-effective on rural two-lane highways at AADTs as low as 300 veh/day. This AADT threshold is merely an example, and agency-specific minimum AADT guidelines can be developed with Spreadsheet Tool 1. However, there are essentially no rural multilane undivided highways with AADTs as low as 300 veh/day, so any agency-specific guidelines are likely to show that installation of centerline or shoulder rumble strips is cost-effective for all rural multilane undivided highways. Highway agencies are encouraged to provide centerline or shoulder rumble strips as part of 3R projects, where they are not already present, and to restore existing rumble strips when the pavement and/or shoulder is resurfaced. Rumble strips should be designed and located in accordance with each agency’s current practices. Rumble strips are appropriate at most rural locations, except where the noise created by the rumble strips may disturb nearby residents. Rumble strips on paved shoulders need to be located sufficiently close to the traveled way that the effectiveness of the paved shoulder as a travel path for bicyclists is not reduced. Where rumble strips are cost-effective, either centerline or shoulder rumble strips, or both, may be used. Use of both centerline and shoulder rumble strips together is very effective, and should be considered, consistent with each agency’s current practices. 6.2.8 Striping and Delineation Improvements Nearly every 3R project includes pavement resurfacing, so the cost of restoring pavement markings after resurfacing is automatically part of most 3R projects. These guidelines assume that, as a default, highway agencies will restore the pavement markings with the equivalent of the existing pavement markings. Conventional paint is the least expensive pavement marking material, and typically has a service life of one to two years, depending on traffic volume and climate conditions. Highway agencies may choose to consider more durable pavement markings with longer life and higher retroreflectivity, as well as an increased implementation cost, as part of some 3R projects. Other delineation improvements may also be considered as part of an overall striping and delineation package. Spreadsheet Tool 1 provides the capability to assess the cost-effectiveness of striping and delineation packages for inclusion in 3R projects. The implementation cost for the striping and delineation package is the full striping and delineation cost minus the cost of the pavement markings that would have been implemented as a default. The crash reduction

121 effectiveness of improved striping and delineation on rural multilane undivided highways is documented in Section 4.3.2.6. 6.2.9 Roadside Slope Flattening Roadside slope flattening should be considered for each 3R project on a rural multilane undivided highway with roadside slopes steeper than 1V:4H where sufficient right-of-way for slope flattening is available (or could be acquired) and where slope flattening would not adversely affect adjacent properties, structures, or environmentally sensitive areas, such as wetlands. Decisions about roadside slope flattening for 3R projects should be based on benefit- cost analysis, and roadside slope flattening is a desirable investment only where the analysis indicates that the expected crash reduction benefits from roadside slope flattening will exceed the improvement costs or a crash analysis finds existing crash patterns (e.g., run-off-road crashes) that can potentially be reduced by roadside slope flattening. In many cases, roadside slope flattening will not be cost-effective because of high project implementation costs. Where there are no existing crash patterns that can potentially be reduced by roadside slope flattening and the expected crash reduction benefits from roadside slope flattening are less than the improvement cost, roadside slope flattening would be a poor investment and available funds would be better invested at another location where the crash reduction benefits would be larger. Roadside slope flattening should be considered only where a benefit-cost analysis with the site- specific benefit-cost analysis tool (Spreadsheet Tool 1) or with the RSAP model (23, 24, 25) indicates that the present value of the benefits of the slope flattening project would exceed the cost. The crash reduction effectiveness of roadside slope flattening on rural multilane undivided highways is documented in Section 4.3.1.7. Procedures for site-specific benefit-cost analysis are illustrated in Section 5.2.2. The benefit-cost analysis tool provided with these guidelines enables site-specific benefit-cost analyses to be performed efficiently. There is no option for developing minimum AADT guidelines for roadside slope flattening projects because the costs of such projects can vary widely from site to site, so site-specific cost estimates are needed. Where roadside slope flattening is considered, but not implemented, in a 3R project, consideration may also be given to mitigation measures such as removing roadside objects (see Section 6.2.10) or providing traffic barriers (see Section 6.2.11), where such improvements are found to be cost-effective using the RSAP model. 6.2.10 Removal of Roadside Objects Where roadside objects are present within the clear zone width on a rural multilane undivided highway, their removal should be considered on the basis of a cost-effectiveness analysis, using the RSAP model (23, 24, 25). Generally, only objects greater than 4 inches in diameter and not of breakaway design need to be considered. Where roadside objects are present continuously or

