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ENGINEERING CRITERIA MANUAL
Page II
TableofContents
Section1.0 Introduction................................. 6
Section2.0 TrafficControlDevices ............................ 7
Section3.0 AccessControl . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83.1 StateHighways . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .83.2 CityStreets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8
Section4.0 SightDistanceRequirements . . . . . . . . . . . . . . . . . . . . . . . . 94.1 ApproachSpeed.......................................94.2 HorizontalSightDistance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .94.3 VerticalSightDistance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 104.4 IntersectionSightDistance. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 104.5 ResidentialDrivewaySightDistance . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Section5.0 IntersectionSpacing. . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
Section6.0 AccessDesign ...............................126.1 AccessGrades . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .126.2 AccessDesign . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .126.3 InternalCirculation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
Section7.0 Medians .................................13
Section8.0 Channelization. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 158.1 TurnChannelApproaches . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .158.2 TurnLaneDesign . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .16
Section9.0 GradeatIntersections . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
Section10.0 AngleofIntersection,MinimumIntersectionCurbRadii...........21
Section11.0 InstallationofCurbs,Mid-blockWalkways,PedestrianRamps,andGuardrails 2211.1 TypesofCurb. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2211.2 Mid-BlockWalkways . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2211.3 PedestrianRamps. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2211.4 Guardrails. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .22
Section12.0 Cul-De-SacRegulations . . . . . . . . . . . . . . . . . . . . . . . . . . 23
Section13.0 PrivateStreets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
Section14.0 StreetNames. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2514.1 Approval . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2514.2 DuplicationofNames. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2514.3 ContinuityofNames . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2514.4 SmallCul-de-sacs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2514.5 StreetNameDesignations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .25
Section15.0 RoadwayStandards . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2615.1 StandardsforFreeways. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
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15.2 StandardsforExpressways. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2715.3 StandardsforPrincipalArterialStreets. . . . . . . . . . . . . . . . . . . . . . . . . . .2815.4 StandardsforMinorArterialStreets. . . . . . . . . . . . . . . . . . . . . . . . . . . .3015.5 StandardsforCollectorStreets. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3115.6 StandardsforResidentialStreets..............................3315.7 StandardsforMinorResidentialStreets . . . . . . . . . . . . . . . . . . . . . . . . . .3415.8 StandardsforIndustrialStreets. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3615.9 StandardsforAlleys. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .37
Section16.0 TableofTrafficEngineeringDesignStandards . . . . . . . . . . . . . . . 39
Section17.0 TransitServices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
Section18.0 Definitions,Abbreviations,andAcronyms. . . . . . . . . . . . . . . . . 43
Section19.0 References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
AppendixA. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
SectionTrafficImpactStudyGuidelinesforDevelopmentProjects . . . . . . . . . . . . . 45
AppendixB . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53
SectionStandardUtilityLocations.............................53
AppendixC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54
SectionRoundaboutDesignGuide . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54
Section1.0 IntroductiontoRoundaboutDesignGuide. . . . . . . . . . . . . . . . . 54
Section2.0 GeneralDesignCriteria. . . . . . . . . . . . . . . . . . . . . . . . . . 552.1 AppropriateRoadways/Locations. . . . . . . . . . . . . . . . . . . . . . . . . . . . 552.2 ApproachandCirculatorySpeeds. . . . . . . . . . . . . . . . . . . . . . . . . . . . .552.3 DesignVehicle. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .562.4 Pedestrian/Bicycles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .572.5 DesignSoftware ......................................572.6 Utilities&Drainage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .582.7 Landscaping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 582.8 Other . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .58
Section3.0 Specific/GeometricDesignElements. . . . . . . . . . . . . . . . . . . . 603.1 ApproachRoadway . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .603.2 CirculatingRoadway. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613.3 SightDistance. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .613.4 SplitterIslands. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .623.5 CentralIsland. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .623.6 SigningandMarking. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 633.7 LandscapingDesignElements. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .64
Section4.0 Definitions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74
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FiguresFigure1 SightDistance. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9Figure2 LowDensityResidentialDriveways. . . . . . . . . . . . . . . . . . . . . .11Figure3 MultiFamilyResidentialDrivewaysandCommercialAccesses . . . . . . . . .11Figure4 Right-In,Right-out,Left-inMedianDesign. . . . . . . . . . . . . . . . . . .13Figure5 MedianDesigntoRestrictExitingLeftTurns . . . . . . . . . . . . . . . . . .14Figure6 MedianOpeningsforIntersectionsandMedianIslandEnds . . . . . . . . . .14Figure7 GuidetoBasicExclusiveTurnLaneElements. . . . . . . . . . . . . . . . . .16Figure8 DesignElementsforLeftandRightTurnLanes. . . . . . . . . . . . . . . . .17Figure9 Cul-De-SacRequirements . . . . . . . . . . . . . . . . . . . . . . . . . . .23Figure10 CrossSectionsforPrincipalArterialStreet(TypeI) ................29Figure11 TypeII(6-Lane,142’Right-of-Way) . . . . . . . . . . . . . . . . . . . . . . .30Figure12 MinorArterial . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .31Figure13 Collector(WithParking). . . . . . . . . . . . . . . . . . . . . . . . . . . .32Figure14 Collector(WithoutParking) . . . . . . . . . . . . . . . . . . . . . . . . . .32Figure15 Residential(Local)Streets(DetachedSidewalk) . . . . . . . . . . . . . . . . .34Figure16 Residential(Local)Streets(AttachedSidewalk) . . . . . . . . . . . . . . . . .34Figure17 MinorResidential(Local)Streets(DetachedSidewalk) ..............35Figure18 MinorResidential(Local)Streets(AttachedSidewalk) . . . . . . . . . . . . . .35Figure19 IndustrialStreets................................36Figure20 ResidentialAlleys. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .38Figure21 CommercialAlleys. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .38
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Tables
Table1 SightDistance. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10
Table2 SummaryofExclusiveTurnLaneRequirements . . . . . . . . . . . . . . . .15
Table3 RequiredDecelerationLaneandTaperLengths . . . . . . . . . . . . . . . .18
Table4 DecelerationLaneGradeAdjustmentFactors. . . . . . . . . . . . . . . . .18
Table5 DesignCriteriaforAccelerationLanes . . . . . . . . . . . . . . . . . . . . .19
Table6 GradeAdjustmentFactorsforAccelerationLanes . . . . . . . . . . . . . . .19
Table7 RedirectTapersforThroughLanes. . . . . . . . . . . . . . . . . . . . . . .20
Table8 RequiredStorageLengthsforStop-ControlledIntersections . . . . . . . . . .20
Table9 MinimumIntersectionCurbRadii. . . . . . . . . . . . . . . . . . . . . . .21
Table10 TrafficEngineeringDesignStandards(Freeways,ExpresswaysandArterials) . . . . . . . . . . . . . . . . . . . . .39
Table11 TrafficEngineeringDesignStandards(Collector,Residential[Local],PublicAlley,Industrial,andCommercialFrontage) . . . . . . . . . . . . . . . . . . . . .40
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1.0 Introduction
Thismanualprovidesrecommendedstandardsfortrafficrelateddesignissues.TheyareintendedtosupplementtheEngineeringCriteriaManualoftheCityofColoradoSpringsandareaimedatensuringconsistentengineeringdesignpracticesandprovidinganadequatecorridorfortheplacementofpublicstreetinfrastructurewithinthecitylimits.CityEngineeringwilladheretothesepoliciesascloselyaspossiblewhenreviewingroadwaydesignproposalswhetheritisfornewdevelopmentorforaCityfundedproject.TheCityEngineerandhisauthorizedrepresentativesmaygrantvariancesfromanyofthesepolicieswhentherearepracticaldifficultiesthatpreventtheapplicationofapolicyandifthegrantingofsuchvariancewillnotbedetrimentaltothepublicsafety.FlexibilitywillbeusedintheCity’sinterpretationandapplicationoftheserequirementswhensuitablejustificationisprovidedforalternativedesignsolutions.
