EVALUATIONOFINTERNATIONALFRICTIONINDEXANDHIGH­FRICTIONSURFACES

ThesissubmittedtothefacultyoftheVirginiaPolytechnicInstituteandStateUniversityinpartialfulfillmentoftherequirementsforthedegreeof

MasterofSciencein

CivilandEnvironmentalEngineering

JulioAlbertoRoa

COMMITTEEMEMBERS:

Dr.GerardoW.Flintsch,ChairDr.AntonioA.TraniDr.LinbingWang

DECEMBER5,2008Blacksburg,Virginia

Keywords:InternationalFrictionIndex,harmonization,high‐frictionsurface,safety,testingdevices.

ii

ABSTRACT

Statehighwayagencieshaveanobligationtoprovideuserswithoptimalsurface

conditionsundervariousweatherconditionsthroughouttheyear.Asatisfactory

pavementsurfaceshouldexhibitgoodfrictionandtexturedepthtoreduceroadway

highwayaccidents.Thisiswhyfrictionisstartingtoreceiveincreasedattentionin

thepavementmanagementprocess.

Therehavebeennumerousresearcheffortsbydifferentcountriesandagenciesto

betterunderstandthebehaviorofdifferentfrictiontestingdevicesandtheinfluence

oftexture,speed,andotherexternalconditionsontheirmeasurements.

Thefirstpartofthisthesispresentsaresearchefforttocompareandharmonize

textureandskidresistancemeasurementstakenwithvariousdeviceson24

pavementsectionswithawiderangeoftextures.Measurementswerecompared

andtheInternationalFrictionIndex(IFI)calculatedfollowingPIARCandASTM

steps.

TheresultsrevealeddiscrepanciesintheIFIvaluescalculatedforthedifferent

devices,suggestingthatthecoefficientsA,B,andCproposedbyPIARCmayneedto

beadjustedforeachdeviceconsideredbeforetheIFIcanbeimplementedbythe

surfacepropertiesconsortiumparticipatingagencies.InthisresearchtheA,B,andC

coefficientswerethenrecalculated,andthepredictedvaluesoffrictionusingthese

revisedcoefficientsarepresented.Thecoefficientsdevelopedwerealsousedto

obtainIFIvaluesforhigh‐frictionsurfaces(HFS).

Ithasbeenfoundthatunderdifferentconditions,differentparametersand

coefficientswillresult.Itisstronglyrecommendedequipmentcomparison

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experiments(liketheNASAandSmartRoadprograms)continuetobetter

determinethecoefficientsnecessaryforharmonization.

HFShaveemergedasviablehigh‐frictionpavementalternativesthatmitigatethe

consequencesofdrivererror,poorgeometricalignmentoftheroadway,and

insufficientfrictionatthetire‐pavementinteraction,especiallyduringwetweather.

ThisthesispresentsastudyoftheHFSavailableintheU.S.marketandtheir

performance(frictionandtexture)indifferentapplications,underdifferentweather

conditions,andinvariouslocations.Thisthesisalsopresentstheresultsofthe

benefit‐costanalysisforthestudiedHFS.

iv

ACKNOWLEDGEMENTS

IwouldliketothankGodforgivingmetheopportunitytostudyinsuchagreat

schoolwithwonderfulprofessorsandcolleagues.

Iwouldalsoliketoexpressmydeepestgratitudetomyparents,mybrother,my

sister,andmyunclesandaunts,whohaveallbeenthereformeinthisprocesswith

wordsofencouragement,support,prayers,andfinancialsupport.

Iwouldliketorecognizemyprofessorsandmentorsfortheinvaluablehelpand

guidancethroughmystudies.

Thankyou,Dr.Flintsch,fortheeverydaylessons,unconditionalhelp,patience,and

fortheprivilegeofworkingwithsuchanoutstandingprofessionallikeyou.

Thankyou,Dr.Trani,forbelievinginmeandbeingmymentor,friend,andsomeone

Ideeplyadmireandrespect.

Thankyou,Dr.Wangforyourguidanceandhelpthroughthisprocess.

Thankyou,Dr.Edgarforyoursincerefriendshipandforalwaysbeingavailableto

teach,explain,guide,andhelpthroughouttheprocessofthisthesis.

ThankyoutoallthepeoplefromtheFederalHighwayAdministration(FHWA)and

theConnecticut,Minnesota,Pennsylvania,SouthCarolina,Wisconsin,andVirginia

departmentsoftransportation(DOTs)andtoKevinMcGheefromtheVirginia

TransportationResearchCouncil.

v

IalsowanttothankmyRepublicaDominicanaforgivingmethedesireandpassion

toworkhard,accomplishgreatthings,andmakeadifference.

FinallythisthesisisdedicatedtomyfriendsinBlacksburgandintheDominican

Republicwhohavebeenpartofthis:Manuel,Henry,Oscar,Mario,Billy,Dana,and

theCranwells.

Thisthesisispossibleonlybecauseofthecombinationofeffortsandsupport

providedbyyouall.

GRACIAS DE TODO CORAZON

vi

TABLEOFCONTENTS

ABSTRACT........................................................................................................................ ii

ACKNOWLEDGEMENTS............................................................................................... iv

LIST OF TABLES............................................................................................................. ix

LIST OF FIGURES ............................................................................................................ x

CHAPTER I Introduction ................................................................................................. 1

1. Background................................................................................................................. 22. Problem Statement...................................................................................................... 23. Objectives ................................................................................................................... 34. Organization of the Thesis.......................................................................................... 4

Chapter 2: Evaluation of the International Friction Index .......................................... 4Chapter 3: Field Performance of High-Friction Surfaces ........................................... 4Chapter 4: Findings, Conclusions, and Recommendations ........................................ 4

5. Significance ................................................................................................................ 5CHAPTER II Evaluation of The International Friction Index Coefficients ...................... 6

ABSTRACT.................................................................................................................... 61. INTRODUCTION ...................................................................................................... 72. OBJECTIVE ............................................................................................................... 73. BACKGROUND ........................................................................................................ 8

3.1 Harmonization Effort ............................................................................................ 83.3.1 PIARC Experiment to Compare and Harmonize Texture and Skid Resistance Measurements ....................................................................................... 83.1.2 NASA Wallops Friction Workshops Program............................................. 103.1.3 HERMES Experiment.................................................................................. 10

4. DATA COLLECTION ............................................................................................. 115. RESULTS AND ANALYSIS................................................................................... 14

5.1 Changes of Friction with Speed.......................................................................... 145.2 IFI Comparisons.................................................................................................. 155.3 Speed Parameter Calculation .............................................................................. 20

6. FINDINGS AND RECOMMENDATIONS ............................................................ 237. ACKNOWLEDGEMENTS...................................................................................... 248. REFERENCES ......................................................................................................... 25

CHAPTER III FIELD PERFORMANCE OF HIGH-FRICTION SURFACES ............ 26

vii

ABSTRACT.................................................................................................................. 261. INTRODUCTION .................................................................................................... 272. OBJECTIVE ............................................................................................................. 283. BACKGROUND ...................................................................................................... 29

3.1 High-Friction Surfaces Application Processes ................................................... 303.2 High-Friction Surface Binders............................................................................ 303.3 Properties of Aggregates for High-Friction Surfaces ......................................... 31

3.3.1 Standard Practice for the Accelerated Polishing of Aggregates Using the British Wheel (AASHTO T279, ASTM D3319).................................................. 313.3.2 Resistance to Degradation and Abrasion (AASHTO T96, ASTM C131) ... 323.3.3 Soundness of Aggregates by Freeze-Thawing (AASHTO T103-91, ASTM C88)....................................................................................................................... 32

3.4 High-Friction Surfaces Aggregates..................................................................... 333.4.1 Calcined Bauxite.......................................................................................... 333.4.2 Dolomite ...................................................................................................... 343.4.3 Granite.......................................................................................................... 343.4.4 Silica ............................................................................................................ 343.4.5 Steel Slag ..................................................................................................... 35

3.5 Previous High-Friction Surfaces Studies ............................................................ 353.5.1 Investigative Study of the Italgrip System – Noise Analysis ...................... 353.5.2 Trials of High-Friction Surfaces for Highways ........................................... 363.5.3 Evaluation of Cargill Safelane Epoxy Overlay............................................ 363.5.4 Performance of Poly-Carb, Inc. Flexogrid Bridge Overlay System ............ 373.5.5 Florida DOT - Tyregrip Forensic Report..................................................... 373.5.6 Evaluation of Innovative Safety Treatments................................................ 373.5.7 Investigative Study of Italgrip System 2008................................................ 38

3.6 High-Friction Surface Systems Studied.............................................................. 383.6.1 Crafco HFS .................................................................................................. 383.6.2 Safelane (Cargill) ......................................................................................... 393.6.3 Tyregrip (Prismo - Ennis Paint)................................................................... 393.6.4 Italgrip.......................................................................................................... 403.6.5 FlexoGrid (Polycarb) ................................................................................... 40

3.7 High Friction Surfaces Typical Application Procedure...................................... 403.8 High-Friction Surface Potential Sources of Failures .......................................... 42

3.8.1 Epoxy Preparation - Composition................................................................ 423.8.2 Epoxy Aggregate Placement........................................................................ 433.8.3 Existing Pavement - Existing Asphalt Compatibility .................................. 433.8.4 Humidity and Moisture (Surface and Aggregate)........................................ 433.8.5 Ambient Temperature .................................................................................. 443.8.6 Curing Time................................................................................................. 44

3.9 High-Friction Surfaces Field Evaluations........................................................... 444. DATA COLLECTION ............................................................................................. 46

4.1 Location of Studied High-Friction Surfaces ....................................................... 464.2 Measurements of Friction and Texture Properties.............................................. 48

4.2.1 DF TESTER (ASTM E1969)....................................................................... 49

viii

4.2.2 CT METER (ASTM E2157)........................................................................ 494.2.3 GRIPTESTER (ASTM E1844).................................................................... 494.2.4 LOCKED WHEEL DEVICE (ASTM E274) .............................................. 50

4.3 Cost Data............................................................................................................. 514.4 Accident Data...................................................................................................... 52

5. RESULTS ................................................................................................................. 525.1 Friction and Texture Data Processing................................................................. 525.2 Initial Friction – Cost .......................................................................................... 56

6. ANALYSIS............................................................................................................... 566.1 Economic Analysis ............................................................................................. 56

6.1.1 Estimated High-Friction Surface Service Lives .......................................... 576.1.2 Values for Transportation Economic Study................................................. 586.1.3 Benefit-Cost ................................................................................................. 59

6.2 International Friction Index for High-Friction Surfaces. .................................... 627. FINDINGS AND RECOMMENDATIONS ............................................................ 638. ACKNOWLEDGEMENTS...................................................................................... 639. REFERENCES ......................................................................................................... 64

CHAPTER IV SUMMARY, FINDINGS, CONCLUSIONS, AND

RECOMMENDATIONS.................................................................................................. 67

1. FINDINGS................................................................................................................ 672. CONCLUSIONS ...................................................................................................... 683. RECOMMENDATIONS FOR FUTURE RESEARCH........................................... 69

ix

LISTOFTABLES

TABLE 1. Summary of IFI’s friction component values for different equipment.......... 17

TABLE 2. Summary of F60 IFI coefficients for different friction units ......................... 19

TABLE 3. Experimental and Calculated Sp Values......................................................... 21

TABLE 4. Coefficients a and b......................................................................................... 23

TABLE 1. Type of Aggregate and Price for Selected HFS.............................................. 33

TABLE 2. HFS Products Installed in the United States ................................................... 45

TABLE 3. HFS Locations Investigated ............................................................................ 46

TABLE 4. Type of Aggregate and Price for Selected HFS............................................. 51

TABLE 5. Crash Values for Economic Study .................................................................. 51

TABLE 6. Friction Measurements for Selected HFS ....................................................... 53

TABLE 7. Friction Texture Measurements for Selected HFS.......................................... 54

TABLE 8. Price and Initial Friction and Macrotexture for Selected HFS........................ 56

TABLE 9. Benefit-Cost Analysis for HFS Locations in Waukesha, Wisconsin.............. 60

TABLE 10. Benefit-Cost Analysis for HFS Locations in LaCrosse, Wisconsin ............. 61

TABLE 12. HFS Friction Measurements using the International Friction Index............. 62

x

LISTOFFIGURES

FIGURE 1. Friction and macrotexture testing equipment ............................................... 13

FIGURE 2. Sample of pavement surfaces available at the Virginia Smart Road............ 14

FIGURE 3. IFI F60 values for different equipment versus DFT F60 values .................. 18

FIGURE 4. Comparison of original and revised F60 values using three-parameter (A, B,

C) models. ................................................................................................................. 20

FIGURE 5. Comparison of computed and experimental Sp values ................................. 22

FIGURE 1. High-friction surface application (Adam and Gansen 2001). ....................... 42

FIGURE 2. High-Friction Surface Raveling (Adam and Gansen 2001) .......................... 44

FIGURE 3. HFS Locations investigated........................................................................... 47

FIGURE 4. Data collection devices.................................................................................. 48

FIGURE 5. Texture and friction whisker box plot for all HFS systems........................... 55

FIGURE 6. HFS wear and scuffing rate. .......................................................................... 58

1

CHAPTERI

INTRODUCTION

Highwayaccidentsarealeadingcauseofdeathandinjuryaroundtheworld.Each

year3.2millionpeopleareinjuredordisabledintheUnitedStatesasaresultof

roadcrashes(N.T.S.1999).Theseaccidentsnotonlycreateanenormoussocialcost

forindividual,families,andcommunitiesbutalsoplaceaheavyburdenonhealth

servicesandeconomies.

IntheUnitedStatesonepersondiesevery12minutesinamotorvehiclecrash

(N.T.S.1999).ThisstaggeringsituationhasledtheFederalHighwayAdministration

(FHWA)todeclaresafetyasoneofitstoppriorities.Wet‐weathercrashesandrun‐

off‐roadincidentsarethetwotypesofhighwayaccidentsresponsibleforthe

majorityofincidents;about25percentofallcrashesand14percentofallfatal

crashesoccuronwetpavementwhile59percentofhighwayfatalitiesoccurwhena

vehicleleavesitslane(JulianandMoler2008).Itisforthisreasonthathigh‐friction

surfaces(HFS)arestartingtobeconsideredforroadwayareaswhereadditional

frictionisneeded.HFShavetheabilityofincreasingfrictionandtexturebyutilizing

non‐polishable,roughaggregates.Differenttypesofbindersareusedtoholdthe

aggregateparticlestogetherandgluedtotheroadsurface.

Statedepartmentsoftransportationstrivetoprovideuserswithsmooth‐riding,safe

surfaceconditionsthroughouttheyear.Todoso,agenciesperiodicallymonitorthe

pavementsurfaceproperties.Themeasurementstakenareusedtodevelopsurface

restorationalternatives,newconstructionspecifications,accidentinvestigations,

pavementmanagementsystemsnetworksurveys,andwinterroadmaintenance.In

particular,agenciesusedifferentdevices,systems,andmethodstomeasurefriction

andsurfacetexture.Thisemphasizestheneedforfrictionmeasurements

harmonizationtoprovidecomparablefrictionmeasurementsamongdifferent

devices(Wamboldetal.1995).

