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Cross‐section and Roadside Elements 1.3‐1
SECTION 1, CHAPTER 3
Cross‐section and Roadside Elements
3.1 Introduction
ThebasicdesigncontrolsdescribedinChapter1‐2influencethewidth,functionalareasofthecross‐section,andaccommodationfordifferentusers.Thecarefulselectionofroadwaycross‐sectionelements(sidewalks,bicycleaccommodation,motorvehiclelanes,etc.)isneededtoachieveacontext‐sensitivedesignthataccommodatesalluserssafely.Thischapterdescribesthevariouscomponentsofroadwaycross‐section,includingrangesofrecommendeddimensionsfordifferent'areaandroadwaytypes.Thischapteralsodescribesbasicelementsofroadsidedesign.
3.1.1 Multimodal Accommodation and Context Sensitivity
Thegoalsofselectinganappropriateroadwaycross‐sectionandthedesignofroadsideelementsare: Todevelopatransportationinfrastructurethatprovidesaccessforall,arealchoice
ofmodes,andsafetyinequalmeasureforeachmodeoftravel.
Toensurethattransportationfacilitiesfittheirphysicalsettingandpreservescenic,historic,aesthetic,community,andenvironmentalresourcestotheextentpossible.
Insomecases,thesedesignobjectivescanbeachievedwithintheavailableright‐of‐way.Inothercases,additionalright‐of‐wayneedstobeacquired.Sometimes,tradeoffsinuseraccommodationneedtobemadetopreserveenvironmentalorcommunityresourceslocatedwithinoradjacenttotheright‐of‐way.Inthesesituations,thechallengeistoprovideaccessandsafetyforeachmodeoftravel.Inothersituations,itwillbenecessarytomodifyenvironmentalcharacteristicsinordertoprovidesafeaccommodation.Toassistdesigners,thisPlanprovidesoptionsandrecommendationsforsafeaccommodationofpedestrians,bicycles,vehiculartraffic,andpublictransitoperations.Generalapproachestocross‐sectionformulationarediscussedinSection3.2.
1.3‐2 Cross‐section and Roadside Elements
Approachestocross‐sectionformulationarepresentedfromright‐of‐wayedgetoedge,ratherthanthemoretraditionalmethodfromcenterlineout.Throughthisapproach,accommodationofpedestriansandbicyclistsispositivelyencouraged,madesafer,andincludedineverytransportationproject.Detaileddescriptionofthefollowingcross‐sectionelementsassociatedwithdifferentroadwayusersaredescribedinSection3.3: Pedestriansincludingpeoplerequiringmobilityaids
Sidewalks Shoulderuse Sharedlanes Sharedusepaths
Bicycles
Bicyclelanes Shoulderuse Sharedlanes Sharedusepaths
MotorVehiclesincludingtransit
Usableshoulders On‐streetparking Travellanes
Oncetheelementsassociatedwithroadwayusergroupsaredescribed,guidanceforassemblingcross‐sectionsisprovided.ThisguidancedescribestheelementstypicallyencounteredfortheroadwayandareatypesdefinedinChapter1‐2.
3.1.2 Additional Topics Covered
Inadditiontocross‐sectionelementsspecificallyassociatedwiththemovementofpedestrians,bicycles,andmotorvehicles,thereareseveralothercross‐sectionelementsincludedinthischapterasdescribedbelow.
3.1.2.1 Public Transit Elements
Publictransitoftenoperatesasamotorvehiclewithinthepublicright‐of‐way.Thereareseveraldesignfeatures,bothwithintheroadwayandonthesidewalk,thatshouldbeconsideredincross‐sectiondesign.ThesearediscussedinSection3.4andinclude: Busstops,and Dedicatedlanes.
The challenge is to balance the competing interests of different users in a limited
amount of right‐of‐way and to provide access for
all, a real choice of modes, and safety in
equal measure for each mode of travel.
Section 1 – Chapter 3
Cross‐section and Roadside Elements 1.3‐3
3.1.2.2 Other Cross‐section Design Features
Section3.5describestheapplicationofthefollowingfeatures: Mediansandauxiliarylanes, Curbs,berms,andedging,and Cross‐slopes.Therelationshipoftheseaspectsofcross‐sectiondesigntomultimodalaccommodationarealsodescribed.
3.1.2.3 Utilities and Signage
Utilitiesarefrequentlylocatedwithintheroadwayright‐of‐way.ConsiderationsfortheplacementofutilitiesandroadsidesignageisdiscussedinSection3.6.
3.1.2.4 Right‐of‐Way
Section3.7describeshowcross‐sectionelementstranslateintoright‐of‐wayrequirements.Thenecessaryright‐of‐wayisthesummationofalldesiredcross‐sectionelements(sidewalks,bufferstrips,curbsandberms,shouldersandon‐streetparking,bicyclelanes,travellanes,andmedians)androadsideelements(clearzones,barriers,drainageditches,utilitypoles,signage,snowstorageareaandmaintenanceareas).
3.2 Multimodal Accommodation
Oncethepurposeandneedforaprojectisdefined,thedesignershoulddeterminethemostappropriatewaytoprovidesafe,convenient,andcomfortableaccommodationforalluserswithinthecontextoftheproject.ThisprocessisaidedbyinputfromthepublicandtheCityofNorwalkduringprojectplanning.Descriptivecasesforarangeofaccommodationsareprovidedtoassistthedesigner’sunderstandingofuseraccommodationapproachesthatmaybeapplicableinavarietyofcontexts.Thefirstthreecasesdescriberoadwaysectionsboundedbycurbandsidewalk.ThesecasesaremostlikelytobefoundinthemoredenselydevelopedareatypesintroducedinChapter1‐2(Urban,SuburbanVillageandTownCenter,SuburbanHighDensity,andRuralVillage).Theremainingtwocasesareforareaswithoutcurbandsidewalkandaremostlikelytobefoundinthelessdevelopedareatypes(RuralNatural,RuralDeveloped,andSuburbanLowDensity).Thesedescriptivecasesarenotintendedtobe“typicalsections”appliedtoroadwayswithoutregardfortravelspeeds,vehiclemix,adjacentlanduse,trafficvolumes,andotherfactorssinceapplicationof“typicalsections”canleadtoinadequateuseraccommodation(underdesign)orsuperfluouswidth(overdesign).Typicalsectionsalsoleavelittleroomfor
Multimodal Accommodation Performance Goal: The designer should provide safe, convenient, and comfortable travel for all roadway users.
1.3‐4 Cross‐section and Roadside Elements
judgmentreflectingthepurposeandcontextofindividualprojectsandcanoversimplifytherangeofvaluesthatmaybeselectedforeachelementofthecross‐section.Inthefollowingdescriptions,themultimodalaccommodationcasesareconceptualandreflectarangeofpotentialdimensionsforeachelement.Oncethedesignerdeterminesthemultimodalaccommodationdesiredfortheproject,thedesignershouldselectspecificdimensionsforeachcross‐sectionelementwithintherangesprovidedlaterinthischapter.Whenassembled,thespecificelementsinfluencethenecessaryright‐of‐waytoachievetheaccommodationdesiredfortheproject.Thisdesiredcross‐sectioncanthenbecomparedtoenvironmentalconstraintsandavailableright‐of‐way.Ifnecessary,additionalright‐of‐wayrequirementscanbeidentifiedand/orfurtherrefinementstothecross‐sectioncanbemade.
3.2.1 Case 1: Separate Accommodation for All Users
Case1providesthemaximumseparateaccommodationforallmodesoftravel,asillustratedinExhibit3‐1.Thisisoftenthepreferredoptionintermsofprovidingsafe,convenient,andcomfortabletravelforallusers.Itisusuallyfoundinareasofmoderatetohighdensity(urbanareas,suburbanvillagesandtowncenters,suburbanhighdensityareas,andruralvillages)withcurbedroadways.Case1providesforthemaximumseparationofusers,whichcanprovidethehighestlevelofsafetyandcomfortforallusersinareaswithhighlevelsofactivityorwherelargespeeddifferentialsbetweenthemotorizedandnon‐motorizedmodesarepresent.Case1usuallyrequiresthemostwidth.Inlocationswherethespeeddifferentialbetweendifferentroadwayusersissmall,oroverallactivityislow,Case1maynotbenecessarytosafelyaccommodateallusers.However,insomeinstances,thiscasemightbeachievedbyreallocatingspacewithinanexistingroadway,thuseliminatingpotentialimpactstotheroadsideenvironment.Thiscasemightbeconsideredinawidevarietyofconditionsincluding:areaswithmoderatetohighpedestrianandbicyclevolumes;areaswithmoderatetohighmotorvehiclespeedsandtrafficvolumes;andareaswithoutsubstantialenvironmentalorright‐of‐wayconstraints.InCase1,pedestriansareprovidedwithasidewalkseparatedfromtheroadwaybyaraisedcurbandpreferablyalandscapedbuffer.Theclearwidthofthesidewalkshouldbesufficienttoallowpedestriansorwheelchairuserstopasswithoutinterferingwitheachothers’movement(atleast5feetexcludingthecurbandclearfromitemsalongthesidewalksuchasfirehydrants,signs,treesandutilitypoles).Sidewalksshouldbeprovidedonbothsidesofthestreetunlessthereisaconditionthatsuggeststhatasidewalkisnotneededononesideofthestreet.Thismighthappen,forexample,ifthereisphysicalimpedimentthatwouldprecludedevelopmentononesideofthestreet,suchasarailroadtrackorstream.
Section 1 – Chapter 3
Cross‐section and Roadside Elements 1.3‐5
Exhibit 3‐1 Case 1: Separate Accommodation For All Users
Provisionofastripedbicyclelaneorshouldersuitableforbicycleuse(4feetminimum,5feetpreferred)encouragescycliststousetheroadway.Thebicyclelane/shoulderalsoprovidesforadditionalseparationbetweenmotorvehicletrafficandpedestrians.Ifon‐streetparkingispresent,thebicyclelaneshouldbeatleast5feetwidesothatthecyclistisprovidedwithanadditionalbufferalongtheparkedcars.Motorvehiclesareaccommodatedwithintravellaneswideenoughtoeliminateencroachmentbywidervehiclesoneithertheadjacentbicyclelaneorontheopposingmotorvehicletravellane.Inadditiontoprovidingspaceforbicycles,shouldersalsoaccommodateemergencystopping,maneuvering,andotherfunctions.Whereon‐streetparkingisprovided,shouldersorbicyclelanesshouldbemaintainedbetweenon‐streetparkingandthetravellane.
3.2.2 Case 2: Partial Sharing for Bicycles and Motor Vehicles
ThereareinstancesinwhichthewidthnecessarytoprovideaccommodationforCase1isnotavailable.Therearealsoinstanceswheresomesharingandoverlapbetweenbicyclistsandmotorvehicletrafficisacceptabletoachieveotherenvironmentalordesignobjectives.Case2describesanapproachtomultimodalaccommodationinthesesituationsandisillustratedinExhibit3‐2.Case2iscommoninareasofmoderatetohighdensity(urbanareas,suburbanvillagesandtowncenters,suburbanhighdensityareas,andruralvillages),wherecurbedroadwaysectionsandseparatesidewalksareprovided.Pedestriansareprovidedwithasidewalkseparatedfromtheroadwaybyaraisedcurbandpreferablyalandscapedbuffer,increasingthesafetyandcomfortofthepedestrian.Theclearwidthofthesidewalkshouldbesufficienttoallowpedestriansorwheelchairuserstopasswithoutinterferingwitheachother’smovement(atleast5feetexcludingthecurbandclearofotherroadsideobstructions).