AlternativedesignstandardsmayapplyforprojectsthatinvolveTraditionalNeighborhoodDesign,MixedUseDevelopment,SmallLotPUDDevelopment,TrafficCalmingDesign,andHillsideDesign.TheappropriateCitymanualsforprojectsinvolvingthesedesignsshouldbeconsulted.Whenthetermspeedisusedinthismanualitreferstothepostedspeedofthestreet.Designspeedistypically5mphabovethepostedspeed.
TrafficImpactStudies(SeeAppendixA)anddesignplansforstreetsinnewdevelopmentsandredevelopmentprojectsmustbesubmittedtotheEngineeringDevelopmentReviewDivisionofCityEngineering.TrafficStudiesandplansforCityfundedprojectsmustbesubmittedtoCityEngineering’sRoadwayTeam.SometrafficstudiesarecommissionedbythetransportationsectionofEconomicDevelopment’sComprehensivePlanninggroupandshouldbesubmitteddirectlytothem.
Thefiguresprovidedinthismanualareillustrativeonly.Theyarenottoscaleandarenotintendedtobeusedfor/asengineeringdesign.Forsimplicity,somedesignelementssuchassidewalksorbicyclelaneshavebeenleftoffcertainfigures.
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2.0 Traffic Control Devices
ThetypeandlocationoftrafficcontroldevicesusedoncitystreetsmustbeapprovedbyCityEngineering.Trafficsignalsshouldbeusedwherenecessary,butalternatetrafficcontrolsuchasstopsignsorroundaboutswillbeconsideredfirst.
Whenitcanbeshownthataparticularzoningaction,masterplan,ordevelopmentplanimpactsthestreetsystemtoapointthatatrafficsignaliswarrantedaccordingtoManualonUniformTrafficControlDevices(MUTCD)andapprovedbyCityEngineering,thedevelopershallberesponsibleforalloraportionofthesignalinstallation.Formoreinformationaboutadeveloper’sresponsibilityfortrafficsignalparticipationandfinancialassurancespleasereferenceSection10.5oftheSubdivisionPolicyManual.
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3.0 Access Control
3.1 State Highways
AccessontoStateHighwaysintheCitywillbesubjecttostipulationscontainedintheStateofColorado,StateHighwayAccessCode.AllaccessestoandfromStateHighwayswillrequireapermitwhichmustbeobtainedfromandapprovedbytheColoradoDepartmentofTransportation(CDOT).AllaccessesfromnewdevelopmentsontoStateHighwaysrequireCityEngineeringreview.
3.2 City Streets
Thedesign,number,andlocationofaccessdrivesshallbeapprovedbyCityEngineering.Thenumberofaccessdrivesshallbeabalancetoallowforefficienttrafficflowwhileprovidingadequateaccesstoprivateproperty.CityEngineeringrealizesthattheadequacyofaccesspointsisacriticalissueintheeconomicsuccessofcommercialdevelopmentsandredevelopmentareas.Thefollowinginformationispresentedasageneralguidelineforthelocationofaccessdrivestopublicstreets.
1. Provisions of Access–Propertyownershavetherightofreasonableaccesstothepublicstreetsystem.ThismanualprovidesstandardsforapprovingaccesstotheCityStreetsystembasedonthestreetclassification.Ifapropertycannotbeservedbyanyaccesspointmeetingthesestandards,CityEngineeringshalldesignateaccesspoint(s)basedontrafficsafety;operationalneeds,economicdevelopment,andconformancetoasmuchoftherequirementsoftheseguidelinesaspossible.Accessdrivesshallnotbeapprovedforparkingorloadingareasthatrequirebackingmovementsinapublicstreetright-of-wayexceptforsinglefamilyorduplexresidentialusesonlocalstreets.
2. Restriction of Turning Movements–Wherenecessaryforthesafeandefficientmovementoftraffic,CityEngineeringmayrequireaccessdrivestoprovideforonlylimitedturningmovements(e.g.,rightturnsonly).
3. Number of Access Drives–OneaccessdriveperpropertyownershipshallbepermittedwhichmaybejointlysharedwithadjacentpropertiesunlessasiteplanorTrafficImpactStudy(TIS)approvedbyCityEngineeringshowsthatadditionalaccessdrivesarerequiredtoadequatelyhandledrivewayvolumesandwillnotbedetrimentaltotrafficflow.PropertieswithextensivestreetfrontagemaybegrantedmorethanonepointofaccessinaccordancewithsafetrafficengineeringdesignandwidthsasreferredtoinSection 5.0andincompliancewithmajorstreetaccesscontrolstandards.
4. Sight Distance Requirements–TheminimumsightdistanceshallbeprovidedatallaccessdrivesasshowninSection 4.0.
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4.0 Sight Distance Requirements
Sightdistanceisoneofthemostimportantdesignissuestobeconsideredfortrafficsafety.Beforeanyaccesstoacollectororhigherstreetclassificationisapproved,CityEngineeringwillreviewdesignplansforadequatesightdistanceatintersections.
4.1 Approach Speed
Thespeedusedfordeterminingminimumenteringsightdistancerequirementsisassumedtobethepostedspeedlimit.IfCityEngineeringhasreasontobelievethattheoperatingspeedissubstantiallydifferentthanthepostedspeedtheycanrequestthatthe85thpercentilespeedbeusedtodeterminesightdistance.Inthecaseofanewfacility,thedesignspeedshouldbeused.Formodifiedcul-de-sacs(knuckles,eyebrows,teeturnarounds,etc)sightdistancemustbeprovidedbasedontheexpectedoperatingspeedofthelocation.
4.2 Horizontal Sight Distance
Thedistanceshallbemeasuredfromthecenteroftheapproachlaneatapointfifteenfeet(15’)behindtheflowlineoftheintersectingstreettothecenterofthenearestapproachingtrafficlaneforeachdirection.RefertoFigure 1.
Figure 1 Sight Distance
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4.3 Vertical Sight Distance
Thedistanceshallbemeasuredtoallowadriverattheheightof3.5feettoseeanobject2.0feetabovetheroadwayattheminimumsightdistancedescribedbelow.Forfurtherdetails,refertoAPolicyonGeometricDesignofHighwaysandStreets,AmericanAssociationofStateHighwayandTransportationOfficials(AASHTO)2004,Chapter3,“ElementsofDesign/VerticalCurves.”
4.4 Intersection Sight Distance
Theminimumsightdistanceatallpublicandprivatestreetintersectionsoraccesses,anddrivewaystocollectorstreetsorgreatershallfollowtheguidelinesbelow.AtnotimeshalltheminimumsightdistancebelessthantheAASHTOstoppingsightdistance.
