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TheAutovadelOlivarwhichunitesbedawithEstepainAndaluciainsouthernSpain.Ageometricdesignsavedonconstructioncostsandimprovedvisibilitywiththeintentiontoreducethelikelihoodoftrafficincidents

GeometricdesignofroadsFromWikipedia,thefreeencyclopedia

Thegeometricdesignofroadsisthebranchofhighwayengineeringconcernedwiththepositioningofthephysicalelementsoftheroadwayaccordingtostandardsandconstraints.Thebasicobjectivesingeometricdesignaretooptimizeefficiencyandsafetywhileminimizingcostandenvironmentaldamage.Geometricdesignalsoaffectsanemergingfifthobjectivecalled"livability,"whichisdefinedasdesigningroadstofosterbroadercommunitygoals,includingprovidingaccesstoemployment,schools,businessesandresidences,accommodatearangeoftravelmodessuchaswalking,bicycling,transit,andautomobiles,andminimizingfueluse,emissionsandenvironmentaldamage.[1]

Geometricroadwaydesigncanbebrokenintothreemainparts:alignment,profile,andcrosssection.Combined,theyprovideathreedimensionallayoutforaroadway.

Thealignmentistherouteoftheroad,definedasaseriesofhorizontaltangentsandcurves.

Theprofileistheverticalaspectoftheroad,includingcrestandsagcurves,andthestraightgradelinesconnectingthem.

Thecrosssectionshowsthepositionandnumberofvehicleandbicyclelanesandsidewalks,alongwiththeircrossslopeorbanking.Crosssectionsalsoshowdrainagefeatures,pavementstructureandotheritemsoutsidethecategoryofgeometricdesign.

Contents

1Designstandards2Profile

2.1Terminology2.2SagCurves2.3CrestCurves

3Alignment3.1Terminology3.2Geometry3.3CurvesightDistance

4Crosssection4.1Lanewidth4.2Crossslope

5Safetyeffectsofroadgeometry



5.1Designconsistency5.2Safetyeffectsofalignment5.3Safetyeffectsofcrosssection

6Sightdistance6.1Stoppingsightdistance6.2Decisionsightdistance6.3Intersectionsightdistance

6.3.1Cornersightdistance6.3.1.1Uncontrolledandyieldcontrolledintersections6.3.1.2Twowaystopcontrol6.3.1.3Allwaystopcontrolandsignalizedintersections

6.4Effectsofinsufficientsightdistance7Seealso

7.1Roadstandardssettingbodies8Notes9References

9.1LawReviews

Designstandards

Roadsaredesignedinconjunctionwithdesignguidelinesandstandards.Theseareadoptedbystateandnationalauthorities.Designguidelinestakeintoaccountspeed,vehicletype,roadgrade(slope),viewobstructions,andstoppingdistance.Withproperapplicationofguidelines,alongwithgoodengineeringjudgement,anengineercandesignaroadwaythatiscomfortable,safe,andappealingtotheeye.

TheprimaryUSguidanceisfoundintheAPolicyonGeometricDesignofHighwaysandStreetspublishedbytheAmericanAssociationofStateHighwayandTransportationOfficials(AASHTO).[2]OtherstandardsincludetheAustralianGuidetoRoadDesign(http://www.austroads.com.au/interest_design.html),andtheBritishDesignManualforRoads.(http://www.dft.gov.uk/ha/standards/dmrb/index.htm)AnopensourceversionofthegreenbookispublishedonlinebyTheCouncilforScientificandIndustrialResearch(CSIR)(http://www.csir.co.za/)officeinZimbabwe.[3]

Profile

Theprofileofaroadconsistsofroadslopes,calledgrades,connectedbyparabolicverticalcurves.Verticalcurvesareusedtoprovideagradualchangefromoneroadslopetoanother,sothatvehiclesmaysmoothlynavigategradechangesastheytravel.

Sagverticalcurvesarethosethathaveatangentslopeattheendofthecurvethatishigherthanthatofthebeginningofthecurve.Whendrivingonaroad,asagcurvewouldappearasavalley,withthevehiclefirstgoingdownhillbeforereachingthebottomofthecurveandcontinuinguphillorlevel.