122 at regular intervals throughout all or part of the length of a 3R project, removal of those objects is not likely to be cost-effective and a formal RSAP analysis is not needed. As alternatives to removing roadside objects, consideration may also be given to replacing the object with a similar object of breakaway design, relocating the object behind an existing guardrail or traffic barrier, or installing a new guardrail or traffic barrier. Decisions concerning the cost-effectiveness of new guardrail or other traffic barriers should be made with the RSAP model (see Section 6.2.11) 6.2.11 Installation/Rehabilitation of Guardrail and Other Traffic Barriers Existing guardrail or other traffic barriers that have reached the end of their useful life or are of obsolete design should generally be rehabilitated or replaced as part of a 3R project. The decision to rehabilitate or replace a guardrail or traffic barrier does not require a formal economic analysis, as long as the highway agency believes that the guardrail or traffic barrier is needed and warranted at its location. If the highway agency has reason to believe that the existing guardrail or traffic barrier may not be warranted, the warrants and length of need for the barrier can be assessed with the AASHTO Roadside Design Guide (30). Installation of new guardrail or other traffic barriers may be considered by highway agencies as part of 3R projects on rural multilane undivided highways. The RSAP model should be used to evaluate the cost-effectiveness of any new guardrail or traffic barrier installations that are considered. 6.2.12 Intersection Turn Lane Improvements The crash reduction effectiveness of intersection turn lane improvements on rural multilane undivided highways is documented in Section 4.3.2.9. Benefit-cost analyses (5) have shown that intersection turn-lane improvements, including installation of left- and right-turn lanes, are likely to be cost-effective at any intersection where installation to the turn lane makes traffic operational sense. Highway agencies should, therefore, assess the traffic operational need to intersection turn lanes using established access management policies or traffic operational analysis tools. If the highway agency concludes that installation of the turn lane is justified on a traffic operational basis, there is little doubt that the turn lane will be cost-effective on a safety basis as well. 6.2.13 Other Intersection Improvements A 3R project may provide an opportunity for implementing other intersection improvements, involving traffic control, signing, delineation, marking, or sight distance. Highway agencies should implement such improvements if a need is identified based on a crash history review.

123 6.3 Rural Multilane Divided Highways (Nonfreeways) 6.3.1 Lane Widening Lane widening should be considered for each 3R project on a rural multilane divided nonfreeway with existing lane widths less than 12 ft. Decisions about lane widening for 3R projects should be based on benefit-cost analysis. Lane widening is a desirable investment only where the analysis indicates that the expected crash reduction benefits from lane widening will exceed the improvement costs or a crash analysis finds existing crash patterns that can potentially be reduced by lane widening. Where there are no existing crash patterns that can potentially be reduced by lane widening and the expected crash reduction benefits from lane widening are less than the improvement cost, lane widening would be a poor investment and available funds would be better invested at another location where the crash reduction benefits would be larger. Two benefit-cost analysis approaches applicable to lane widening analysis are presented below. The most desirable approach (Option 1) for cost-effective lane widening decisions is to conduct a site-specific benefit-cost analysis for each individual 3R project. Site-specific benefit-cost analyses are desirable because even nominally similar sites may differ in roadway characteristics, traffic volumes, crash history, and improvement costs, such that lane widening may be cost-effective at one site and not at another. The crash reduction effectiveness of lane widening on rural multilane divided nonfreeways is documented in Section 4.3.3.1. Procedures for site-specific benefit-cost analysis are illustrated in Section 5.2.2. The benefit-cost analysis tool provided with these guidelines enables site-specific benefit-cost analyses to be performed efficiently. An example of the application of Spreadsheet Tool 1 to a lane widening improvement on a rural two-lane highway has been presented above in Section 6.1.1. Analysis of lane widening for rural multilane divided nonfreeways can be performed in the same manner, with the only differences in input data being the roadway type and the addition of a value for the existing median width. A less desirable, but still acceptable, approach (Option 2) for cost-effective lane widening decisions in 3R projects is to develop agency-specific guidelines for minimum traffic volumes that justify lane widening, analogous to the example shown in Table 37. Minimum traffic volume guidelines analogous to Table 37 can be developed by each highway agency (or in some cases by individual districts or regions within a highway agency) as a basis for lane widening decisions. Section 5.4 illustrates procedures for developing minimum traffic volume guidelines like Table 37. An example benefit-cost analysis to develop minimum AADT guidelines for rural two-lane highways has been presented in Table 37. The same analysis approach can be applied to lane widening on rural multilane divided highways.