2

1.BACKGROUND

High‐frictionsurfaces,orHFS,arespecialsurfacetreatmentsthatutilizeanon‐

polishableaggregateandaresin‐basedbindertoholdtheaggregatetotheroad

surface.Thistechnologywasoriginatedinthe1950swhentheU.K.government’s

TransportandRoadResearchLaboratory(TRRL)begantotesthardaggregateswith

variousbinderstoproduceextremelyhigh‐frictionsurfaces(Nicholls1998).Inthe

late1980sresearchersintheUnitedStatesbegantoinvestigatetheeffectivenessof

thesesurfacingsystemstoreducecrashesonblackspots.In1989astudyforthe

FederalHighwayAdministration(FHWA)donebyUniversityofMichiganon15

rampsat11interchangesin5statesfoundthatsurfacepropertieswererelatedto

truckcrashes,alongwithgeometryandvehicledynamics(JulianandMoler2008).

Inadditiontherehavebeennumerousresearcheffortsbydifferentorganizationsto

betterunderstandthebehaviorofdifferentfrictiontestingdevicesandtheinfluence

oftexture,speed,andotherexternalconditionsontheirmeasurements.These

effortsincludethePIARCExperimenttoCompareandHarmonizeTextureandSkid

ResistanceMeasurements,theNASAWallopsFrictionWorkshops,andtheHERMES

Experiment.

2.PROBLEMSTATEMENT

ThemainobjectiveofthisthesisistostudysomeoftheHFSsystemsavailableinthe

U.S.marketbymeasuringtheirperformanceindifferentapplications,under

differentweatherconditions,andinvariouslocations(states).Theresultsobtained

inthisresearchwillinformagenciesabouttheHFSavailableintheUnitedStates

andwillprovideapracticaltooltoestimatetheexpectedincreaseinskidresistance,

theexpectedservicelife,andthecostforeachavailableproduct.

3

Asecondaryobjectiveofthisthesisistocomparefrictionmeasureresultsfor

differentsurfaces,includingHFS,andshowifthepreviouslyadoptedmodelsfor

normalizingthesemeasurementsarevalid.Thecalibratedmodelsshouldpresent

theresultingmeasurementsinauniversalscale.

3.OBJECTIVES

ThemaingoalofthisthesisistostudysomeoftheHigh‐frictionsurfacesavailablein

theUnitedStatesmarket;bymeasuringtheirperformanceondifferentapplications,

underdifferentweatherconditions,andinvariouslocations(states).Thankstothe

resultsobtainedinthisresearch,agencieswillbeinformedonthehigh–friction

surfacesavailableonUnitedStates,andapracticaltooltoestimatetheexpected

increaseonskid,theexpectedservicelife,andthecostforeachavailableproduct.

Asecondarygoalistocomparefriction‐measuringresultsondifferentsurfaces

includinghigh‐frictionsurfacesandshowifthepreviouslyadoptedmodelsto

normalizethesemeasurementsarevalid.Thecalibratedmodelsshouldallow

presentingtheresultingmeasurementsinauniversalscale.

Thespecificobjectivesdefinedtoaccomplishthesegoalsarethefollowing:

• Comparefrictionmeasuringresultsmadewithdifferentdevices.

• Evaluateifavailableharmonizationadoptedmodelsarevalid.

• Investigatethehigh‐frictionsurfacesintheU.S.market

• Measuretheirperformanceindifferentapplications.

• Compiletheresultsobtainedinapracticaltooltosupportdecision‐making.

4

4.ORGANIZATIONOFTHETHESIS

ComplyingwiththeVirginiaTech’sgraduateschoolguidelinesthatencourage

publicationofresearchresults,thisthesisfollowsamanuscriptformatthatincludes

twomanuscripts.Eachmanuscriptisusedasanindividualchapterofthethesis.

Togethertheyrepresenttheresearchworkinwhichtheauthorwasinvolvedat

VirginiaTechduringthedurationofthemasterstudies.Thefirstchapterofthe

thesisisthisintroduction,whichprovidesanoutlinefortherestofthedocument.

Chapter2:EvaluationoftheInternationalFrictionIndex

Thisevaluationcomparesfrictionmeasurementsobtainedwithdifferentdevices

andevaluatesifthepreviouslyadoptedfrictionharmonizationmodelsarevalid.

Thechaptercomparesmacrotextureandskidresistancemeasurementstakenatthe

VirginiaSmartRoadin2008andprovidesgroundworkfortheharmonizationof

frictionmeasurementstakenondifferentHFSwithvariousdevices.Thispaperis

scheduledforpresentationatthe88thannualmeetingoftheTransportation

ResearchBoardandhasbeenrecommendedforpublicationintheJournalofthe

TransportationResearchBoard.

Chapter3:FieldPerformanceofHigh­FrictionSurfaces

ThischapterpresentsacriticalreviewoftheliteratureonHFSbinders,aggregates,

applicationprocesses,HFSwearrate,savedlives,andtheHFSavailableinthe

UnitedStates.ItalsocontainsexpectedinitialfrictionforHFSsystemsandasample

benefit‐costanalysisforanapplicationtestedinWisconsin.

Chapter4:Findings,Conclusions,andRecommendations

Thischapterpresentsasummaryoftheconcludingideasthatresultfromthe

researchpresentedinChapters2and3andgivesrecommendationsforfuture

researchintheseareasofstudy.

5

5.SIGNIFICANCE

Surfacepropertiesofroadsandrunwaysplayanimportantroleinroadandairport

safety.Roadandrunwaysurfacesmustprovideadequatelevelsoffrictionand

textureforthevehiclestravelingonthem.Thepurposeofthisthesisisto compare

frictionmeasureresultsondifferentsurfaces,includingHFS,andshowifthe

previouslyadoptedmodelsfornormalizingthesemeasurementsarevalid. The

resultsconcerningthevalidityofnormalizingmodelsareinvaluableforachieving

consistentpavementmanagementpracticesacrossnationalboundaries.Theyalso

contributetothestandardizationofspecificationsforpavingmaterials,highway

design,andrunwaydesign.

ThisresearchproducednewInternationalFrictionIndexcoefficientstocompare

andharmonizetextureandskidresistancemeasurementstakenwithdifferent

devicesandappliedthesecoefficientstothestudiedHFSsurfacestocompare

calculatedfrictiontomeasuredfriction.

Thisthesisprovidesagencieswithdetailedinformationonfrictionandtexture

performanceoftheHFSavailableintheUnitedStates.Inadditionitpresentsthe

methodologyandsampledatanecessarytoperformbenefit‐costanalysisforsome

oftheavailableHFS,anditpresentsthedurability,performance,andcostofthese

treatmentsinapracticalandaccessibleguideline.

6

CHAPTERII

EVALUATIONOFTHEINTERNATIONALFRICTION

INDEXCOEFFICIENTS

ABSTRACT

Thispaperpresentsaresearchefforttocompareandharmonizetextureandskid

resistancemeasurementstakenwithvariousdevicesattheVirginiaSmartRoadin

May2008bythemembersoftheVirginiaConsortiumforPavementSurface

Properties.

Therehavebeennumerouseffortsbydifferentcountriesandagenciestobetter

understandtherelationshipandbehaviorofdifferentfrictiontestingdevicesand

theinfluenceoftexture,speed,andotherexternalconditionsonthese

measurements.Measurementsobtainedwithdifferenttypesofequipmenton24

pavementsectionswithawiderangeoftextureswerecompared,andthe

relationshipbetweenfrictionandspeedforthedifferentpavementsectionsand

deviceswasstudied.Datawascollectedusingtwolocked‐wheelskidtrailers,a

GriptesterandaDynamicFrictionTester(DFT).Nineasphaltsectionsweretested;

sixareSUPERPAVEmixes,twoareStoneMatrixAsphaltandoneisanOpenGraded

FrictionCoarse.TheconcretesectionstestedincludedoneContinuouslyReinforced

ConcretePavementwithtinedfinishingandtwoepoxyoverlays.

Eventhoughallofthestepsincludedinthespecificationsderivedfromthe

experimentsbythePermanentInternationalAssociationofRoadCongresses

(PIARC)werefollowed,theresultsobtainedarenotsatisfactory.Fromatheoretical

stand‐pointallthevaluescomputedwiththeInternationalFrictionIndex(IFI)F60

7

shouldbeequal,butthisisnotthecase.DiscrepanciesintheIFIvaluescalculated

forthedifferentdevicessuggestthattheoriginalcoefficientsdeterminedduringthe

PIARCexperimentmayneedtobeadjustedforthedevicesevaluatedbeforetheIFI

canbeimplementedbytheparticipatingagencies.

1.INTRODUCTION

Asatisfactorypavementsurfaceshouldexhibitgoodqualitiesintermsoffriction,

smoothness,durability,lightreflection,tire‐pavementnoise,splash/spray,and

rollingresistanceinordertoprovidethedriverasafeandcomfortableride.Ofall

thefactors,frictionand/ortexturedepthofthesurfaceisparamounttocontrolling

andreducinghighwayaccidents.Thisiswhyfrictionisstartingtoreceiveincreased

attentioninthepavementmanagementprocess.StateHighwayAgencieshavean

obligationtoprovideuserswithoptimalsurfaceconditionsthroughouttheyear.To

doso,agenciesmustperiodicallymonitorthesurfaceproperties.The

measurementstakencouldbeusedtodevelopspecificationsforsurfacerestoration,

specificationsfornewconstructions,accidentinvestigations,networksurveysfor

pavementmanagementsystems,andmeasurementsforwinterroadmaintenance.

Therearedifferentdevicesusedbystatehighwayagenciestomeasurefriction.

Evenwhentakenbythesametypeofequipment,frictionmeasurementsarenot

consistentandthereforesometimescannotbecompared.Thisphenomenon

emphasizestheneedforharmonizationinordertoprovidecomparablefriction

surfacesfromonedevicetoanotherorfromstatetostate.

2.OBJECTIVE

Differentresearcheffortshavestudiedprocedurestonormalizesurface

measurementsmadebydifferenttypesoffrictionmeasuringequipment.The

objectiveofthispaperistocomparefrictionmeasuringresultsandshowifthe

previouslyadoptedmodelsarevalid.Theresearcheffortisaimedatcomparingand

8

harmonizingtextureandskidresistancemeasurementstakenattheVirginiaSmart

Roadin2008bythemembersofthePavementSurfacePropertiesConsortium.This

consortiumisajointeffortbytheFederalHighwayAdministration(FHWA)andthe

Connecticut,Georgia,Mississippi,Pennsylvania,SouthCarolina,andVirginia

departmentsoftransportation(DOTs).

3.BACKGROUND

3.1HarmonizationEffort

Therehavebeennumerouseffortsbydifferentorganizationstobetterunderstand

therelationshipandbehaviorofdifferentfrictiontestingdevicesandtheinfluence

oftexture,speed,andotherexternalconditionsontheirmeasurements.Someof

themaresummarizedfollowing.

3.3.1PIARCExperimenttoCompareandHarmonizeTextureandSkidResistance

Measurements

ThePermanentInternationalAssociationofRoadCongresses(PIARC)conducteda

seriesofexperimentstocomparetextureandfrictionmeasurements.Thefirstone

wasin1992whenPIARCundertookanexperimentthatencompassed16countries,

47measuringsystems,and54siteswiththeintentionofcomparingand

harmonizingtextureandskidresistancemeasurements.Underthiseffortawide

varietyofsurfacesweretestedandfrictionwasmeasuredwithfixed‐slip,side‐force,

andlocked‐wheeledsystemsatvariousspeeds.Texturewasmeasuredbystationary

andmobileequipment.

Aseriesofrelationshipsweredevelopedfromthecomparisonsofthe

measurements,whichproducedacommonharmonizedindexcalledthe

InternationalFrictionIndex(IFI)(Wamboldetal.1995).ThePIARCmodel,asitis

latercalled,incorporatedmacrotexturemeasurementswithside‐force,fixed‐slip,

andlocked‐wheelfrictionmeasurements,torecognizethepreviouslyidentified

dependenceoffrictiononspeedandtexture.

9

Macrotexturemeasurementswerefoundtobeexcellentpredictorsofthespeed

constantgradientneededtostandardizethefrictionmeasurementsusingtheIFI.

Textureclassificationswereproposedandaproceduretoestimatemacrotexture

fromtheprofiledatawasincorporatedintotheIFItoestimatetheMeanProfile

Depth(MPD).TheIFIcanthenbecalculatedfromtheresultsoffrictionvaluesand

speedconstant(Wamboldetal.1995).

TheIFIisamethodtoevaluateincommonscaledifferentmeasurementsproduced

bydifferentdevices.Thisindexconsistsoftwoparameters:thespeedconstant(Sp),

predictedthroughthemacrotexturemeasurements,andtheharmonizedfrictionat

60km/h(F60)(Wamboldetal.1995;Henry2000).

TheIFIcalculationfollowsthreesteps:

1) EstimatethespeedgradientcoefficientSp,usingthemeasuredmacrotexture:

Sp=a+b∗TX (1)

where

TX=macrotexturemeasurement(mm)

a,b=constantsfordifferentmethods/devicesused

2) ObtainthefrictionmeasurementfromthespecifiedslipspeedSforthefriction

instrumentusedatthestandardspeed,setat(60km/h):

(2)

where

FR(60)=Adjustedvalueoffriction

FR(S)=FrictionvalueatrecommendedslipspeedSfordevicesused

S=Recommendedslipspeedforeachdevice[km/h]

10

3) CalculatetheIFIfrictionnumberF(60)orgoldenstandardestimate,usingthe

coefficientsdevelopedbyPIARCforeachdevice:

F(60)=A+B∗FR(60)+C∗TX (3)

where

A,B,C=calibrationconstantsfortheselectedfrictionmeasuringdevice

TX=macrotexturemeasurement(mm)

3.1.2NASAWallopsFrictionWorkshopsProgram

TheNASAWallopsFrictionWorkshopshavebeenamulti‐yearprogramwhere

texture,friction,androughnessdatahasbeencollectedthroughvariousdevices,

someofwhichwerealsousedforthePIARCExperimentin1992.Measurements

aretakenatdifferentspeedsandalldevicesareoperatedaccordingtothe

manufacturer’sprocedures(Wamboldetal.2004).

Forself‐wettingfrictiondevices,runsaremadeconsecutively,andsome

nonstandardrunsareperformed,withvariationsonwaterfilmthickness,tiretypes,

inflationpressures,slipspeeds,andnormalloads.

3.1.3HERMESExperiment

In2001‐2002theHERMESprojectwasformedwiththeobjectiveofanalyzingthe

resultsoffieldtrialsinordertooptimizetheproceduresandprecisionofcalibrating

methodspreviouslydeveloped.Thisprojectconsidered15testingdevices,7

texturemeasuringdevices,and61testsurfacesinfivecountries(Descornet2004).

Ninecomparisonmeetingswereruninthefivemembercountries—Belgium,the

Netherlands,Spain,GreatBritain,andFrance—onawiderangeofsurfacescovering

mostmaterialsandtexturesavailableinEurope.Therewerethreemeetingsinthe

fallof2001,threeinthespringof2002,andthreeinthefallof2002.

11

Someofthefindingsforthisprojectstatethatusingthepowerlawforconstant

speedversusmeanprofiledepthbetterfitsthedata.Thisprocedurealsoconcludes

thatregardingconsistencytheEuropeanFrictionIndexworkssatisfactorily

nevertheless,regardingprecisionitishardlyacceptable.

4.DATACOLLECTION

In2006,theVirginiaTransportationResearchCouncil(VTRC)andtheVirginiaTech

TransportationInstitute(VTTI),initiatedaregionalpooled‐fundprojectknownas

thePavementSurfacePropertiesConsortiumtoestablisharesearchprogram

focusedonenhancingthelevelofserviceprovidedbytheroadwaytransportation

systembyoptimizingpavementsurfacetexturecharacteristics.Theprogramwas

setupwithsupportfromtheFHWAandnowincludessixDOTsfromthestatesof

Connecticut,Georgia,Mississippi,Pennsylvania,SouthCarolina,andVirginia.