Crestverticalcurvesarethosethathaveatangentslopeattheendofthecurvethatislowerthanthatofthebeginningofthecurve.Whendrivingonacrestcurve,theroadappearsasahill,withthevehiclefirstgoinguphillbeforereachingthetopofthecurveandcontinuingdownhill.

Theprofilealsoaffectsroaddrainage.Veryflatroadsandsagcurvesmayhavepoordrainage,andsteeproadshavehighvelocityflows.

Terminology

BVC=BeginningofVerticalCurve

EVC=EndofVerticalCurve

=initialroadwaygrade,expressedinpercent

=finalroadwaygrade,expressedinpercent

A=absolutevalueofthedifferenceingrades(initialminusfinal),expressedinpercent

=Heightofeyeaboveroadway,measuredinmetersorfeet

=Heightofobjectaboveroadway,measuredinmetersorfeet

L=curvelength(alongthexaxis)

PVI=pointofverticalinterception(intersectionofinitialandfinalgrades)

tangentelevation=elevationofapointalongtheinitialtangent

x=horizontaldistancefromBVC

Y(offset)=verticaldistancefromtheinitialtangenttoapointonthecurve

Y=curveelevation=tangentelevationoffset[2]

SagCurves

Sagverticalcurvesarecurveswhich,whenviewedfromtheside,areconcaveupwards.Thisincludesverticalcurvesatvalleybottoms,butitalsoincludeslocationswhereanuphillgradebecomessteeper,oradownhillgradebecomeslesssteep.

Themostimportantdesigncriterionforthesecurvesisheadlightsightdistance.[2]Whenadriverisdrivingonasagcurveatnight,thesightdistanceislimitedbythehighergradeinfrontofthevehicle.Thisdistancemustbelongenoughthatthedrivercanseeanyobstructionontheroadandstopthevehiclewithintheheadlightsightdistance.Theheadlightsightdistance(S)isdeterminedbytheangleoftheheadlightandangleofthetangentslopeattheendofthecurve.Byfirstfindingtheheadlightsightdistance(S)andthensolvingforthecurvelength(L)ineachoftheequationsbelow,thecorrectcurvelengthcanbedetermined.IftheSLcurvelengthissmallerthantheheadlightsightdistance,thenthisnumbercanbeused.Ifitislarger,thisvaluecannotbeused.[4]



Units SightDistanceL)

Metric

USCustomary

Theseequationsassumethattheheadlightsare600millimetres(2.0ft)abovetheground,andtheheadlightbeamdiverges1degreeabovethelongitudinalaxisofthevehicle.[5]

CrestCurves

Crestverticalcurvesarecurveswhich,whenviewedfromtheside,areconvexupwards.Thisincludesverticalcurvesathillcrests,butitalsoincludeslocationswhereanuphillgradebecomeslesssteep,oradownhillgradebecomessteeper.

Themostimportantdesigncriterionforthesecurvesisstoppingsightdistance.[2]Thisisthedistanceadrivercanseeoverthecrestofthecurve.Ifthedrivercannotseeanyobstructionsintheroadway,suchasastalledvehicleoranimal,thedrivermaynotbeabletostopthevehicleintimetoavoidacrash.Thedesiredstoppingsightdistance(S)isdeterminedbythespeedoftrafficonaroad.Byfirstfindingthestoppingsightdistance(S)andthensolvingforthecurvelength(L)ineachoftheequationsbelow,thecorrectcurvelengthcanbedetermined.Theproperequationdependsonwhethertheverticalcurveisshorterorlongerthantheavailablesightdistance.Normally,bothequationsaresolved,thentheresultsarecomparedtothecurvelength.[4][5]

SightDistance>CurveLength(S>L)

SightDistance



UsingAASHTOstandards,anengineerworkstodesignaroadthatissafeandcomfortable.Ifahorizontalcurvehasahighspeedandasmallradius,anincreasedsuperelevation(bank)isneededinordertoassuresafety.Ifthereisanobjectobstructingtheviewaroundacornerorcurve,theengineermustworktoensurethatdriverscanseefarenoughtostoptoavoidanaccidentoracceleratetojointraffic.