124 6.3.2 Shoulder Widening and Paving Shoulder widening should be considered for each 3R project on a rural multilane divided nonfreeway with existing shoulder widths less than 8 ft. Decisions about shoulder widening for 3R projects should be based on benefit-cost analysis, and shoulder widening is a desirable investment only where the analysis indicates that the expected crash reduction benefits from shoulder widening will exceed the improvement costs or a crash analysis finds existing crash patterns that can potentially be reduced by shoulder widening. Where there are no existing crash patterns that can potentially be reduced by shoulder widening and the expected crash reduction benefits from shoulder widening are less than the improvement cost, shoulder widening would be a poor investment and available funds would be better invested at another location where the crash reduction benefits would be larger. Two benefit-cost analysis approaches applicable to shoulder widening analysis are presented below. The most desirable approach (Option 1) for cost-effective shoulder widening decisions is to conduct a site-specific benefit-cost analysis for each individual 3R project. Site-specific benefit-cost analyses are desirable because even nominally similar sites may differ in roadway characteristics, traffic volumes, crash history, and improvement costs, such that shoulder widening may be cost-effective at one site and not at another. The crash reduction effectiveness of shoulder widening on rural multilane divided nonfreeways is documented in Section 4.3.3.2. Procedures for site-specific benefit-cost analysis are illustrated in Section 5.2.2. The benefit-cost analysis tool provided with these guidelines enables site-specific benefit-cost analyses to be performed efficiently. An example of the application of Spreadsheet Tool 1 to a shoulder widening improvement on a rural two-lane highway has been presented above in Section 6.1.2. Analysis of shoulder widening for rural multilane divided nonfreeways can be performed in the same manner, with the only difference in input data being the roadway type. A less desirable, but still acceptable, approach (Option 2) for cost-effective shoulder widening decisions in 3R projects is to develop agency-specific guidelines for minimum traffic volumes that justify shoulder widening, analogous to the example shown in Table 38. Minimum traffic volume guidelines analogous to Table 38 can be developed by each highway agency (or in some cases by individual districts or regions within a highway agency) as a basis for shoulder widening decisions. Section 5.4 illustrates procedures for developing minimum traffic volume guidelines like Table 38. Benefit-cost analyses can also be applied to rural multilane divided nonfreeway sites with unpaved shoulders to consider whether the shoulder should be paved. The most desirable approach is to consider shoulder paving alternatives for each shoulder width alternative evaluated. A less desirable, but still acceptable approach is to determine the optimal shoulder width for the project and then evaluate whether the shoulder should be paved. Many highway agencies have design policies that utilize paved shoulders only for specific roadway types or above specific traffic volume levels. Nothing in these guidelines requires a highway agency to provide paved shoulders on projects where the agency’s design policy calls for unpaved shoulders.

125 6.3.3 Horizontal Curve Improvements Realignment of horizontal curves on rural multilane divided highways is considered reconstruction and is, therefore, outside the scope of a 3R project. Superelevation variances greater than 1 percent on horizontal curves on rural multilane divided highways should be restored in 3R projects. 6.3.4 Sight Distance Improvements Stopping sight distance (SSD) is provided along roadways to assist drivers in detecting and responding to situations on the roadway ahead that may require drivers to slow or stop. Sight distance limitations may include crest vertical curves or objects on the inside of horizontal curves. The SSD design criteria used by most states are based on the SSD values in the AASHTO Green Book (4). Recent research (5) has shown that limited SSD on rural two-lane highways is unlikely to lead to crashes unless the portion of the roadway hidden from the driver’s view by the sight distance limitation includes a roadway feature that may require drivers to take steering or braking action, such as an intersection, a driveway, or a horizontal curve. There has been no similar research on rural multilane divided nonfreeways, but the research findings for rural two-lane highways can logically be extended to rural multilane highways as well. Where an area with SSD less than the Green Book SSD design criteria is present on a rural multilane divided nonfreeway, but there are no hidden features such as intersections, driveways, ramp terminals, or horizontal curves and no history of crashes related to limited SSD, sight distance improvements are unlikely to be cost- effective and need not be considered in 3R projects. By contrast, where a portion of the highway has SSD less than the Green Book SSD design criteria, and an intersection, driveway, or horizontal curve is present in the area with limited SSD, or the crash history shows a pattern of crashes potentially related to limited SSD, an SSD improvement is desirable. SSD improvements can include realigning a crest vertical curve or removing or relocating objects on the inside of a horizontal curve. Where the cost of the SSD improvement is substantial, consideration may be given to mitigation measures such as providing wider shoulders and/or advance warning signs. 6.3.5 Bridge Width Recent research (5) has shown that narrow bridges on rural two-lane highways, defined as bridges where the curb-to-curb bridge roadway width is less than the approach roadway width (lanes and shoulders combined) are not typically associated with increases in crash frequency. Crash reductions are not likely to result from bridge widening or replacement for bridges on two- lane highways, even narrow bridges. There has been no similar research on rural multilane divided nonfreeways, but the research findings for rural two-lane highways can logically be extended to rural multilane highways as well. Bridges on rural multilane divided nonfreeways should remain in place in 3R projects unless (a) there is either a structural need to strengthen or