Table 1 Sight Distance
Speed of Thru Roadway (MPH)
Minimum Sight Distance for Stopped
Vehicle (FT)
Grade Correction Distance (FT)
Upgrade To: Downgrade To:
3% 6% 9% 3% 6% 9%
15 80 0 -5 -10 +5 +10 +20
20 115 0 -5 -10 +5 +10 +20
25 280 0 -10 -20 +10 +20 +30
30 335 0 -10 -20 +10 +20 +30
35 390 -10 -15 -25 +10 +25 +40
40 445 -10 -20 -30 +10 +30 +50
45 500 -15 -25 -30 +15 +40 +60
50 555 -20 -35 -45 +20 +50 +70
4.5 Residential Driveway Sight Distance
Theprevioussightdistancecriteriadoesnotapplytosingle-familyback-outdriveswheresightdistancewillbeprovidedbasedonlocationofthedriverseyewhencommencingtheback-outmaneuver.Toprovidesightdistancefromdrivewaystoboththestreetandsidewalkitemstallerthanthree(3)feetshouldnotbeplacedwithinfive(5)feetoftheedgeofdriveway.Thisrestrictionextendsfromtheedgeofstreettoten(10)feetbehindthebackofsidewalk.Thisrestrictionincludessolidsurfacefencesandlargeshrubs.Utilitypoles,firehydrants,openlyspacedtrees,andtrafficdevicesareallowableifvisualobstructionisminimal.
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5.0 Intersection Spacing
EachhighdensityresidentialandcommercialaccessshouldbeseparatedataminimumbyadistanceequaltothestoppingsightdistancedescribedintheTable of Traffic Engineering Design Standards inSection 15.Whendecelerationoraccelerationlanesareorwillberequired,itisdesirablethattheaccessesbeseparatedbyasufficientdistancesothatthespeedchangelanesincludingtransitiontapersdonotoverlap.Accessshouldnotbeplannedwithintheacceleration,deceleration,taperorstoragelengthsofotheraccesspointsorintersections.RefertoFigures 2 and 3. Thecenterofcommercial/multi-familyaccessesnotinalignmentwillnormallybeoffsetaminimumofonehundredfiftyfeet(150’)onalllocalandcollectorstreets;threehundredfeet(300’)onallarterials.Theoff-setofintersectionsmayneedtobeadjustedtoaccommodateadequateleftturnstoragelength.
Figure 2 Low Density Residential Driveways
Figure 3 Multi Family Residential Driveways and Commercial Accesses
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6.0 Access Design
6.1 Access Grades
CommercialorhighdensityresidentialaccessthatmaybesignalizedinthefutureshallmeetthegradestandardsforsignalizedCitystreets(See9.0).Nonsignalizedcommercialorhighdensityresidentialaccessdrivesshouldprovideagradeof4%orlessatthestreetapproach.
6.2 Access Design
Commercialorhighdensityresidentialaccessshallbeaminimumof24feetinwidth.Widthsgreaterthan36feetmustbeapprovedbyCityEngineering.Drivewaysshallhaveaminimumcurbreturnof15feet.Drivewaysintersectingprincipalarterialsshallhaveaminimumcurbreturnof20feet.
6.3 Internal Circulation
PrivateinternaltrafficcirculationoncommercialsitesisreviewedbyLandUseReviewatthetimeofdevelopmentplan.EDRDreviewsaccessesontothepublicstreetandrelatedissues,butEDRDdoesnotreviewprivateinternaltrafficcirculation.Asneeded,EDRDprovidessupporttotheLURplannerorcanmediatebetweenLURandanapplicantaboutinternalcirculationissuesifrequested.Theonlyexceptionsareschoolsites.CityEngineeringreviewsinternalcirculationonschoolsites.CityEngineeringsupportsthedevelopmentplancriteriainSection7.5.502oftheCodewhichasks,“Havetheinternaldrives,externalaccesspoints,andpedestrianwalkwaysbeendesignedtoprovidesafeandconvenientvehicularandpedestrianaccesswithintheproject?”
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7.0 Medians
Raisedmediansshallberequiredonprincipalarterialsandmaybeallowedonlocals,collectorsandminorarterials.AlldesignsaresubjecttoreviewandapprovalbyCityEngineering.RefertoFigures 4, 5, and 6.
IfrequiredbyCityEngineeringorrequestedbythedeveloper,allraisedmediansshallbeaminimumofseventeenfeet(17’)inwidth(faceofcurbtofaceofcurb).Alongprincipalarterialdesignsofsixlanesormore,themedianwidthshallbenolessthantwenty-eightfeet(28’)faceofcurbtofaceofcurb.OpeningsinexistingmediansmustbeapprovedbyCityEngineering.
Theuseof3/4intersectionmediandesignandchannelized“T”intersectionsrequireamedianwiderthantheminimum17’median.A22’medianwidthissuggestedwherethesedesignsareanticipated.
Medianopeningsvoidofleftturnlanesshallbedesignedinthebulletnoseconfiguration,withallowancesforpedestriancrossings.Leftturnlanesshallbedesignedtoaccommodatethe20-yearleftturnvolumebasedonthe95%queueoftheleftturn.
Figure 4 Right-In, Right-out, Left-in Median Design
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Figure 5 Median Design to Restrict Exiting Left Turns
Figure 6 Median Openings for Intersections and Median Island Ends
Thissketchisforathreelegintersection.Iftheintersectionhasfourlegs,theleftsidewillalsohaveanauxiliarylaneforleftturns,andthemedianontheleftsidewillhavethesameconfigurationastheoneontherightsiderotated180degrees.
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8.0 Channelization
Leftorrightturnlanesmayberequiredalongcollectororarterialroadwaysifdeemednecessaryforthesafeandefficientflowoftraffic.Thedesignofsuchlanesshallbebasedon20-yeartrafficprojectionsforthatroadway.Thedesignwillconsistofadequatetaperlengths,decelerationoraccelerationlength,storagecapacity,andturninggeometrics.Theinstallationcostswillberequiredofthedeveloperifitisdeterminedthatamajorproportionofitsneediscreatedbytheimpactofaproposeddevelopment.
8.1 Turn Channel Approaches1. Exclusive Turn Lane Requirements - Exclusiveleftturn,rightturn,andacceleration
lanesshallbeprovidedwhereverleftturn,rightturn,oraccelerationlanesarespecifiedasbeingneededbyanapprovedTrafficImpactStudy(TIS).TherequirementsforuseofturnlanesareshowninTable 2.
Table 2 Summary of Exclusive Turn Lane Requirements
Left Turn Lane Left Turn Acceleration Lane Right Turn Lane Right Turn
Acceleration Lane
Expr
essw
ay Aleftturnlaneisrequiredforanyaccessthatallowsleftturningressmovement.
Aleftturnaccelerationlanemayberequiredifthedesignwouldbeabenefittothesafetyandoperationoftheroadway.
Arightturnlaneisrequiredforanyaccesswithaprojectedpeakhourrightturningressturningvolumeof10VPHorgreater.
Arightturnaccelerationlaneisrequiredforanyunsignalizedaccesswithaprojectedpeakhourrightturnegressturningvolumeof10VPHorgreaterforroadwayswithpostedspeedsof50mphorgreater.
Prin
cipa
l Art
eria
l Aleftturnlaneisrequiredforanaccesswithaprojectedpeakhourleftingressturningvolumeof10VPHorgreater.
Aleftturnaccelerationlanemayberequiredifitwouldbeabenefittothesafetyandoperationoftheroadway.
Arightturnlaneisrequiredforanyaccesswithaprojectedpeakhourrightingressturningvolumeof25VPHorgreater.
Arightturnaccelerationlaneisnotrequired.
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Left Turn Lane Left Turn Acceleration Lane Right Turn Lane Right Turn
Acceleration Lane
Min
or A
rter
ial Aleftturnlane
isrequiredforanyaccesswithaprojectedpeakhouringressturningvolumeof25VPHorgreater.
Anaccelerationlaneisgenerallynotrequired.
Arightturnlaneisrequiredforanyaccesswithaprojectedpeakhourrightturningvolumeof50VPHorgreater.
Anaccelerationlaneisnotrequired.
Note:Turnlanerequirementsonlowerclassificationroadstobedeterminedonacase-by-casebasisdependingonrecommendationsfromatrafficimpactstudyandapprovedbyCityEngineering.