Terminology

R=Radius

PC=PointofCurvature(pointatwhichthecurvebegins)

PT=PointofTangent(pointatwhichthecurveends)

PI=PointofIntersection(pointatwhichthetwotangentsintersect)

T=TangentLength

C=LongChordLength(straightlinebetweenPCandPT)

L=CurveLength

M=MiddleOrdinate,nowknownasHSOHorizontalSightlineOffset(distancefromsightobstructingobjecttothemiddleoftheoutsidelane)

E=ExternalDistance

=CoefficientofSideFriction

u=VehicleSpeed

=DeflectionAngle[2]

Geometry

[2]



CurvesightDistance

Crosssection

Thecrosssectionofaroadwaycanbeconsideredarepresentationofwhatonewouldseeifanexcavatordugatrenchacrossaroadway,showingthenumberoflanes,theirwidthsandcrossslopes,aswellasthepresenceorabsenceofshoulders,curbs,sidewalks,drains,ditches,andotherroadwayfeatures.

Lanewidth

Theselectionoflanewidthaffectsthecostandperformanceofahighway.Typicallanewidthsrangefrom3metres(9.8ft)to3.6metres(12ft).Widerlanesandshouldersareusuallyusedonroadswithhigherspeedandhighervolumetraffic,andsignificantnumbersoftrucksandotherlargevehicles.Narrowerlanesmaybeusedonroadswithlowerspeedorlowervolumetraffic.

Narrowlanescostlesstobuildandmaintain,butalsoreducethecapacityofaroadtoconveytraffic.Onruralroads,narrowlanesarelikelytoexperiencehigherratesofrunoffroadandheadoncollisions.Widerroadsincreasethetimeneededtowalkacross,andincreasestormwaterrunoff.

Crossslope

Crossslopedescribestheslopeofaroadwayperpendiculartothecenterline.Ifaroadwerecompletelylevel,waterwoulddrainoffitveryslowly.Thiswouldcreateproblemswithhydroplaning,andiceaccumulationincoldweather.

Intangent(straight)sections,theroadsurfacecrossslopeiscommonly12%toenablewatertodrainfromtheroadway.Crossslopesofthissize,especiallywhenappliedinbothdirectionsoftravelwithacrownpointalongthecenterlineofaroadwayarecommonlyreferredtoas"normalcrown"andaregenerallyimperceptibletotravelingmotorists.

Incurvedsections,theoutsideedgeoftheroadissuperelevatedabovethecenterline.Sincetheroadisslopeddowntotheinsideofthecurve,gravitypullsthevehicledowntowardstheinsideofthecurve.Thisallowsgravitytohelpprovidesomeofthecentripetalforceneededtogoaroundthecurve.

Superelevationslopesofupto4to10%areappliedinordertoaidmotoristsinsafelytraversingthesesectionswhilemaintainingentryspeedofthevehiclealongthelengthofthecurve.Anupperboundof12%waschosentoreflecttheeffectsofconstructionandmaintenancepractices,aswellasthedifficultyofdrivingasteepcrossslopeatlowspeeds.Inareasthatreceivesignificantsnowandice,mostagenciesuseamaximumcrossslopeof6to8%.Steepercrossslopesmakeitdifficulttotraversetheslopeatlowspeedwhenthesurfaceisicy,nottomentionacceleratingfromzerowithwarmtyresontheice.Lowercrossslopeincreasetheriskforlossofcontrolathighspeedwhenthesurfaceisicy.Sincetheconsequenceofhighspeedskiddingismuchworsethanfromslidingatlowspeed,thenetsafetyinsharpcurvesgainsfromselectingupto8%superelevationinsteadof4%.Thelowerslopeof4%ismostlyusedonurbanroadwayswherespeedsarelower,andwheresteeperslopeswouldraisetheoutsideroadedgeaboveadjacentproperties.[5]



Theequationforthedesiredradiusofacurveisfoundfromtheequationbelowwhichtakesintoaccountfactorsforspeedandsuperelevationrate(e).Thisequationcanberearrangedalgebraicallytoobtaindesiredratesofsuperelevationbasedonthedesignspeedofaroadwayandtheradius.

TheAmericanAssociationofStateHighwayandTransportationofficials(AASHTO)providesatablefromwhichdesiredsuperelevationratescanbeeasilyinterpolatedbasedonthedesignspeedandradiusofacurvedsectionofroadway.ThistablecanalsobeseenreprintedinmanystateroadwaydesignguidesandmanualsintheU.S.