Establishedasafive‐yearprogram,theconsortiumispartoftheactivitiesofthe

VirginiaSustainablePavementResearchConsortium(VA‐SPRC)andismanagedby

VTRCandrunbytheCenterforSustainableTransportationInfrastructureatVTTI.

Everyyearsinceitsinceptiontwoyearsago,alloftheparticipantmembersmeetfor

oneweekinMayattheVirginiaSmartRoadatVTTIwiththegoalofcomparingand

verifyingsurfacepropertymeasurementsonthesurfacesavailableatthefacility

witheachofthemember’sdifferentdevices.ThiseventistermedtheSurface

PropertiesRodeo,whichisacollaborativeresearcheffortoftheConsortiumthat

helpstheparticipantorganizationsverifytheoperation,reliability,andaccuracyof

theequipmentusedforpavementevaluationsandroadconstructionqualitycontrol.

Themay2008frictiontestingincludedtwolocked‐wheelskidtrailers,aGriptester

andadynamicfrictiontester(DFT).Oneofthelocked‐wheeltrailers(LWS1)used

onlyasmoothtire(ASTME‐524)whiletheothertrailer(LWS2)testedthesections

twice,oncewiththesmoothtireandthenwiththeribbedtire(LWR1)(ASTME‐

12

501).ThetestingwasconductedinaccordancewithASTME‐274(HenryandSiato

1983).TestingdonewiththeGriptesterutilizedthetesttiresuitableforthisfixed‐

slipdeviceinaccordancewith(ASTME1844)(Wamboldetal.2006).The

macrotexturedatawascollectedwithacirculartexturemeter(CTmeter)(Flintsch

etal.2003)inaccordancewithASTME2157.Figure1showspicturesofsomeofthe

participantdevices.

TheVirginiaSmartRoadisa3.2km(2‐mile),test‐adaptablefacilityfor

transportationresearchandevaluation.Thetestroadincludes12flexiblepavement

testsections;atransversallytinedcontinuouslyreinforcedconcretepavement

(CRCP)section,ajointedreinforcedconcretepavement(JRCP)sectionwithsome

groundareas,andtwohigh‐frictionepoxy‐basedsurfacetreatments.Theroadhasa

maximumlongitudinalgradeof6percent.Sincethetwolaneswerepavedat

slightlydifferenttimes,theuphill(westbound)anddownhill(eastbound)laneshave

slightlydifferentsurfacemicro‐andmacrotexture.Bothdirectionsweretestedin

eachrun.Twelvesectionseachapproximately100meters(300feet)longwere

selectedforthefrictioncomparisons,andeachsectionwastestedinboth

lanes/directions,resultinginatotalof24testlocations.Fiverepetitionswere

completedforeachdeviceateachlocation.

Ofthenineasphaltsectionstested,sixareSUPERPAVEmixes,twoareStoneMatrix

Asphalt(SMA)andoneisanOpenGradedFrictionCoarse(OGFC).Theconcrete

sectionsincludedaCRCPwithtinedfinishing,andtwoepoxyoverlaysconsistingof

adoublelayerofaggregatebondedbyepoxycoatings.Figure2showsexampleof

thedifferenttypesofpavementsurfacestested.Withineachpavementsection,

frictiondatawascollectedwiththelocked‐wheelskidtestersandtheGriptester

tiresalignedtothecenteroftheleftwheelpath.Fiverepetitionswereplannedat

targetspeedsof20,40and50mphtoanalyzetheeffectsofspeedonskid

resistance.Frictionatspeedsof20,40,60and80km/hwererecordedfortheDFT

(asperASTME1911,(ASTM1998).

13

a) Lockedwheelsmooth/ribbed

(LWS1)and(LWR1)

b) Griptester

(GT)

c) Lockedwheelsmooth

(LWS2)

d) Skidwheeltesters

(LWS2)

e) CircularTrackMeter

(CTM1)

f) DynamicFrictionTester

(DFT)

FIGURE1.Frictionandmacrotexturetestingequipment

14

SM9.5DSUPERPAVE

OGFC

SMA9.5D

TinedCRCP

StandardVDOTepoxyoverlay(EP)

Proprietaryepoxyoverlay(Cg)

FIGURE2.SampleofpavementsurfacesavailableattheVirginiaSmartRoad.

5.RESULTSANDANALYSIS

5.1ChangesofFrictionwithSpeed

Inordertostandardizetheresultsofthefrictionmeasurementsatvariousspeeds,

anexponentialregressioncurvewasfittedtothesetofpointsonthefrictionversus

speedrelationshipforeachsectionandforeachdevice.Theequationswereusedto

obtainnormalizedvaluesoffrictionforthespecificslipspeedsasrecommendedby

Wamboldetal.(Wamboldetal.1995).Theexponentialregressionfitwasselected

basedontherecommendationsofthePennStateModel,onwhichthePIARCmodel

wasestablished,tocalculatetheskidnumberatthespecifiedSslipspeed(Henry

2000):

15

(4)

where,

μ=calculatedcoefficientoffrictionatthespecifiedslipspeedforeachdevice

μ0=projectedcoefficientoffrictioninterceptatzerospeed

PNG=percentnormalizedgradient(thespeedgradienttimes100dividedby

thefriction,asdefinedby:

€

PNG = −100

µdµds

S=slidingvelocity

5.2IFIComparisons

ToevaluatewhetherornotthecoefficientsdevelopedduringthePIARCexperiment

applytothedevices,theIFIvalueswerecomputedusingthedifferentfrictionvalues

(FR)measuredbythevariousdevicesusedintheequipmentcomparison.

Table1showstheIFIvaluescalculatedforthevariousdevicesandforevery

pavementsectionontheuphillanddownhilllanes.Theprocedurefollowedto

obtaintheIFIwastheonespecifiedinPIARC(1):computeF(60)valuesusing

equations(1),(2),and(3)andincorporatingtherespectivefrictionvaluesatthe

recommendedslip[FR(S)]fromequation(4).ThestandardIFIequationforthe

DFTesterandCTMeterinASTM1960‐07(HenryandSiato1983)wereused.The

specifiedslipspeedswere65km/hfortheskidtesters,20km/hfortheDFT.Witha

15.6percentslipratioas(intheGriptestermanufacturerspecifications,the

Griptesternumbers(GN)weretakenat9.4km/htomatchthePIARCconditions;

otherwisethecoefficientstoestimateF(60)wouldnotapply.

ThemacrotexturemeasurementsobtainedfromtheCTMeterwereusedto

determineSpusingequation(1)anda=14.2andb=89.7(Wamboldetal.2006).

16

ThefrictionnumberF60wasfinallycomputedusingequation(3),withthe

coefficientscorrespondingtoeachdeviceintheoriginalPIARCreport(Wamboldet

al.2006).Themarkerslabeledare“original”inFigure3comparetheresultsfor

eachofthefourdevicesusedwiththestandardDFTvalues,asrecommendedin

ASTM1960‐07.ThecomputedIFIvaluesforthesamepavementsectionsobtained

usingdifferentdevicesareclearlynotinagreement.UsingtheoriginalPIARC

coefficients,theregressioncorrelationcoefficientsforthemeasurementswith

smoothtiresshowrelativelyweakcoefficientsofdetermination(R2).Thissuggests

thatthecoefficientsA,B,andCmayneedtobeadjustedforeachdeviceconsidered

beforetheIFIcanbeimplementedbytheparticipatingagencies.

TheA,B,andCcoefficientswerethenrecalculatedbyplottingtheF60DFTvalues

againstalltheFR60valuesforallthefrictioninstrumentsandfittingalinearmodel

usingregressionanalysis(asrecommendedbyASTM1960‐07).Twoparameters,A

andB,weredeterminedforthemeasurementswiththesmoothtires.Fortheribbed

tireresults(LWR1),amultipleregressionwasperformedincludingallthreeA,B,

andCcoefficients,whichproducedahigheradjustedR2.Thepredictedvaluesusing

theserevisedcoefficientsarealsodisplayedinFigure3(redtriangles).

17

TABLE1.SummaryofIFI’sfrictioncomponentvaluesfordifferentequipmentCTM DFT F60WithOriginalCoefficients F60WithRevisedCoefficients

SectionMPD F60 LWS1 LWS2 GT LWR1 LWS1 LWS2 GT LWR1

1 Loop 1.003 0.482 0.596 0.531 0.534 0.485 0.480 0.472 0.479 0.460

2 A 0.530 0.412 0.519 0.497 0.392 0.476 0.448 0.461 0.425 0.444

3 B 0.680 0.457 0.538 0.468 0.454 0.474 0.456 0.451 0.448 0.447

4 C 0.710 0.445 0.545 0.431 0.439 0.459 0.459 0.440 0.443 0.440

5 D 0.557 0.394 0.438 0.355 0.419 0.428 0.414 0.415 0.435 0.421

6 I 0.923 0.481 0.552 0.544 0.489 0.489 0.462 0.476 0.462 0.460

7 J 1.047 0.460 0.572 0.499 0.492 0.491 0.470 0.462 0.463 0.464

8 K 1.627 0.452 0.501 0.488 0.551 0.448 0.440 0.458 0.485 0.458

9 L 1.003 0.449 0.506 0.448 0.547 0.435 0.442 0.445 0.484 0.436

10 Cg 1.837 0.516 0.597 0.492 0.522 0.562 0.481 0.459 0.474 0.518

11 EP 1.197 0.432 0.520 0.436 0.428 0.467 0.448 0.441 0.439 0.456

12 CRCP 0.703 0.439 0.434 0.357 0.414 0.479 0.412 0.416 0.433 0.450

13 CRCP 0.803 0.465 0.568 0.486 0.455 0.495 0.469 0.457 0.449 0.460

14 Cg 1.860 0.538 0.607 0.552 0.537 0.609 0.485 0.478 0.480 0.541

15 EP 1.173 0.458 0.602 0.545 0.434 0.486 0.483 0.476 0.441 0.465

16 L 1.083 0.450 0.524 0.487 0.529 0.451 0.450 0.458 0.477 0.446

17 K 1.803 0.457 0.495 0.483 0.539 0.452 0.438 0.456 0.481 0.464

18 J 0.847 0.442 0.550 0.520 0.426 0.468 0.461 0.468 0.438 0.448

19 I 0.727 0.436 0.572 0.492 0.417 0.468 0.470 0.459 0.435 0.445

20 D 0.697 0.436 0.493 0.435 0.448 0.443 0.437 0.441 0.446 0.432

21 C 0.787 0.441 0.544 0.484 0.441 0.462 0.459 0.457 0.444 0.444

22 B 1.007 0.477 0.580 0.567 0.515 0.492 0.473 0.483 0.472 0.464

23 A 0.887 0.468 0.574 0.546 0.489 0.460 0.471 0.477 0.462 0.445

24 Loop 0.797 0.447 0.471 0.405 0.434 0.431 0.428 0.431 0.441 0.429

18

a)Locked‐wheelTrailer1w/smoothtire b)Locked‐wheelTrailer2w/smoothtire

c)Griptester(smoothtire)

d)Locked‐wheelTrailer1w/ribbedtire

FIGURE3.IFIF60valuesfordifferentequipmentversusDFTF60values

Furthermore,thecoefficientsofdetermination(R2)forthesmoothtiresindicate

relativelyweakrelationships(lefthalfofTable2),withtheGriptesterhavinga

relativelybettercorrelation.Someofthedifferencesmaybeexplainedbecauseof

theuseofthedefaulttexture‐Sprelationship(equation(6))asdiscussedintheNext

section.Table2comparesthePIARCcoefficientswiththerevisedcoefficients

computedforeachofthedevices.

19

TABLE2.SummaryofF60IFIcoefficientsfordifferentfrictionunits

OriginalCoefficients RevisedCoefficientsFrictionUnit A B C R2 A B C R2

0.2480 0.3898 ‐ 0.48LWS1 0.0446 0.9250 ‐ 0.35

0.2595 0.2957 0.0382 0.700.3152 0.2976 ‐ 0.38

LWS2 0.0446 0.9250 ‐ 0.370.3194 0.2042 0.0395 0.610.3072 0.3460 ‐ 0.41

GT 0.0821 0.9104 ‐ 0.620.3385 0.2018 0.0308 0.50

LWR1 ‐0.0228 0.6068 0.0976 0.78 0.1905 0.2925 0.0718 0.75

Althoughthebiasiscorrectedwiththerevisedcoefficients,therearestillsome

sectionsforwhichtheequationsforthesmoothtiredonotwork.Somepointswith

lowandhighDFTF60arequitefarfromtheequalityline.Sincethesesectionshad

thelowestandhighestmacrotexturevalues,newlinearregressionswithtwo

variables(FR(60)andTX)weredetermined.Thebest‐fitcoefficientsareshownin

blueintherighthalfofTable2andthepredictedvaluesarepresentedgraphically

(asgreensolidcircles)inFigure4.Thefittingwassignificantlyimprovedas

indicatedbythehighercoefficientsofdeterminationobtained.

20

FIGURE4.ComparisonoforiginalandrevisedF60valuesusingthree­

parameter(A,B,C)models.

5.3SpeedParameterCalculation

ToevaluatetheappropriatenessofthecoefficientsusedtocomputetheSpbasedon

theMPDvaluesobtainedwiththeCTMeter,thecomputedSpvalueswerecompared

withtheexperimentalvaluesobtainedfromthemodelfittingwithequation4

(PennsylvaniaStateUniversitymodel).Theoretically,theSpfactorshouldbeequal

totheinverseofthePNGvalueindecimalform(100/PNG),orasreferredinother

publicationsastheSo(Henry2000).Sincetheexponentialmodelsweredefinedfor

thevariousdevicesandthevariouspavementsections,itwaspossibletodetermine

anexperimentalSpthatcouldbecomparedwiththeSpvaluecomputedasa

functionoftexture.Itisimportanttonotethattheresultingrelationshipsarevalid

21

onlyforthesurfacesevaluated.Table3showstheresultsofcomparingthe

experimentalvaluesofSpandthecomputedvalueinaccordancewiththeASTM

coefficientcalculationprocedure.Figure5comparestheexperimentaland

computedSpvaluesandshowsthebest‐fitlineal(Sp=a+b∗TX)andpower(Sp=

a∗TXb)models.

TABLE3.ExperimentalandCalculatedSpValuesCTM ASTM ExperimentalSp(km/h)

SectionMPD Sp(MPD) LWS1 LWS2 GT LWR1 DFT

1 Loop 1.00 104 68 75 40 109 2932 A 0.53 62 51 50 16 127 2913 B 0.68 75 44 49 20 154 3014 C 0.71 78 40 63 21 159 3165 D 0.56 64 32 38 24 167 3286 I 0.92 97 68 56 27 141 3377 J 1.05 108 53 83 125 132 3388 K 1.63 160 76 86 28 87 3269 L 1.00 104 53 67 31 99 30710 Cg 1.84 179 48 127 45 169 59911 EP 1.20 122 55 88 53 200 12 PCC 0.70 77 30 34 15 156 54613 PCC 0.80 86 51 69 29 156 51514 Cg 1.86 181 54 89 93 159 58815 EP5 1.17 119 104 175 83 164 16 L 1.08 111 69 81 23 99 39217 K 1.80 176 84 83 127 69 40218 J 0.85 90 67 62 70 161 44119 I 0.73 79 47 64 29 139 33120 D 0.70 77 42 45 25 147 33221 C 0.79 85 53 58 28 164 36522 B 1.01 104 75 73 68 175 39523 A 0.89 94 68 81 54 164 33224 Loop 0.80 86 45 46 19 97 282

22

FIGURE5.ComparisonofcomputedandexperimentalSpvalues

23

Thebest‐fitmodelparametersforeachdevicearepresentedinTable4.Theplotsin

Figure5showthatneitherofthemodelsresultsinhighcoefficientsof

determination.AlthoughitwasreportedintheresultsoftheHERMESexperiment

thatSphadbettercorrespondencewhenusingapowermodeloftheformSp=

a∗TXb,theresultsofthemeasurementsshowthattheexperimentaldataanalyzed

onlyconfirmedthisforthedeviceswithsmoothtires,whereasthecoefficientsof

determinationfortheDFTandribbedtiredonotimprovewithapowermodel.