1.3‐6 Cross‐section and Roadside Elements
Exhibit 3‐2 Case 2: Partial Sharing for Bicycles and Motor Vehicles
InCase2,thereissomeoverlapbetweenthespaceprovidedforbicycleuseandthatprovidedformotorvehicletravel.SignsorpavementmarkingsindicatingthattheroadwayissharedbetweencyclistsandmotorvehiclesareappropriateforCase2roadways.Thistypeofaccommodationisoftenusedinareaswithlowmotorvehiclespeeds,lowtomoderatemotorvehicletrafficvolumes,andareasofenvironmentalorright‐of‐wayconstraintwhereasmallercross‐sectionisnecessary.Thedesignershouldcarefullyconsidertheallocationofwidthtotravellanesandbicyclelanes/shoulderstoprovidethebestbalanceofaccommodationbetweenbicyclesandmotorvehicles.Inmanyinstances,on‐streetparkingwillalsobeprovidedandadditionalwidthmaybeneededtoreduceconflictsbetweenbicyclesandtheadjacentparking.TherearedifferentpossibleconfigurationsoflanesandshoulderspossibleinCase2,butallfeaturesomeoverlapinthespaceneededbybicyclistsandmotorvehicles: Typicaltravellanescombinedwithnarrowshoulders(i.e.11‐to12‐footlaneswith
2‐to3‐footshoulders)providemaneuveringwidthfortruckandbustrafficwithinthetravellane;however,bicyclistsmaybeforcedtoridealongandoverthepavementmarkings.
Narrowtravellanescombinedwithwideshoulders(i.e.9to11‐footlaneswith4to8footshoulders)providegreaterseparationbetweenmotorvehicleandbicycletraffic,butmayresultinmotorvehicletrafficoperatingclosertothecenterlineoroccasionallyencroachingintotheopposingtravellane.
WidecurblaneshavealsobeenusedinCase2;however,studieshaveshownthatmotoristsandbicyclesarelesslikelytoconflictwitheachotherandmotoristsarelesslikelytoswerveintooncomingtrafficastheypassabicyclistwhenshoulderstripingisprovided.
Section 1 – Chapter 3
Cross‐section and Roadside Elements 1.3‐7
3.2.3 Case 3: Shared Bicycle/Motor Vehicle Accommodation
InCase3,theaccommodationofbicyclesandmotorvehiclesissharedandseparatepedestrianaccommodationismaintainedasillustratedinExhibit3‐3.Case3ismostlikelytobefoundinthemostdenselydevelopedareas(urbanareas,suburbanvillagesandtowncentersandsomeruralvillages)whereright‐of‐wayismostconstrained.Itisalsoapplicabletomostresidentialstreetswherespeedsandtrafficvolumesarelow.
Exhibit 3‐3 Case 3: Shared Bicycle/Motor Vehicle Accommodation
Pedestriansareprovidedwithasidewalkseparatedfromtheroadwaybyaraisedcurbandpreferablyalandscapedbuffer,increasingthesafetyandcomfortofwalkingalongthisroadway.Theclearwidthofthesidewalkshouldbesufficienttoallowpedestriansorwheelchairuserstopasswithoutinterferingwitheachother’smovement(atleast5feetexcludingthecurbandsidewalkclearofotherroadsideobstructions).InCase3,onelaneisprovidedforjointusebymotorvehiclesandbicycles.Thistypeofaccommodationisusedinthefollowingconditions:areaswithlowtomoderatemotorvehicletrafficvolumes;lowmotorvehiclespeeds;andareasofsevererightofwayconstraintwhereonlyaminimumpavementsectionisfeasible.SignsandpavementmarkingsindicatingthattheroadwayissharedbetweencyclistsandmotorvehiclesshouldbeprovidedforCase3roadways.On‐streetparkingisoftenfoundontheseroadwaysandseparateshouldersorbicyclelanesarenotavailable.
3.2.4 Case 4: Shared Bicycle/Pedestrian Accommodation
Insparselydevelopedareas(suchasruralnatural,ruraldeveloped,andsuburbanlowdensityareas),curbedroadwaysectionsboundedbysidewalkarelesscommon.ThiscaseisillustratedinExhibit3‐4.
1.3‐8 Cross‐section and Roadside Elements
Exhibit 3‐4 Case 4: Shared Bicycle/Pedestrian Accommodation
Intheseareas,pedestriansandcyclistsareoftenaccommodatedontheroadwayshoulder.Thistypeofaccommodationmaybeappropriateforareaswithinfrequentpedestrianactivity.Inareaswithhigherpedestrianvolumes(eithercurrentoranticipated),thepedestrianaccommodationdescribedinCases1,2,and3isdesirable.Pavementstripingandapavedshoulder(atleast4‐feetwide)forsharedpedestrianandbicycleusehelpsdelineatethetravelwayformotorvehicles,thusincreasingsafetyforallusers.Widershouldersshouldbeprovidedasmotorvehiclespeedsandtrafficvolumesincrease.InCase4,motorvehiclesareaccommodatedwithintravellaneswideenoughtoeliminateencroachmentontheshoulderortheopposingmotorvehiclelane.ForCase4,thedesignershouldcarefullyconsidertheallocationofright‐of‐waybetweentravellanesandshoulders.Forexample:
Typicaltravellanescombinedwithwideshoulders(i.e.11or12‐footlaneswith6‐footorwidershoulders)provideforincreasedseparationbetweenpedestrians,bicyclistsmotorvehicles.Widershouldersalsoprovideclearanceforemergencystoppingandmaneuvering.
Typicaltravellanescombinedwithnarrowshoulders(i.e.11or12‐footlaneswith4‐footshoulders)providemaneuveringwidthfortruckandbustrafficwithinthetravellane,reducingencroachmentintoopposinglanesandtheshoulder.However,conflictsbetweenbicyclesandpedestriansaremorelikely.
Narrowtravellanescombinedwithwideshoulders(i.e.,10to11‐footlaneswith6to8footshoulders)providegreaterseparationbetweenbicyclistsandpedestrians,butmayresultinmotorvehicletrafficoperatingclosertothecenterlineorencroachingontheshoulder.
Section 1 – Chapter 3
Cross‐section and Roadside Elements 1.3‐9
3.2.5 Case 5: Shared Accommodation for All Users
Vehicles,bicycles,andpedestriansaresometimesaccommodatedinonesharedtravellane,asillustratedinExhibit3‐5.Thisconditionoccurswhenthereislowuserdemandandspeedsareverylow,orwhensevereconstraintslimitthefeasibilityofprovidingshoulders.Thiscaseprovidesthesmallestpavementwidthwhileaccommodatingalluserseffectivelyonlyinlowvolume,lowspeedconditions.Fences,rockwalls,treelines,andotherroadsideconstraints,canfurtherrestrictemergencymovementbyallusers.Additionalunpavedshouldersorclearzonesshouldbecarefullyconsideredtoprovideadditionalflexibilityandsafety.Additionallyoff‐roadpathsshouldbeconsideredtoimprovetheaccommodationofpedestrians.Thesepathsdonotneedtofollowtheroadalignmentpreciselyandcansometimesavoidobstaclesthatprecludesidewalksandshoulders.
Exhibit 3‐5 Case 5: Shared Accommodation for All Users
3.2.6 Summary of Accommodation Option
Exhibit3‐6providesasummaryofthemultimodalaccommodationoptionsavailabletothedesigner.
1.3‐10 Cross‐section and Roadside Elements
Exhibit 3‐6 Summary of Multi‐modal Accommodation Options
Case 1: Separate Accommodation for All Users Often the preferred option to provide safe, convenient, and
comfortable travel for all users. Appropriate for areas with moderate to high levels of
pedestrian and bicycle activity. Appropriate for roadways with moderate to high motor vehicle
speeds. Appropriate in areas without substantial environmental or
right-of-way constraints.
Case 2: Partial Sharing for Bicycles and Motor Vehicles
Used in areas where the width necessary to provide Case 1 accommodation is not available.
Under Case 2, pedestrians are provided with a sidewalk or separate path while space for bicyclists and drivers overlap somewhat.
Appropriate in areas with low motor vehicle speeds and low to moderate motor vehicle volumes.
Case 3: Shared Bicycle/Motor Vehicle Accommodation
Under Case 3, pedestrians remain separate but bicycle and motor vehicle space is shared.
Used in densely developed areas where right-of-way is constrained.
Also applicable to most residential/local streets where speeds and traffic volumes are low.
Case 4: Shared Bicycle/Pedestrian Accommodation
Under Case 4, pedestrians and bicyclists share the shoulder.
Common in rural or sparsely developed areas.
Appropriate for areas with infrequent pedestrian and bicycle use.
Case 5: Shared Accommodation for All Users
Under Case 5, all users share the roadway. Appropriate where user demands and motor vehicle speeds
are very low or when severe constraints limit the feasibility of providing separate accommodation.
Section 1 – Chapter 3
Cross‐section and Roadside Elements 1.3‐11
3.3 Design Elements
Oncetheapproachtomultimodalaccommodationisdetermined,thedesignershoulddeterminethedimensionsofeachelementtobeincludedinthecross‐section.Theseelementsareassembledtodevelopadesiredcross‐section.Thefollowingsectionsdescribethedimensionsofspecificcross‐sectionelementsthatservedifferentroadwayusers.
3.3.1 Pedestrians
Pedestrianaccommodationshouldbeconsistentwiththeprojectcontext,includingcurrentoranticipateddevelopmentdensity,roadwaycharacteristics,right‐of‐waydimensionsandavailability,andcommunityplans.Optionsforpedestrianaccommodationincludesidewalks,shoulderuse,andsharedlanes,asdescribedbelow,andoff‐roadorsharedusepaths.Inadditiontothetypeofaccommodation,thedesignershouldincludeotherdesignfeaturesthatimprovethepedestrianenvironment.Forexample,thedesignercanconsiderselectingalowermotorvehicledesignspeedthatwillincreasethecomfortandsafetyofthefacilityforpedestrians.Similarly,thedesignershouldconsidergeometricfeaturesthatimprovethepedestrianenvironment,suchascrossingislands,curbextensions,andothertrafficcalmingfeaturesdiscussedinmoredetailinChapter1‐6.Thewalkingpathshouldhaveasmooth,stableandslipresistantsurfacethatdoesnotinducevibrationinwheelchairsandisfreeoftrippinghazards.TheserequirementsarefurtherdiscussedinChapter1‐4.
3.3.1.1 Sidewalks and Buffers
Sidewalksarepavedareasprovidedalongtheedgesofroadwayssuitableforpedestrianuse.Sidewalksarethemostcommonaccommodationprovidedforpedestrians.Sidewalksaredesirableinallareaswherepedestrianactivityispresent,expected,ordesired.Sidewalksshouldbeprovidedinresidentialareas,nearschools,libraries,parks,andcommercialareas.Sidewalksshouldalsobeprovidedbetweentransitstopsandnearbydestinations.Sidewalksshouldbeprovidedtolinkresidentialareaswithnearbyemployment,shopping,andservicecenters.Inurbanareasorvillage/towncenters,raisedcurbandcurbcutrampsareusuallyprovidedwithsidewalks.Alandscapedbufferbetweenvehiculartrafficandthesidewalkcanprovidegreaterseparationfrommotorvehicles,increasingthecomfortandsafetyofpedestrians.Inruralorsuburbansettingsforminorarterialsorcollectorroadswith5feetormoreofbuffer
All roadways along which pedestrians are not prohibited should include an area where occasional pedestrians can safely walk, whether on unpaved walkways, on shoulders in rural or less developed areas, or on
sidewalks in more urban areas.
1.3‐12 Cross‐section and Roadside Elements
space,curbingmaynotbeneeded.On‐streetparking,shoulders,andbicyclelanescanalsoactassidewalkbuffers.
Dimensions and Clear Width
ThespatialrequirementsofpedestriansaredescribedinChapter1‐2.Theminimumwidthforasidewalkis5feetexcludingthewidthofthecurb,althougha4footclearwidth(plusthewidthofthecurb)issufficienttobypassoccasionalobstructions,asillustratedinExhibit3‐7.Whendevelopingplans,thesidewalkissometimesmeasuredincludingthewidthofthecurb.Ifthismethodofmeasurementisused,theminimumwidthofsidewalkis5½feet.