Safetyeffectsofroadgeometry

Thegeometryofaroadinfluencesitssafetyperformance.Whilestudiesofcontributingfactorstoroadaccidentsshowthathumanfactorspredominate,roadwayfactorsarethesecondmostcommoncategory,withvehiclefactorslast.

Designconsistency

Collisionstendtobemorefrequentinlocationswhereasuddenchangeinroadcharacterviolatesthedriver'sexpectations.Acommonexampleisasharpcurveattheendofalongtangentsectionofroad.Theconceptofdesignconsistencyaddressesthisbycomparingadjacentroadsegmentsandidentifyingsiteswithchangesthedrivermightfindsuddenorunexpected.Locationswithlargechangesinthepredictedoperatingspeedarelikelytobenefitfromadditionaldesigneffort.Ahorizontalcurvewithasignificantlysmallerradiusthanthosebeforeitmayneedenhancedcurvesigns.[8]Thisisanimprovementontheconceptofdesignspeed,whichonlysetsalowerlimitforgeometricdesign.Intheexamplegivenabove,alongtangentfollowedbyasharpcurvewouldbeacceptableifa30mphdesignspeedwaschosen.Designconsistencyanalysiswouldflagthedecreaseinoperatingspeedatthecurve.

Safetyeffectsofalignment

Thesafetyofahorizontalcurveisaffectedbythelengthofthecurve,thecurveradius,whetherspiraltransitioncurvesareused,andthesuperelevationoftheroadway.Foragivencurvedeflection,crashesaremorelikelyoncurveswithasmallerradius.Spiraltransitionsdecreasecrashes,andinsufficientsuperelevationincreasescrashes.

Asafetyperformancefunctiontomodelcurveperformanceontwolaneroadsis:[9]

where

AMF=Accidentmodificationfactor,amultiplierthatdescribeshowmanymorecrashesarelikelytooccuronthecurvecomparedtoastraightroadLc=Lengthofthehorizontalcurveinmiles.

R=Radiusofthecurveinfeet.



S=1ifspiraltransitioncurvesarepresent

=0ifspiraltransitioncurvesareabsent

Safetyeffectsofcrosssection

Crossslopeandlanewidthaffectthesafetyperformanceofaroad.

Certaintypesofcrashes,termed"lanedeparturecrashes",aremorelikelyonroadswithnarrowlanes.Theseincluderunoffroadcollisions,sideswipes,andheadoncollisions.Fortwolaneruralroadscarryingover2000vehiclesperday,theexpectedincreaseincrashesis:

Lanewidth Expectedincreaseincrashes12feet(3.7m) 0%11feet(3.4m) 5%10feet(3.0m) 30%9feet(2.7m) 50%

Theeffectoflanewidthisreducedonurbanandsuburbanroads[10]andlowvolumeroads.[9]

Insufficientsuperelevationwillalsoresultinanincreaseincrashrate.Theexpectedincreaseisshownbelow:[9]

Superelevationdeficiency

Expectedincreaseincrashesforcars

Expectedincreaseincrashesforheavytrucks[11]



Duringhighwaydesignandtrafficsafetyinvestigations,highwayengineerscomparetheavailablesightdistancetohowmuchsightdistanceisneededforthesituation.Dependingonthesituation,oneofthreetypesofsightdistanceswillbeused:

Stoppingsightdistance

Stoppingsightdistanceisthedistancetraveledduringperceptionreactiontime(whilethevehicledriverperceivesasituationrequiringastop,realizesthatstoppingisnecessary,andappliesthebrake),andmaneuvertime(whilethedriverdeceleratesandcomestoastop).Actualstoppingdistancesarealsoaffectedbyroadconditions,themassofthecar,theinclineoftheroad,andnumerousotherfactors.Fordesign,aconservativedistanceisneededtoallowavehicletravelingatdesignspeedtostopbeforereachingastationaryobjectinitspath.Typicallythedesignsightdistanceallowsabelowaveragedrivertostopintimetoavoidacollision.[12][13]

Decisionsightdistance

Decisionsightdistanceisusedwhendriversmustmakedecisionsmorecomplexthanstopordon'tstop.Itislongerthanstoppingsightdistancetoallowforthedistancetraveledwhilemakingamorecomplexdecision.Thedecisionsightdistanceis"distancerequiredforadrivertodetectanunexpectedorotherwisedifficulttoperceiveinformationsourceorhazardinaroadwayenvironmentthatmaybevisuallycluttered,recognizethehazardoritsthreatpotential,selectanappropriatespeedandpath,andinitiateandcompletetherequiredmaneuversafelyandefficiently.[14]Ideally,roadsaredesignedforthedecisionsightdistance,using6to10secondsforperceptionreactiontimeand4to5secondstoperformtherightmaneuver.