TABLE4.Coefficientsaandb.Lineal Power

Devicesa b R2 a b R2

DFTSp 122 259 0.2611 378 0.300 0.2247

LWR1Sp 18.3 160 0.0492 136 ‐0.211 0.0823

LWS1Sp 20.0 37.1 0.2096 56.4 0.469 0.3156

LWS2Sp 47.1 25.0 0.3848 70.7 0.767 0.5609

GT 48.0 ‐2.95 0.3342 39.4 1.168 0.4312

6.FINDINGSANDRECOMMENDATIONS

Inthispapermeasurementsobtainedwithdifferenttypesoffrictionmeasuring

equipmenton24pavementsectionswithawiderangeoftextureswerecompared.

Therelationshipbetweenfrictionandspeedforthedifferentpavementsectionsand

deviceswasstudied.Themainconclusionsoftheanalysisofthedatacollectedare

presentedfollowing.

ThedatacollectedforthisprojectshowedthatthemodeldevelopedbyPIARCdoes

notproduceharmoniousresultsamongthedevicesusedbytheconsortium

membersintheVirginiaSmartRoadRodeoforthesurfacestested.Discrepanciesin

theIFIvaluescalculatedforthedifferentdevicessuggestthattheoriginal

24

coefficientsdeterminedduringthePIARCexperimentmayneedtobeadjustedfor

thedevicesevaluatedbeforetheIFIcanbeimplementedbytheparticipatingDOTs.

Thereseemstobeaslightlybettercorrelationofthespeedconstantgradientvalue

withthepowermodelasrecommendedbytheHERMESProjectthanwiththelinear

modelasusedintheoriginalPIARCmodel,particularlyforinstrumentsusing

smoothtires.Basedontheresults,newcoefficientshavebeenproposedforthe

equipmentusedintheSmartRoadRodeoforthetypesofsurfacestested.

StartingwiththePIARCexperiment,harmonizationinitiativesaredoneregularly

becauseithasbeenfoundthatunderdifferentconditionsdifferentparametersand

coefficientswillresult.Itisstronglyrecommendedequipmentcomparison

experiments(liketheNASAandSmartRoadprograms)continueinordertobetter

determinethecoefficientsnecessaryforharmonization.

7.ACKNOWLEDGEMENTS

ThedatausedforthispaperwascollectedduringtheSecondAnnualEquipment

ComparisonProjectaspartoftheVirginiaConsortiumforPavementSurface

Properties.Thisexperimenthasbeenmadepossiblethankstothecontributionsof

theVirginiaTransportationResearchCouncil(VTRC),theFederalHighway

Administration(FHWA),andtheConnecticut,Georgia,Mississippi,Pennsylvania,

SouthCarolina,andVirginiaDepartmentsofTransportationandtheVirginiaTech

TransportationInstitute(VTTI).

25

8.REFERENCES

ASTMStandardE1960‐98StandardPracticeforCalculatingInternationalFriction

IndexofaPavementSurface,ASTMInternational,WestConshohocken,PA.

Descornet,G.TheHERMESProject.InSURF2004.(CD‐ROM).5thSymposiumon

PavementSurfaceCharacteristics,WorldRoadAssociation,Paris,2004.

Flintsch,G.W.,deLeon,E.,McGhee,K.K.,andI.L.Al‐Qadi.PavementSurface

MacrotextureMeasurementandApplications.JournaloftheTransportation

ResearchBoard,TRR1860,Washington,D.C.,2003,pp.168‐177.

Henry,J.J.NCHRPSynthesisoftheHighwayPractice291:EvaluationofPavement

FrictionCharacteristics.TransportationResearchBoardoftheNational

Academies,Washington,D.C.,2000.

Henry,J.J.,andK.Siato.SkidResistanceMeasurementswithBlankandRibbed

TesterTiresandTheirRelationshiptoPavementTexture.Journalofthe

TransportationResearchBoard,TRR946,Washington,D.C.,1983,pp.38‐43.

Wambold,J.,Henry,J.,andT.Yager.NASAWallopsTire/RunwayFriction.InSURF

2004.(CD‐ROM).5thSymposiumonPavementSurfaceCharacteristics,

WorldRoadAssociation,Paris,2004.

Wambold,J.C.,C.E.Antle,J.J.Henry,andZ.Rado.PIARCFinalReport.International

PIARCExperimenttoCompareandHarmonizeTextureandSkidResistance

Measurements.PIARC:PermanentInternationalAssociationofRoad

Congresses.Paris,1995.

Wambold,J.C.,T.J.Yager,J.J.Henry,andZ.Rado(April2006).AWhitePaperon

CorrelationoftheGriptesterTrailertotheASTME274SkidTrailer.

26

CHAPTERIII

FIELDPERFORMANCEOFHIGH­FRICTIONSURFACES

ABSTRACT

Eventhoughtherelationshipbetweenroadwaysafetyandpavementfrictionhas

longbeenrecognized,thelackofsufficientfrictionatthetire‐pavementinteraction

isstilloneofthemajorcontributingfactorstovehicleaccidents.Duetothe

relationshipbetweenskidresistanceandaccidentsandtheincreaseoffatalitieson

highways(N.T.S.1999),optimumlevelsofskidresistancemustbemaintainedon

pavementsunderextremeweatherconditions.High‐frictionsurfaces(HFS)are

consistentlybeingconsideredbecausetheyprovidethepavementfrictionneeded

withoutnegativelyaffectingotherpavementqualities,likenoiseordurability.

Theobjectivesofthispaperaretostudysomeofthehigh‐frictionsurfacesavailable

intheUnitedStatesmarket;measuretheirperformance(frictionandtexture)on

differentapplications,underdifferentweatherconditions,andonvariouslocations;

andpresentagenciestheresultsobtainedinapractical,easy‐to‐useform.The

resultsofthebenefit‐costanalysisforthestudiedHFSshowthatonallfourstudied

sectionstheHFSalternativeiseconomicallyjustifiedcomparedtothebasecase.

ThecoefficientsdevelopedwereusedtoobtainInternationalFrictionIndex(IFI)

valuesforeachHFSstudied.Itisrecommendedthatmoreexperimentsberunwith

differenttypesofpavementssurfaces,includingHFSandothertypesofsurface

treatments,todemonstratethevalidityofthespeedgradientcoefficientSp

coefficientsrecommendedbyASTMandalsothevalidityofusingtheDynamic

FrictionTesterasthestandarddevicetomeasurefrictionfortheIFIcalculations.

Researchisrecommendedonpredictingminimumsurfacefrictionvaluesindicating

thenecessityofroadwayrehabilitation.Todeveloptheseparameters,itisnecessary

tostudy,monitor,andcorrelatetexture,friction,andaccidentdata.

1.INTRODUCTION

Roadwayaccidentsarealeadingcauseofdeathandinjuryaroundtheworld.Each

year1.2millionpeopledieandmillionsmoreareinjuredordisabledasaresultof

roadcrashes(Hayesetal.2007).Thisnotonlycreatesanenormoussocialcostfor

individuals,families,andcommunitiesbutalsoplacesaheavyburdenonhealth

servicesandeconomies.

Therelationshipbetweenroadwaysafetyandpavementfrictionhaslongbeen

recognized,butoneofthemajorcontributingfactorstovehicleaccidentson

highwaysisstillinsufficientfrictionatthetire‐pavementinteraction.Ithasbeen

reportedthatwetpavementsareinvolvedin25percentofallcrashesandthat

vehiclesleavingtheirlaneorrunningofftheroadareinvolvedin59percentof

roadwayfatalities(NTS1999).

ThevolumeandseverityofmotorvehiclecrashesintheUnitedStateshasledthe

FederalHighwayAdministration(FHWA)todeclaresafetyasoneoftheirtop

priorities.Itisforthisreasonthathigh‐frictionsurfaces(HFS)arebecomingan

appealingpavementhighfrictionapplicationalternativesincetheyhavetheability

toincreasefrictionandimprovetexturebyutilizingahigh‐polished‐stone‐value

(PSV)aggregateandsometypeofresintoholdtheaggregateparticlestogetherand

gluedtotheroadsurface.

Motorvehiclecrashesresultfromnumerouscontributingfactors,includingdriver

error,poorgeometricalignmentoftheroadway,andinsufficientfrictionatthetire‐

pavementinteraction,especiallyduringwetweather.HFSshaveemergedasviable

pavementhigh‐frictionalternativesthatmitigatesomeofthesefactors.

BesidesHFSthereareotheralternativesthathavetheabilitytoincreaseskid

resistanceonpavements,suchastinningorgroovingonrigidpavements.However,

28

mostofthesesurfacealterationsadverselyaffectothersurfaceproperties,suchas

noisegeneratedbetweentireandpavement.HFSareusedforincreasingroad

surfaceskidresistance,driverawareness,andwaterdrainageanddecreasing

brakingdistance,hydroplaning,splash,andspray.

2.OBJECTIVE

AstudyconductedbytheUniversityofMichiganon15rampsat11interchangesin

5statesfoundthatsurfacepropertieswererelatedtotruckalongwithgeometry,

andvehicledynamics(JulianandMoler2008).

Ithasalsobeenshownthereisastatisticallysignificanteffectofskidresistanceon

wetaccidentrate:thewetaccidentrateincreaseswithdecreasingskidresistance

(Kuttesch2004).Duetothisrelationshipandtheincreasingnumberoffatalitieson

highways,optimumpavementskidresistancemustbemaintainedunderextreme

weatherconditions(N.T.S.1999).High‐frictionsurfaces(HFS)arebecomingan

appealingpavementhighfrictionapplicationalternativebecausetheysupplythe

neededpavementfrictionwithoutnegativelyaffectingotherpavementqualities,

suchasnoiseanddurability.

Theobjectivesofthispaperare:

1)ToidentifythemainHFSavailableintheUnitedStatesmarket.

2)Tomeasuretheirperformance(frictionandtexture)ondifferentapplications,

underdifferentweatherconditions,andonvariouslocations,and

3)Topresentagenciestheresultsobtainedinapractical,easy‐to‐useformat.

ThispaperisaimedathelpingagenciesdecidewhetherornotanHFSshouldbe

appliedataparticularlocationandwhichHFSisthemostappropriateforaspecific

application.Theinformationcompiledwillhelpdecisionmakersallocatetheneeded

resourcestoaddressthemostserioussafetyrisks.

29

In2006,theVirginiaTransportationResearchCouncil(VTRC)andtheVirginiaTech

TransportationInstitute(VTTI)initiatedaregionalpooled‐fundprojectknownas

thePavementSurfacePropertiesConsortium.Thisprojectestablishedaresearch

programfocusedonenhancingthelevelofserviceprovidedbytheroadway

transportationsystembyoptimizingpavementsurfacetextureandfriction

characteristics.TheprogramwassetupwithsupportfromtheFHWAandincludes

sixDOTsfromthestatesofConnecticut,Georgia,Mississippi,Pennsylvania,South

Carolina,andVirginia.Thisfive‐yearprogramispartoftheactivitiesoftheVirginia

SustainablePavementResearchConsortium(VA‐SPRC)andismanagedbyVTRC

andrunbytheCenterforSustainableTransportationInfrastructure(CSTI)atVTTI.

3.BACKGROUND

Thetermhigh­frictionsurface,orHFS,referstosurfacetreatmentsthatutilizeanon‐

polishableaggregate(withhighpolishedstonevalue,PSV)andsometypeofresin

(binder)toholdtheaggregateparticlestogetherandgluedtotheroadsurface.The

mostcommonlyusedaggregateiscalcinedbauxite.

TheoriginofHFSdatestothemid1950swhentheuseofepoxy‐resinsasbinderson

surfaceswasfirststudied(Nicholls1998).Inthe1960stheU.K.government’s

TransportandRoadResearchLaboratory(TRRL)begantotesthardaggregateswith

variousbinderstoproduceextremelyhigh‐frictionsurfaces.Yearslater,theGreater

LondonCouncil(GLC)concludedthatthemosteffectiveHFSresultedfromthe

combinationofcalcinedbauxiteof0.32cmwithabitumenextendedepoxy‐resin

binder(JulianandMoler2008).Inthelate1980sresearchersintheUnitedStates

begantoinvestigatetheeffectivenessofthesesurfacingsystemsinreducingcrashes

onblackspots.

30

3.1High­FrictionSurfacesApplicationProcesses

Accordingtotheformofapplication,HFScanbeclassifiedintotwocategories:cold‐

appliedandhot‐appliedprocesses(Nicholls1997).Cold‐appliedHFSuse

thermosettingresinslikeepoxyorpolyurethane,whicharesuppliedindifferent

containersandthenmixedtobeginaheat‐producingchemicalreactionthatresults

inhardening.Inthehot‐appliedprocessthepremixedgranularmaterialisprovided

inbags,thenheatedinaboilerandappliedtothesurfacewhilestillhot.Inthiscase

theresinusedisthermoplastic.

3.2High­FrictionSurfaceBinders

ThereareseveraltypesofresinsusedonHFS,andeachaddsuniquecapabilitiesto

thesystem.Themainresinsare:epoxy‐resin,rosin‐ester,polyurethane‐resin,and

acrylic‐resin(Nicholls1998).

3.2.1Epoxy­Resin

TheoldestresinusedonHFSistheepoxy‐resin.Itconsistsofatwo‐component

systemmixedonsiteatequalquantitiesbyweight.Onecomponentcontainsthe

resintogetherwithaproportionofoilthatreducestheviscosityoftheresinand

actsasanextender,whiletheothercontainsthecuringagenttogetherwith

bitumen,anoilextender,andaccelerators.Thepropertiesofthebindercanbe

adjustedbychangingtheproportionsofthecomponentsofthesystem;

nevertheless,atypicalcuringtimeoscillatesbetweenthreetofourhoursfor

temperaturesabove10°C.

3.2.2Rosin­Ester

Apre‐blendedsystemliketherosin‐esterfacilitatesinsituinstallationoperations

sincetheresinandaggregatesarealreadymixedandbaggedtogether,readytobe

heatedatthespecifiedtemperatureandplacedonthesurface.

31

ThistypeofHFSisappliedwithahandheldbox,resultingina5‐mmthicknessthat

stiffensquicklybecauseofitsthermoplasticnature,allowingDOTstoreopenthe

roadwithminimumdelay.

3.2.3Polyurethane­Resin

Thepolyurethane‐resinwasmainlydevelopedtoachievequickercuringtimesat

lowtemperaturesthanotherexistingsystems.Itisachemicallycuringmultiple‐

componentsystem.Thecomponentsaremixedtogetherwithahandheldbeaterand

laidbyhand.Afterward,theaggregateisspreadseparatelyandalsobyhand.

3.2.4Acrylic­Resin

Thisisatwo‐componentsystemwithmuchfastercuringtimethanepoxy‐resin.