126 replace the bridge or (b) there is a documented pattern of crashes at the bridge that can potentially be reduced by widening or replacing the bridge. 6.3.6 Normal Pavement Cross Slope Pavement cross slope is needed for drainage so that water flows off the pavement during and after precipitation. Each highway agency has their own design criteria for normal pavement cross slope; these criteria are typically selected as suitable for local climate conditions. Where the pavement cross section within a 3R project does have sufficient cross slope for drainage, the pavement cross slope should be restored to meet the highway agency’s applicable design criteria for pavement cross slope. Given the importance of pavement cross slope to drainage, no benefit- cost analysis is needed to justify restoration of normal pavement cross slope in a 3R project on a rural multilane divided nonfreeway. 6.3.7 Rumble Strip Improvements Shoulder rumble strips are provided on a paved shoulder or at the edge of the traveled way on rural multilane divided nonfreeways to provide an audible and tactile warning to drivers when their vehicle is leaving the roadway and begins to encroach on the shoulder. These warnings alert the driver to take corrective action—steering and, where appropriate, braking—to return to their intended travel lane. Shoulder rumble strips are typically used on both the right (outside) and left (inside) shoulders of rural multilane divided nonfreeways. An example benefit-cost analysis (7) has shown that installation of shoulder rumble strips in conjunction with a resurfacing project can become cost-effective on rural multilane divided nonfreeways at AADTs as low as 400 veh/day. This AADT threshold is merely an example, and agency-specific minimum AADT guidelines can be developed with Spreadsheet Tool 1. However, there are essentially no rural multilane divided nonfreeways with AADTs as low as 400 veh/day, so any agency-specific guidelines are likely to show that installation of shoulder rumble strips is cost-effective for all rural multilane divided nonfreeways. Highway agencies are encouraged to provide shoulder rumble strips as part of 3R projects, where they are not already present, and to restore existing rumble strips when the pavement and/or shoulder is resurfaced. Rumble strips should be designed and located in accordance with each agency’s current practices. Rumble strips are appropriate at most rural locations, except where the noise created by the rumble strips may disturb nearby residents. Rumble strips on paved shoulders need to be located sufficiently close to the traveled way that the effectiveness of the paved shoulder as a travel path for bicyclists is not reduced. 6.3.8 Striping and Delineation Improvements Nearly every 3R project includes pavement resurfacing, so the cost of restoring pavement markings after resurfacing is automatically part of most 3R projects. These guidelines assume