Intersectionsightdistance

Intersectionsightdistanceisthesightdistanceneededtosafelyproceedthroughanintersection.Thedistanceneededdependsonthetypeoftrafficcontrolattheintersection(uncontrolled,yieldsign,stopsignorsignal),andthemaneuver(leftturn,rightturn,orproceedingstraight).Allwaystopintersectionsneedtheleast,anduncontrolledintersectionsrequirethemost.Intersectionsightdistanceisakeyfactorinwhethernocontroloryieldcontrolcanbesafelyused,otmorerestrictivecontrolinneeded.[15]

Cornersightdistance

Cornersightdistance(CSD)istheroadalignmentspecificationwhichprovidesasubstantiallyclearlineofsightsothatthedriverofavehicle,bicyclistorpedestrianwaitingatthecrossroadmaysafelyanticipatethedriverofanapproachingvehicle.Cornersightprovidesanadequatetimeforthewaitingusertoeithercrossalllanesofthroughtraffic,crossthenearlanesandturnleft,orturnright,withoutrequiringthroughtraffictoradicallyaltertheirspeed.

Uncontrolledandyieldcontrolledintersections

Uncontrolledandyield(giveway)controlledintersectionsrequirelargesighttrianglesclearofobstructionsinordertooperatesafely.Atuncontrolledintersections,thebasicrightofwayrulesapply(eitheryieldtothevehicleontheright,ortheboulevardrule,dependingonthelocation).Vehicledriversmustbeabletoseetrafficapproachingontheintersectingroadatapointwheretheycanadjusttheirspeed,orstopifneedbe,toyieldtotheothertrafficbeforereachingtheintersection.Itisn'ttheonlycriterionforallowingthesetypesofintersectioncontrol.Changinganintersectiontostopcontrolisacommonresponsetopoorsafetyperformance.



Twowaystopcontrol

Whendeterminingcornersightdistance,asetbackdistanceforthevehiclewaitingatthecrossroadmustbeassumed.SetbackforthedriverofthevehicleonthecrossroadhasbeenstandardizedbysomestateMUTCDsanddesignmanualstobeuptoaminimumof10feetplustheshoulderwidthofthemajorroadbutnotlessthan15feet.[16]However,theFederalMUTCDrequiresthatastopline,ifused,shallbeatleast4feetfromthenearesttravellane.[17]Lineofsightforcornersightdistanceistobedeterminedfroma3and1/2footeyeheightatthevehicledriver'slocationontheminorroadtoa4and1/4footobjectheightinthecenteroftheapproachinglaneofthemajorroad.[18][19]Cornersightdistance, ,isequivalenttoaspecifiedtimegap, ,atthedesignspeed, ,requiredforastoppedvehicletoturnrightorleft:

Forpassengervehiclesattwolaneintersections,thistimegapequivalenceiscommonlyadistance7.5secondsawayatthedesignspeed.Longergapsarerequiredfortrucksandbuses,andformultilaneroads.[20]Generally,thepublicrightofwayshouldincludeandmaintainthislineofsight.

Allwaystopcontrolandsignalizedintersections

Driversatintersectionswithallwaystopcontrolortrafficsignalsneedtheleastsightdistance.Atallwaystops,driversneedtobeabletoseevehiclesstoppedatotherapproaches.Atsignals,driversapproachingtheintersectionsneedtoseethesignalheads.Injurisdictionsthatallowrightturnonred,driversintherightlanestopcontrolneedthesamesightdistanceastwowaystopcontrol.Althoughnotneededduringnormaloperations,additionalsightdistanceshouldbeprovidedforsignalmalfunctionsandpoweroutages.