2. Lane Shifts or Drops Required - Laneshiftsordropsshallbeprovidedwhereverredirectionoftrafficisspecifiedasbeingneededbyanapprovedsigningandstripingplan.
3. Conflicts between Exclusive Turn Lanes-Wheretwointersectionshaveexclusiveturnlanesthatoverlap,ortheendingpointsoftheexclusiveturnlaneshavelessthan300feetorone-halftheirlengthofseparation(whicheverisshorter)andasignificantstructureortopographicalfeaturedoesnotprecludewidening,acontinuousexclusiveturnlaneshallbeestablishedbetweentheintersectionstoimproveroadwayconsistency,safety,andtomaintainedgeofpavementcontinuity.
Ifrestrictivetopographyallowsonlyoneexclusiveturnlane,normallyaleftturndecelerationlaneisgivenfirstpriority.Wherethetravellanesmustberedirectedduetotheadditionofaleftturnlane,apavementoverlayisrequired.
8.2 Turn Lane Design
Turnlanestypicallyconsistofacombinationofseveralcomponents(i.e.tapers,lanelength,andstorage).Theuseanddesignofthesecomponentsvariesbasedonthetypeofaccess,roadwayclassification,andsite-specificconditions.Figures 7 and 8 presentagraphicalguidetobasicexclusiveturnlaneelements.
Figure 7 Guide to Basic Exclusive Turn Lane Elements
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*Additionallengthmayberequiredforstorageturningvehiclesatpotentialcontrolledintersections.
Figure 8 Design Elements for Left and Right Turn Lanes
NOTE:Thisfullintersectiondesignisasymmetrical.LeftTurnandThruLanesmustalignwiththeoppositeintersectionapproach.
1. Deceleration/Acceleration Lanes
a. Deceleration LengthThebasisfordesigningadecelerationlaneandtaperistoprovidesufficientlengthforavehicletodecelerateandbrakeentirelyoutsidethethroughtrafficlanes.Table 3providestherequireddecelerationlaneandtaperdesignlengthsbyspeed.Decelerationlanelengthsshallbeadjustedforagradeof3%ormoreusingthefactorsinTable 4.Therequiredlengthallowsamotoristtodecelerateingearforatleast3secondsfollowedbysafebrakingtoacompletestop.Whendesignconstraintsnecessitatereducingpartofthedecelerationlength,thetapershallbereducedfirstandthenthedecelerationlength.AllreductionsindecelerationlanelengthmustbeapprovedbyCityEngineering.
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Table 3 Required Deceleration Lane and Taper Lengths
Speed (MPH) Lane Length (feet) Approach Taper (feet) Total Length (feet)
25 115 120 235
30 115 120 235
35 120 140 260
40 155 160 315
45 200 180 380
50 235 200 435
60 290 240 530
70 SpecialDesign SpecialDesign SpecialDesign
Table 4 Deceleration Lane Grade Adjustment Factors
Roadway Grade Factors
Upgrade
3%to4.9% 0.90
5%to7.5% 0.80
Downgrade
3%to4.9% 1.20
5%to7.5% 1.35
b. Bay Tapers Forarterialstreetsthestraightlinetapershouldbereplacedwithabaytaper(asymmetricalreversecurve).Thebaytapershouldbeatleast1/3thelengthoftheappropriatestraightlinetaper.Theturn-offcurveshouldbeapproximatelytwicethesizeofthesecondcurve.AdesigndetailforabaytaperisavailableinAASHTO,Exhibit9-95.
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c. Acceleration LengthThebasisfordesigninganaccelerationlaneandtransitiontaperistoprovidesufficientlengthforavehicletoacceleratetotheappropriatespeedandmergeintothethroughtrafficlaneswithoutdisruptingtrafficflow.Table 5providestherequiredaccelerationlaneandtransitiontaperdesignlengthsbyspeed.AccelerationlanelengthsinTable 5shallbeadjustedforagradeof3%ormoreusingthefactorsinTable 6.Wheredesignconstraintsnecessitatereducingpartoftheaccelerationlane,thetaperlengthshouldbereducedfirst.AllreductionstoaccelerationlanesmustbeapprovedbyCityEngineering.
Table 5 Design Criteria for Acceleration Lanes
Speed (MPH) Lane Length (feet) Straight-line Taper (feet)
40 236 12:1
45 388 13.5:1
50 580 15:1
60 930 20:1
70 1290 25:1
Table 6 Grade Adjustment Factors for Acceleration Lanes
Speed (MPH)
40 to 50 60 70
Upgrade
3to4.9% 1.3 1.5 1.7
5to7.5% 1.5 2.0 2.5
Downgrade
3to4.9% 0.7 0.65 0.6
5to7.5% 0.6 0.55 0.5
d. Redirect TapersWhenconstructingaroadwaythatwilldirectlyconnectwithanexistingroadwayofadifferentwidth,itisnecessarytoinstallaredirecttaperbetweenthetwo.Redirecttapersshallbeusedwhereanexclusiveturnlane(droplane),medianorotherredirectionofvehiclesisnecessaryandwhereredirectionoftheflowoftrafficisnecessarytoaccommodatetheexclusiveturnlaneormedian.RedirecttapersshallbeinstalledinconformancewithTable 7.Theseratiosarenottobeusedinthedesignofacceleration,deceleration,orstoragelanes.Iftheredirecttaperwouldresultinahorizontalcurvedesigndeficiencyforthethroughmovement,thehorizontalcurveshallbecorrected.Redirecttapershouldbedesignedasstraighttaperswiththebeginningandendingpointsrounded.
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Table 7 Redirect Tapers for Through Lanes
Speed (MPH) 20 25 30 35 40 45 50 55 60 65 70
Straight Taper Ratio
10:1 12.5:1 15:1 20:1 25:1 30:1 45:1 50:1 55:1 60:1 65:1
2. Storage Lengths for left turn lanes
Thelengthofaleftturnlaneforallcitystreets,otherthanexpressways,shallbebasedonprovidingadequatestoragelength.Decelerationlengthisnottobeincludedfortheleftturnlanedesign.
Thebasisfordesigningthelengthofrequiredstorageistoprovidesufficientlengthforvehiclestoqueuewithinthelanewithoutaffectingothermovements.Table 8providestherequiredstoragelengthsforstop-controlledintersections.IfCityEngineeringdeterminesthatmeetingtherequiredstoragelengthisimpracticalorresultsinanunsafecondition,theminimumstoragelengthshallbebasedonthemeanarrivalrate,butinnocaseshalltheminimumstoragelengthbelessthan50feet.Onexpressways,leftturnlanesshallbedesignedtoincludethedecelerationlengthandstoragelength.
Table 8 Required Storage Lengths for Stop-Controlled Intersections
DHV (VPH) <60 61-120 121-180 181-250 >250
Storage Length (feet) 50-75 100 150 200 250ormore
Note:Atsignalizedintersectionstheleftturnlanestoragelengthshallbebasedonthe95%queue.
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9.0 Grade at Intersections
Flatgradesarepreferredinalldirectionsfromanintersection,butinnocaseshallgradesexceedfourpercent(4%)foradistanceofatleastfifty(50)feetfromallcurbintersectionsunlessphysicalfactorswarrantspecialconsideration.Atsignalizedintersections(orintersectionsexpectedtobesignalizedinthefuture),twopercent(2%)maximumgradesarerequiredfortwohundred(200)feetineachdirectionontheapproachasmeasuredfromthecrossstreetcurbline.RefertoAASHTOStandardsfordesignofcrestandsagverticalcurves.