Consequently,thecuringprocessdoesnotbeginuntiltheaggregate,whichcontains

thecuringagent,isspreadoverthesurface.Theconsistencyofthisbinderis

designedtowettheaggregatesufficiently,inordertoprovideanadequatebond

withoutthebindersubmergingthechips.

3.3PropertiesofAggregatesforHigh­FrictionSurfaces

AggregatesonHFSshouldprovideaskid‐resistantsurfacewhilebeingnon‐

polishable,durableagainsttheabrasioneffectsoftraffic,andresistanttothe

disintegrationprovokedbyweathering. Thesurfacelayerneedstoretainitstexture

foraslongaspossibletoprovideskidresistancefortraffic.ThehigherthePSV,the

longertheaggregatewillremainroughwhenusedinroadsurfacing.

3.3.1StandardPracticefortheAcceleratedPolishingofAggregatesUsingthe

BritishWheel(AASHTOT279,ASTMD3319)

Thismethodsimulatesthepolishingactionofvehiculartrafficonaggregatesusedin

pavements.Polishvalue,isameasureofthestateofpolishreachedbytest

specimenssubjectedtoaspecifiednumberofhoursofacceleratedpolishingusing

32

theBritishwheel,thisvaluemaybeusedtorateorclassifyaggregatesfortheir

abilitytoresistpolishingundertraffic.

Thefirststepinthisprocedureistodeterminetheinitialfrictionvalueofeach

preparedtestspecimenbyusingtheBritishPendulum,thenthespecimensare

clamparoundtheperipheryoftheroadwheelusingrubbero‐ringsneartheedgeof

thespecimensinordertoformacontinuousstripofparticlesuponwhichthetired

wheelshallridefreelywithoutbumpingorslipping.

Duringthetest,specimensaresubjectedtoa320rpmroadwheelwithatotal

surfaceloadof391N(88lbf),anda66g/minrateofsiliconcarbide.Afterthe

polishingactionhaspassedthespecimensareremovedfromthefixture,wash

thoroughlytoremovegritanditsfrictionvalueobtainedthrutheBritishpendulum,

inordertodeterminethepolishvalue(ASTM2006).

Duringtestingaggregatesshouldbesubjectedtoapolishingactionof10h,unless

maximumpolishisachievedinashortertime.Maximumpolishisachievedwhenno

changeisdetectedonsuccessivemeasurements.

3.3.2ResistancetoDegradationandAbrasion(AASHTOT96,ASTMC131)

Thismethodsimulatesdegradationbyabrasionofsmall‐sizedaggregates.Thefirst

stepinthisprocedureistoweighthesample.Thenthesampleandthechargeare

placedintheLosAngelestestingmachineat30rpmfor500revolutions.Afterward,

thematerialisdischargedandasieveanalysisisdone.Lastly,theaggregatesare

washedandweighedtodeterminetheabrasion(AASHTO1991).

3.3.3SoundnessofAggregatesbyFreeze­Thawing(AASHTOT103­91,ASTMC88)

Thistestmethodsimulatesthebehavioroftheaggregateunderfreeze‐thaw

conditionstodeterminedisintegration.Inthisprocedurethetestspecimenshould

bewashed,ovendried,sieved,andweighed.Thenthesamplesareimmersedin

33

waterfor24hourspriorthestartofthefreezingcycleandmustbefrozenand

thawedinthiscompletelyimmersedcondition.Incaseofpartialimmersion,other

proceduresdescribedbyAASHTOmustbefollowed.

Inmanyinstancesafreezingperiodoftwohoursissuitable,dependingonfreezing

equipment.Followingfreezing,thesamplesmustbethawedfor30minutesat70°F

inanalcohol‐watersolution.Thisproceduremustberepeatedfor50cycles.After

thecompletionofthefinalcycle,thespecimensmustbedriedandsievedto

determinedthelossineachsieve(AASHTO1991).

3.4High­FrictionSurfacesAggregates

Theselectionofaggregateswilldependontheirperformanceduringthetests

describedintheprevioussection.Table1presentsthetypesofaggregatesusedin

thestudiedapplications.Themostcommonlyusedsourcesaredescribedbelow.

TABLE1.TypeofAggregateandPriceforSelectedHFSProduct TypeofAggregate AggregateSize

CrafcoHFS Bauxite(China‐Guyana)Granite

1‐3mm1‐3mm

Flexogrid Basalt+graniteSilica

2‐3mm2‐3mm

Italgrip Steelslag(patented) 3‐4mm

Safelane(Cargill) Dolomite 1‐3mm

Safe‐T‐Grip Granite 1.5‐3.2mm

Tyregrip Calcinedbauxite(buffandgrey) 1‐3mm

3.4.1CalcinedBauxite

CalcinedbauxiteaggregatecomesfromanaluminumorecommonlyminedinChina

thatisexposedtoprolongedheatingattemperaturesof1,600°Ctoincreaseits

hardnessandphysicalstability.

34

Thedensityofcalcinedbauxitevariesfrom2.6to3.4g/m3dependingonitssource.

ThispropertyistypicallyagoodindicatorofthePSV:highdensityindicateshigh

PSV.Guyananbauxite(darkgrey)hasaPSVof72whileChinesebauxite

(buff/creamycolor)exhibitsvaluesof67PSV.

3.4.2Dolomite

Somerecentlydevelopedanti‐icingsurfacesuseaggregatesmadeinlargepartofthe

mineraldolomite,whichisthedoublecarbonateofcalciumandmagnesium.

Replacementofpartofthecalciumfromlimestonebymagnesiumisthemost

importantprocessintheformationofdolomite.Thisreplacementisseldom

complete,andmanygradationsexistbetweenlimestoneanddolomite(Huhtaetal.

2001).Dolomiteiscommonlylightincolorandoftenhasferrousironcompounds

thatmayoxidize,tintingtherockshadesofbuffandbrown.

3.4.3Granite

Granitesarecomposedofquartzandpotassiumfeldspar,anditscolorvariesfrom

verylighttomediumtonesofgray.Duetoitsmineralcompositionandinterlocking

crystals,graniteishardandabrasionresistant.Thetoughnessofgraniteisusually

superiortothatofsandstone,limestone,andmarble(Huhtaetal.2001).Itprovides

aPSVof62orgreater.

3.4.4Silica

Silicaoccurscommonlyinnatureassandstone,silicasand,orquartzite.Itistheraw

materialusedfortheproductionofsilicateglassesandceramics.Silicaisoneofthe

mostabundantoxidesintheearth'scrust.Itcanexistinanamorphousform

(vitreoussilica)orinavarietyofcrystallineforms(Huhtaetal.2001).

Therearethreecrystallineformsofsilica:quartz,tridymite,cristobaliteandtwo

variationsofeach(highandlow.)Silicahasgoodabrasionresistanceandhigh

35

thermalstability.Itisinsolubleinallacidswiththeexceptionofhydrogenfluoride

(HF).

3.4.5SteelSlag

Slagisaby‐productofsteelmaking,producedduringtheseparationofthemolten

steelfromimpuritiesinsteel‐makingfurnaces.Theslagformsasamoltenliquid

meltandisacomplexsolutionofsilicatesandoxidesthatsolidifiesuponcooling.

SteelslagmustbecrushedandscreenedtoproduceasuitableaggregateforHFS

(Shi2004).

OtheraggregatesmaybeselectedforuseonHFSfortheirnaturalcolors,whichcan,

bycolorpigmenting,accentuatetheaggregateforgreatervisualimpact.

3.5PreviousHigh­FrictionSurfacesStudies

TherehavebeenseveraleffortsbydifferentagenciestoevaluateifHFSaresuitable,

durable,andcost‐effectivetechniquestoenhancethesafetyanddrainage

characteristicsofroadways.Themostrelevantarebrieflydescribedinthissection.

3.5.1InvestigativeStudyoftheItalgripSystem–NoiseAnalysis

TheWisconsinDepartmentofTransportationconductedastudytoidentifyand

quantifytheimpactonexteriorvehiclenoiseofapplyingItalgriponaPortland

CementConcrete(PCC)pavement.Thesurfacetreatmentwasinstalledonajointed,

undoweled,transversely‐tinedPCCpavementinWaukeshaCounty.A3‐mm

aggregatewasappliedtobotheastboundlanes,while4‐mmaggregateswere

appliedtowestboundlanes(Kuemmeletal.2000).

ThisstudyconcludedthatItalgripproducesa2‐3decibeldecreaseinnoiselevel

whencomparedtootherpavementsatspeedsof60mphand65mph,anoticeable

changeinsoundtotheear.Itwasalsofoundthatthenoiseleveldifferencebetween

3‐mmand4‐mmaggregatesisinsignificant.

36

3.5.2TrialsofHigh­FrictionSurfacesforHighways

TheTransportationResearchLaboratoryintheUnitedKingdomconductedaproject

tobetterunderstandthemainfeaturesandperformanceofthedifferentbinder

systemsavailableforHFSapplication.Thebindersystemsstudiedwereepoxy‐resin,

rosin‐ester,polyurethane‐resin,andacrylicresin.

Thisreportdescribesaseriesoftrialsconductedatdifferenttimesusingdifferent

typesofHFS.Thesystemswererankedintermsofmaintainedskidresistance,

texturedepthandlongevity.Thestudyshowedthattheepoxy‐resinand

polyurethane‐resinsystemsmaintainedtheirpropertiesmostconsistently,followed

bytheacrylic‐resinsystemandthentherosin‐estersystem.Itwasalsofoundthat

polyurethaneandacrylic‐resinsystemshaveshortercuringtimesthantheepoxy‐

resinsystems,althoughnotasshortastherosin‐ester,whichallowstheroadtobe

openedtotrafficfaster(Nicholls1998).

3.5.3EvaluationofCargillSafelaneEpoxyOverlay

(Sprinkeletal.2008))evaluatedtheperformanceoftheSafelanesystemwhen

comparedtoaconventionalmodified‐epoxyconcreteoverlay.TwoSafelaneandtwo

EP5systemswereplacedonaninterstate’sbridgedecksandontheVirginiaSmart

Road.

ThestudyshowedthatSafelaneoverlaycouldprovideaskid‐resistantwearingand

protectivesurfaceforbridgedecks.Theprojectwasnotabletodeterminethe

performanceoftheoverlaywithrespecttoprovidingasurfacewithless

accumulationoficeorsnowwhencomparedtotheconventionalepoxyoverlay.

37

3.5.4PerformanceofPoly­Carb,Inc.FlexogridBridgeOverlaySystem

(AdamandGansen2001)evaluatedtheperformanceoftheFlexoGridsystemona

highwaybridgedeckinthestateofIowaoverafive‐yearperiod.Resultsshowed

thatthisHFSsystemincreasedfrictionmeasuredwithalocked‐wheeltrailerfrom

36.5SNto67.5SN,andfouryearsafterapplicationarecordedfrictionof64.5

resulted.Itwasalsofoundthatonthesixthyear,530ft2ofthe14,080‐ft2bridgewas

alreadydelaminated.Thisresearchattributesthedelaminatingproblemtomoisture

trappedbelowtheimpermeablePolycarblayer.

3.5.5FloridaDOT­TyregripForensicReport

In2008theFloridaDOT(FDOT)studiedoneoftheirItalgripHFSapplicationsto

investigatemixedreviewsfromthoseinvolvedwiththeapplicationconcerningthe

causesofravelingonthesystem.Theresearchdiscoveredthatthemaincausesof

ravelingonthisapplicationwereimproperepoxypreparation,humidityofsurface

priortoapplication,andthinningofepoxyapplication.Thisstudyshowsthe

importanceofmechanicalapplicationinachievinguniformityalongthesurfaceand

avoidingraveling(Kelly2008).

3.5.6EvaluationofInnovativeSafetyTreatments

(Reddyetal.2008)evaluatedinnovativesafetytreatmentsimplementedby(FDOT)

andotheragenciestodeterminetheirimpactoncrashesandothersurrogate

measures.Thesetreatmentsincludedtemporaryrumblestrips,whiteenforcement

lights,motoristawarenesssystem,countdownpedestriansignals,in‐roadwaylights

andTyregriphigh‐frictionsurface.ThisevaluationconcludedthattheHFS

(Tyregrip)areeffectiveinincreasingfrictionbetweentheroadwayandvehicletires.

Thesystemiseffectiveinassistingdriversinmaintainingtheirlanepositionunder

wetpavementconditions.Thisresearchalsoinfersthatdriverstendtoslowdown

whentravelingovertheHFSsection.

38

3.5.7InvestigativeStudyofItalgripSystem2008

(Bischoff2008)studiedfivedifferentItalgripapplicationstoassessifthissystemis

asuitable,durable,andcost‐effectivetechniquetoenhancethesafetyanddrainage

characteristicsofroadways.Locked‐wheelfrictiontestingshowedthatthesystem

increasedthefrictionnumberfromanaverageof42.9SNto72.6SNafter

application.Afterfiveyearsinservicethesiteshadanaverageof59.4SN.This

showedthateventhoughfrictiondecreased,theaveragefrictionnumberwasstill

38percenthigherthanbeforetheapplication.Theresultsalsoshowedthatnumber

ofaccidentsatsitesdecreasedby93percent,thenumberofvehiclesinvolvedin

accidentsdecreasedby89percent,andthenumberofaccident‐relatedinjuriesby

86percentduringathree‐yearperiod.Itwasalsofoundthat4‐mmaggregates

showedbetterfrictionthan3‐mmaggregatesandthatthisHFSsystemcouldreduce

thetire‐pavementnoiseby4decibels.

3.6High­FrictionSurfaceSystemsStudied

TheHFSinvestigatedforthisthesiswereselectedbysearchingontheworldwide

webforHFSavailableallovertheworldandthencontactingthosecompaniesto

findaU.S.supplier.Inaddition,theFederalHighwayAdministration(FHWA)

providedalistofdepartmentsoftransportationthathadtriedsomeofthehigh‐

frictionproducts,andtheywerecontacted.Theproductsevaluatedarediscussed

below.

3.6.1CrafcoHFS

TheHFSofferedbyCrafcoisachemically‐engineeredmodified‐epoxyoverlay

designedtoprovideaflexiblehigh‐frictioncoatingforbridges,highways,andother

roadways.Thisepoxy‐polymeroverlayconsistsofatwo‐componentepoxybinder

thatisappliedtothesurface,whichisthencoveredbyselectedaggregates.Because

oftheirproperties,theseselectedaggregatesensurethatuponfracturetheywill

micro‐fracture,remainingsharpandretaininghighskidresistance(Crafco,2008).

39

TheCrafcosystemoffersvariousaggregateschoices,whichprovidedistinct

frictionalcharacteristics,colors,anduses.BauxitechippingsfromChinaandGuyana

areavailableinnaturalcolorsandareusedwherehighsurfacefrictionandlong‐

termwearresistancearerequired.Americangraniteaggregate(suppliedinnatural

silverandred)isusedwhengoodsurfacefrictioniswanted.Othercolored‐coated

aggregatesmaybeusedtoimprovedriverawareness.

CrafcoHFSiscomposedofathermosetting,primerless,low‐odorepoxycompound,

whichexhibitsplastoelasticpropertiesbondingtheaggregatepermanentlyin

position.Thisflexiblesurfaceisdesignedtoberesistanttofuel,de‐icers,oil,and

impacts.

3.6.2Safelane(Cargill)

TheSafelanesystemconsistsofacombinationofepoxyandproprietarydomestic

dolomiteaggregateusedtoimprovefriction.Thissurfacecanbechargedwith

standardanti‐icingfluidsthatstorethechemicalsandreleasethemautomatically

undersnowconditions,preventingicefromformingonroadwaysandbridgedecks

(Cargill,2008).