Exhibit 3‐7 Clear Accessible Path
Source: Adapted from the Guide for the Planning, Design, and Operation of Pedestrian Facilities, AASHTO, 2004. Chapter 3
Pedestrian Facility Design
Section 1 – Chapter 3
Cross‐section and Roadside Elements 1.3‐13
Widersidewalksaredesirablewheretherearehighpedestrianvolumesandwherethereisnobufferbetweenhighspeedorhighvolumeroadways.Sidewalkwidthsof6to12feetarepreferredformosttowncenterandurbanlocations.Verywidesidewalks(12to20+feet)arealsoencounteredinthesesettings.Commonwidthsoflandscapebufferarebetween2and6feet,althoughlargerbuffersarepossible.Ifthesidewalkisnotbufferedfrommotorvehicletraffic,thenthedesirabletotalwidthforacurb‐attachedsidewalkis6feetinresidentialareasand8feetincommercialareas.Sidewalkscommonlyaccommodatestreetfurniturewhichincludesitemssuchas,trees,utilities,trafficsignals,trafficsigns,streetlights,parkingmeters,bicycleparking,benches,andrefusebarrels.Additionally,sidewalksoftenabutfences,buildingedges,orvegetationalongtheiroutsideedge.Theseelementsinfluencetherequiredwidthnecessarytoaccommodatepedestrians,aspedestrianstendto“shy”fromtheseobstructions.Thedesignershouldconsiderthedesiredlocationforthesesidewalkfeaturesand,wheretheyexist,thedesignershouldprovideappropriateoffsets(orshydistances)tothepedestrianpath.TypicalshydistancesareillustratedinExhibit3‐8.
Exhibit 3‐8 Typical Shy Distances Between Sidewalk Elements and Effective Pedestrian Path
Source: Adapted from the Guide for the Planning, Design, and Operation of Pedestrian Facilities, AASHTO, 2004. Chapter 3 Pedestrian Facility Design
Landscape buffers accommodate a variety of functions, including: safety separation, snow storage,
street furniture, landscaping, utilities and traffic control devices. As such, it is
preferable that such buffers be at least 5 feet wide..
1.3‐14 Cross‐section and Roadside Elements
Allnewandreconstructedsidewalksmustbeaccessibletoandusablebypersonswithdisabilities.Aminimumclearpath(WE)of3feetmustbecontinuouslyprovidedalongasidewalk.SidewalkdimensionsandclearwidthsmustconformtotheaccessibilityrequirementsestablishedunderConnecticutGeneralLaws.Toallowfreepassingofpedestrians,includingthosewithdisabilities,awalkwaythatisatleastfive‐feetwide(excludingthecurbwidth)andclearofobstructionsisrequiredatevery200‐feetintervals.Sidewalksarealsocrossedbydrivewaysandintersectedbystreets.ThesecrossingsaredescribedinmoredetailinChapter1‐4.Asageneralapproach,thesidewalkshouldbecontinuousacrossdrivewaysandincludeappropriatetransitionsforthegradechangesassociatedwiththeseinterfaces.Formostdriveways,itisdesirableforthesidewalkelevationtocontrolthedrivewaydesign,ratherthanforthedrivewaytocutthroughthesidewalk.However,highvolumedrivewaysordrivewaysexitinghighspeedroadsmaybemoreappropriatelydesignedasintersections,withlevelconnectionsbetweentheroadwayandthedriveway.Inthesecases,pedestrianrampsandcrosswalksshouldbeincludedtoprovideacontinuouspathoftravel.AllfacilitiesshouldcomplywithADArequirementsincludingthesidewalks,pedestrianrampsandcrosswalks.
Placement
Indevelopedareas,continuoussidewalksshouldbeprovidedonbothsidesofaroadway,minimizingthenumberofpedestriancrossingsrequired.Ifasidewalkisprovidedononlyonesideofaroadway,thecontextoftheroadwayshouldbethebasisforthisdecision.Forexample,inundevelopedorlow‐densityareas,orwheredevelopmentisheavilyconcentratedononesideoftheroadway,orthereareasignificantnumberofpublicshadetrees,sidewalksononlyonesideoftheroadmaybesufficient.Inthesecases,thesidewalkshouldbeprovidedonthesidethatminimizesthenumberofpedestriancrossings.Crosswalksshouldbeprovidedatreasonableintervals(typicallyevery200to300feetwithmaximumseparationindevelopedareasofapproximately500feet).
3.3.1.2 Shoulder Use
Inareaswherepedestrianvolumesarelow,orwherebothtrafficvolumesandspeedarelow,apavedusableshoulder,asdescribedinSection3.3.3.1,canprovidepedestrianaccommodation.Thisoccursprimarilyinruralnaturalareas,ruraldeveloped,andsomesuburbanlowdensityareas.Onmostroadwaysthroughsparselydevelopedareas,aminimum4‐footshoulderisusuallyadequateforpedestrianuse.Awidershoulderisdesirablewhenthereissignificanttrucktrafficorhightrafficspeeds.Thewidthofshouldersisusuallydeterminedthroughanassessmentofpedestrian,bicycle,andmotorvehicleneeds.Thedecisiontouseshouldersratherthansidewalksorparallelpathsshouldconsiderexistingandfuturepedestrianvolumes.Evenwithlowpedestrianvolumes,itisdesirabletoprovidesidewalksorpathstoserveschools,libraries,shopsandtransitstops.
Section 1 – Chapter 3
Cross‐section and Roadside Elements 1.3‐15
3.3.1.3 Shared Lanes
Walkingwithintravellanesmaybeappropriateforsomeroadwayswithverylowtrafficvolumesandvehiclespeeds.However,sidewalksorusableshouldersarethepreferredaccommodation.Beforedecidingtoprovidesharedlanesastheonlypedestrianaccommodation,thedesignershouldbecertainthatthetrafficvolumesandvehiclespeedswillbelowenough,nowandinthefuture,sothatallpedestrianscancomfortablyusethestreet.
3.3.1.4 Off Road and Shared Use Paths
Asharedusepathisadedicatedfacilityforpedestrians,bicyclists,rollerbladers,etc.Althoughsidewalksaregenerallypreferred,off‐roadpathsaresometimessuitableinruralandsuburbanlow‐densityareas.Thepathshouldprovidethesameconnectivityastheroadwaybutcanbesetbackfromtheroadwayanditsroutecandeviatearoundsensitiveenvironmentalareas.ThisisdiscussedindetailinChapter1‐4.TheU.S.AccessBoardguidelinespresentedinitsproposedGuidelinesforOutdoorDevelopedAreasprovideadditionalinformationonthedesignofpathsasdoesAASHTO’s2012GuidefortheDevelopmentofBicycleFacilities.
3.3.2 Bicycles
Bicycleaccommodationshouldalsobeconsistentwiththeproject’scontext,roadwaycharacteristics,right‐of‐way,communityplans,andthelevelofserviceprovidedforthebicyclist.Thedesignershouldensurethatbicycleaccommodationisbasedonanticipateddevelopment,communityplans,andtheexpectedlevelofskilloftheintendedbicyclist.Bicyclesmaybepresentonallhighwayswheretheyarepermitted(bicyclesaretypicallyexcludedfromfreeways).Inadditiontodeterminingthetypeofaccommodationforbicyclists,thedesignershouldincludeotherdesignfeaturesthatimprovethesafetyandcomfortoftheroadwayforbicyclists.Forexample,ifmotorvehiclespeedsaretoohigh,thedesignershouldconsiderselectingalowermotorvehicledesignspeedtoincreasethecomfortandsafetyofthefacilityforbicycles.Additionally,thedesignercouldconsidernarrowingmotorvehiclelanestoprovidewidershoulders.Inconstrainedcorridors,evenafewfeetofstripedshouldercanmaketravelingalongaroadwaymoreaccommodatingforbicycles.Specificdesignfeaturesthatcanmakeroadwaysmorecompatibletobicycletravelincludeuniformwidths(wherepossible),bicycle‐safedrainagegrates,smoothpavements,adequatesightdistances,andtrafficsignalsthatdetectandrespondtobicycles.Thesedesignfeaturesshouldbeincludedonallroadways.Widecracks,joints,ordrop‐offsattheedgeofthetraveledwayparalleltothedirectionoftravelcantrapabicyclewheelandcauselossofcontrol,ascanholesandbumpsinthepavementsurface.Theseconditionsshouldbeavoidedonallroadways.
1.3‐16 Cross‐section and Roadside Elements
Drainageinletgratesandutilitycoversarepotentialobstructionstobicyclists.Therefore,bicycle‐safegratesmustbeused,andgratesandcoversshouldbelocatedtominimizesevereand/orfrequentavoidancemaneuveringbycyclists.Inletgratesorutilitycoversinthepathofbicycletravel,mustbeinstalledflushwiththepavementsurface.Gratesshouldbehydraulically‐efficientversionsthatdonotposeahazardtocyclists.ThespatialrequirementsofbicyclesaredescribedinChapter1‐2.Fordesignpurposesawidthof4or5feetiscommonlyusedtoaccommodatebicycletravel.Thisportionoftheroadwayshouldhaveadequatedrainagetopreventponding,washouts,debrisaccumulationandotherpotentiallyhazardoussituationsforbicyclists.Approachestobicycleaccommodationincludebicyclelanes,theuseofshoulders,andsharedroadways.Off‐roadshared‐useorbicyclepathsarealsoanoptionforbicycleaccommodationinsomelimitedcases.Also,insomecases,novicebicyclistsandchildrenalsousesidewalksforcycling.TheFHWA’sBicycleCompatibilityIndexandAASHTO’s2012GuidefortheDevelopmentofBicycleFacilitiesservesasusefultoolsforreviewingthesuitabilityofvariousapproachestobicycleaccommodation.Thetypesofaccommodationtypicallyusedaredescribedinthefollowingsections.
3.3.2.1 Bicycle Lanes
Bicyclelanesareportionsofthetraveledwaydesignedforbicycleuse.Bicyclelanesshouldbeincorporatedintoaroadwaywhenitisdesirabletodelineateavailableroadspaceforpreferentialusebybicyclistsandmotorists,andtoprovideformorepredictablemovementsbyeach.Bicyclelanemarkingscanincreaseabicyclist’sconfidenceinmotoristsnotstrayingintotheirpathoftravel.Likewise,passingmotoristsarelesslikelytoswervetotheleftoutoftheirlanetoavoidbicyclistsontheirright.Bicyclelanesaregenerallyconsideredthepreferredtreatmentforbicycleaccommodation.Insomecases,theyareneithernecessarynordesirableduetolow‐trafficconditions.Bicyclelanesaremostcommonlyimplementedinurbanandsuburbansettings.Frequently,bicyclelanesarefoundincombinationwithon‐streetparking,raisedcurbs,andsidewalks.Intheseareas,thebicyclelanealsoservestheroadwayshoulderfunctionsassociatedwithmotorvehicles,describedinmoredetaillaterinthischapter.Contraflowbicyclelanesmaybeappropriateonone‐waystreetstoincreasecyclistsconnectivity.ThetreatmentofbicyclelanesatintersectionsandtheirrelationshiptoturninglanesisprovidedinChapter1‐4.BicyclelanesproposedonallroadwaysunderStatejurisdictionwillrequireapprovalfromtheOfficeofStateTrafficAdministration(OSTA).
Section 1 – Chapter 3
Cross‐section and Roadside Elements 1.3‐17
Dimensions and Clear Width
Theminimumwidthforbicyclelanesis4feetwhenthebicyclelaneisadjacenttotheedgeofpavement;however,5‐footbicyclelanesarepreferredformostconditions,especiallywhenthelaneisadjacenttocurbsideparking,verticalcurb,orguardrail.Onroadwayswithhigherspeeds(50milesperhourormore)orhighervolumesoftrucksandbuses(30ormoreperhour)theminimumbicyclelanewidthis5feetand6‐footbicyclelanesaredesirable.Bicyclelaneswiderthan6feetaregenerallynotusedsincetheymayencourageinappropriateusebymotorvehicles.