10.0 Angle of Intersection, Minimum Intersection Curb Radii
Proposedstreetsanddrivewaysshallintersectoneanotheratninetydegree(90°)anglesorasclosetoninetydegreesasisfeasible;nolessthaneightydegrees(80°).Thenumberofintersectionsalongarterialsshallnormallynotbespacedlessthanone-quartermile.(Apairofoffset“T”intersectionsshallbetreatedasoneintersectionforquartermilespacingpurposes).Intersectionsoflocalstreetswitharterialsshouldbe“T”intersectionstoreducethenumberofconflictingmovementsattheseintersections.When“T”intersectionsareused,thecenterlinesofthestreetsnotinalignmentshallnormallybeoffsetaminimumofonehundredandfiftyfeet(150’)onlocalstreetsandthreehundredfeet(300’)oncommerciallocals,collectors,andarterials,unlessanacceptedTISjustifiesasmallerseparation.Onarterialstreets,iftheleftturnstoragefortwo“T”intersectionsoverlap,theminimumspacingshallbeincreasedtoaccommodatetheleftturnqueues.Aminimumof100’tangentpriortobeginningofcurvemeasuredfromthecenterlineoftheintersectedstreetshallbemaintainedforallresidentialstreetintersectionsalongacollectorstreet.Atstreetintersections,theminimumcurbradiiforstandardstreetsareillustratedinTable 9.Streetintersectionswithnon-standardcrosssectionsornotatninetydegree(90)angleswillrequiretruckturninganalysisforboththewheelbaseandtheoverhangpath.ThetruckturninganalysisshallbesubmittedtoCityEngineeringforreview.Waiversoftheminimumcurbreturnradiiwillbeconsideredonacase-by-casebasiswithsufficientjustificationandinspecialzonedistricts(TND,MixedUse,etc.)
Table 9 Minimum Intersection Curb Radii
Type of Intersection Curb Radii
Local–Local 15’
Local–Collector 20’
Collector–Collector 25’
Local–Arterial 25’
Collector–Arterial 30’
Arterial–Arterial 40’
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11.0 Installation of Curbs, Mid-block Walkways, Pedestrian Ramps, and Guardrails
11.1 Types of Curb
CurbandgutterisrequiredonallCitystreetsinaccordancewithSection7.7.704oftheCityCode.StandardType1,8”verticalcurbandgutterorequivalent6”curbmustbeusedonallCollectors,Major,andMinorArterials.RampcurbmaybeusedonresidentialstreetswhendrainageconsiderationswarrantitsusesubjecttotheapprovaloftheCityEngineer.Rampcurbshallnotbeapprovedabuttingmulti-family,commercial,industrial,parkorschoollanduses.Inallcasesthesamecurbtypeshallbeusedonbothsidesofthestreet.
Streetswithoutcurbswillbeconsideredonacase-by-casebasisiftheproposeddevelopmentisdesignedasaLowImpactDevelopment(LID)anduniquestreetcrosssectionshelpachievethedesiredgoalofincreasedstormwaterinfiltration.
11.2 Mid-Block Walkways
CityEngineeringmayrequireaconcretemid-blockwalkway,notlessthansix(6)feetinwidth,onlocalandcollectorstreetswhenitisdeemednecessarytoprovideaccesstoschools,shoppingcenters,transportationfacilities,orothercommunityfacilitiesandservices.
11.3 Pedestrian Ramps
PedestrianrampsshallbeinstalledasrequiredbyCityEngineeringperCityofColoradoSpringsPedestrianRampdesigndetailascontainedintheCityofColoradoSpringsCityEngineeringStandardSpecificationsasrequiredbyOrdinance(7.7.704-E3).
11.4 Guardrails
GuardrailsshallbeinstalledasrequiredbyCityEngineeringperAASHTOwarrantsandshallcomplywithAASHTOdesignguidelines.
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12.0 Cul-De-Sac Regulations
Thedesignandoveralllengthofacul-de-sacshallbedeterminedbytopography,typeofdevelopment,proposeddensity,andotherphysicalfactorswhichmaywarrantspecialconsideration.Theoveralllengthofacul-de-sacstreetnormallyshallnotexceedfivehundredfeet(500’).Thecul-de-sacwillgenerallybedesignedwithaturn-aroundright-of-wayradiusoffiftyfeet(50’)inresidentialdevelopmentandsixtyfeet(60’)inindustrialdevelopmentandwitharadiustocurbflowlineofforty-twofeet(42’)inresidentialdevelopmentandfiftyfeet(50’)inindustrialdevelopment,seeFigure9.Alternatecul-de-sacdesigngeometrywillbeconsideredonacase-by-casebasiswithsufficientjustificationwhendesignconstraintsexistorwhenLIDorotherspecialzonedistrictgoalsarebeingincorporatedinthedesign.
Modifiedcul-de-sacs(knuckles,eyebrows,teeturn-around,etc.)canbeusedonlocalstreetsaslongassightdistancecriteriacontainedinsection4.2ismet.Forexample,aknuckledesignona90degree(90o)curve wouldneedtoprovideadequatesightdistancebasedona15mphdesignsincethatwouldbetheexpectedoperatingspeedofavehiclemakinga90degree(90o)turn.Sightdistancecanbeprotectedbyadditionalright-of-wayorprovidinglegalrestrictionsforlandscaping,buildings,fences,andotherobjectsthatwouldblockadriver’sview.Anyrestrictionsforsightdistancepurposesshallbeidentifiedonthedevelopmentplan.Allcul-de-sacdesignsmustmeetFireCodeprovisionsforcul-de-sacs.
Figure 9 Cul-De-Sac Requirements
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13.0 Private Streets
PrivatestreetsareacceptableinnewdevelopmentatthediscretionofthedeveloperandsubjecttoCityreview.Section7.7.704(C)oftheCityCodestatesthatthelocationanddesignofprivatestreetsissubjecttothereviewandapprovalofTrafficEngineering[administeredbytheEngineeringDevelopmentReviewDivision(EDRD)]andtheFireDepartment.ThisreviewisdoneatthetimeoftheDevelopmentPlan.EDRDapprovalisnotrequiredonthedesignplansandprofilesforprivatestreetsexceptforintersectionswithapublicstreet.Gatedresidentialcommunitiesmustuseprivatestreets.Thedevelopermustmakefinancialarrangementsfortheperpetualownershipandmaintenanceofprivatestreets(i.e.ahomeowners’association)toincludelife-cyclerepairandreplacementofthefacilities.EDRDrequiresthatthereceptionnumberoftheassociatedrecordeddocumentsbereferencedonthefinalplat.Citypolicyrequiresthatprivatestreetsbedesignedstructurally(i.e.pavementthickness)tomeetorexceedCitystandardsandspecifications.SigningandstripingofprivatestreetsmustbeconsistentwiththeManualforUniformTrafficControlDevices(MUTCD).
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14.0 Street Names
14.1 Approval
StreetnamesandnumberingshallbesubjecttotheapprovaloftheRegionalBuildingDepartment,PoliceDepartment,FireDepartment(911),andCityEngineering.Residentialstreetnamesshallbelimitedto10letters(refertotheAddressingOrdinance7.7.704-D).
14.2 Duplication of Names
StreetnamesshallnotduplicatenorbetoocloselyapproximatedphoneticallytoanynameofanexistingCityorCountystreetinElPasoCounty.
14.3 Continuity of Names
Anystreetwhichisacontinuationoranapproximateorlogicalcontinuationofanexistingdedicatedstreetshallbearthesamenameastheexistingstreet.