Effectsofinsufficientsightdistance

Manyroadswerecreatedlongbeforethecurrentsightdistancestandardswereadopted,andthefinancialburdenonmanyjurisdictionswouldbeformidableto:acquireandmaintainadditionalrightofwayredesignroadbedsonallofthemorimplementfutureprojectsonroughterrain,orenvironmentallysensitiveareas.Insuchcases,thebareminimumcornersightdistanceshouldbeequaltothestoppingsightdistance.[21]Whileacornersightdistancewhichfarexceedthebrakingdistanceatthedesignspeedshouldbeaffordedtothedriver,heorsheisstillgenerallyrequiredtomaintainsuchcontrolandoperatingspeedastobeabletostopwithintheAssuredClearDistanceAhead(ACDA),[22]andthebasicspeedrulealwaysapplies.Jurisdictionsoftenprovidesomelevelofdesignimmunityagainstgovernmentclaimsactions,insuchcases.[Note1]

Warningsignsareoftenusedwheresightdistanceisinsufficient.TheUSMUTCDrequiresStopAhead,YieldAheadorSignalAheadsignsatintersectionswherethetrafficcontroldeviceisnotvisiblefromadistanceequaltothestoppingsightdistanceatspeedofapproachingtraffic.HillBlocksViewsignscanbeusedwherecrestverticalcurvesrestrictsightdistance.[23]However,manyjurisdictionsstillexpectdriverstouseordinarycareregardingconditionsreadilyapparenttoadriver,withoutthepromptingofasign.[Note2]Thecareandfocusordinarilyrequiredofadriveragainstcertaintypesofhazardsmaybesomewhatamplifiedonroadswithlowerfunctionalclassification.[24][25]Theprobabilityofspontaneoustrafficincreasesproportionallytothedensityofaccesspoints,andthisdensityshouldbereadily



apparenttoadriverevenwhenaspecificaccesspointisnot.[26]Forthisreason,fullcornersightdistanceisalmostneverrequiredforindividualdrivewaysinurbanhighdensityresidentialareas,andstreetparkingiscommonlypermittedwithintherightofway.

Seealso

CognitiveergonomicsDegreeofcurvatureDesignspeedHumanfactorsRoadtrafficsafetyStoppingsightdistanceTrafficpsychologyTransitioncurve

Roadstandardssettingbodies

AmericanAssociationofStateHighwayandTransportationOfficialsNationalCooperativeHighwayResearchProgramTransportationResearchBoard

Notes

References

1. ^Forexample,seeCaliforniaGovernmentClaimsAct(http://www.leginfo.ca.gov/cgibin/displaycode?section=gov&group=0000101000&file=815818.9)andVehicleCodeSection22358.5(http://www.dmv.ca.gov/pubs/vctop/d11/vc22358_5.htm)

2. ^Forexample,theCaliforniaGovernmentClaimsAct'sCGC830.4(http://law.onecle.com/california/government/830.4.html):"Aconditionisnotadangerousconditionwithinthemeaningofthischaptermerelybecauseofthefailuretoprovideregulatorytrafficcontrolsignals,stopsigns,yieldrightofwaysigns,orspeedrestrictionsigns..."andCGC830.8(http://law.onecle.com/california/government/830.8.html):"Neitherapublicentitynorapublicemployeeisliableunderthischapterforaninjurycausedbythefailuretoprovidetrafficorwarningsignals,signs,markingsordevicesdescribedintheVehicleCode.Nothinginthissectionexoneratesapublicentityorpublicemployeefromliabilityforinjuryproximatelycausedbysuchfailureifasignal,sign,markingordevice(otherthanonedescribedinSection830.4)wasnecessarytowarnofadangerousconditionwhichendangeredthesafemovementoftrafficandwhichwouldnotbereasonablyapparentto,andwouldnothavebeenanticipatedby,apersonexercisingduecare."SeealsoCalVeh.Code22350(http://www.dmv.ca.gov/pubs/vctop/d11/vc22350.htm),CalVeh.Code22358.5(http://www.dmv.ca.gov/pubs/vctop/d11/vc22358_5.htm),CalGov.Code831(http://law.onecle.com/california/government/831.html),andCACIForm1120(http://www.justia.com/trialslitigation/docs/caci/1100/1120.html).



1. ^"TheRoleofFHWAProgramsinLivability:StateofthePracticeSummary"(http://www.fhwa.dot.gov/livability/state_of_the_practice_summary/research00.cfm).FederalHighwayAdministration.Retrieved16April2012.