Placement
Bicyclelanesareone‐wayfacilitiesthatcarrybiketrafficinthesamedirectionastheadjacentmotorvehicletraffic.Bicycle‐specificwrong‐waysignagemaybeusedtodiscouragewrong‐waytravel.Onone‐waystreets,bicyclelanesshouldbeprovidedalongtherightsideoftheroadunlessunusualconditionssuggestotherwise.Bicyclelanesshouldbedesignatedbya6‐inchsolidwhitelineontherightedgeofthemotorvehicletravellane.Bicyclelaneswithinroadwaysshouldnotbeplacedbetweenaparkinglaneandthecurb.Thissituationcreatespoorvisibilityatintersectionsanddrivewaysanditisdifficulttopreventdriversfromparkinginthebicyclelane.Bicyclelanesshallbedesignatedbyasolidwhitelineontherightedgeofthemotorvehicletravellane(4‐inchminimum,6‐inchpreferred)andbicyclesymbolorwordmarkings.Thismarkingshouldchangetoabrokenwhitelinebeforeanyintersectionsontherightside,providingsufficientdistanceformotoriststomergetotherightsideoftheroadwaybeforemakingaright‐turn.A4‐inchsolidwhitelineorparkingspacemarkingsontherightedgeofthebicyclelanearerecommendedforaddeddelineationofthebicyclelanewhenadjacenttoparkingareas.Thesemarkingswillencourageparkingclosertothecurb,providinggreaterseparationbetweenbicycles,parkedcars,andmovingmotorvehicles.Thesemarkingscanalsodiscourageuseoftheparkinglaneandbicyclelaneformotorvehicletravelwhenparkingactivityislight.Additionalbicyclelanepavementmarkings,asillustratedinExhibit3‐9,andsignagecanalsobeinstalledtoreinforcetheintendeduseofthebicyclelane.
3.3.2.2 Shoulder Use
Muchlikebicyclelanes,pavedshouldersprovidespaceforbicyclingoutsideofthetravellanes.Onedifferencebetweenshouldersandbicyclelanesisthatshouldersareusuallyusedforbicycleaccommodationinruralandsuburbanlowdensityareas,whereon‐streetparking,curbs,andsidewalksarerarelyencountered.Intheselocations,shouldersmayprovidesharedaccommodationforpedestriansandbicyclists.Anotherdifferencebetweenshouldersandbicyclelanesisthatthewidthofshouldersisusuallydeterminedthroughanassessmentofcombinedpedestrian,bicycle,andmotorvehicleneeds,discussedlaterinthischapter,inthecontextofprojectgoalsandavailablespace.Additionally,shouldersdonottypicallyincludebicyclelanepavementmarkings.
1.3‐18 Cross‐section and Roadside Elements
Exhibit 3‐9 Bicycle Lane Pavement Markings
Source: Manual on Uniform Traffic Control Devices, FHWA, 2009. Chapter 9 Traffic Control for Bicycle Facilities
Toprovidebicycleaccommodation,shouldersshouldbeatleast4feetwide.Themeasurementoftheusableshouldershouldnotincludetheshydistancefromacurborguardrailwherea5‐footminimumwidthisrecommended.Minimum5‐footshouldersarealsorecommendedinareaswithvehicularspeedsover50milesperhour,orwheretruckandbusvolumesexceed30vehiclesperhour,orinareaswithonstreetparking.Rumblestrips,raisedpavementmarkers,orembeddedreflectorsshouldnotbeusedwhereshouldersaretobeusedbybicyclists,unlessthereisaminimumclearpathof1‐footfromtherumblestriptothetraveledwayand4feetfromtherumblestriptotheoutsideedgeofpavedshoulder.Inplacesadjacenttocurb,edging,guardrailorotherverticalobstacles,5feetbetweentherumblestripandtheoutsideedgeofpavementisdesirable.Withrumblestrips,thetotalwidthoftheshouldershouldbebetween7and8feet.
Section 1 – Chapter 3
Cross‐section and Roadside Elements 1.3‐19
3.3.2.3 Shared Lanes
Sharedlanesrefertouseofthenormaltravellanesbybothmotorvehiclesandbicyclists.Bylaw,bicyclistsmayusethetravellane.MostroadwaysinNorwalkhaveneithershouldersnorbicyclelanes.Thuslanessharedbymotoristsandbicyclistsarethemostcommonsituation.Lanesatleast14feetwidearegenerallywideenoughtopermitmotoriststopassbicyclistswithoutchanginglanes.Onlow‐volumeroadways,motoristswillgenerallybeabletopassbicyclistswithoutwaiting.Iftrafficvolumesareaboveacriticalthreshold,itisdesirabletoprovideenoughwidthforlanesharing.Incasesoflowspeed,lowtomoderatetrafficvolumes,andlowoccurrenceoftrucksandbuses,thesharedlanesmaybeadequatetosupportbicycling.Beforedecidingtoprovidesharedlanesasbicycleaccommodation,thedesignershouldbecertainthatthetrafficvolumesandmotorvehiclespeedswillbelowenoughsothatalltypesofbicyclistscancomfortablyusetheroadway.Inlocationswheresharedlanesareused,thedesignershouldconsiderusingsharedlanepavementmarkingssuchasthoseillustratedinExhibit3‐10.“BicyclesMayUseFullLane”signsasdefinedintheManualonUniformTrafficControlDevices(MUTCD)mayalsobeincludedinthedesign.Itisimportanttobearinmindthatsignsareonlyasupplementtoadequatebicycleaccommodationandshouldneverbeconsideredasubstituteforthem.
1.3‐20 Cross‐section and Roadside Elements
Exhibit 3‐10 Shared Lane Pavement Markings
Source: Manual on Uniform Traffic Control Devices, FHWA, 2009. Chapter 9 Traffic Control for Bicycle Facilities
3.3.2.4 Shared Use Paths
Sharedusepathsarefacilitiesonexclusiveright‐of‐waywithminimalcrossflowbymotorvehicles.Sharedusepathsshouldbethoughtofasacomplementarysystemofoff‐roadtransportationroutesforbicyclistsandothersthatservesasanecessaryextensiontotheroadwaynetwork.Thepresenceofasharedusepathneararoadwaydoesnoteliminatetheneedtoaccommodatebicyclistswithinaroadway.Provisionofshared‐usepathsisparticularlysuitedtohigh‐speed,high‐volumeroadwayswherethecharacteristicsoftrafficflow,roadwaygeometricsandtrafficcontrolareincompatiblewithbicycleuse,exceptforadvancedcyclists.Similarly,shared‐usepathscanprovideabicyclingrouteparalleltofreeways,wherebicyclingisprohibited.Shared‐usepathsarealsoanoptioninareasoflimitedrightofwayorwhereenvironmentalorculturalresourceslimitthewidthofaroadwayandanearbypathwayisavailable.Finally,sharedusepathscanproviderecreationalamenitiesinwaterfrontareasornearotherattractions.
3.3.3 Motor Vehicles
Themajorcomponentsoftheroadwaycross‐sectionservingmotorvehicletravelareusableshouldersoron‐streetparking,andtravellanes.Inadditiontothewidthoftheseindividualelements,therightlaneplusshoulderdimensionisimportantfordeterminingtheminimumwidthforatwo‐lanetwo‐wayroadway,asdescribedlaterinthischapter.
Section 1 – Chapter 3
Cross‐section and Roadside Elements 1.3‐21
ThewidthrecommendationspresentedinthissectionarebasedonestablishedpracticesandsupplementedbyguidelinesfromAASHTOincludingtheGuideforAchievingFlexibilityinHighwayDesign.Flexibilityispermittedtoencourageindependentdesignstailoredtoparticularsituations.Forexample,designerscanseekexemptionsfromestablisheddesigncriteriaunderspecificconditionstoprovideforthepreservationofrural,suburban,andvillageroads.Thewidthassociatedwiththecross‐sectionelementsdescribedinthissectionisbasedonthespatialdimensionsofdesignvehiclesdiscussedinChapter1‐2.Thelargestvehiclelikelytousethefacilityonaregularbasisisusuallyselectedasthedesignvehicleandimpactstheselectionofshoulderandlanewidth.Usableshoulders,on‐streetparking,travellanes,andtheright‐laneplusshoulderdimensionaredescribedinthefollowingsections.
3.3.3.1 Shoulders
Theuseofshouldersforpedestrianandbicycleaccommodationisdiscussedintheprevioussections.ShouldersarepavedandgradedareasalongthetravellanestoserveanumberofpurposesasshowninExhibit3‐11.Theyshouldbedelineatedbya4‐inchwidesolidwhitestripetoseparatethetravellaneandtheedgeofpavement.Shouldersdonotincludeon‐streetparkingsincetheshoulderscannotservethepurposeslistedinExhibit3‐11iftheyareoccupiedbyparkedcars.On‐streetparkinganditsrelationshiptopedestrianandbicycleaccommodationarediscussedlaterinthischapter.Duringtheplanningprocess,thedesignershouldselectanappropriateshoulderwidthgiventheroadway’scontext,purposeandneed,bicycleandpedestrianaccommodation,speed,andtransportationdemandcharacteristics.
Exhibit 3‐11 Minimum Shoulder Width (in feet) to Provide Various Functions
Roadway Type Shoulder Function Arterials Collectors
Drainage of Traveled Way 1.0 1.0 Lateral Support of Pavement 1.5 1.0 Encroachment of Wide Vehicles 2.0 2.0 Off-tracking of Wide Vehicles 2.0 2.0 Errant Vehicles 3.0 2.0 Bicycle and Pedestrian Use 4.0 4.0 Emergency Stopping 6.0 6.0 Emergency Travel 6.0 6.0 Mail Delivery and Garbage Pickup 6.0 6.0 Law Enforcement Operations 8.0 6.0 Large Vehicle Emergency Stopping 10.0 10.0 Occasional Travel/Detours 10.0 9.0 Highway Maintenance 8.0 8.0 Source: Flexibility in Highway Design, AASHTO 2004. Chapter 6 Cross Section Elements
1.3‐22 Cross‐section and Roadside Elements
Exhibit3‐12providesrangesofshoulderwidthfordifferentareaandroadwaytypes.Asshownabove,shouldersprovidemanyimportantsafetyandoperationaladvantagesandthedesignershouldstrivetoprovide6‐to8‐footshouldersformostarterials.Asdescribedintheprevioussections,ifshouldersareprovidedforpedestrianorbicycleaccommodationtheirminimumwidthshouldbe4feet.
Exhibit 3‐12 Widths of Usable Shoulders (In Feet)
Roadway Type Area Type Arterials1 Collectors1 Local Roads
Rural Natural 4 to 12 4 to 10 2 to 8 Rural Developed 4 to 12 4 to 10 2 to 8 Rural Village 4 to 12 4 to 10 2 to 8 Suburban Low Density 4 to 12 4 to 10 2 to 8 Suburban High Density 4 to 12 4 to 10 2 to 8 Suburban Village/Town Center 4 to 12 4 to 10 2 to 8 Urban 4 to 12 4 to 10 2 to 8
Source: Flexibility in Highway Design, AASHTO 2004. Chapter 6 Cross Section Elements 1 Shoulder widths less than the values shown above may be used if approval from the City of Norwalk is obtained.
Situations where narrower shoulders may be considered are described below. Note: An additional 2-foot offset from the edge of the shoulder is required to vertical elements over 6-inches in height
(such as guardrail).
Minimum4‐footshouldersarerecommendedforallarterialsandcollectorsbecauseofthevaluetheyprovideforbicycleandpedestrian(particularlyinruralareas)accommodation,andmotorvehiclesafety.IfapprovalfromtheCityofNorwalkisobtained,shouldersnarrowerthan4feetmaybeusedinconstrainedareaswhereseparatepedestrianaccommodationisprovidedandsharedbicycle/motorvehicleaccommodationissuitable.Examplesoftheseconditionsarewheredesignspeedsarelessthan45milesperhourandtrafficvolumesarerelativelylow(lessthan4,000vehiclesperday),orwherethedesignspeedis30milesperhourorless.Theusableshoulderiscomposedofbothagradedshoulder,and,insomecases,roundingofgradetransitionsattheedgeoftheroadway,asshowninExhibit3‐13.Usableshouldershavethefollowingcharacteristics: Theareamusthaveasideslopeof1footverticalto6feethorizontal(1v:6h)or
flatter,includingroundedareasforgradetransitions.
Theareaisusuallyflushwiththeadjacentroadwayandmustbefreeofverticalobstructionshigherthan0.5feet(guardrail,walls,trees,utilitypoles).
Shouldersareusuallypaved.Ifunpaved,shouldersshouldbeflushwiththeroadwaysurfaceandsufficientlystabletosupportvehicularuseinallkindsofweatherwithoutrutting.Additionally,sufficientpavedwidthtoaccommodatebicyclesshouldbeprovided.