3.6.3Tyregrip(Prismo­EnnisPaint)

TheTyregripsystemisatwo‐partcold‐appliedexothermictreatmentformedbyan

epoxy/aminebinderandnaturalorpigmentedaggregates,whichusuallyarebuffor

graycalcinedbauxite.Theaggregateusedinthissystemisgradedfrom1mmto

3mm.Theleveloffrictionforthesystemcanbevaried.Forexample,calcined

bauxitecanbeusedtorenderaPSVof68orgreater.ThisHFSisavailableina

varietyofcolors.Tyregripofferscolor‐coatedchippingsaswellaspigmentedand

unpigmentedbinders(Tyregrip,2008).

40

3.6.4Italgrip

ItalgripwasimplementedforthefirsttimeintheUnitedStatesin1999.ThisHFS

systemconsistsofatwo‐partpolymer‐resinplacedoneitherasphaltconcrete(AC)

orPCCpavementsurfaceandcoveredwithanartificialaggregateofre‐workedsteel

slag3to4mminsize.TheItalgripsystemprovideshighfrictionandhasalsobeen

foundtoreducehighwaynoise.Thisthinsurfacetreatmentisprimarilyintendedfor

applicationinheavilytraffickedareasexperiencingfrictionproblemsorhigh

accidentratesovershortsectionsofroadway(Italgrip,2008).

3.6.5FlexoGrid(Polycarb)

TheFlexoGridsystembinderisachemicalcombinationformedbyanepoxyand

urethanedesignedtoprovideaflexible,waterproofingmembranewithsufficient

strengthtowithstandsnowplows,coldandhotweather,andthepoundingfrom

carsandtrucks(Polycarb,2008).Thisproductutilizesflintaggregate(silica)ora

combinationofbasalt‐granitechipstoprovidethedesiredsurfacefriction.The

materialsusedforthisapplicationaredomestic,includingthebinder.This

applicationisdesignedtobeinstalledonconventionalconcrete,concrete‐filledsteel

griddecks,steelplatedecks,fiberreinforcedpolymerdecks,andasphalt.

3.7HighFrictionSurfacesTypicalApplicationProcedure

ThetypicallyrecommendedlocationsforHFSinstallationsincludeareasofhigh‐

frictiondemandlikebridges,intersections,roundabouts,tollplazas,buslanes,exit‐

entranceramps,approachestocrosswalks,schoolcrossings,corners,steepgrades,

horizontalcurves,andotheridentifiedhazardousareas.ThemainbenefitofHFS

systemsisthattheysavelives;applicationinthecorrectlocationshasbeenproven

toresultinaccidentreductions(JulianandMoler2008).Otherreportedbenefitsof

HFSarefastapplication,retro‐reflectionnighttimehazard‐warningcapabilities,and

simplehandormachineapplication.

41

ThegeneralprocedureforinstallinganHFSstartsbypreparingtheroadsurface.It

mustbeclean,dry,andfreefromice,frost,looseaggregate,oil,grease,roadsalt,and

otherloosematterlikelytoimpairadhesionofthesystemtotheroadsurface.This

isaccomplishedusingbrooms,compressedair,andshotblastingonconcrete

surfaces.Then,thesurfacetemperatureshouldbemeasuredtoensureitisabove

theresininstallationstandard.Subsequentlydrainsandexpansiondevicesmustbe

coveredwithducttapeandplastictopreventcloggingwithepoxyandaggregates.

Thetwocomponentsoftheepoxyareusuallydeliveredin55‐gallonsdrumsthatare

laiddownatthesiteandgravityfedintobucketsofpredeterminedvolumeinapre‐

establishedproportion.Thiscombinationismixedwithaslow‐speeddrillfitted

withahelicalmixingblade.However,thisstepisnotnecessarywhenmetered

sprayingisusedtoplacetheepoxy.

Beforetheresinisspreadmanually,gridsshouldbelaidoutwithtapetocontrolthe

applicationrateoftheepoxy.Immediatelyaftertheepoxyisspread,workersuse

shovelsandbroomstoevenlyspreadtheaggregatesoverthebinderaspresentedin

Figure1.Finallytheexcessaggregateisremovedandthesystemislefttocurefora

periodoftwotofourhours.

Inatypicalapplication,theepoxyisspreadatanapproximaterateof2.6to3square

yards(27sq.ft)pergallon,andtheaggregateisspreadatarateof14‐15square

yardsper200poundsofaggregate.Thisissimilartotheapplicationrateofone

epoxygallonforeach25sq.ftcoveredforSafelaneapplicationattheVirginiaTech

SmartRoad.

42

a)MixingA‐BEpoxycomponents

b)Binderisspreadbycrew

c)Aggregateisspreadbycrew

FIGURE1.High­frictionsurfaceapplication(AdamandGansen2001).

3.8High­FrictionSurfacePotentialSourcesofFailures

AnHFScanfailbecauseofravelingofthematerial,delaminating,orpolishingofthe

aggregate.Thefailurecanbeattributedtoconstructionmethods,product

performance,and/orenvironmentalconditionsduringapplicationandinservice.

Themostimportantconcernsarediscussedbelow.

3.8.1EpoxyPreparation­Composition

Thetwo‐partmodifiedepoxyusedonmostoftheHFSapplicationsistobemixedin

aspecificratio,andsometimesduetoconstructionerrorsthismaynotbethecase.

43

Thiscouldaffecttheepoxyperformance.Thecompositionofthebindermayalso

affecttheadhesionwiththeaggregateparticlesand/orthepavementsurface.

Somestudiessuggestthatduetothedecreasinguseofcreosolbecauseofitsstrong

odorandabilitytoburntheskinduringapplication,newepoxyformulationsexhibit

worseperformancethanpreviouslyusedcombinations(Kelly2008).

3.8.2EpoxyAggregatePlacement

Epoxyshouldbespreadhomogeneouslyoverthesurfaceandatthecorrectrateto

preventthebinderfromcoveringtheaggregate.Thereneedstobeacomplete

coverageofthewetbinderwithaggregatetoachieveauniformfrictionsurface,and

nowetspotsshouldbevisibleoncetheaggregateisplaced.Thiscouldbedifficultto

accomplishatthemomentofinstallationsincemostofthesesurfacesareappliedat

nightforconvenienttrafficcontrolandtoreduceimpactontrafficflow.

3.8.3ExistingPavement­ExistingAsphaltCompatibility

SometypesofpavementsareparticularlydifficultfortheinstallationofanHFS.For

example,thehighpermeabilityofporousasphaltsposesathreatinaccomplishinga

uniformepoxysurface(Kelly2008).ItisalsonotrecommendedthatanHFSbe

placedonpavementslessthanonemonthold.Also,sufficientcleaningisnecessary

forallpavements.

3.8.4HumidityandMoisture(SurfaceandAggregate)

HumidityandmoistureareofgreatconcernatthemomentofHFSapplication.

Surfacehumiditycausedbycondensationandfogimpedesthefulladhesionand

performanceoftheepoxyoverthesurface.Likewise,highmoisturecontentinthe

aggregatebeforethesystemisinstalledcouldcompromisetheaggregate’sabilityto

bondwiththeepoxy.Thismoisturecouldcauseravelingandpeel‐offwhentheHFS

isinservice.Forexample,severeravelingmaydevelopasthesurfaceundergoes

freeze‐thawactionduetomoisturetrappedbelowtheimpermeablelayerasshown

inFigure2.

44

FIGURE2.High­FrictionSurfaceRaveling(AdamandGansen2001)

3.8.5AmbientTemperature

Althoughthespecificapplicationtemperaturevariesfromproducttoproduct,the

rangeoftemperatureoverwhichanHFSinstallationisrecommendedisbetween

55°Fand100°F.Toapplythebinderbelowthesetemperatures,thesurfaceshould

beheatedandthesystem’scuringtimeiselongated.

3.8.6CuringTime

Acuringtimeoftwotothreehoursisrequiredformostapplicationsunder

convenientambienttemperatures.Curingwilltakelongeratlowtemperatures,and

optimumperformanceoftheHFSmaybecompromised.

3.9High­FrictionSurfacesFieldEvaluations

SeveralexistinginstallationshavebeenidentifiedintheUnitedStateswithproducts

fromCrafco,Safelane,Tyregrip,Italgrip,andSafe‐T‐Grip.Thecontactinformation

foreachsupplierispresentedinTable2.Themainexperimentalcomponentofthis

thesisstudiesandanalyzestheperformanceoftheseapplications.

45

TABLE2.HFSProductsInstalledintheUnitedStatesProducts Evaluated

Websites Contacts

CrafcoHFS(CrafcoINC)

http://www.crafco.com/ NickNedasOffice:(512)432‐5170Mobile:(602)228‐1269E‐mail:nick.nedas@crafco.com

Italgrip(ItalgripUSA)

http://www.italgrip.com/ RobertB.SchmiedlinOffice:(608)592‐2725Mobile:(608)698‐1712E‐mail:schmiedlin@italgrip.com

Flexogrid(Polycarb)

http://www.poly‐carb.com/ PunitZenMobile:(678)296‐9910Office:(440)248‐1223E‐mail:info@poly‐carb.com

Safelane(Cargill)

http://www.cargillsafelane.com AnthonyHenseyOffice:(866)900‐7258Mobile:(423)488‐6884E‐mail:SafeLane@Cargill.com

Safe‐T‐Grip(TrafficCalmingUSA)

http://www.trafficcalmingusa.com GlynOwenOffice:(770)505‐4044Mobile:(404)512‐1792E‐mail:glyn@trafficcalmingusa.com

Tyregrip(PrismoUSA)(EnnisPaint)

http://www.prismousa.com/ RichardJ.BakerOffice:(804)213‐0335Fax:(804)213‐0337Mobile:(804)319‐7456E‐mail:rbaker@ennispaint.netDaveBelannyMobile:(678)296‐9910E‐mail:dave@ennispaint.net

46

4.DATACOLLECTION

4.1LocationofStudiedHigh­FrictionSurfaces

AllofthetestingwasdoneinthestatesandatthelocationspresentedinTable3.

Thedistinctnessoftestingsitesandtheuniquenessofeachlocationprovidedthe

opportunitytoobtainanencompassingideaofHFSperformance.

TABLE3.HFSLocationsInvestigatedHFS State Code Location

CrafcoHFS Tennessee TN‐C SpringHill,WestboundEndSouthernparkwaytowardColumbia

Italgrip Tennessee TN‐I‐4 SpringHill,WestboundEndSouthernparkwaytowardColumbia

Italgrip Wisconsin W‐I‐1 LaCrosseHighway35NWisconsin

Italgrip Wisconsin W‐I‐2 LaCrosseHighway16WWisconsin

Italgrip Wisconsin W‐I‐3 LaCrosseHighway16EWisconsin

FlexoGrid Wisconsin W‐P LaCrosseHighway35SWisconsin

Safelane Virginia VA‐S‐1 I‐81MileMarker219S

Safelane Virginia VA‐S‐2 I‐81MileMarker239N

Safe‐T‐Grip Tennessee TN‐G SpringHill,WestboundEndSouthernparkwaytowardColumbia

Tyregrip Virginia VA‐T I‐81MileMarker210S

EP‐5* Virginia VA‐E I‐81MileMarker240S

*StandardepoxyoverlayforbridgedeckusedbyVDOT;evaluatedforcomparisononly.Figure3showsexamplesoflocationswherethestudiedproductshavebeen

applied.PicturecinthisfigureshowsabridgeapplicationbyItalgripwherethe

HFShasbeeninplacefornineyears,andpicturedpresentsaPolycarbHFSapplied

inthesameyear.Acleardifferencebetweentheconditionsoftheseproductsplaced

inthesameyearcanbenoticed.

47

a)CrafcoTennessee

b) Cargill‐EP‐5Smart‐Road

c) ItalgripWisconsin

d) PolycarbWisconsin

e) SafelaneVirginia f)SafelaneVirginia

FIGURE3.HFSLocationsinvestigated.

48

4.2MeasurementsofFrictionandTextureProperties

TextureandfrictionpropertiesfortheselectedHFSapplicationshavebeen

measuredwiththeDFTester(ASTME1969),CTMeter(ASTME2157),and

GRIPTESTER(ASTME1844);thesedevices(Figure4)arefurtherdescribedinthe

followingsections.Allfrictionandtexturemeasurementswerecollectedinsummer

monthstoavoidseasonalvariationeffectsontherecordedmeasurements.

a)CircularTrackMeter(CTMeter)

b)DynamicFrictionTester(DFTester)

c)Griptester(GT)

d)LockedWheelDevice(LWD)

FIGURE4.Datacollectiondevices.

49

4.2.1DFTESTER(ASTME1969)

TheDFTestermeasuresfrictionbyspinningahorizontaldiskfittedwiththree

spring‐loadedrubberslidersthatcontactthepavedsurface.Thiscausesthedisk’s

rotationalspeedtodecreaseduetothefrictiongeneratedbetweentheslidersand

thepavedsurface.Awatersupplyunitdeliverswatertothepavedsurfacebeing

tested.Thetorquegeneratedbytheslidingismeasuredduringthespindownand

thenusedtocalculatethefrictionasafunctionofspeed.Thisdevicemeasuresthe

dynamicfrictionofthepavementcontinuously,andtheresultsaretypically

recordedatspeedsof20,40,60,and80km/h.Forthisinvestigation,staticfriction

measurementsweretakenateightdifferentlocations:fouroneachwheelpath

alongtheHFS.Onlythetravellanewasmeasuredbecausetorecordthis

measurementthelanehadtobeclosed.Thesamefrictionpadswereusedforthe

entiresection.

4.2.2CTMETER(ASTME2157)

Thisequipmentconsistsofachargecoupleddevice(CCD)laser‐displacement

sensormountedonanarmthatrotatessuchthatthedisplacementsensorfollowsa

circulartrackhavingadiameterof284mm(11.2in.).TheCTMeterisdesignedto

measurethesamecirculartrackthatismeasuredbytheDFTester,anditreports

theMeanProfileDepth(MPD)andtheRootMeanSquare(RMS)valuesofthe

macrotextureprofiles.ThevaluesstatedinSI(metric)unitsareregardedas

standard.TheCTMeterwasusedinthisstudytomeasuresurfacetextureatthe

sameeightspotsusedforthefrictionmeasurementswiththeDFTester.

4.2.3GRIPTESTER(ASTME1844)

AFindlayIrvineGriptesterwasusedtomeasurecontinuousskidresistancealong

theinsidewheelpathofthetravellaneofthetestsections.Thissystemconsistsofa

fixedslipdevicewherethetesttireisconnectedtothetrailerwheelaxlebyachain,

allowingittomeasuretherotationalresistanceofaconstantslippingsmoothtireat

50

a15.6percentslipratio.

Measurementsaretakenatspeedsof50mphoninterstatesand40mphonother

roadways,utilizingaconstantwaterfilmthicknessof0.05cm(8.9gal/minat

80km/h).Thespeedofthetesttireis15.6percentofthespeedofthevehicle

becausethisdeviceusesaconstantslipratio.Rawdataforlongitudinalfriction

forcesandtestwheelloadsarebydefaultrecordedevery0.9m,buttheintervalcan

beadjustedaccordingtotheneedsoftheexperiment.

DuetothelocationofthetestwheelwhentheGriptesterisattachedtothevehicle,

onlytheoutsidewheelpathfrictionisrecorded(seeFigure4c).Severalrunswere

madeforeachHFSsection,andtriggeringpointsbetweeneachrunwerecompared

toaccountforpossibleerrors.