2. âbcdefgGarber,N.J.,andHoel,L.,A.,TrafficandHighwayEngineering,3rdEdition.Brooks/ColePublishing,2001

3. ^"SANRALGeometricDesignGuideline"(http://geometricdesign.csir.co.za/).TheCouncilforScientificandIndustrialResearch(CSIR)inSouthAfrica.Retrieved20130728.

4. âbcHomburger,W.S.,Hall,J.W.,reilly,W.R.andSullivan,E.C.,FundamentalsofTrafficEngineering(15thed),ITSCourseNotesUCBITSCN011,2001

5. âbcAPolicyonGeometricDesignofHighwaysandStreets.WashingtonD.C.:AmericanAssociationofStateHighwayandTransportationOfficials.2004.

6. ^"MnDOTRoadDesignManual"(http://dotapp7.dot.state.mn.us/edms/download?docId=1062355).MnDOT.Retrieved6September2012.

7. ^MinnesotaDepartmentofTransportation,BikewayFacilityDesignManual,section53.5.1,http://www.dot.state.mn.us/bike/pdfs/Chapter5_Bw.pdf,retrieved4/20/2010

8. ^"DesignConsistencyModuleEngineersManual"(http://www.ihsdm.org/public/html/user/dcm/dcm_em.1.html#overview_dcm).InteractiveHighwayDesignModelEngineer'sManual.FederalHighwaysAdministration.Retrieved3/6/2012.Checkdatevaluesin:|accessdate=(help)

9. âbcD.W.Harwood,F.M.Council,E.Hauer,W.E.Hughes,andA.Vogt(2000).PredictionoftheExpectedSafetyPerformanceofRuralTwoLaneHighways(http://www.fhwa.dot.gov/publications/research/safety/99207/99207.pdf).Washington,D.C.:FederalHighwayAdministration.

10. ^Potts,IngridB.(2007).RelationshipofLaneWidthtoSafetyforUrbanandSuburbanArterials(http://www.completestreets.org/webdocs/resources/lanewidthsafety.pdf).TransportationResearchBoard.

11. ^TheEffectofCrossSectionalGeometryonHeavyVehiclePerformanceandSafety(http://www.nzta.govt.nz/resources/research/reports/263/docs/263.pdf)

12. ^HighwayDesignManual(http://www.dot.ca.gov/hq/oppd/hdm/hdmtoc.htm).6thEd.CaliforniaDepartmentofTransportation.2012.p.200.SeeChapter200onStoppingSightDistance(http://www.dot.ca.gov/hq/oppd/hdm/pdf/english/chp0200.pdf)

13. ^NationalCooperativeHighwayResearchProgram(1997).NCHRPReport400:DeterminationofStoppingSightDistances(http://onlinepubs.trb.org/onlinepubs/nchrp/nchrp_rpt_400.pdf).TransportationResearchBoard(NationalAcademyPress).p.I13.ISBN0309060737.

14. ÂmericanAssociationofStateHighwayandTransportationOfficials(1994)APolicyonGeometricDesignofHighwaysandStreets(pp.117118)

15. ÂmericanAssociationofStateHighwayandTransportationOfficials(1994)APolicyonGeometricDesignofHighwaysandStreets(pp.650679)

16. ^HighwayDesignManual(http://www.dot.ca.gov/hq/oppd/hdm/hdmtoc.htm).6thEd.CaliforniaDepartmentofTransportation.2012.pp.40014.SeeChapter405.1onSightDistance(http://www.dot.ca.gov/hq/oppd/hdm/pdf/english/chp0400.pdf)

17. ^"ManualonUniformTrafficControlDevices(MUCTD)"(http://mutcd.fhwa.dot.gov/).UnitedStatesDepartmentofTransportationFederalHighwayAdministration,.|chapter=ignored(help)

18. ^HighwayDesignManual(http://www.dot.ca.gov/hq/oppd/hdm/hdmtoc.htm).6thEd.CaliforniaDepartmentofTransportation.2012.p.200.SeeChapter405.1onSightDistance



(http://www.dot.ca.gov/hq/oppd/hdm/pdf/english/chp0400.pdf)19. ^"300".APolicyonGeometricDesignofHighwaysandStreets(http://www.transportation.org).4thEd.