127 that, as a default, highway agencies will restore the pavement markings with the equivalent of the existing pavement markings. Conventional paint is the least expensive pavement marking material, and typically has a service life of one to two years, depending on traffic volume and climate conditions. Highway agencies may choose to consider more durable pavement markings with longer life and higher retroreflectivity, as well as an increased implementation cost, as part of some 3R projects. Other delineation improvements may also be considered as part of an overall striping and delineation package. Spreadsheet Tool 1 provides the capability to assess the cost-effectiveness of striping and delineation packages for inclusion in 3R projects. The implementation cost for the striping and delineation package is the full striping and delineation cost minus the cost of the pavement markings that would have been implemented as a default. The crash reduction effectiveness of improved striping and delineation on rural multilane nonfreeways is documented in Section 4.3.3.6. 6.3.9 Roadside Slope Flattening Roadside slope flattening should be considered for each 3R project on a rural multilane divided nonfreeway with roadside slopes steeper than 1V:4H where sufficient right-of-way for slope flattening is available (or could be acquired) and where slope flattening would not adversely affect adjacent properties, structures, or environmentally sensitive areas, such as wetlands. Decisions about roadside slope flattening for 3R projects should be based on benefit-cost analysis, and roadside slope flattening is a desirable investment only where the analysis indicates that the expected crash reduction benefits from roadside slope flattening will exceed the improvement costs or a crash analysis finds existing crash patterns (e.g., run-off-road crashes) that can potentially be reduced by roadside slope flattening. In many cases, roadside slope flattening will not be cost-effective because of high project implementation costs. Where there are no existing crash patterns that can potentially be reduced by roadside slope flattening and the expected crash reduction benefits from roadside slope flattening are less than the improvement cost, roadside slope flattening would be a poor investment and available funds would be better invested at another location where the crash reduction benefits would be larger. Roadside slope flattening should be considered only where a benefit-cost analysis with the site- specific benefit-cost analysis tool (Spreadsheet Tool 1) or with the RSAP model (23, 24, 25) indicates that the present value of the benefits of the slope flattening project would exceed the cost. The crash reduction effectiveness of roadside slope flattening on rural multilane divided nonfreeways is documented in Section 4.3.2.7 and 4.3.3.7. Procedures for site-specific benefit- cost analysis are illustrated in Section 5.4. The benefit-cost analysis tool provided with these guidelines enables site-specific benefit-cost analyses to be performed efficiently. There is no option for developing minimum AADT guidelines for roadside slope flattening projects because the costs of such projects can vary widely from site to site, so site-specific cost estimates are needed.

128 Where roadside slope flattening is considered, but not implemented, in a 3R project, consideration may also be given to mitigation measures such as removing roadside objects (see Section 6.3.10) or providing traffic barriers (see Section 6.3.11), where such improvements are found to be cost-effective using the RSAP model. 6.3.10 Removal of Roadside Objects Where roadside objects are present within the clear zone width on a rural multilane divided nonfreeway, their removal should be considered on the basis of a cost-effectiveness analysis, using the RSAP model (23, 24, 25). Generally, only objects greater than 4 inches in diameter and not of breakaway design need to be considered. Where roadside objects are present continuously or at regular intervals throughout all or part of the length of a 3R project, removal of those objects is not likely to be cost-effective and a formal RSAP analysis is not needed. As alternatives to removing roadside objects, consideration may also be given to replacing the object with a similar object of breakaway design, relocating the object behind an existing guardrail or traffic barrier, or installing a new guardrail or traffic barrier. Decisions concerning the cost-effectiveness of new guardrail or other traffic barriers should be made with the RSAP model (see Section 6.3.11) 6.3.11 Installation/Rehabilitation of Guardrail and Other Traffic Barriers Existing guardrail or other traffic barriers that have reached the end of their useful life or are of obsolete design should generally be rehabilitated or replaced as part of a 3R project. The decision to rehabilitate or replace a guardrail or traffic barrier does not require a formal economic analysis, as long as the highway agency believes that the guardrail or traffic barrier is needed and warranted at its location. If the highway agency has reason to believe that the existing guardrail or traffic barrier may not be warranted, the warrants and length of need for the barrier can be assessed with the AASHTO Roadside Design Guide (30). Installation of new guardrail or other traffic barriers may be considered by highway agencies as part of 3R projects on rural multilane divided nonfreeways. The RSAP model should be used to evaluate the cost-effectiveness of any new guardrail or traffic barrier installations that are considered. 6.3.12 Intersection Turn Lane Improvements The crash reduction effectiveness of intersection turn lane improvements on rural multilane divided nonfreeways is documented in Section 4.3.3.9. Benefit-cost analyses (5) have shown that intersection turn-lane improvements, including installation of left- and right-turn lanes, are likely to be cost-effective at any intersection where installation of the turn lane makes traffic operational sense. Highway agencies should, therefore, assess the traffic operational need to intersection turn lanes using established access management policies or traffic operational