4.2.4LOCKEDWHEELDEVICE(ASTME274)

Thisfrictionmeasuringdevicerecordsthesteady‐statefrictionforceofalocked

wheelonawettedpavementsurfaceasthewheelslidesatconstantspeed.The

deviceconsistsofavehicletowingatrailerequippedwithtestswheels.Duringthe

test,whenthevehiclereachesthedesiredspeed,waterisdeliveredaheadofthetest

tireandthebrakingsystemisactivatedproducing100percentslipratio.Thewheel

remainslockedforapproximately1second,andthedataismeasuredandaveraged.

Theskidresistanceofthepavedsurfaceisreportedasskidnumber(SN)(ASTME‐

274),whichistheforcerequiredtoslidethelockedtesttireatastatedspeed,

dividedbytheeffectivewheelloadandmultipliedby100(ASTME‐274).

Thelockedwheelfrictionmeasurementsusedinthisstudywereobtainedfrom

DOTs.Informationwasobtainedonlyforalimitednumberofsections.

51

4.3CostData

ThecompaniesresponsiblefortheinstallationoftheselectedHFSsystemswere

contactedtoobtainacostestimatefortheapplicationofeachproduct.This

informationwasusedtofurtheranalyzeandcomparethecostofeachproductwith

itsperformance.HFScostvaluespresentedinTable4donotincludetrafficcontrol

andotherinstallationandsupervisioncosts.

TABLE4.TypeofAggregateandPriceforSelectedHFSProduct TypeofAggregate TotalPriceperft2

Crafco Bauxite(China‐Guyana)Granite

$3$2.25

FlexoGrid Basalt+graniteSilica

$4.5–5$2.2‐2.7

Italgrip Steelslag(patented) $2.2

Safelane(Cargill) Dolomite $6

Safe‐T‐Grip Granite $1.6

Tyregrip Calcinedbauxite(buffandgrey) $1.7

Monetaryvaluesassignedtoaccidents(Table5),injuries,andpropertydamage

wereobtainedfromtheMinnesotaDepartmentofTransportationbenefit‐cost

analysis(Mn/DOT2005).

TABLE5.CrashValuesforEconomicStudy

MN/DOTCrashValues DollarsperCrash

Fatal $3,600,000

InjuryTypeAonly $280,000

InjuryTypeBonly $61,000

InjuryTypeConly $30,000

Propertydamageonly $4,400

52

4.4AccidentData

Before‐and‐afteraccidentdatawereobtainedfromonlyonelocation:theWisconsin

DepartmentofTransportation.Accidentdatawerecollectedforaperiodofthree

yearspriortotheinstallationoftheHFStothreeyearsafterward.Itispossiblethat

someaccidentsmayhavebeenoverlookedinthisdataforseveralreasons,

including:vehicleleavingthescene,accidentnotbeingreported,exactlocation

beingincorrectlydocumentedontheaccidentreport,orbeingmissedbythe

databasesearch(Bischoff2008).

5.RESULTS

ThelocationsshowninTable3werevisitedin2008,andfrictionandmacrotexture

measurementsweretakenwiththeDFTester,CTMeterandGriptesterasdiscussed

intheprevioussection.Thissectionpresentsthemaindatacollected.

5.1FrictionandTextureDataProcessing

Theaverageandstandarddeviationwerecomputedforeachofthecollectedfriction

properties.ThevaluesobtainedfromfrictionmeasurementswiththeGriptesterat

thebeginningandendofeachdifferentpavementsectionwereomittedfromthe

datasettoaccountforpossibletriggeringerror.Inaddition,engineeringjudgment

wasusedwhenprocessingthisdatabecausejointscausedtheequipmenttojump

whenmeasuringathighspeeds,resultinginerroneousvaluesclosetothe

transitionsbetweensections.InthecaseoftheDFTesterandCTMeter,theaverage

andstandarddeviationoftheeightmeasurementsforeachHFSapplicationare

presentedinTables6and7.Thevaluesprovideanindicationoftypicalvaluesof

initialfrictionandtexturethatcouldbeexpectedofanHFSsystemonhighways.For

comparisonpurposesthetablesalsoincludevaluesoffrictionandtexturefortypical

flexibleandrigidpavementsurfaces.

53

TABLE6.FrictionMeasurementsforSelectedHFS

HFS Code Appl.Date

Friction(GN)at40mph*

Std.Dev.

Friction(DFT)at20kph

Std.Dev.

Crafco TN‐C 2008 1.05 0.05 0.98 0.02

Italgrip TN‐I 2008 1.02 0.04 1.01 0.01

Italgrip W‐I‐1 1999 0.67 0.07 0.78 0.04

Italgrip W‐I‐2 1999 0.53 0.08 0.68 0.04

Italgrip W‐I‐3 1999 0.63 0.07 0.68 0.02

Polycarb W‐P 1999 0.69 0.03 0.65 0.02

Safe‐T‐Grip TN‐G 2008 0.90 0.12 1.01 0.02

Safelane VA‐S‐1 2005 0.50 0.05 0.48 0.04

Safelane VA‐S‐2 2005 0.57 0.06 0.55 0.05

Tyregrip VA‐T 2005 0.90 0.14 1.00 0.02

EP­5 Ref. 2005 0.65 0.11 0.62 0.03

SM­9.5D Ref. 1999 0.77 0.01 0.82 0.03

SMA­12.5 Ref. 1999 0.74 0.01 0.72 0.04

OGFC Ref. 1999 0.68 0.01 0.63 0.04

TinnedCRCP Ref. 1999 0.82 0.02 0.77 0.01

Pavementspresentedinitalicarenon‐HFSusedhereasreferencevaluesandwerecollectedontheVirginiaSmartthathasveryonlyresearchtraffic.

*Thismeasurementcorrespondsto10.14‐12.48km/hslipspeed.

Table6showsthatsomeoftheHFShaveconsiderablyhigherfrictionthanthe

conventionalsurfaces.Thedifferenceininitialfrictionbetweentheserigidand

flexiblepavementsandtheHFSsystemsemphasizestheneedforHFSsystemson

blackspotswherewet‐weathercrashesorcrashescausedbydeficientsurface

propertiesoccurfrequentlyandwhereadditionalfrictionmaybeneeded.

54

TABLE7.FrictionTextureMeasurementsforSelectedHFSHFS Code Application

DateTexture(MPD) Std.Dev.

Crafco TN‐C 2008 1.46 0.09

Italgrip TN‐I 2008 1.61 0.12

Italgrip W‐I‐1 1999 1.03 0.10

Italgrip W‐I‐2 1999 1.07 0.06

Italgrip W‐I‐3 1999 1.04 0.08

Polycarb W‐P 1999 1.07 0.24

Safelane VA‐S‐1 2005 1.53 0.16

Safelane VA‐S‐2 2005 1.56 0.20

Safe‐T‐Grip TN‐G 2008 1.57 0.23

Tyregrip VA‐T 2005 1.28 0.10

EP­5 Ref. 2005 1.16 0.09

SM­9.5D Ref. 1999 1.05 0.11

SMA­12.5 Ref. 1999 0.91 0.13

OGFC Ref. 1999 1.58 0.09

TinnedCRCP Ref. 1999 1.17 0.09

PavementspresentedinitalicareNon‐HFSusedhereasreferencevalues.

Figure6Summarizesthedatacollectedinwhiskerboxplotsforthefrictionand

macrotextureonalloftheHFS.Table6showsthatthemacrotexturevalues

providedbytheHFSaresimilartothosemeasuredonOGFCandconsiderably

higherthanthetypicalflexibleandrigidpavementsurfaces.

55

FIGURE5.TextureandfrictionwhiskerboxplotforallHFSsystems.

Toillustratetheinfluenceofthefrictioncoefficientsonareal‐lifesituation,the

followingscenarioisproposed.A2,500‐lbvehicletravelingat65mphona

2percentdownhillgradewithabrakeefficiencyof100percentrequires210.2ftof

minimumstoppingdistanceonapavementwithafrictionof0.735DFT(average

initialfrictionofnon‐HFSpavementsfromTable6).Ontheotherhand,158.4ftis

theminimumstoppingdistanceforthesamevehicleonanHFSsurfacewitha

coefficientoffrictionof0.963DFT(averageinitialfrictionofHFSfromTable5).

0.00.20.40.60.81.01.2

DFT(FN)

HFSSystems

0.0

0.5

1.0

1.5

2.0

CTMeter(MPD)

HFSSystems

56

5.2InitialFriction–Cost

Table7summarizesthecost,initialfriction,andtexturevaluesassociatedwitheach

HFSproductforwhichenoughinformationwasobtained.Thesourceofthesecost

valuesisexplainedinSection4.2.ThepurposeofTable8istohelpagenciesidentify

whichHFSwouldbetterfulfilltheirspecificneedandatthesametimeadjustto

theirbudget.

TABLE8.PriceandInitialFrictionandMacrotextureforSelectedHFS

HFS TypeofAggregate

InitialFriction(GN)at40mph

Friction(DFT)at20km/h

Texture(MPD)

TotalPriceperft2

Crafco Bauxite 1.05 0.98 1.46 $3

Italgrip Steelslag(patented) 0.98 1.01 1.61 $2.2‐2.7

Safe‐T‐Grip* Granite 0.90 1.01 1.52 $2.2

Tyregrip CalcinedBauxite 0.90 1.01 1.28 $1.7

Safelane‐Cargill** Dolomite 0.86 1.02 1.21 $6

*Whenmeasurementswererecorded,thesystemwasnotcompletelycured.

**MeasurementswererecordedfromSmartRoadandtrafficwasassumedtobezero.

6.ANALYSIS

6.1EconomicAnalysis

Abenefit‐coststudyisaneconomicevaluationoftheadvantagesanddisadvantages

onasetofinvestmentalternatives,whereiftheratioofthebenefit‐costisgreater

thanonethealternativeissaidtobeeconomicallyjustifiable.

InthiscasethebasescenarioisaroadwaysectionwithoutanHFSapplication

(roadwaywithrigidorflexiblepavement)andthealternativeisanHFSsystem.A

57

simplifiedcost‐benefitanalysisisusedtocompareanHFSalternativewithanon‐

HFSpavementtodeterminethemostcosteffectivealternative.Thismethod

considersinitsanalysisthecostsassociatedwiththeinitialconstructionofsurface

treatment;itdoesnotincludefuturemaintenancebecauseonthesesystems

rehabilitationmeansoverlay.Thebenefitsusedintheanalysisaresafety

performanceimprovements;suchasreductionsindeaths,injuries,andproperty

damagebeforeandafterthesystemwasplaced.Theobjectiveofthiseconomic

analysisistoillustrateamethodologythatcanbeusedtoanalyzethefeasibilityof

HFSapplications.

6.1.1EstimatedHigh­FrictionSurfaceServiceLives

FourItalgripHFSsectionsplacedinthestateofWisconsinwerestudied.This

productandlocationwereselectedbecausehistoricalfrictionmeasurementsand

accidentdatawereonlyfoundforthisinstallation.Figure7showsmeasurementsof

frictionovertimefortwooftheselectedsurfacesamples(estimationforother

consideredlocationscanbefoundinAppendixI).Aftertrialswithdifferentmodels,

apowerregressionmodelwasselectedbecauseitexhibitedthebestbehaviorofall

HFSandalsorepresentedthephysicalwearingprocesstypicallyobserved.

Thepowertrendfittedtothedatashowedthatthevariousmaterialsdonotreach

unacceptedfrictionvalueswithintheanalysisperiod.However,basedon

engineeringjudgmentandtheobservationofthesectionsevaluatedinWisconsin,a

HFSservicelifeof10yearswasconsideredappropriate.Accordingtothedatain

Tables6and7itmaybeexpectedforthesystemtomaintainacceptablefriction

levelsafter10years;however,theravelingprocesswouldbeveryadvancedas

showninFigure3,picturec.ApplicationsW‐I‐1,W‐I‐2,W‐I‐3,andW‐Phavebeenin

servicefornineyearsandstillexhibitgoodfrictionandmacrotexturelevelsbutthe

firstthreealsoshowsignificantraveling.

58

FIGURE6.HFSwearandscuffingrate.

6.1.2ValuesforTransportationEconomicStudy

Reductioninthenumberofskid‐relatedaccidentsistheprincipalbenefitfromthe

applicationofHFS.Benefitsoccurwhenseverityornumberofcrashesisreducedin

asystemduetoroadwaysurfacepropertiesimprovement.Fortheanalysis

presentedinthisthesis,theleastsevereinjuries(typeC)forhighwayuserswere

R²=0.83

0102030405060708090100110

1 2 3 4 5 6 7 8 9 10 11

Skid

Num

ber

(SN

)

Year

HFS WI-USH 53 N Smooth40mph

Power(Smooth40mph)

R²=0.31

0102030405060708090100110

1 2 3 4 5 6 7 8 9 10 11

Skid

Num

ber

(SN

)

Year

HFS WI-STH 16 WDL Smooth40mph

Power(Smooth40mph)

59

assumedandonlypropertydamagewasconsideredforvehiclesinvolvedinthese

accidentstoevaluateHFSunderaconservativescenario.

6.1.3Benefit­Cost

Thebenefitoftheprojectisderivedfromcomparingthe“before”basecasehighway

accidentsthatoccurwithinthestudyareatothoseofthe“after”alternative

scenarios.ThestudyareaincludestworoadwaysectionsinthetownsofLaCrosse

andWaukesha,Wisconsin.Thebasecasescenariosaredefinedforthisthesisasthe

existingconditionsbeforetheapplicationoftheHFS,whereastheproposed

alternativescenariosaretheconditionsaftertheapplicationoftheHFS.The

analysisperiodis10years,thebaseyearis2008,andthediscountrateis4percent.

Thebenefitismeasuredasthereductionofannualnumberofcrashes,injuries,and

deathsfromthebasecasetothealternativecase.Theeconomicvaluesofthecrash

eventswereobtainedfromTable5.Thetotalpresentcostofaccidentsforthebase

andalternativecasesarecalculatedasthesumofthediscountedannualcostfound

foreachyearinthe10‐yearanalysisperiod.Thedifferenceincrashcostsbetween

thebaseandalternativearereportedasthepresentworthofbenefits.

Typicalconstructioncostswereobtainedfromthematerialsuppliersandwere

reportedinTable5.Routinemaintenancecostswereassumedtobethesamefor

thebaseandalternativescenariossincethealternativedoesnothaveasignificantly

differenteffectonmaintenanceandtheybothrequireplowing,debrisremoval,etc.

Theresultsofthebenefit‐costanalyzesforthetwostudiedareasarepresentedin

Table9andTable10.Thetablealsoshowsthebenefit‐costratiocomputedasthe

ratiobetweenthesavingsincrashcostandthecostofapplyingtheHFS.These

resultsshowthatinallfourofthestudiedsectionsthealternativeiseconomically

justifiedcomparedtothebasescenario,withbenefitcostratiosrangingbetween4

and20.