14.4 Small Cul-de-sacs
Smallcul-de-sacswhichhavelessthanfiveinteriorlotsmaybeomittedfornamepurposeswhenthehousenumbersarecontinuouswiththoseofthestreettowhichtheyhaveaccess.
14.5 Street Name Designations
Streetnamedesignationsshallbeusedasfollows:
1. Boulevard or Parkway–ShallbereservedforroadwaysdesignatedontheIntermodalTransportationPlanhavingamediandividerofsufficientsizetoallowforlandscaping.(Example:ResearchParkway)
2. Avenue or Road–ShallbereservedforstreetsofsubstantialcontinuitysuchasprimaryorsecondarylinksoftheIntermodalTransportationPlan.
3. Street or Drive –Shallbereservedforstreetsoflesscontinuitysuchaslocalorcollectorstreets.
4. Court, Place, Circle, Way, Terrace or Lane–Shallbereservedforstreetswithnocontinuitywhatsoever,andcontainsmallnumbersoflots;usuallycul-de-sacs
5. Grove, Heights, Point, or View shallbeusedforprivatestreets.PrivatestreetsshallbesignedbythedeveloperperCityspecificationswithbrownbackground/whiteletters.
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15.0 Roadway Standards
TheCityofColoradoSpringsusesaroadwayhierarchytoprovidesafeandcontinuoustravelandaccess.Afunctionalclassificationofroadwaysprovidesthehierarchyneededtoaccomplishthisgoal.Streetsaredividedintocategorieswithdifferentdesigncriteriatomaintainandprotecttheprimarypurposeoftheroadway.Theroadwaystandardsprovidedinthismanualaretoprovideastandardforstreetsections,butvariancestothesesectionscanberequested.Roadwayreductionswillbeconsideredifalessercross-sectioncanbeshowntoadequatelyaccommodatetheprojectedlong-termtrafficvolumes.Thecross-sectionsprovidedinthismanualareillustrativeonly.Therearenottoscaleandarenotintendedtobeusedasengineeringdesign.Forsimplicity,somedesignelementssuchassidewalksorbicyclelaneshavebeenleftoffcertainfigures.Thefunctionalclassificationsaredescribedbelow:
15.1 Standards for Freeways1. Function - Freewayspermitrapidandunimpededmovementoftrafficthroughand
aroundtheCity
2. Right-of-Way Widths-420feet,minimumwithfrontageroads,332feet,minimumwithoutfrontageroads
3. Number of Moving Lanes - Sixtoeightlanes
4. Access Conditions
a. Accessshallbegradeseparated
b. Interchangesshallbemadewithmajorarterialstreetsandfreewaysonly
c. Nointersectionsatgradeshallbepermitted
5. Traffic Characteristics
a. Notrafficsignals
b. Parkingprohibited
c. Bicyclesprohibited
d. Twoseparateone-wayroadwayswithadividingmedianstrip
6. Planning Characteristics
a. FreewaysshouldconnectwithmainhighwaysapproachingandleavingtheCityfromalldirections
b. FreewaysshouldbesoalignedastoservethemajortrafficgeneratorswithintheCity,suchasthecentralbusinessdistrict,majorindustrialareas,regionalshoppingcenters,etc.
c. Freewaysshouldnotbisectneighborhoodsorcommunitiesbutshouldactasboundariesbetweenthem
d. Addedright-of-wayisprovidedforlandscaping,grassplanting,addedsafety,andnoiseattenuation
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e. Atinterchangeareas:
1. Fordiamondinterchanges,right-of-wayshouldflareto580’inwidthfrom1000’eachsideoftheintersectionright-of-waylineattheintersectingcrossstreet.
2. Forcloverleafinterchanges,right-of-wayshouldflareto1300’inwidthfrom1300’eachsideoftheintersectionright-of-waylineattheintersectingcrossstreet.
3. Foralternativeinterchangedesigns(SPUI’s,flyovers,etc.)ROWrequirementswillbeprovidedbasedonthedesign.
7. Design Characteristics
a. Grades
1. Notlessthanonepercent(1%)ontangents;normorethanfourpercent(4%)
b. Crosssections
1. Crosssectionswilbedeterminedbyspecificdesign
15.2 Standards for Expressways1. Function - Expresswayspermitrapidandrelativelyunimpededmovementoftraffic
throughandaroundtheCity.
2. Right-of-Way - 210feetminimum,withadditionalright-of-wayforfrontageroads,ifrequired
3. Number of Moving Lanes - Fourtosixlanes
4. Access Conditions
a. Accessshallbecompletelycontrolled
b. Interchangesshallbemadewithfreewaysandmaybemadewithmajorarterialstreets.
c. Signalizedintersectionsarepermittedwitharterialstreetsonly,preferablywithonemilespacing.Signalizedintersectionsat½milelocationsmaybeallowedbyCityEngineering.
d. Turnrestrictedintersectionsmaybeallowedathalfmilespacingorwheretheycanbeshowntobenefitoperationsontheexpressway.
e. Highdensityorcongestedareasmayrequirespecificaccessplans.
5. Traffic Characteristics
a. Trafficcontroldevicesandchannelizationshallbeprovidedateachintersectionatgrade.
b. Parkingprohibited
c. Twoseparateone-wayroadwayswithadividingraisedmedian
d. Bicyclesmaybepermittedontheshoulderoronseparatedbikewaysforportionsofexpressways.
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6. Planning Characteristics
a. ExpresswaysshouldconnectwithmainhighwaysapproachingandleavingtheCityfromalldirections.
b. ExpresswaysshouldbesoalignedastoservethemajortrafficgeneratorswithintheCity,suchasthecentralbusinessdistrict,majoremploymentcenters,militaryinstallations,regionalshoppingcenters,etc.
c. Expresswaysshouldnotbisectneighborhoodsorcommunitiesbutshouldactasboundariesbetweenthem
d. Addedright-of-wayisprovidedforlandscaping,grassplanting,addedsafety,andnoiseattenuation
e. Atinterchangeareas:
1. Fordiamondinterchanges,right-of-wayshouldflareto580’inwidthfrom1000’eachsideoftheintersectionright-of-waylineattheintersectingcrossstreets
2. 2.Forcloverleafinterchanges,right-of-wayshouldflareto1300’inwidthfrom1300’eachsideoftheintersectionright-of-waylineattheintersectingcrossstreet
3. SeeFreeway#3
7. Design Characteristics
a. Grades
1. Notlessthanonepercent(1%)ontangentsormorethanfourpercent(4%)
b. Crosssection
1. Crosssectionswillbedeterminedbyspecificdesign
15.3 Standards for Principal Arterial Streets1. Function - Majorarterialstreetspermitrapidandrelativelyunimpededtrafficmovement
throughouttheCityandcarryhighvolumesofinterandintratrafficwhichconnectsmajorlanduseelementsaswellascommunitieswithoneanother.Majorfunctionistoservethroughtraffic.Thesecondaryfunctionistoserveabuttingproperty.Thisfunctionaldescriptionpertainstofourlaneandgreaterfacilities.
2. Right-of-Way Width - 107-142feet
3. Number of Moving Lanes - Fourtosixlanes,withleftandrightturnbays.Rightturnlanesshallbeconstructedatintersectionsofallarterialstreets.
4. Access Conditions
a. Intersectionsandcurbcutsshallbelimited,asapprovedbyCityEngineering.
b. Signalizedintersectionsshallbelimitedto1/2milespacingunlessadeequatejustificationisprovidedtoapprovesignalizedintersectionsatotherlocations.
c. Mediancutswillbepermittedatmajororsignificantstreetintersections,generallyatintervalsofapproximately¼to½milesasapprovedbyCityEngineering.