129 analysis tools. If the highway agency concludes that installation of the turn lane is justified on a traffic operational basis, there is little doubt that the turn lane will be cost-effective on a safety basis as well. 6.3.13 Other Intersection Improvements A 3R project may provide an opportunity for implementing other intersection improvements, involving traffic control, signing, delineation, marking, or sight distance. Highway agencies should implement such improvements if a need is identified based on a crash history review. 6.4 Urban and Suburban Arterials 6.4.1 Lane Widening Benefit-cost analyses cannot be applied to lane widening on urban and suburban arterials at this time, because there are no documented CMFs for lane widening in HSM Chapter 12. However, the AASHTO Green Book (4) provides broad flexibility for use of 10-, 11-, and 12-ft lanes on urban and suburban arterials. Recent research (see Section 4.3.4.1) also suggests that, in most cases, there are no substantial differences in safety performance between 10-, 11-, and 12-ft lanes on urban and suburban arterials. In addition, narrower through travel lanes can have substantive advantages on urban and suburban arterials by providing space in the cross section for turn lanes, median treatments, bicycle lanes, and shorter pedestrian crossings, all of which can themselves reduce crashes. Therefore, lane widening is not a desirable investment in 3R projects on urban and suburban arterials with existing lane widths of 10 ft or more unless there is a documented crash pattern that can potentially be mitigated with wider lanes or there is a documented traffic operational need for wider lanes. 6.4.2 Shoulder Widening Benefit-cost analyses cannot be applied to shoulder widening on urban and suburban arterials at this time, because there are no documented CMFs for shoulder widening in HSM Chapter 12. However, the AASHTO Green Book (4) provides broad flexibility for use of shoulders with a range of widths on urban and suburban arterials including, in appropriate speed ranges, the use of curb-and-gutter sections with no shoulder. For many low- and intermediate-speed roads, curb- and-gutter sections without shoulders are appropriate because they enhance drainage. Therefore, shoulder widening is not a desirable investment in 3R projects on urban and suburban arterials unless there is a documented crash pattern that can potentially be mitigated with wider shoulders or there is a documented traffic operational need for wider shoulders.

130 6.4.3 Horizontal Curve Improvements Realignment of horizontal curves on urban and suburban arterials is considered reconstruction and is, therefore, outside the scope of a 3R project. 6.4.4 Striping and Delineation Improvements Nearly every 3R project includes pavement resurfacing, so the cost of restoring pavement markings after resurfacing is automatically part of most 3R projects. These guidelines assume that, as a default, highway agencies will restore the pavement markings with the equivalent of the existing pavement markings. Conventional paint is the least expensive pavement marking material, and typically has a service life of one to two years, depending on traffic volume and climate conditions. Highway agencies may choose to consider more durable pavement markings with longer life and higher retroreflectivity, as well as an increased implementation cost, as part of some 3R projects. Other delineation improvements may also be considered as part of an overall striping and delineation package. There are no documented crash reduction effectiveness measures for striping and delineation packages on urban and suburban arterials, so highway agencies should exercise judgement based on their experience with striping and delineation packages on other roadway types to assess when striping and delineation improvements are appropriate on urban and suburban arterials. Spreadsheet Tool 1 provides the capability to assess the cost-effectiveness of striping and delineation packages for inclusion in 3R projects. The implementation cost for the striping and delineation package is the full striping and delineation cost minus the cost of the pavement markings that would have been implemented as a default. The crash reduction effectiveness of improved striping and delineation on rural two-lane highways is documented in Section 4.3.1.7. 6.4.5 Rumble Strip Improvements Centerline and shoulder rumble strips are effective in reducing crashes on urban and suburban arterials, although there are no documented crash reduction effectiveness estimates for rumble strips in HSM Chapter 12. The literature includes the crash reduction effectiveness for one application on urban and suburban arterials—centerline rumble strips on urban two-lane arterials (see Section 4.3.4.5). Nevertheless, it is expected that most urban and suburban arterials have traffic volumes sufficiently high to make rumble strips cost-effective for use on urban and suburban arterials. Noise that can potentially disturb nearby residents is an elevated concern in urban and suburban areas. Highway agencies should exercise judgment based on current agency policies about locations where installation of centerline and shoulder rumble strips is or is not desirable on urban and suburban arterials.

