Geometric Design of Roads - Wikipedia, The Free Encyclopedia
14
2/6/2015 Geometric design of roads Wikipedia, the free encyclopedia http://en.wikipedia.org/wiki/Geometric_design_of_roads#Profile 1/14 The Autovía del Olivar which unites Úbeda with Estepa in Andalucia in southern Spain. A geometric design saved on construction costs and improved visibility with the intention to reduce the likelihood of traffic incidents Geometric design of roads From Wikipedia, the free encyclopedia The geometric design of roads is the branch of highway engineering concerned with the positioning of the physical elements of the roadway according to standards and constraints. The basic objectives in geometric design are to optimize efficiency and safety while minimizing cost and environmental damage. Geometric design also affects an emerging fifth objective called "livability," which is defined as designing roads to foster broader community goals, including providing access to employment, schools, businesses and residences, accommodate a range of travel modes such as walking, bicycling, transit, and automobiles, and minimizing fuel use, emissions and environmental damage. [1] Geometric roadway design can be broken into three main parts: alignment, profile, and crosssection. Combined, they provide a threedimensional layout for a roadway. The alignment is the route of the road, defined as a series of horizontal tangents and curves. The profile is the vertical aspect of the road, including crest and sag curves, and the straight grade lines connecting them. The cross section shows the position and number of vehicle and bicycle lanes and sidewalks, along with their cross slope or banking. Cross sections also show drainage features, pavement structure and other items outside the category of geometric design. Contents 1 Design standards 2 Profile 2.1 Terminology 2.2 Sag Curves 2.3 Crest Curves 3 Alignment 3.1 Terminology 3.2 Geometry 3.3 Curve sight Distance 4 Cross section 4.1 Lane width 4.2 Cross slope 5 Safety effects of road geometry
description
W
Transcript of Geometric Design of Roads - Wikipedia, The Free Encyclopedia
-
2/6/2015 GeometricdesignofroadsWikipedia,thefreeencyclopedia
http://en.wikipedia.org/wiki/Geometric_design_of_roads#Profile 1/14
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
-
2/6/2015 GeometricdesignofroadsWikipedia,thefreeencyclopedia
http://en.wikipedia.org/wiki/Geometric_design_of_roads#Profile 2/14
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.
-
2/6/2015 GeometricdesignofroadsWikipedia,thefreeencyclopedia
http://en.wikipedia.org/wiki/Geometric_design_of_roads#Profile 3/14
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]
-
2/6/2015 GeometricdesignofroadsWikipedia,thefreeencyclopedia
http://en.wikipedia.org/wiki/Geometric_design_of_roads#Profile 4/14
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
-
2/6/2015 GeometricdesignofroadsWikipedia,thefreeencyclopedia
http://en.wikipedia.org/wiki/Geometric_design_of_roads#Profile 5/14
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]
-
2/6/2015 GeometricdesignofroadsWikipedia,thefreeencyclopedia
http://en.wikipedia.org/wiki/Geometric_design_of_roads#Profile 6/14
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]
-
2/6/2015 GeometricdesignofroadsWikipedia,thefreeencyclopedia
http://en.wikipedia.org/wiki/Geometric_design_of_roads#Profile 7/14
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.
-
2/6/2015 GeometricdesignofroadsWikipedia,thefreeencyclopedia
http://en.wikipedia.org/wiki/Geometric_design_of_roads#Profile 8/14
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]
-
2/6/2015 GeometricdesignofroadsWikipedia,thefreeencyclopedia
http://en.wikipedia.org/wiki/Geometric_design_of_roads#Profile 9/14
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.
-
2/6/2015 GeometricdesignofroadsWikipedia,thefreeencyclopedia
http://en.wikipedia.org/wiki/Geometric_design_of_roads#Profile 10/14
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
-
2/6/2015 GeometricdesignofroadsWikipedia,thefreeencyclopedia
http://en.wikipedia.org/wiki/Geometric_design_of_roads#Profile 11/14
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).
-
2/6/2015 GeometricdesignofroadsWikipedia,thefreeencyclopedia
http://en.wikipedia.org/wiki/Geometric_design_of_roads#Profile 12/14
1. ^"TheRoleofFHWAProgramsinLivability:StateofthePracticeSummary"(http://www.fhwa.dot.gov/livability/state_of_the_practice_summary/research00.cfm).FederalHighwayAdministration.Retrieved16April2012.
2. ^abcdefgGarber,N.J.,andHoel,L.,A.,TrafficandHighwayEngineering,3rdEdition.Brooks/ColePublishing,2001
3. ^"SANRALGeometricDesignGuideline"(http://geometricdesign.csir.co.za/).TheCouncilforScientificandIndustrialResearch(CSIR)inSouthAfrica.Retrieved20130728.
4. ^abcHomburger,W.S.,Hall,J.W.,reilly,W.R.andSullivan,E.C.,FundamentalsofTrafficEngineering(15thed),ITSCourseNotesUCBITSCN011,2001
5. ^abcAPolicyonGeometricDesignofHighwaysandStreets.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. ^abcD.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. ^AmericanAssociationofStateHighwayandTransportationOfficials(1994)APolicyonGeometricDesignofHighwaysandStreets(pp.117118)
15. ^AmericanAssociationofStateHighwayandTransportationOfficials(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
-
2/6/2015 GeometricdesignofroadsWikipedia,thefreeencyclopedia
http://en.wikipedia.org/wiki/Geometric_design_of_roads#Profile 13/14
(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.
-
2/6/2015 GeometricdesignofroadsWikipedia,thefreeencyclopedia
http://en.wikipedia.org/wiki/Geometric_design_of_roads#Profile 14/14
"CommentNote:GovernmentalLiabilityforFailuretoReduceVegetationObscuringViewatRailroadCrossingoratStreetorHighwayIntersection,".AmericanLawReportsAnnotated,6thSeries50.TheLawyersCooperativePublishingCompanyBancroftWhitneyWestGroupAnnotationCompany.p.95.
Retrievedfrom"http://en.wikipedia.org/w/index.php?title=Geometric_design_of_roads&oldid=643183819"
Categories: Transportationengineering
Thispagewaslastmodifiedon19January2015,at10:05.TextisavailableundertheCreativeCommonsAttributionShareAlikeLicenseadditionaltermsmayapply.Byusingthissite,youagreetotheTermsofUseandPrivacyPolicy.WikipediaisaregisteredtrademarkoftheWikimediaFoundation,Inc.,anonprofitorganization.
![By David Torgesen. [1] Wikipedia contributors. "Pneumatic artificial muscles." Wikipedia, The Free Encyclopedia. Wikipedia, The Free Encyclopedia, 3 Feb.](https://static.fdocuments.in/doc/165x107/5519c0e055034660578b4b80/by-david-torgesen-1-wikipedia-contributors-pneumatic-artificial-muscles-wikipedia-the-free-encyclopedia-wikipedia-the-free-encyclopedia-3-feb.jpg)