AmericanAssociationofStateHighwayandTransportationOfficials.2004.20. ^"300".APolicyonGeometricDesignofHighwaysandStreets(http://www.transportation.org).4thEd.

AmericanAssociationofStateHighwayandTransportationOfficials.2004.SeeExhibit954.TimeGapforCaseB1LeftTurnfromStop

21. ^HighwayDesignManual(http://www.dot.ca.gov/hq/oppd/hdm/hdmtoc.htm).6thEd.CaliforniaDepartmentofTransportation.2012.pp.40022.SeeChapter405.1onSightDistance(http://www.dot.ca.gov/hq/oppd/hdm/pdf/english/chp0400.pdf)

22. ^USLegalDictionary(http://definitions.uslegal.com/a/assuredcleardistanceahead/)23. ^"ManualonUniformTrafficControlDevices(MUCTD)"(http://mutcd.fhwa.dot.gov/).UnitedStates

DepartmentofTransportationFederalHighwayAdministration,.|chapter=ignored(help)24. ^"Riggsv.GasserMotors,22Cal.App.2d636"

(http://law.justia.com/cases/california/calapp2d/22/636.html).OfficialCaliforniaAppellateReports(2ndSeriesVol.22,p.636).September25,1937.Retrieved20130727.""Itiscommonknowledgethatintersectingstreetsincitiespresentacontinuinghazard,thedegreeofhazarddependingupontheextentoftheuseoftheintersectingstreetsandthesurroundingcircumstancesorconditionsofeachintersection.Undersuchcircumstancesthebasiclaw...isalwaysgoverning.""SeeOfficialReportsOpinionsOnline(http://courts.ca.gov/opinionsslip.htm)

25. ^"Reaughv.CudahyPackingCo.,189Cal.335"(http://www.lexisnexis.com/clients/CACourts/).OfficialCaliforniaReports,Vol.189,p.335,(CaliforniaSupremeCourtreporter).July27,1922.Retrieved20130727.""motorvehicles,mustbespeciallywatchfulinanticipationofthepresenceofothersatplaceswhereothervehiclesareconstantlypassing,andwheremen,women,andchildrenareliabletobecrossing,suchascornersattheintersectionsofstreetsorothersimilarplacesorsituationswherepeoplearelikelytofailtoobserveanapproachingautomobile.""SeeOfficialReportsOpinionsOnline(http://www.lexisnexis.com/clients/CACourts/)

26. ^"Leeperv.Nelson,139Cal.App.2d65"(http://law.justia.com/cases/california/calapp2d/139/65.html).OfficialCaliforniaAppellateReports(2ndSeriesVol.139,p.65).Feb6,1956.Retrieved20130727.""Theoperatorofanautomobileisboundtoanticipatethathemaymeetpersonsorvehiclesatanypointofthestreet,andhemustinordertoavoidachargeofnegligence,keepaproperlookoutforthemandkeephismachineundersuchcontrolaswillenablehimtoavoidacollisionwithanotherautomobiledrivenwithcareandcautionasareasonablyprudentpersonwoulddoundersimilarconditions.""SeeHuetterv.Andrews,91Cal.App.2d142(http://law.justia.com/cases/california/calapp2d/91/142.html),Berlinv.Violett,129Cal.App.337(http://www.lexisnexis.com/clients/CACourts/),Reaughv.CudahyPackingCo.,189Cal.335(http://www.lexisnexis.com/clients/CACourts/),andOfficialReportsOpinionsOnline(http://courts.ca.gov/opinionsslip.htm)

LawReviews

"Liabilityofhighwayauthoritiesarisingoutofmotorvehicleaccidentallegedlycausedbyfailuretoerectorproperlymaintaintrafficcontroldeviceatintersection".AmericanLawReportsAnnotated,3rdSeries34.TheLawyersCooperativePublishingCompanyBancroftWhitneyWestGroupAnnotationCompany.p.1008.



"CommentNote:GovernmentalLiabilityforFailuretoReduceVegetationObscuringViewatRailroadCrossingoratStreetorHighwayIntersection,".AmericanLawReportsAnnotated,6thSeries50.TheLawyersCooperativePublishingCompanyBancroftWhitneyWestGroupAnnotationCompany.p.95.

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