Section 1 – Chapter 3
Cross‐section and Roadside Elements 1.3‐23
Anadditional2feetofclearanceshouldbeaddedtotheusableshoulderdimensiontoallowforanoffsettoverticalroadwayelementsover0.5feetinheight,suchasguardrail,bridgerail,concretebarrier,walls,trees,utilitypoles,etc.
Usableshouldersmustbeclearedofsnowandiceduringthewintermonthsinordertofunctionproperly.Therefore,itisoftenpracticalforusableshoulderstobepaved.
Theedgeoftheusableshouldershouldnotbelocatedattheedgeofright‐of‐way.Anoffsetisrequiredforroadmaintenance,snowremoval,andplacementofsigns.
Incertaininstances,usuallytocontroldrainage,theuseofamountablebermoredgingispermissiblewithinashoulderarea,asdiscussedlaterinthischapter.
Atintersections,usableshouldersmaybeeliminatedinordertobetterprovideforturningmovementsorshortenpedestriancrossingdistances.Howeverprovisionsforbicyclistsmustbeconsideredwhentheshoulderiseliminatedatintersections.
1.3‐24 Cross‐section and Roadside Elements
Exhibit 3‐13 Usable Shoulders
Source: Adapted from A Policy on Geometric Design of Highways and Streets, AASHTO 2011, Chapter 4 Cross-Section Elements.
3.3.3.2 On‐street Parking
On‐streetparkingisprovidedinplaceofusableshouldersinmanydifferentsettingstosupportadjacentlanduses.Ifshouldersareusedtoaccommodatebicyclesoutsideoftheon‐streetparkingzone,thedesignershouldmaintainthecontinuityofbicycleroutesthroughtheparkingzonethroughtheuseofbicyclelanesor,ataminimumsharedlanemarkings.Curbextensionsareaneffectivedesigntreatmentatintersectionsandpedestriancrossingsthathelpprohibitillegalparking,reducethecrossingdistanceforpedestrians,andimprovevisibility.Curbextensionscanbecarefullydesignedsothatbicycletravelisnotcompromisedandshouldonlybeusedinconjunctionwithactivecurb‐sideuses(suchasparkingortransitstops).Curbextensionsshouldextendnofurtherthan6feetfromthecurb.Sidewalksarealmostalwaysprovidedadjacenttoon‐streetparking.Parkingprovidesabufferbetweenmotorvehicletrafficandpedestriansonthesidewalk.On‐streetparkingcanalsoinfluencethetrafficflowalongroadways,sometimesresultinginreducedspeeds,reducedcapacity,andincreasedconflictsforbothbicycleandmotorvehicletraffic.AlthoughnotcommononNorwalkroadwaysnotunderstatejurisdiction,on‐streetparkingshouldnotbeprovidedwithhighdesignspeeds(over45milesperhour)duetoitsimpactsontrafficflowandthesafetyimplicationsofparkingmaneuversathighspeeds.Parallelon‐streetparkingrequiresaminimumof7feetofpavedcross‐sectioninadditiontotherequiredtravellanewidthandshouldnotbepermittedwherethiswidthisnotavailable.Forareaswithhighturnover,areaswithtruckloading,
Parking often replaces usable shoulders in village, town center, and urban settings.
Section 1 – Chapter 3
Cross‐section and Roadside Elements 1.3‐25
andareaswithbusstops,8feetofwidthisrecommended.Parkinglanewidthsof10feetaredesirableinareaswithsubstantialamountsoftruckparkingorbusstops.Widerparkinglanes,upto12feet,areestablishedtopreserveroadwaycapacityforpossibleconversiontotravellanes,orforuseastravellanesduringpeakperiods.However,parkingregulationsandenforcementarerequiredtopreservethedesiredoperationalcharacteristicsoftheroadwayintheseinstances.Requirementsforthestripingandsignageofparallelon‐streetparkingisprovidedintheManualonUniformTrafficControlDevices(MUTCD).Parkingcanbemarkedandregulatedbytime‐of‐dayorotherrestrictionsinhighdemand/highturnoverareas.Inotherlocations,parkingmaybepermitted,butisnotformallymarkedorregulated.AccessibleparkingspacesshouldbeprovidedinnumbersagreedtobytheCityofNorwalkortheState,andshouldbelocatedattheendofablocksothattheyarenearacurbcutramp.EachaccessibleparkingspaceshouldbedesignatedwithanInternationalSymbolofAccessandbeconsistentwiththerequirementssetforthintheConnDOTHighwayDesignManualatleastonroadwaysunderStatejurisdiction,butpreferablyonallroads.ParkingshouldalsomeetcurrentAmericanswithDisabilitiesAct(ADA)designguidelines.On‐streetangleparkingiscurrentlypermittedinsomeruralvillages,suburbantowncenters,andurbanareas.Whereangleparkingiscreatedorretained,thedesignershouldconsiderback‐inangleparkingasanalternativetotraditionalhead‐inangleparking.Accessibleparkingshouldbeprovidedwithanadjacent5‐footto8‐footaccessaisle.Eightfootacceptableaislescanaccommodatevanswithlifts.AllparkinglocatedonStateroadways,includingNoParking,durationalparking,handicapparking,andloadingzonesrequireapprovalfromtheOfficeofStateTrafficAdministration(OSTA).TheCTGeneralStatutesprohibitson‐streetparkingwithin10feetofafirehydrantandwithin25feetofanintersection,markedcrosswalkorstopsign.
3.3.3.3 Travel Lanes
Travellanesarethecomponentoftheroadwaycrosssectionthatservemotorvehicletravel,orinsomecases,jointuse.Inmostcases,thetravellanesarethewidestcomponentoftheroadwaycross‐section.Thenumberoflanesineachdirectionshouldbedeterminedbasedonthedesignyeartransportationdemandestimatesandtheselecteddesignlevelofservicedeterminedintheprojectplanningprocess(seeChapter1‐2).Insomeinstancesitmaybepossibletoreducethenumberoftravellanestoprovidesidewalks,landscapebuffers,bicyclelanes,andcrossingislands.Thewidthoftravellanesisselectedthroughconsiderationoftheroadwaycontext,approachtomultimodalaccommodation,thephysicaldimensionsofvehicles,speeds,andothertrafficflowcharacteristics.Thenormalrangeofdesignlanewidthisbetween
1.3‐26 Cross‐section and Roadside Elements
10and12feet.Travellanesbetween11and12feetinwidthareusuallyselectedfordesigncross‐sectionsandareparticularlydesirableforroadwayswithhigherdesignspeeds(45milesperhourormore),highertrafficvolumes(2,000ormorevehiclesperday),orhighertruckandbusactivity(greaterthan30perhour).Exhibit3‐14summarizestravellanewidthsforvariousareaandroadwaytypes.OnStateroadways,lanewidthsshouldbeconsistentwiththeDepartment’sHighwayDesignManual.
Exhibit 3‐14 Range of Travel Lane Widths (In Feet)
Roadway Type Area Type Arterials1 Collectors2 Local Roads
Rural Natural 11 to 12 10 to 12 9 to 12
Rural Developed 11 to 12 10 to 12 9 to 12
Rural Village 11 to 12 10 to 12 9 to 12
Suburban Low Density 11 to 12 10 to 12 9 to 12
Suburban High Density 11 to 12 10 to 12 9 to 12
Suburban Village/Town Center 11 to 12 10 to 12 9 to 12
Urban 11 to 12 10 to 12 9 to 12 1 Lane widths less than the values shown above may be used if approval from the City of Norwalk is obtained.
Situations where narrower lanes may be considered are described below. 2 Minimum 11-foot lanes are required for design speeds of 45 miles per hour or greater. N/A Not Applicable Source: Adapted from A Policy on Geometric Design of Highways and Streets, AASHTO 2011, Chapter 4 Cross-Section Elements.
Inadditiontothroughlanes,auxiliarylanessuchasadditionalturninglanes,climbinglanes,orotherlanesmaybeprovidedonsteepgrades,atintersections,orinotherspecialcircumstances.TurninglanesatintersectionsarediscussedindetailinChapter1‐4.Otherauxiliarylanesarediscussedlaterinthischapter.Formultilaneroadways,theadditionallanes(ifprovided)maybedifferentwidthsthanthecurblanes.
Lanes Wider than 12 Feet
Laneswiderthan12feetaresometimesusedwhereshouldersarenotprovided,suchasinruralvillages,suburbanhigh‐densityareas,suburbanvillagesandtowncenters,orurbanareas.Anotherapplicationofwidelanesisinareaswithhighdrivewaydensity.Thisapplicationprovidesmoremaneuveringroomfordriversenteringorexitingdriveways,orinareasoflimitedsightdistance.Inthesecaseswidelanesaretypically12to14feetwide.However,ifmorethan12feetisavailable,itisoftenpreferabletostripeashoulder.Ifnecessary,thedesignershouldincludeadditionalwidthoncurvestominimizeencroachmentintoopposingtraffic,adjacenttravellanes,bicyclelanes,orsidewalkssincevehiclesoff‐track,whichmeansthattheirtravelpathexceedsthewidthofthevehicle.Ifhighvolumesofbusandtrucktrafficareanticipatedonaroadway,suchasinanindustrialpark,oronadedicatedbusway,thedesignermayconsiderwhetherlaneswiderthan12feetareappropriate.
Section 1 – Chapter 3
Cross‐section and Roadside Elements 1.3‐27
Lanes Narrower than 11‐Feet
Narrowerlanesreducetheamountofright‐of‐waydedicatedtomotorvehicletravel,leavingroomforwidersidewalks,bicyclelanes,shouldersandon‐streetparking.Narrowerlanesalsoreducethecrossingdistanceforpedestriansandcanencourageloweroperatingspeeds.Insomesettings,narrowerlaneshelptoreducetheimpacttoroadsideenvironmentalorculturalresources.Forlowerspeed,lowervolumeroadsthatprimarilyprovideaccesstoadjoiningproperty,(suchasminorcollectorsandlocalroads)narrowerlanesmaybeappropriatetominimizeright‐of‐wayrequirementsandpotentialimpactstothebuiltandnaturalenvironment.Inareasoflimitedright‐of‐way,10‐footlanescanbeprovidedsothatthewidthoftheshouldercanbeincreasedtoprovidegreaterseparationbetweenpedestriansandbicyclesandmotorvehicles.Thefollowingsectiondiscussestherelationshipbetweenlanewidthandshoulderwidth.Travellanesnarrowerthan10feetareonlyappropriateforlocalroadwaysandsomeminorcollectorswithverylowtrafficvolumesandspeeds.Lanesnarrowerthan9feetaregenerallynotrecommended.However,onsomelow‐volumelocalroadsinresidentialareas,sharedstreetsthatdonotallowtwocarstopasssimultaneouslymaybeprovided.
3.3.3.4 Curb Lane Plus Shoulder Width
Independentoftheallocationbetweenshouldersandtravellanes,thetotalwidthofthecurblaneplusshoulderavailableforbicycleandmotorvehicletravelisanimportantdesignelement.Fortwo‐laneroadways,thecurblaneplusshoulderwidthiskeyfordeterminingtheminimumcross‐section.Forexample,a14‐footcurblaneplusshoulderdimensionwillallowamotorvehicletopassabicyclistwithoutneedingtochangelanes(onamultilanesection)orswerveintotheoncominglane(onatwolanesection)andistheminimumvalueforcollectorsdeterminedusingExhibit3‐11and3‐14.Thisexampleresultsinawidthof28feetforatwo‐lanecollector.UsingtheminimumvaluesinExhibits3‐11and3‐14,theminimumwidthforatwo‐lanearterialis30feet.Althoughtheseminimumexamplesareprovided,theallocationofthepavementwidthbetweenthecurblaneandshouldershouldbedeterminedonaproject‐specificbasis,asdescribedinSection3.2.