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5. Traffic Characteristics
a. Regulationoftrafficshallbeaccomplishedbytrafficcontroldevicesandchannelization.
b. On-streetparkingprohibited
c. Verticalcurbrequiredwithdetachedsidewalks
d. Medianshallberaisedwithcurbandgutter(CityStandardDetailD-6andD-24)
e. Highdensityorcongestedareasmayrequirespecificaccessplans.
6. Planning Characteristics
a. PrincipalarterialstreetsshouldbespacedapproximatelyonemileapartinthesuburbanareasoftheCityto¼mileapartinareasofhighpopulationdensityandintenselandusage.
b. Principalarterialstreetsshouldnotbisectneighborhoods,butshouldactasboundariesbetweenthem.
c. Sidewalksshallbesetbackfromthestreet.
d. Ingeneral,abuttingpropertiesshouldnotfaceontheroadwayunlessseparatedfromitbyafrontageroad.Lotsthatdirectlyabutthearterialshallhaveaminimumdepthof120feet.
e. Bicycleaccessshallbepartofa4’multi-useshoulder.
7. Design Characteristics
a. Grades
1. Notlessthanonepercent(1%)ontangents;normorethanfourpercent(4%).Gradesofsixpercent(6%)maybeconsideredforunique,shortdistances.
b. Alignment
1. Horizontal–1040footminimumradiusatcenterlineforstandardcrownedcross-slopes
2. Vertical–minimumlengthequivalenttoKvaluetimesthealgebraicdifferenceintherateofgrade.
Figure 10 Cross Sections for Principal Arterial Streets
Type I (4- Lane, 107’ Right-of-Way)
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Figure 11 Type II (6-Lane, 142’ Right-of-Way)
15.4 Standards for Minor Arterial Streets1. Function - Minorarterialstreetspermitrapidandrelativelyunimpededtrafficmovement
throughouttheCityandcarryhighvolumesofinterandintra-trafficwhichconnectmajorlanduseelements.
2. Right-of-Way Width - 90feet(withtwo5footeasements)
3. Number of Moving Lanes - Fourlanes
4. Access Conditions
a. Intersectionswillgenerallybe“T”typeatgradeasapprovedbyCityEngineering.
b. IntersectionsandcurbcutsshallbelimitedasapprovedbyCityEngineering.
5. Traffic Characteristics
a. Regulationoftrafficshallbeaccomplishedbytrafficcontroldevicesandchannelization.
b. On-streetparkingprohibited
c. Verticalcurbsrequiredwithdetachedsidewalks
d. Medianswillberaised.Paintedmedianswillbeconsideredwithadequatejustifications.
6. Planning Characteristics
a. MinorarterialstreetsshouldbespacedapproximatelyonemileapartinthesuburbanareasoftheCitytoafewblocksapartinareasofhighpopulationdensityandintenselandusage.
b. Minorarterialstreetspreferablyshouldnotbisectneighborhoods.
c. Bicycleaccessshallbepartofa4’multi-useshoulder.
7. Design Characteristics
a. Grades
1. Notlessthanonepercent(1%)ontangents;normorethanfourpercent(4%).Gradesofsixpercent(6%)maybeconsideredforunique,shortdistances.
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b. Alignment
1. Horizontal–765footminimumradiusatcenterlineforstandardcrownedcross-slopes.
2. Vertical–minimumlengthequivalenttotheKvaluetimesthealgebraicdifferenceapprovalofgrades.
c. Frequencyofintersections
1. Intersectionsalongminorarterialstreetsshallbelimitedtoasfewaspossible
Figure 12 Minor Arterial
15.5 Standards for Collector Streets1. Function - Collectorstreetsaredesignedtoservethelocalneedsoftheneighborhood
andtoprovidedirectaccesstonon-residential,abuttingproperties.Alltrafficcarriedbycollectorstreetsshouldhaveanoriginoradestinationwithintheneighborhood.
2. Right-of-Way Width-57feet(noparking)to67feet(parking)
3. Number of Moving Lanes-Twolanes
4. Access Conditions - Directaccesstoresidentialpropertiesisbywayofcurbcuts.
5. Traffic Characteristics
a. On-streetparkingisallowedonbothsidesofminorcollectorstreetsunlessprohibited.
b. Intersectionsareatgrade
6. Planning Characteristics
a. Sidewalkswillbedetachedfromverticalcurbs
b. Bicycletravelcanbeaccommodatedwith14’sharedlanes.
c. NoresidentialfrontageallowedoncollectorswithADTgreaterthan2500.
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7. Design Characteristics
a. Grades
1. Notlessthanonepercent(1%)ontangents;collectornotmorethantenpercent(10%).
b. Alignment
1. Horizontalcurves–collector335footminimumradiusatcenterlineforstandardcrownedcross-slopes.
2. Verticalcurves–AminimumlengthequivalenttotheKvaluetimesthealgebraicdifferenceofapproachgrades.
c. Frequencyofintersections
1. Intersectionsalongcollectorstreetsshallbelimitedtoasfewpointsaspossible,whileprovidingcommercialaccesstoabuttingpropertiesandconnectingtolocalstreetsystem.
Figure 13 Collector(WithParking)
Figure 14 Collector (Without Parking)
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15.6 Standards for Residential Streets1. Function - Designedtoservethelocalneedsoftheneighborhoodandtoprovidedirect
accesstoabuttingresidentialproperties.Alltrafficcarriedbyresidentialstreetsshouldhaveanoriginoradestinationwithintheneighborhood.
2. Right-of-Way Width - 50feetminimumplus5footeasementsoneachsideofright-of-wayforutilitiesandsidewalks.
3. Number of Moving Lanes - Twolanes
4. Access Conditions - Intersectionsareatgradewithdirectaccesstoabuttingpropertiesbywayofcurbcutsorramp-typecurbing.
5. Traffic Characteristics - On-streetparkingisallowedonbothsidesofthestreet
6. Planning Characteristics
a. Residentialstreetsshouldbedesignedtodiscouragethroughtrafficandtoencouragetrafficspeedsof25mphorless.Thesestreetsshouldnotexceed1200feetinlengthandshouldincludegeometricfeaturesatintervalsof600’maximum.Examplesoffeaturesincludechokers(chicanes),trafficcircles,medianisland/barriers,cul-de-sacs,andcurvatures.DesigncriteriaforthesetechniquesareavailableintheTrafficCalmingDesignManual.
b. Insubdivisiondesign,residentialstreetsarediscouragedfromintersectionswithmajorandsecondaryarterialstreets.
c. Sidewalksmaybedetachedfromorattachedtothecurb,dependinguponthetypeofcurb.
d. Bicycletravelcanbeaccommodatedinthetravellanesduetothelowvolume,lowspeednatureofthistypeofroadway.
7. Design Characteristics
a. Grades
1. Notlessthanonepercent(1%)ontangents;normorethantenpercent(10%)
b. Alignment
1. Horizontalcurves–200footminimumradiusatcenterlineforstandardcrownedcross-slopes.
2. Verticalcurves–aminimumlengthequaltotheKtimesthealgebraicdifferenceofapproachgrades.
c. FrequencyofIntersections
1. Intersectionsalongresidentialstreetsshallbeallowedasneededtoprovideconnectionstootherlocalstreetsandcollectorstreets.
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Figure 15 Residential (Local) Streets (Detached Sidewalk)
Figure 16 Residential (Local) Streets (Attached Sidewalk)
15.7 Standards for Minor Residential Streets1. Function - Designedtoprovidedirectaccesstoabuttingsingle-familyresidential
propertiesorcul-de-sacshavingalengthofnogreaterthan500feet.Apavementmatof24feetisallowedonminorresidentialstreetswhichcontainnomorethan20single-familylots.Anyotherresidentialstreethavingmorethan20single-familylotsmustinstalla28footpavementmat.