60

TABLE9.Benefit­CostAnalysisforHFSLocationsinWaukesha,WisconsinWaukeshaCounty

STH16

Accidents BeforeItalgrip(perYear) incidents 1.6vehicles 2.3injured/0killed 0.67 AfterItalgrip(perYear) incidents 0vehicles 0injured/0killed 0

LaCrosseCountySTH16­NBandSB

Accidents BeforeItalgrip(perYear)Incidents 3.66Vehicles 10injured/0killed 2 AfterItalgrip(perYear)Incidents 0.33Vehicles 1.33injured/0killed 0

AccidentsBenefits Vehicles‐PropertyBenefit* $85,366Injuries‐DeathBenefit** $169,550

PresentWorthBenefit $254,916 CostofHFS #ofLanes 2lanewidth 12Typicalsectionlength 400price/ft2 $2.20

TotalHFSCost $21,120

B/C 12.07

AccidentsBenefits Vehicles‐PropertyBenefit* $321,791Injuries‐DeathBenefit** $506,120

PresentWorthBenefit $827,911 CostofHFS #oflanes 4lanewidth 12Typicalsectionlength 400price/ft2 $2.20

TotalHFSCost $42,240

B/C 19.60

61

TABLE10.Benefit­CostAnalysisforHFSLocationsinLaCrosse,WisconsinLaCrosseCounty

STH35NB

Accidents BeforeItalgrip(peryear)incidents 1vehicles 5.33injured/0killed 1 AfterItalgrip(Nov99­Oct02)incidents 0vehicles 0injured/0killed 0

LaCrosseCountySTH53NBandSB

Accidents BeforeItalgrip(peryear)incidents 3vehicles 3.33injured/0killed 1 AfterItalgrip(Nov99­Oct02)incidents 0.33vehicles 1injured/0killed 0.66

Benefits Vehicles–PropertyBenefit* $191,986Injuries‐DeathBenefit** $245,590PresentWorthBenefit $437,576

Cost #oflanes 2lanewidth 12Typicalsectionlength 400price/ft2 $2.20

HFSCost $21,120

B/C 20.72

Benefits Vehicles‐PropertyBenefit* $83,926Injuries‐DeathBenefit** $83,501PresentWorthBenefit $167,427

Cost #oflanes 4lanewidth 12Typicalsectionlength 400price/ft2 $2.20

HFSCost $42,240

B/C 3.96

62

6.2InternationalFrictionIndexforHigh­FrictionSurfaces.

Inordertoprovidestandardreferencevaluesforthedifferentproductsevaluated,

theInternationalFrictionIndexparameters,F(60)andSp, werecomputedusing

ASTM1960withsmallmodifications.

Table12presentstheresultsbasedontheDFTesterandCTMetermeasurements

andusingtheoriginalcoefficientsdevelopedbyPIARCandtherevisedcoefficient

presentedinChapter2andEquations(1)through(3).Inadditionthetablealso

includesthemeasuredGripnumber(GN)andthevalues“estimated”usingthe

originalandrevisedIFIcoefficients.Unfortunately,noneofthesetofconfidentscan

beusedtoaccuratelyharmonizetheDFTesterandGriptestermeasurements,since

theestimatedGripnumbersdonotmatchtheactualfieldmeasurements.This

suggeststhatmoredataonawiderrangeofpavementsurfaces,including

positively‐texturedsurfacessuchasHFS,maybeneededtoaccuratedeterminethe

harmonizationconfidents.

TABLE12.HFSFrictionMeasurementsusingtheInternationalFrictionIndex. PIARC REVISED

COEF. COEF. CODE TX Sp F(60) FR(S) FR(S) GNFIELD

TN­C 1.46 145.16 0.625 0.84 0.47 1.05TN­I­4 1.61 158.62 0.655 0.86 1.02 1.02W­I­1 1.03 106.59 0.473 0.69 0.35 0.67W­I­2 1.07 110.18 0.427 0.60 0.14 0.53W­I­3 1.04 107.49 0.424 0.60 0.12 0.63W­P 1.07 110.18 0.412 0.57 0.07 0.69VA­S­1 1.53 151.44 0.351 0.41 ‐0.19 0.50VA­S­2 1.56 154.13 0.392 0.47 ‐0.02 0.57TN­G 1.52 150.54 0.648 0.87 1.01 0.90VA­T 1.28 129.02 0.623 0.87 0.96 0.90

63

7.FINDINGSANDRECOMMENDATIONS

High‐frictionsurfaces(HFS)areincreasinglybeingconsideredforareaswhere

additionalfrictionmaybeneededbecausetheyprovidehighlevelsoffriction

withoutnegativelyaffectingotherpavementqualities,likenoiseordurability.The

reviewconductedshowedthattheproductsavailableintheUnitedStatesmarket

includeCrafcoHFS,Italgrip,FlexoGrid,Safelane,SafeTGrip,andTyregrip.Someof

theavailableapplicationsfortheseproductswereevaluatedandacost‐benefits

methodologywasproposed.

Thefieldevaluationsshowedthatmostoftheseproductsprovideveryhighinitial

levelsoffrictionandmacrotexture.Thelimitedhistoricaldataalsoshowthatat

leastsomeofthesystemscanmaintainhighfrictionvaluesafter9yearsofservice.

Furthermore,inthefewapplicationswherebeforeandaftercrashdatawere

recorded,abenefit‐costanalysisshowedthattheuseofHFSiseconomically

justified.Thereductionincrashcostis4to20timesthecostofthetreatmentsfor

theselocations.Similaranalyzesshouldbeconductedforotherproductsand

installationlocationsand/orconditionsbeforestrongconclusionscanbedrawn.

ComparisonsbetweenfrictiondatacollectedwiththeDFtesterandtheGriptester

showedthattheavailableharmonizationmodelscannotbeaccuratelyappliedto

HFS.Moreharmonizationexperimentsarerecommendedwithawiderrangeof

pavementsurfaces,includingHFSandothertypesofsurfacetreatments,to

determinetheIFIcoefficientsrecommendedbyASTM1960.

8.ACKNOWLEDGEMENTS

Thedatausedforthispaperwascollectedbyvisitingthephysicallocationsofthe

selectedinstallations.Thisexperimenthasbeenmadepossiblethankstothe

contributionsoftheTennessee,Connecticut,Wisconsin,Minnesota,andVirginia

64

departmentsoftransportation,theVirginiaTechTransportationInstitute(VTTI),

theVirginiaTransportationResearchCouncil(VTRC),theFederalHighway

Administration(FHWA),GlynOwen(Safe‐T‐Grip),NickNedas(Crafco),Robert

Schmiedlin(Crafco),AnthonyHensey(Cargill),RichardBaker(Tyregrip)andDeb

Bischoff.WilliamHobbs,OscarGonzalez,MarioCandia,KevinMcGee,andEdgarde

Leoncollaboratedwiththedatacollectionandprocessing.

9.REFERENCES

AASHTO(1991).ResistancetoDegredationofSmall‐SizeCoarseAggreagatebyAbrasionandImpactintheLosAngelesMachine.T96‐87.InterimSpecificationsforTransportationMaterialsandMethodsofSamplingandTesting.Washington,D.C.:122. AASHTO(1991).SoundnessofAggregatesbyFreezingandThawningT103‐91I.I.InterimSpecificationsforTransportationMaterialsandMethodsofSamplingandTestingTesting.Washington,D.C.:122. Adam,J.F.andE.Gansen(2001).PerformanceofPoly‐CarbFlexogridBridgeOverlaySystem.TechnicalReport.Ames,Iowa,IowaDepartmentofTransportation:10. ASTM(1998).StandardTestMethodforMeasuringPavedSurfaceFrictionalPropertiesUsingtheDynamicFrictionTester.E1911‐98.ASTM.WestConshohocken,PA:7. ASTM(2006).StandardPracticefortheAcceleratedPolishingofAggregatesUsingtheBritishWheel.D‐3319‐06.ASTM.Westconshohoken,PA:5. Bischoff,D.(2008)."InvestigativeStudyofItalgripSystem2008"(WI‐04‐08):21.Crafco,www.crafco.com/(accessed4/2008) Descornet,G.(2004).TheHERMESProject.5thSymposiumonPavementSurfaceCharacteristics.W.R.Association.Toronto,Canada,SURF:11. Flintsch,G.,E.d.Leon,McGhee,K.,AlQadyl.(2003).PavementSurfaceMacrotextureMeasurementandApplicattions.TransportationResearchBoard.WashingtonD.C.,TransportationResearchRecord.No.1860:168‐177.

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FlexoGrid,www.poly‐carb.com/flexogrid/system.php(accessed7/2008)

Hayes,L.,M.Rosenberg,J.Abraham.(2007).MakingRoadsSafe.WorldBankGlobalRoadSafetyDecaturGeorgia,WorldBank23. Henry,J.J.(2000)."EvaluationofPavementFrictionCharacteristics."NationalCooperativeHighwayResearchProgramNCHRPSynthesisoftheHighwayPractice(291):61. Henry,J.J.andK.Siato(1983).SkidResistanceMeasurementswithBlankandRibbedTesterTiresandTheirRelationshiptoPavementTexture.TransportationResearchBoard.WashingtonD.C.,TransportationResearchRecord.No.946:38‐43. Huhta,R.S.,D.A.Meyer, P.Zelnak.(2001).TheAggregateHandbook.Arlington,Virginia. Julian,F.andS.Moler(2008)."GainingTractioninRoadwaySafety."FederalHighwayAdministrationVol.72(No.1):10.Italgrip,www.italgrip.com/usa/italgrip.htm(accessed5/2008) Kelly,T.(2008).ForensicReportoftheFailureofTyregrip.MaterialsForensicReport.PolkParkway,FloridaFloridaDepartmentofTransportation. Kuemmel,D.A.,J.R.Jaeckel,A,Satanovsky.(2000)."InvestigativeStudyoftheItalgripSystem‐NoiseAnalysis."(WI/SPR‐02‐00):20. Kuttesch,J.S.(2004).QuantifyingtheRelationshipbeweenSkidResistanceandWetWeatherAccidentsforVirginiaData.CivilandEnvironmentalBlacksburg,Virgina,VirginiaPolytechnicInstittuteandStateUniversityMasterofScience. Mn/DOT(2005)."BenefitCostAnalysisforTransportationProjects."BenefitCostAnalysisGuidance:33. N.T.S.(1999).NationalTransportationSafetyBoardAnnualReport.WashingtonD.C.NTSB/SPC‐00/03:83. Nicholls,J.C.(1997).LaboratoryTestsonHigh‐FrictionSurfacesforHighways.TransportationResearchLaboratory.England,TRL.Report176:36. Nicholls,J.C.(1998).TrialsofHigh‐FrictionSurfacesforHighways.TransportationResearchLaboratory.England,TRL.Report125:22. NTS(1999).NationalTransportationSafetyBoardAnnualReport.WashingtonD.C.NTSB/SPC‐00/03:83.

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Reddy,V.,T.Datta,McAvoy,D.,P.Savolainen,.M,Abdel‐Aty.,S,Pinapaka.(2008).EvaluationofInnovativeSafetyTreatments.EvaluationReportOrlando,Florida,FloridaDepartementofTransportation36. Safelane‐Cargill,www.cargillsafelane.com/(accessed5/2008)

Safe‐T‐Grip,www.trafficcalmingusa.com(accessed8/2008)

Shi,C.(2004)."Steelslag:Production,processing,characteristicsandcementiousproperties."JournalofMaterialsinCivilEngineeringNo.16(No.3):7. Sprinkel,M.M.,D.Roosevelt,.Flintsch,G.,E.d.Leon.,Mokaren,D.(2008).EvaluationofCargillSafelaneEpoxyOverlay.VTRC.Charlottesville,Virginia.08‐R:45. Tyregrip,www.ennispaint.com(accessed4/2008)

Wambold,J.C.,C.E.Antle,.(1995).InternationalPIARCExperimenttoCompareandHarmonizeTextureandskidResistanceMeasurements.Paris,France,PermanentInternationalAssociationofRoadCongressesPIARC. Wambold,J.C.,J.J.Henry.,T,Yager.(2004).NASAWallopsTire/RunwayFriction.5thSymposiumonPavementSurfaceCharacteristics.W.R.Association.Toronto,Canada,SURF:19. Wambold,J.C.,T.J.Yager,JJHenry.,ZRado.(2006).AWhitePaperonCorrelationoftheGriptesterTrailertotheASTME274SkidTrailer.

67

CHAPTERIV

SUMMARY,FINDINGS,CONCLUSIONS,AND

RECOMMENDATIONS

Itisimportantthathighwayagenciesprovidedriverswithsafe,smoothrides

throughouttheyear.Itisforthisreasonthatfriction,textureandothersurface

propertiesmustbemonitoredperiodically.Roadwaysectionswithdeficientfriction

mustbetreatedtoimprovesafetyandHFSarestartingtobeconsideredasaviable

treatmentinareaswithhighnumberofskidding‐relatedaccidents.

ThethesispresentedadetailedevaluationofthemainHFSproductsavailableinthe

UnitedStatesmarket;bymeasuringtheirperformanceondifferentapplications,

underdifferentweatherconditions,andinvariouslocations(states).

Inaddition,italsopresentedeffortstocompareandharmonizetextureandskid

resistancemeasurementstakenwithvariousdevices.

1.FINDINGS

IntheprocessofevaluatingtheIFIcoefficients,discrepancieswerefoundintheIFI

valuescalculatedforthedifferentdevices:

• Thedatacollectedforthisprojectshowedthatthemodeldevelopedby

PIARCdoesnotproduceharmoniousresultsamongthedevicesusedbythe

consortiummembersintheVirginiaSmartRoadRodeoforthesurfaces

tested.

• ThissuggeststhattheoriginalcoefficientsdeterminedduringthePIARC

experimentmayneedtobeadjustedforthedevicesevaluatedbeforetheIFI

canbeimplementedintheU.S.

68

• Furthermore,itwasnotpossibletoharmonizethemeasurementsobtained

withthevariousdevicesusedinthisthesisonallthestudiedHFS.

TheevaluationofthevariousidentifiedHFSproductsandapplicationspermittedto

drawthefollowingfindings:

• TherearevariousHFSproductsavailableintheU.S.market,whichhavebeen

usedbydifferentagencies.

• ThedatacollectedforthisprojectshowedthatHFScanmaintaingoodlevels

offrictionandmacrotexturetextureforatleast9yearsofservice.

• However,someoftheevaluatedapplicationsdevelopedsignificantlevelof

ravelingafter10years.

• Thebenefit‐coststudyfoundthatatleastinareaswithhighnumberof

skidding‐relatedcrashes,HFScanbeeconomicallyjustifiabletreatments.

• Someoftheapplicationsevaluatedresultedinpresentbenefit‐costratiosof4

to20.

2.CONCLUSIONS

TheresultsoftheevaluationofthevariousidentifiedHFSproductsand

applicationssuggestedthatHFSareanappealingalternativeforareaswithfrequent

wetweatherand/orrun‐off‐the‐roadcrashes.Therefore,HFSsystemsshould

continuetobeconsideredinthepoolofavailablesafetyimprovementalternates.

Additionalapplicationandbeforeandaftercrashstudiesfordifferentapplication

conditionsmayprovideadditionalunderstandingofthebenefitsofthevarious

availablesystems.

69

3.RECOMMENDATIONSFORFUTURERESEARCH

Theuseofrecordedaccidentdataonblackspotswherefrictionisbeingmonitored

frequentlyisrecommendedtodeterminerequiredthresholdlevelsforsurface

properties’maintenanceandrehabilitation.

Itisnecessarytostudy,monitorandcorrelatetexture,frictionandaccidentdatato

predictminimumacceptablesurfacefrictionvaluesaccordingtosafetystandards.

Theexistingcorrelationbetweenaccidents,skidresistanceandgeometricdesign

parameters,likeradiusofcurvature,couldbefurtherstudied,forthereasonthata

highpercentageofaccidentsoccuroncurves.

Moreexperimentsarerecommendedwithdifferenttypesofpavementsurfaces,

includingHFSandothertypesofsurfacetreatments,todemonstratethevalidityof

theSpcoefficientsrecommendedbyASTMandalsothevalidityofusingtheDF

TesterasthestandarddevicetogatherfrictionmeasurementsfortheIFI

calculations.