3.3.4 Complete Cross‐Section Guidance
Theprevioussectionsprovideguidanceanddimensionsforaccommodationofindividualroadwayuserswithinthecross‐section.Thefollowingsectionsprovidemorespecificguidancefortheassemblyofcross‐sectionsbasedontheareaandroadwaytypesintroducedinChapter1‐2includingadiscussionofthespecificelementsand
Curb lane plus shoulder
Shoulder Curb Lane
1.3‐28 Cross‐section and Roadside Elements
dimensionscommonlyusedindifferentareatypes.AdiscussionoffreewayshasbeenintentionallyomittedfromthisPlan.AlthoughtherearefreewaysinNorwalk,theyareunderthejurisdictionoftheStateofConnecticutandaresubjecttodesignstandardsforInterstateHighwaysestablishedbytheFederalHighwayAdministration(FHWA)sincetheyarecomponentsoftheNationalHighwaySystem(NHS).
3.3.4.1 Arterials and Major Collectors
Arterialsandmajorcollectorsvarywidelyincharacterdependingupontheareasthroughwhichtheypass.Arterialsandmajorcollectorsalmostalwaysaccommodatepedestrianandbicycletravel.Inmostinstances,arterialsandmajorcollectorsaredesignedtoaccommodatepedestriansandbicyclesusingthefirstfourcasesdescribedinSection3.2.Sidewalksareusuallyprovidedindevelopedareas(suburbanhighdensityareas,suburbanvillagesandtowncentersandurbanareas).Sidewalksmayalsobedesirableinareaswithlowerdevelopmentdensitysuchassuburbanlowdensityareas,ruraldevelopedareasandruralvillages.Inruralnaturalareasandothersparselydevelopedareas,pedestriantravelisoftenaccommodatedintheshoulderorbysidepaths.Usableshouldersareusuallyprovidedonarterialsandmajorcollectorsoutsideofdenselydevelopedareas.Inmostcases,theseshouldersareatleast4feetwidetoaccommodatebicycletravel.Shouldersbetween6and8feetwidearedesirableforemergencystoppingandotherfunctions,especiallyinhighvolumeandhightruckandbusareas.AlthoughnotcommoninNorwalk,inthecaseofhighdesignspeeds(greaterthan45milesperhour)10‐footshouldersshouldbeconsidered.Inthecaseofwideshoulders,itispossibletoprovideacombinationofpavedandunpavedsurfacesifthecircumstancesdictatesuchatreatment.Inruralvillages,suburbantowncenters,andurbanareas,usableshouldersareoftenreplacedwithon‐streetparking.Intheseareasitisdesirabletoprovidebicyclelanestomaintainseparateaccommodationforbicycles.Ifthereisinsufficientright‐of‐waytosupportbicyclelanesandparking,thenthedesignershoulddeterminewhichelementtoprovidewithintheavailableright‐of‐wayorshouldconsidertrafficcalmingandsharedlanepavementmarkingstoimprovetheperformanceofsharedbicycle/motorvehicleaccommodation.Travellanesof11and12feetareusuallyprovidedonarterialsandmajorcollectors.Inhighvolume,hightruckandbuspercentage,andhighdesignspeedareas,12footlanesareparticularlydesirable.10‐footlanesaresometimesusedifspeedsandtruckandbusvolumesarelow(lessthan250perdayor30inonehour),inmultilanesections,ortoprovidewidershouldersinareasoflimitedright‐of‐way.Majorcollectorsaresometimesconstructedwith10footlanesinruralvillages,suburbanvillagesandtowncenters,andurbanareaswhererightofwayisparticularlylimitedandcompetingdemandsareespeciallyhigh.Lanesnarrowerthan10feetaregenerallynotusedonarterialsormajorcollectors.
Minor arterial in a town center
Section 1 – Chapter 3
Cross‐section and Roadside Elements 1.3‐29
Inmostcases,thedesignershouldprovideacombinedshoulderpluscurblanedimensionofatleast14feetsothatmotorvehiclescanpassbicycleswithoutchanginglanesorswerving.OnStateroadways,however,themaximumshoulderwidthshallbe8‐feet.
3.3.4.2 Minor Collectors
Thedesignofminorcollectorsissimilartothatdescribedabove,especiallyforareaswithhighertrafficvolumesandspeeds.However,minorcollectorsareoftendesignedforlowspeed,lowvolumeoperations.Inthesecases,minorcollectorsaresometimesdesignedtoprovidesharedaccommodationforallusers,asdescribedinSection3.2,Case5,withacurb‐laneplusshoulderwidthofatleast12feet.Thedesignermayneedtoconsidertrafficcalmingmeasurestoensurethatmotorvehiclespeedsareappropriateforshareduseoftheroadway.
3.3.4.3 Local Roads
Theguidanceprovidedforarterialsandmajorcollectorsissuitableforlocalroadswithhighvolumesandhighspeeds.Muchlikeminorcollectors,localroadsaresometimesdesignedtoprovidesharedaccommodationforallusers.Onsomelow‐volumelocalroadsinresidentialareas,sharedstreetsthatdonotallowmotorvehiclestopasssimultaneouslyareacceptable.Thedesignermayneedtoconsidertrafficcalmingmeasurestoensurethatmotorvehiclespeedsareappropriateforshareduseoftheroadway.
3.4 Public Transit Operations
Publictransitoftenoperatesonroadways.Insomecases,busesoperatewithinmixedtrafficandstopalongthecurbside.Also,aroadwaydesigncanincorporatelanesdedicatedto,orwithpriorityfor,transitoperations.Thefollowingsectionsdiscussthesepublictransitconsiderationsassociatedwithroadwaycross‐section.AmoredetaileddiscussionofdesignfortransitstopsatintersectionsisprovidedinChapter1‐4.
3.4.1 Bus Stops
Thespacingofbusstopsisacriticaldeterminantoftransitvehicleandsystemperformance.Theconsiderationofwheretolocatebusstopsisabalancebetweenprovidingshortwalkingdistancestobusstopsandtheincreasedtraveltimewhenthebusstopsfrequently.Thus,thedecisionofbusstoplocationshouldbemadebythetransitagenciesandtheCity.OnStateroadways,busstopdeterminationsrequireapprovalfromtheOfficeofStateTrafficAdministration(OSTA)andshouldbemadeinconjunctionwithitsstaff.Busstoplocationsalsoneedtocarefullyconsidertheavailabilityofsidewalks,crosswalks,andwaitingareas.Theroleofthedesigneristoevaluateproposedlocationstoensurethattheyareappropriatewithregardstosafetyandoperations.
Project designers must consult with regional transit authorities to
determine proper locations for bus stops..
1.3‐30 Cross‐section and Roadside Elements
Thischapterfocusesonmid‐blockbusstopssincebusstopslocatedatintersectionsarediscussedinChapter1‐4.Mid‐blockstopsaregenerallylocatedadjacenttomajorgeneratorsoftransitridershipandofferthefollowingadvantages: Mid‐blockstopsminimizethesightdistanceimpactsofbusesonpedestrians
crossings(i.e.limitedabilitytoseearoundthebus).
Mid‐blockstopsmayresultinlesscongestedpassengerwaitingareas.Therearedifficultiesassociatedwithmid‐blockstops;forexample,mid‐blockstopscreatecrossingdifficultiesforpedestriansunlessamid‐blockcrosswalkisalsoprovided.Busstopsandpedestrianroutesshouldbeconsideredtogethertomakesurethatthestopsaresafeandconvenientforusers(peopletendtowalkupto¼miletoaccessbusroutes).Mid‐blockstopsalsorequiretheremovalofon‐streetparkingforasubstantialdistancetoaccommodatethepull‐in,stop,andpull‐outmaneuvers.
3.4.1.1 Bus Stop Dimensions
Thetwoprimarycategoriesofbusstopsare(1)curb‐sidebusstopsand(2)busbays.Themostcommonarecurb‐sidebusstopswherethebussimplystopsatthecurbinthetravellane,shoulderorparkinglane.Avariationofthisisastopatacurbextension.Busbaysallowthethroughtraffictoflowfreelypastthestoppedbus.Mostbusbaysoccuratmid‐blocklocations,althoughitissometimesdesirabletocreatebusbaysforfar‐sidestops,withorwithoutaqueuejumperlane.
Curbside Bus Stop Zones
Theminimumlengthofbusstopsis80feetformid‐blockbusstopsand60feetforbusstopsatintersections.Thesedimensionsareforatypical40‐foottransitbus.Ifarticulatedbusesareused,anadditional20feetisrequired.Shorterdistancesmaybeacceptabletoaccommodatetransitvansormid‐sizebuses.Anadditional50feetoflengthisneededforeveryadditionalbusthatistypicallyatthestopatthesametime.Unlessthestopisusedforthelayoverofbuses,asinglestoppositionwillbeadequateifpeakhourbusflowislessthan30perhour.Oftenthecurbsidestopmakesuseofaparkinglane.Parkinglanesaretypically7to8feetwide.Busesrequireaminimumwidthof10feet.Therefore,ifthereissignificantbusactivityalongacorridoranditisdesirabletoallowthroughtraffictopassunimpeded,awiderparkinglaneshouldbeprovided.Inareaswithouton‐streetparking,awideshouldershouldbeprovidedifbusstopsarefrequentanddwelltimesarelong.Somevariationtotheseguidelinesmaybenecessaryinconstrainedareaswithsensitiveroadsideresources.
Bus Bays
Thedesignermustdeterminewhenbusbaysaremoreappropriatethancurb‐sidebusstopzones.Amongthefactorsare:
Section 1 – Chapter 3
Cross‐section and Roadside Elements 1.3‐31
Trafficinthecurblaneexceeds250vehiclesduringthepeakhour, Trafficspeedisgreaterthan40mph, Busvolumesare10ormoreperpeakhourontheroadway, Passengervolumesexceed20to40boardingsanhour, Averagepeak‐perioddwelltimesexceed30secondsperbus,and Busesareexpectedtolayoveratthelocation.Itshouldbenoted,however,thatwhentrafficvolumesapproach1,000vehiclesperhourperlane,busdriverstendnottousebusbaysduetodifficultiesencounteredinre‐enteringtrafficlanes.Considerationshouldbegiventotheseoperationalissueswhencontemplatingthedesignofabayonahigh‐volumeroad.Accelerationlanes,signalpriority,orfar‐sideplacementsarepotentialsolutions.Ideallythedesignofbusturnoutsshouldincludetapersandlanesfordecelerationandmerging,butitisusuallynotpracticaltoprovidedecelerationandmerginglanes.Somekeydesignelementsare: Ataperof5feetinlengthforevery1footofdepth(5:1)istheminimumfor
deceleration.Whenthebusstopisonthefarsideoftheintersection,theintersectionmaybeusedastheentryareatothestop.
Ataperof3feetoflengthforevery1footofdepth(3:1)istheminimumforreentry.Wherethestopisonthenearsideoftheintersection,thewidthofthecrossstreetisusuallysufficienttoprovidetheneededmergingspace.
Busbaywidthsshouldbe12feet,although10feetissufficientwhentrafficspeedsare30mphorless.
3.4.1.2 Bus Stop Waiting Areas
Thedesignforthecurb‐sideelementsofthebusstop(shelters,boardingplatforms,walkways)mustconformtoADArequirements.TheADAregulations,aswellastheTCRPreportGuidelinesfortheLocationandDesignofBusStops,providedetailedinformation.Amongthekeydesignelementsare: Anaccessiblepedestrianroutetothebusstop.
Toaccommodateuseofawheelchairlift,theremustbealevel(2percent)landingareaatleast60incheswide.Thedepthofthelandingareamustbe8feet.Thebusstoppadmustbefreeofobstructions.
Bus waiting area
60-foot transit
1.3‐32 Cross‐section and Roadside Elements
Bussheltersaretypically5to6feetwideand10feetlong.Interiorclearanceof4feetisrequired.Ideally,thesheltersareashouldbesizedfortheanticipatedvolumeofwaitingpassengersduringpeakboardingperiods.Theymustbeat‐gradeorrampedtoaccommodateapersonusingawheelchair.Bussheltersshouldnotbeplacedwheretheywillrestrictvehicularsightdistance.
InadditiontoADArequirements,thedesignershouldconsiderurbandesignissuesassociatedwiththelocationofbusstopsincluding: Thecharacterandadequacyofaccessroutesforpedestrians,cyclists,andother
potentialtransitusers,
Connectivitytonearbydemandcenters,
Streetscapetreatmentstoimprovethevisualcharacterofthebusstop,and
Architecturalelementsofshelterdesignorselection.