131 6.4.6 Removal of Roadside Objects Where roadside objects are present within the clear zone width on an urban or suburban arterial, their removal may be considered on the basis of a cost-effectiveness analysis, using the RSAP model (23, 24, 25). Generally, only objects greater than 4 inches in diameter and not of breakaway design are considered. Where roadside objects are present continuously or at regular intervals throughout all or part of the length of a 3R project, as is the case on many urban and suburban arterials, removal of those objects is not likely to be cost-effective and a formal RSAP analysis is not needed. As alternatives to removing roadside objects, consideration may also be given to replacing the object with a similar object of breakaway design, relocating the object behind an existing guardrail or traffic barrier, or installing a new guardrail or traffic barrier. Decisions concerning the cost-effectiveness of new guardrail or other traffic barriers should be made with the RSAP model (see Section 6.4.7). 6.4.7 Installation/Rehabilitation of Guardrail and Other Traffic Barriers Existing guardrail or other traffic barriers that have reached the end of their useful life or are of obsolete design should generally be rehabilitated or replaced as part of a 3R project. The decision to rehabilitate or replace a guardrail or traffic barrier does not require a formal economic analysis, as long as the highway agency believes that the guardrail or traffic barrier is needed and warranted at its location. If the highway agency has reason to believe that the existing guardrail or traffic barrier may not be warranted, the warrants and length of need for the barrier can be assessed with the AASHTO Roadside Design Guide (30). Installation of new guardrail or other traffic barriers may be considered by highway agencies as part of 3R projects on urban and suburban arterials. The RSAP model should be used to evaluate the cost-effectiveness of any new guardrail or traffic barrier installations that are considered. 6.4.8 Intersection Turn Lane Improvements Benefit-cost analyses (5) have shown that intersection turn-lane improvements, including installation of left- and right-turn lanes, are likely to be cost-effective at any intersection where installation of the turn lane makes traffic operational sense. Highway agencies should, therefore, assess the traffic operational need for intersection turn lanes using established access management policies or traffic operational analysis tools. If the highway agency concludes that installation of the turn lane is justified on a traffic operational basis, there is little doubt that the turn lane will be cost-effective on a safety basis as well.

132 6.4.9 Other Intersection Improvements A 3R project may provide an opportunity for implementing other intersection improvements, involving traffic control, signing, delineation, marking, or sight distance. Highway agencies should implement such improvements if a need is identified based on a crash history review. 6.5 Rural and Urban Freeways 6.5.1 Lane Widening Most urban and rural freeways have existing 12-ft lanes, except at locations where a highway agency has made a previous decision to use narrower lanes to provide space for additional through lanes. At locations that were built with lanes less than 12 ft in width, Spreadsheet Tool 1 can be used for benefit-cost evaluation of lane widening alternatives. In such cases, widening to 12-ft lanes is likely to be cost-effective over the typical range of freeway volumes. Site-specific analyses with Tool 1 are recommended, however, to justify such projects. 6.5.2 Outside Shoulder Widening Existing freeways may have a range of outside shoulder widths. Most existing freeways have outside shoulder widths of at least 10 ft, although a few sites may have narrower shoulders. At locations that were built with outside shoulders less than 12 ft in width, Spreadsheet Tool 1 can be used for benefit-cost evaluation of shoulder widening alternatives. In such cases, widening to 12-ft shoulders is likely to be cost-effective over the typical range of freeway volumes. Site- specific analyses with Tool 1 are recommended, however, to justify such projects. 6.5.3 Inside Shoulder Widening Existing freeways may have a range of inside (median) shoulder widths. Most existing freeways have inside shoulder widths of at least 4 ft, although a few sites may have narrower shoulders. At locations that were built with inside shoulders less than 12 ft in width, Spreadsheet Tool 1 can be used for benefit-cost evaluation of shoulder widening alternatives. In such cases, widening to 12-ft shoulders is likely to be cost-effective over the typical range of freeway volumes. Site- specific analyses with Tool 1 are recommended, however, to justify such projects. Many highway agencies prefer to limit inside shoulder widths to a maximum of 4 ft to encourage motorists to stop on the outside shoulder, rather than the inside shoulder, when the need to stop arises. Nothing in these guidelines suggests that highway agencies should change such policies if highway agency experience indicates that vehicles stopping on the inside shoulder are undesirable.