3.4.2 Dedicated Lanes
Insomelocations,lanesareprovidedfortheexclusiveorpreferentialusebytransitvehicles.Onmostarterialsandcollectors,thecurblaneismostcommonlydesignatedasadedicatedorprioritytransitlane.Thischoiceallowsthetransitvehicletostopatcurbsidebusstops.Often,theselanesaresharedwithbicycles,right‐turningvehicles,taxicabs,bicyclists,orhighoccupancyvehicles.Anotheralternativeistoprovidededicatedtransitlaneswithinacentermedian.Inthiscase,passengersmustcrosstheotherroadwaylanestoreachthetransitfacility.Thisalternativeoperatesinamannersimilartorailtransit,describedearlierinthissection.Foralldedicatedorprioritylanes,thedesignershouldstrivetoprovideadequatelaneandshoulderwidthsothattransitvehiclesoperatewithminimalinterferencefromgeneraltraffic.
3.5 Other Cross‐section Elements
Thefollowingsectionsdescribethreeimportantelementsofcrosssectiondesign,mediansandauxiliarylanes,cross‐slopesrequiredforpositivedrainage,andcurbing.
3.5.1 Medians and Auxiliary Lanes
Amedianistheportionofaroadwayseparatingopposingdirectionsofthetraveledway.Medianscaninfluencethequalityofserviceandsafetyprovidedforallroadwayusers.Forexample,medianscanbreakupthewidthofaroadwayandproviderefugeforpedestrianscrossingthestreetandvehicles(includingbicycles)makingturningorcrossingmovements.
Section 1 – Chapter 3
Cross‐section and Roadside Elements 1.3‐33
Continuousmedianscanincreasethespeedsalongaroadway,improvingitsefficiencyformotorvehicles;however,thisincreasedspeedcanhaveanegativeimpactonneighborhoodsandonthesafetyofpedestriansandbicyclists.PotentialtrafficcalmingapplicationsofmediansarediscussedfurtherinChapter1‐6.Medianscanalsobeusedtomanagepropertyaccess,channelizetrafficmovements,andaccommodateaesthetictreatments.Medianwidthisexpressedasthedimensionbetweentheedgesoftraveledwayandincludesleftshouldersiftheyareprovided.Auniformmedianwidthisdesirable.However,variablewidthmediansmaybeadvantageouswhererightofwayisrestricted,at‐gradeintersectionsarewidelyspaced,oranindependentalignmentisdesirabletominimizecutandfill,tominimizeenvironmentalimpacts,orforaestheticpurposes.Thetypeofmedianselectedanditsdimensionswilldependuponmanyfactors,including: Areatype, Roadwaytype, Availabilityofrightofway, Transportationdemands, Pedestrianandbicyclecrossings, Presenceandtypeoftransitoperations, Designspeed, Clearzoneandrecoveryareaguidelines, Landscapingandaestheticconsiderations, Drainageneeds, Snowandiceimpacts, Maintenanceconsiderations,and Superelevationimpacts.Mediansaremostfrequentlyusedonmultilaneroads.Mediansmayalsobeincludedontwo‐laneroadways;howeveradditionaltravelwaywidthisoftenrequiredforemergencyvehicleaccess.Insomecases,mediansincludeauxiliary(turning)lanesthatprovideaccesstodrivewaysorincreasecapacityandsafetyatintersections.TheseauxiliarylanesarediscussedinmoredetailinChapter1‐4.Severaldifferenttypesofmediansarepossibleasdescribedinthefollowingsections.
3.5.1.1 Raised Medians
Raisedmediansarecentralareasatanelevationhigherthanthesurfaceoftheroad.Araisedcurbusuallyprovidesthiselevationdifference.Raisedmediansareusuallyfoundonarterials,collectorsandlocalroadsinmoredenselydevelopedareaswithdesignspeedsof45milesperhourorless.
1.3‐34 Cross‐section and Roadside Elements
Raisedmediansareoftenthepreferredmediantypeinareaswithhighpedestriancrossings,whereaccesscontrolisdesired,orwheredecorativelandscapingisdesired.Raisedmediansoffersomeadvantagesoverothermediantreatmentsincluding: Mid‐blockleftturnsareeliminated,
Spaceisavailableforaesthetictreatments,
Aprotectedlocationisavailablefortrafficsigns,signals,pedestrian,bicycle,andturningtrafficrefuge;,
Left‐turnscanbemoreeffectivelychannelized,
Alocationisprovidedforsnowstorage,
Themedianedgesarediscernible,and
Drainagemaybeimproved.Somedisadvantagesofraisedmedianswhencomparedtoothermediantreatmentsinclude: Theyaremoreexpensivetoconstruct,
Theymayrequiregreaterwidthsthanothermediantoservethesamefunction(e.g.,left‐turnlanesatintersections),
Curbsmaycauseadrivertolosecontrolifstruck,and
Prohibitingmid‐blockleftturnsmayoverloadstreetintersectionsandmayincreasethenumberofU‐turns
Theminimumtotalwidthoftheraisedmedianshouldbe4feetincludingcurbs,andonStateroadwaysitshouldbeconsistentwiththeDepartment’sHighwayDesignManual.Inareaswithlowpedestrianandbicycleactivity,raisedareasmayuseslopededging.Thisconfigurationprovidestheminimalwidthmedianandminimumoffsetsbetweenthetravellaneandverticalcurb.Inmostcases,itisdesirabletoprovidean8‐to10‐footmedianwitha6‐footraisedrefugeareaand1‐to2‐footoffsetsbetweentheverticalcurbandthetravellane.Whererefugeisrequiredforpedestriansandbicyclesverticalcurbshouldbeused.Additionally,crossingsshouldbecarefullylocatedtoservedesiredcrossinglocationsandaccessibilitymustbeprovidedforwheelchairusers.
Typical raised median on an urban arterial
Section 1 – Chapter 3
Cross‐section and Roadside Elements 1.3‐35
Widermedians,between10and18feet,moreeffectivelysupportlandscaping,providehigherqualityrefuge,provideincreasedlateralclearancetosignage,streetlights,andlandscapefeatures,andsupportleft‐turnlanes.Whenleftturnsareprovidedatintersections,an18‐footwidthisdesirabletosupporta12‐footturnlaneandmaintaina6‐footmedian,althoughnarrowerconfigurationsarepossible.Thedesignermustconsidersightdistancelimitationsandpotentialobstacleswhenselectingmedianplantings.
3.5.1.2 Flush Medians
Flushmedianscontainacentralareaatapproximatelythesameelevationastheroadwaysurface.Flushmediansareusuallyfoundonarterials,collectorsandlocalroadsinareaswithlimitedright‐of‐way.Flushmediansmaybefoundonfreewaysifcombinedwithamedianbarrier.Aflushmedianisgenerallypavedandmayormaynothaveabarrierdependingontrafficconditions.Itisnormallycrownedtoprovidepositivedrainageanddiscourageparking.Themedianisoftendesignatedusingscoredconcreteorpavementmarkings.AllflushmediansshouldbemarkedaccordingtothecriteriaintheManualonUniformTrafficControlDevices(MUTCD).Whenincludedonarterials,collectorsandlocalroadstoprovideleft‐turnlanes,themedianisusuallybetween12feetand16feetwide.The16‐footmedianprovidesfora4‐footseparationfromtheopposingtraffic.Inareaswithlowtruckandbusvolumes,aleft‐turnlaneasnarrowas10feetcanbeprovided,reducingthedesirablemedianwidthto14feet.Whereleftshouldersareprovided,thedimensionrequiredforusableshouldershouldbeaddedtotheabovemedianwidths.
Two‐Way Continuous Left‐Turn (TWLT) Lanes
Thetwo‐wayleft‐turnlaneisaspecialapplicationofflushmedianswhichallowsturningmovementsalongitsentirelength.TWLTsmaybeappropriateinareaswithfrequentdrivewayspacinginhighlydeveloped,orcommercializedareas.Two‐wayleft‐turnlanesareappropriateonroadwayswithnomorethantwothroughlanesineachdirectionandwhereoperatingspeedsareintherangeof30milesperhour.TWLTlanesmaybeusedwheredailytrafficthroughvolumesarebetween10,000and20,000vehicleperdayfor4‐laneroadwaysandbetween5,000and12,000vehiclesperdayfor
Center two-way left turn lane striping
8 to 16 ft.
1.3‐36 Cross‐section and Roadside Elements
2‐laneroadways.Left‐turnmovementsshouldconsistofatleast70turnsperquartermileduringthepeakhoursand/or20percentofthetotalvolume.CarefulevaluationofindividualsitesisrequiredforimplementationofTWLTlanes.ThesignageandstripingpatternsforTWLTlanesshouldbedesignedinaccordancewiththeMUTCD.Lanewidthsbetween12and16feetaresuitableforTWLTlanes.Onroadwayswithhighvolumes,ormoderatetohighspeeds(30to45milesperhour)a14‐footTWLTlaneshouldbeprovided.TWLTlanesarenotappropriateonroadwayswithdesignspeedsgreaterthan45milesperhour.Inmostcases,itispreferabletoprovidearaisedmedianwithperiodicturnlanesservingmajordrivewaysandintersectingstreetsinsteadofaTWLTlane.Thispreferredtreatmentprovidesimproveddelineationofturningmovementsandimprovedpedestrianrefuge.However,ifdrivewayspacingisfrequentandturningvolumesareheavy,thenthetwo‐wayleft‐turnlanemaybesuitable.AccessmanagementtechniquessuchasdrivewayconsolidationtofacilitatethepreferredtreatmentarediscussedinChapter1‐7.
3.5.1.3 Context Influence on Median Design
Designofmediansvariesconsiderablybasedontheareathroughwhichtheroadwaypasses.Inruralnatural,ruraldeveloped,andsuburbanlowdensityareas,widermediansareoftenselected.Insuburbanhighdensity,andurbanareas,narrowmediansaremorefrequentlyencountered.Theadditionofmediansinruralvillages,suburbanvillagesandtowncenters,andsomeurbanareasmayconflictwiththecharacteroftheseareasandshouldbeconsideredcarefullyfromanurbandesignperspective.Similarly,theadditionalright‐of‐wayrequiredformediansmayresultinincreasedcosts,environmentalimpacts,andcommunityimpacts.Thebenefitsandimpactsofprovidingamediananditswidthshouldalsobecarefullyconsidered.Inmanycasesmedianscanoccupyright‐of‐waythatcouldbeusedforotherpurposessuchasbicyclelanes,on‐streetparking,andwidersidewalks.Incaseswheremediansareproposedforaestheticpurposes,thedesignershouldconsiderwhetheritismoreadvantageoustolocatethelandscapedspacealongthesidesoftheroadway.Inallareas,ifamedianisdesired,anarrowmedianorbarrier,suchasdouble‐facedguardrailorconcrete“jersey”barriers,maybeappropriatetolimittheneededrightofwayandimpactstothenaturalorbuiltenvironment.However,forfreewaysandmajorarterials,widermediansmayprovidegreatersafetyandoperationalbenefitsandmayallowseparatealignmentsforeachdirectionoftravel,reducingtheimpactoftheroadwayonthesurroundingcontext.Whiledouble‐facedguardrailorconcrete“jersey”barriersmayconflictwiththecharacterofaparticulararea,therearetimeswhenaconstrainedwidththatrequiresseparationcallsforthesetypesofbarrierstominimizelanduseimpacts.
Section 1 – Chapter 3
Cross‐section and Roadside Elements 1.3‐37
3.5.1.4 Roadway Type Influence on Median Design
Thefunctionsthatamedianprovidesvarydependingonthetypeofroadwayonwhichtheyarefound.Mediansareprovidedonallfreewaysandsomearterials,primarilytoachievesafetyandoperationalbenefitsthroughaccessmanagement.Oncollectorsandlocalroads,mediansareprovidedprimarilyforaccessmanagement,aestheticreasons,toprovidealocationfortrafficsignalsandsignage,andtoproviderefugeforpedestriansorbicyclistscrossingtheroad.TypicalmedianfunctionsfordifferentroadwaytypesareshowninExhibit3‐15anddiscussedinthefollowingsections.
Exhibit 3‐15 Typical Median Functions by Roadway Type
Median Function
Arterials
Collectors and Local Roads
Separation from opposing traffic X
Access management X X
Refuge area for pedestrians and bicyclists X X
Refuge for emergency stops X
Area for control of errant vehicles X
Reduction in headlight glare X
Area for deceleration and storage of left-turning and U-turning vehicles X X
Enforcement and traffic management areas X X
Area for storage of vehicles crossing at intersections X X
Space for snow storage X
Landscaping (Medians greater than 10 feet wide) X X
Increased drainage collection area X
Area for placement of luminary supports, traffic signs, traffic signals, guardrail, and bridge piers X X
Area for future additional lanes (Medians greater than 30 feet wide) X X
Source: Flexibility in Highway Design, AASHTO 2004. Chapter 6 Cross Section Elements
Arterials
Mediansaredesirableonarterialscarryingfourormorelanes.However,thedesignershouldusuallyprovidethemostdesirableaccommodationforroadwayusersbeforededicatingspacetoamedian.Themedianwidthisoftenselectedbasedontheneedforleft‐turnstoragelanes.Additionally,forunsignalizedorruralroadways,amedianmustbeatleast25feetwidetoallowacrossingpassengervehicletostopsafelybetweenthetworoadways;however,atsignalizedintersections,widemedianscanleadtoinefficienttrafficoperations.Mediansintherangeof12to25feetarecommonlyselectedforthesetypesofroadways.
1.3‐38 Cross‐section and Roadside Elements
Collectors and Local Roads
Mediansmayalsobeincludedinthedesignofcollectorsandlocalstreets,althoughtheseapplicationsarelessfrequentgiventhelowerspeedsandvolumesassociatedwiththeseroadwaytypes.Inthesecases,mediansareoftenincludedtoenhancethevisualappearanceofaroadwaythroughdecorativelandscapingratherthantorealizesubstantialsafetyoroperationalbenefits.Mediansinthesecircumstancesareusuallyatleast10feetwidetoimprovethehealthofthelandscapingandtofacilitateitsmaintenance.
3.5.2 Cross Slopes
Surfacecrossslopesarenecessaryonallcomponentsofthecross‐sectiontofacilitatedrainage.Thisreducesthehazardofwetpavementsandstandingwater.Onhot‐mixasphaltpavementtravellanesshouldbedesignedforacrossslopeof2percent.Concretepavementscrossslopesshouldbedesignedto1.6percentforlanesadjacenttothecrown,and2percentforallotherlanes.Forlowerclassesofpavement,highercrossslopesmaybedesirabletoachievethedesigndrainage.Cross‐slopesshouldalsobeprovidedonsidewalks,shoulders,parkinglanes,intersections,drivewaycrossings,andbicyclelanes.
3.5.3 Curbs, Berms and Edging
Curbs,berms,andedgingareroadsideelements,usuallyconstructedofgraniteorextrudedbituminousconcreteusedtodefinethepavementedgeandtocontroldrainage.Typicaltypesofcurbs,berms,andedgingandtheirheightsareprovidedinExhibit3‐16.
Exhibit 3‐16 Typical Curb Heights
Curb Type Vertical Height
(inches)
Bridge curb 8
Barrier curb 6
Sloped edging 4
Type A berm 2 Adapted from A Policy on Geometric Design of Highways and Streets, AASHTO, 2011. Chapter 4 Cross Section Elements
Barriercurbsareverticalandareusuallygranite.Barriercurbsrangeinheightfrom6to8incheswithabatterof15:1orsteeper.Six‐inchcurbsaretypicallyusedalongroadways.Bridgecurbsarebarriercurbs,usuallywith8‐inchrevealusedonbridgestoprovideadditionalprotectionforpedestriansorotherbridgeelementsalongtheroadside.However,eventhesecurbsarenotadequatetopreventavehiclefromleavingtheroadway.Wherepositiveprotectionisrequired,asuitabletrafficbarriershouldbeprovided.
Section 1 – Chapter 3
Cross‐section and Roadside Elements 1.3‐39
Curbsareusedextensivelyonurbanandsuburbanstreetsandhighways.Curbsarenotcommonlyusedinruralareasunlesstheyareprotectinganadjacentsidewalk.Curbshelprestrictvehiclestothepavementarea,anddefinepointsofaccesstoabuttingproperties.Verticalcurbingisappropriateonlowerspeed,urbanstreetswherelandscaping,signalequipment,streetlights,orotherfeaturesarelocatedwithinthemedianoralongtheroadside.Verticalcurbingshouldalsobeusedoncrossingislandsandotherlocationswhereprotectionofpedestriansisneeded.Slopededgingisusuallygraniteandshouldbeusedforedgedelineationandontrafficislandswhendesignspeedsaregreaterthan45milesperhoursinceverticalcurbsarenotsuitableforthehighspeedenvironment.TypeABermisusuallyextrudedbituminousconcreteandcanbeusedwhendrainagecontrolisneededonroadwaysthatdonothavecontinuouscurb.Itdirectswatertocloseddrainagesystems,preventssloughingofthepavementedgeandprovidesadditionallateralsupport.TheTypeAbermshouldbeusedonly: wherethelongitudinalgradeexceeds5%foranextendedlength,or wherecontrolandcollectionofdrainageisotherwiserequired.Pavementmillingmulch,orothersuitablematerial,shouldbeusedinlieuofbermunderguardrailsandinotherareaswherecontroloferosionfromroadwayrunoffisaconcern.Ifthepavedshouldersonhighspeedfacilitiesarenotwideenoughforavehicletomoveoutofthetraveledway,slopededgingorbermsshouldbeeasilymountabletoencouragemotoriststoparkclearofthetraveledway.Bermsorslopededgingusedinthesesituationsis4inchesorlessinheightandhaveroundedorplaneslopingfaces.
3.6 Roadside Elements
Roadsidefeaturessignificantlyaffectsafety,constructionandmaintenancecosts,rightofwayrequirements,drainage,environmentalimpacts,andaesthetics.Thedesignershouldconsultthe2011AASHTORoadsideDesignGuide(ormostrecentversion)whichprovidesstandardsandrecommendationsonthedesignofroadsideelementsincludingclearzones,roadsidebarriers,medianbarriers,impactattenuators,sideslopes/cuts,andditchsections.
3.7 Utilities and Signage
Thelocationofutilitiesandtheplacementofsignageareoftensignificantissuesinthedesignofroadwayimprovementsasdescribedbelow.
1.3‐40 Cross‐section and Roadside Elements
3.7.1 Utility Placement or Relocation
Sincetheyprovideapublicservice,utilitiesareallowedtooccupythepublicright‐of‐way.Coordinationwithutilitycompaniesisessentialduringthedesignandconstructionprocesstoidentifytheappropriatelocationforutilitiesandthenecessarystepsforrelocationofexistingutilities(ifrequired).Ideally,utilityplacementorrelocationwilloccurissequencewiththeconstructionoftheroadwayprojectsothatdisruptiontothepublicminimized.Ingeneral,overheadutilitypolesshouldbelocatedoutsidetheshoulders,sidewalk,androadsiderecoveryareas(ifprovided).Ifutilitypolescannotbelocatedoutsideofthesidewalkarea,itisimportantthattheminimumclearpathoftravelforpedestriansdescribedpreviouslyisprovided.Additionally,utilitypolesshouldbeoffsetatleasttwofeetfromthefaceofcurbwhenlocatedwithinthesidewalkareaorbufferstrip.Itisusuallyadvisabletoassesstheconditionandneedforreplacementofbelow‐gradeutilitiesduringtheplannedroadwayconstruction.Theproponentshouldcoordinatewithmunicipaldepartmentsandotherutilitiestoidentifyanyutilityworktobecoordinatedwiththeroadwayproject.
3.7.2 Signage Placement
Thetypesandmountingsofsignsvariessignificantlydependingontheroadwaytypeandsetting.DetailedguidancefortheplacementofsignsiscontainedintheMUTCD.Similartoutilities,signagecannotprotrudeintotheshouldersortraveledway.Inlocationswherethesidewalkisimmediatelyadjacenttothestreet,itisoftendesirabletoplacesignageatthebackofsidewalk.Ifsignageisplacedalongthecurbedge,signpostsshouldbelocatednocloserthan½thewidthofthesignfaceplusoneadditionalfootfromthefaceofcurb.
3.8 Right‐of‐Way
Thenecessaryright‐of‐way(ROW)widthisthesummationofallcross‐sectionelements:utilityaccommodations,clearzones,drainageditches,sidewalks,bufferstrips,curbsorberms,shouldersandbicyclelanes,motorvehicletravellanes,andmedians.Considerationshouldalsobegiventothepossibilityofaddingtravellanesinthefuture.However,landusepatterns,availabilityandcostofright‐of‐waymaydictatethetypeandwidthofcross‐sectionelementsthatareprovided.TheROWwidthwillvarygreatlyandthedesignermustalwaysresearchthecurrentROWwidthasaninitialstep.Typically,anundivided,two‐laneruralmajorcollectororarterialhasaROWwidthof66feet.LowerclassesofroadwayorlowvolumefacilitiesmighthavenarrowerROWswhilemajorhighwaysrequiremoreROW.Inmostcases,urbanstreetsandhighwayshavelessavailableROWthanruralhighways.Ideally,ROWwidthshouldbeuniformalongaroadwaysegment.Inurbanareas,variablewidthsmaybenecessaryduetoexistingdevelopment.Varyingsideslopesandembankmentheights
Section 1 – Chapter 3
Cross‐section and Roadside Elements 1.3‐41
maymakeitdesirabletovaryROWwidthandROWlimitswilllikelyhavetobeadjustedatintersectionsandfreewayinterchanges.OtherspecialROWcontrolsshouldalsobeconsidered: AthorizontalcurvesandintersectionsadditionalROWacquisitionmaybewarranted
toensurethatthenecessarysightdistanceisalwaysavailableinthefuture.
InareaswherethedesiredROWwidthscannotbereasonablyobtained,thedesignerwillhavetoconsidertheadvisabilityofusingsteeperslopes,revisinggrades,orusingsloperetainingtreatments.
Rightofwayshouldbeacquiredandreservedforfutureimprovementssuchasroadwaywideningandinterchangecompletion.
Onsectionsofhighwayadjacenttorailroads,anyencroachmentonrailroadROWshouldbeavoided,wheneverpossible.
Permanentslopeeasementswithmaintenancerightsshouldbeconsideredtominimizepublicownershipofland.
Becausearoadisaninherentpartofacommunity,theengineerneedstopayspecialattentiontoright‐of‐wayimpactonculturalandcommercialfeatures.
Additionalrightofwayisoftenrequiredforwetlandmitigation.
3.9 For Further Information
HighwaySafetyManual,1stEdition,AASHTO2010.
AGuidetoAchievingFlexibilityinHighwayDesign,AASHTO2004.
FlexibilityinHighwayDesign,FHWA,1997.
APolicyonGeometricDesignofHighwaysandStreets,AASHTO,2011.
HighwayCapacityManual,SpecialReportNo.209,TransportationResearchBoard1995.
RoadsideDesignGuide,4thEdition,AASHTO,2011.
AGuideforTransportationLandscapeandEnvironmentalDesign,AASHTO,1991.
GuideforHighOccupancyVehicleFacilities,AASHTO,2004.
CompendiumoftheSafetyEffectivenessofHighwayDesignFeatures,PublicationFHWA‐RD‐91‐044through049(6volumes),1991.
AmericanswithDisabilitiesActHandbook,December1991.
AASHTOGuidefortheDevelopmentofBicycleFacilities,2012.
UrbanBikewayDesignGuide,NACTO,2011.
FHWABicycleCompatibilityIndex,ALevelofServiceConcept,ImplementationManual,PublicationFHWA‐RD‐98‐095,1998.
1.3‐42 Cross‐section and Roadside Elements
AASHTOGuideforthePlanningDesignandOperationofPedestrianFacilities,July2004.
ManualforAssessingSafetyHardware,1stEdition,AASHTO,2009.
ManualonUniformTrafficControlDevices,FederalHighwayAdministration,2009.
TCRPReport19–GuidelinesfortheLocationandDesignofBusStops,1996.