133 6.5.4 Install Median Barriers While Spreadsheet Tools 1 and 2 can be used to assess the cost-effectiveness of median barrier installation, these spreadsheet tools for 3R projects based on HSM Chapter 18 (3) are not well suited to assessing the shifts in crash severity distributions that may result from median-barrier installation. Research generally indicates that median-barrier installation reduces the frequency of fatal-and-serious injury crashes, but may increase the frequency of less severe crashes. In general, the AASHTO Roadside Design Guide (30) is better suited to assessing the need for median barriers than the HSM Chapter 18 predictive models. Therefore, the Roadside Design Guide is preferred to Spreadsheet Tools 1 and 2 for such analyses. 6.5.5 Install or Restore Guardrail or Other Barrier Types on the Roadside Outside the Traveled Way While Spreadsheet Tools 1 and 2 can be used to assess the cost-effectiveness of guardrail or other roadside barrier installation, these spreadsheet tools for 3R projects based on HSM Chapter 18 (3) are not well suited to assessing the shifts in crash severity distributions that may result from guardrail and other roadside barrier installation. Research generally indicates that barrier installation reduces fatal-and-serious injury crashes, but may increase less severe crashes. In general, the AASHTO Roadside Design Guide (30) is better suited to assessing the need for guardrail or other roadside barriers than the HSM Chapter 18 predictive models. Therefore, the Roadside Design Guide is preferred to Spreadsheet Tools 1 and 2 for such analyses. 6.5.6 Shoulder Rumble Strips Spreadsheet Tools 1 and 2 are well suited to estimating the anticipated cost-effectiveness for installation of centerline and rumble strips. Calculations with these spreadsheet tools indicate that shoulder rumble strips on either or both sides of the roadway are generally cost-effective on rural and urban freeways over the full range of traffic volume levels typically present on those freeways. 6.5.7 Horizontal Curve Improvements Where the superelevation of an existing curve is less than the design superelevation value in the AASHTO Green Book (4) by more than 1 percent, restoration of superelevation to the Green Book value should be considered as part of any 3R project conducted. There is no formal benefit- cost tool for superelevation improvement in this situation, so decisions should be based on engineering judgment. Realignment of one or more horizontal curves on a freeway is considered reconstruction and is outside the scope of 3R work.

134 6.5.8 Sight Distance Improvements As on rural two-lane highways, stopping sight distance improvements on freeways are only likely to be cost-effective where the sight distance limitation hides key roadway features from the driver’s view. On freeways, the roadway features whose presence may indicate the need for a sight distance improvement or mitigation measures include horizontal curves, ramp terminals, and locations where standing queues are frequently present (e.g., on a daily basis). Where such features are present in an area with limited sight distance, alignment improvements to provide more sight distance should be considered. However, projects to realign freeways are generally considered reconstruction rather than 3R work. 6.5.9 Normal Pavement Cross Slope Pavement cross slope is needed for drainage so that water flows off the pavement during and after precipitation. Each highway agency has their own design criteria for normal pavement cross slope; these criteria are typically selected as suitable for local climate conditions. Where the pavement cross section within a 3R project does not have sufficient cross slope for drainage, the pavement cross slope should be restored to meet the highway agency’s applicable design criteria for pavement cross slope. Given the importance of pavement cross slope to drainage, no benefit- cost analysis is needed to justify restoration of normal pavement cross slope in a 3R project on a freeway.

Next: Chapter 7. Summary of 3R Design Guidelines »
Guidelines for Integrating Safety and Cost-Effectiveness into Resurfacing, Restoration, and Rehabilitation (3R) Projects Get This Book
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TRB's National Cooperative Highway Research Program (NCHRP) has released a pre-publication, non-edited version of Research Report 876: Guidelines for Integrating Safety and Cost-Effectiveness into Resurfacing, Restoration, and Rehabilitation (3R) Projects. The report presents an approach for estimating the cost-effectiveness of including safety and operational improvements in a resurfacing, restoration, or rehabilitation (3R) project. The approach uses the performance of the existing road in estimating the benefits of a proposed design improvement and in determining if it is worthwhile. These guidelines are intended to replace TRB Special Report 214: Designing Safer Roads: Practices for Resurfacing, Restoration, and Rehabilitation. The guidelines are accompanied by two spreadsheet tools available for download through a .zip file: one for analyzing a single design alternative and one for comparing several alternatives or combinations of alternatives.

Disclaimer: This software is offered as is, without warranty or promise of support of any kind either expressed or implied. Under no circumstance will the National Academy of Sciences or the Transportation Research Board (collectively "TRB") be liable for any loss or damage caused by the installation or operation of this product. TRB makes no representation or warranty of any kind, expressed or implied, in fact or in law, including without limitation, the warranty of merchantability or the warranty of fitness for a particular purpose, and shall not in any case be liable for any consequential or special damages.

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