2. Right-of-Way - 47feetminimumplus5footeasementsoneachsideofright-of-wayforutilitiesandsidewalks.
3. Number of Moving Lanes - Twolanes
4. Access Conditions - Directaccesstoresidentialpropertiesisbywayofcurbcutsorbyramptypecurbs.
5. Traffic Characteristics
a. On-streetparkingisallowedononesideofthestreet
b. Intersectionsareatgrade
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6. Planning Characteristics
a. Minorresidentialstreetsshouldbedesignedasshortlooporcul-de-sacstreetsonly.
b. Minorresidentialstreetsshouldnotintersectmajorarterialstreets.
7. Design Characteristics
a. Grades
1. Notlessthanonepercent(1%)ontangents;normorethantenpercent(10%)
b. b.Alignment
1. Horizontalcurves–200footminimumradiusatcenterlineforstandardcrownedcross-slopes.
2. Verticalcurves–AminimumlengthequivalenttotheKvaluetimesthealgebraicdifferenceoftheapproachgrades.
Figure 17 Minor Residential (Local) Streets (Detached Sidewalk)
Figure 18 Minor Residential (Local) Streets (Attached Sidewalk)(Servinglessthan20singlefamilylots)
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15.8 Standards for Industrial Streets1. Function - Industrial/commercialstreetsaredesignedtoservefacilitieswithinindustrial/
commercialareasandtoconnectsuchareaswithmajorarterialandcollectorstreets.
2. Right-of-Way Width - 70feet(withtwo5footeasements)
3. Number of Moving Lanes - Twolanestofourlanes
4. Access Conditions - Directaccesstoabuttingindustrial/commercialpropertiesisbywayofcurbcuts.
5. Traffic Characteristics
a. On-streetparkingmaybepermittedonbothsidesofthestreet
b. Intersectionsareatgrade
6. Planning Characteristics
a. Onlylocalindustrial/commercialtrafficshouldbeencouragedonindustrialstreets
b. Sidewalkswillbedetachedfromthecurbwhererequired
7. 7. Design Characteristics
a. Grades
1. Nolessthanonepercent(1%)ontangents;normorethaneightpercent(8%)
b. Alignment
1. Horizontal–335footminimumradiusatcenterline
2. Vertical–AminimumlengthequivalenttotheKvaluetimesthealgebraicdifferenceoftheapproachgrades.
c. FrequencyofIntersections
1. Intersectionsalongindustrial/commercialstreetsshallbelimitedtoasfewaspossible,whileconnectingtothecollectorstreetsystemandprovidingaccesstolocallanduses.
Figure 19 Industrial Streets
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15.9 Standards for Alleys1. Function - Designedtoprovideaccesstoabuttingpropertyatrearlotlines.
2. Right-of-Way Widths - 20foot(Residential)/25foot(Commercial)
3. Number of Moving Lanes - Twolanes
4. Access Conditions
a. Provideaccesstoabuttingpropertyatrearoflots
5. Traffic Characteristics
a. Normallyalleysshallintersectatperpendicularangleswithstreets
b. Noparkingshallbepermitted
6. Planning Characteristics
a. Alleysshallbeopenatbothends
b. Normallyalleysshallnotintersectwithcollectorstreetsorarterialstreets.
7. Design Characteristics
a. Grade
1. Notlessthanonepercent(1%)ontangents;normorethantenpercent(10%)
8. Alley Drainage
Alleysurfacesmaybedesignedtodraininthreeways.
- ConcreteV-shaped.Theentirealleymustbeconcrete.Concretepansdownthecenterofasphaltalleysarenotpermitted.
- Asphaltcrownedwithvalleyguttersoneachside,or
- Asphaltcross-slopedwithavalleygutteronthelowside.
Flowspreadinalleysshallbeconfinedtotheright-of-wayatreasonabledepths.Stormflowsinalleysshallbelimitedtotheflowsgeneratedfromtherearofthelotsadjoiningthealley.Alleyflowsshallnotcrosstheintersectingstreetsintoanotheralleybutshallbecapturedordivertedattheintersectingstreet.FormoreinformationaboutalleydesignreferenceismadetothedesignmanualsforTraditionalNeighborhoodandMixedUseDevelopment.
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Figure 20 Residential Alleys
Figure 21 Commercial Alleys
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16.0 Table of Traffic Engineering Design Standards
Table 10 Traffic Engineering Design Standards (Freeways, Expressways and Arterials)
Design Element Functional Classification
Freeway ExpresswayPrincipal Arterial
Type 2 (6 lane)
Principal Arterial
Type 1 (4 lane)
Minor Arterial
Speeds (1) 65 55 45 45 40
Design ADT 85,000-100,000 60,000-85,000 25,000-60,000 10,000-25,000 5,000-25,000
Trip Length Over5miles Over5miles 1-2miles 1-2miles Over1mile
Corridor ROW Width 332’-420’ 210’ 142’ 107’ 90’w/(2)5’easements
Roadway Width (pavement mat) Var.Width 2-50’
pavementmat2-40’pavement
mat2-28’pavement
mat 69’
# of Lanes 6-8 4-6 6 4 4
Lane Widths 12’ 12’ 11’ 11’ 11’
Shoulder Width 12’ 10’ 4’ 4’ 4’
Median Var.Width Raised28’ Raised28’ Raised17’ Raised17’
Sidewalk Requirement (placement) N/A N/A Detached6’ Detached6’ Detached6’
Bicycle Accommodation N/A N/A 6’Multi-Use
Shoulder6’Multi-Use
Shoulder5’Multi-Use
Shoulder
Tree lawn Width N/A N/A 7’ 7’ 7’
Parking No No No No No
Access FullControl FullControl FullControl FullControl FullControl
Design Vehicle WB67 WB67 WB67 WB67 WB50
Signalized Intersection Frequency N/A 1mile ½mile ½mile ½mile
Unsignalized Intersection Frequency 1mile N/A ¼mile ¼mile 600’
Vertical Alignment RefertoVerticalCurveDesigninAASHTOGeometricDesignofHighwaysandStreets
Horizontal Alignment Radius N/A N/A 1045’ 1040’ 765’
Grade (min-max) 1%-4% 1%-4% 1%-4% 1%-4% 1%-4%
Intersection Grade GradeSepar. 1%min 1%min 1%min 1%min
Intersection Sight Distance 775’ 665’ 500’ 500’ 445’
Stopping Sight Distance (2) 730’ 570’ 360’ 360’ 305’
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Traffic Engineering Design Standards (Collector, Residential [Local], Public Alley, and Industrial)
Design Element
Collector Residential (Local)
Minor Residential
(Local)Public Alley Industrial
Speeds(1) 30 25 25 15 30
DesignADT 1,500-5,000 300-1,500 50-300 50-300 <10,000
TripLength 1mile Local Local Local TruckLocal
MaximumUninterruptedFacilityLength ¼mile 600’ 300’
AdjacentStreetLength 1mile
CorridorROWWidth
57’(noparking)
67’(parking)
50’w/(2)5’easements
47’w/(2)5’easements
20’Residential25’Commercial
70’w/(2)5’easements
RoadwayWidth(pavementmat)
28’(noparking)
38’(parking)30’ 24’(<21Lots)
28’(>20Lots)16’Residential
22’Commercial 51’
#ofLanes 2 2 2 2 3
LaneWidths 14’w/sharedbike 9’ N/A N/A 14’w/shared
bikew/12’ctl
ShoulderWidth N/A N/A N/A N/A N/A
Median N/A N/A N/A N/A N/A
SidewalkRequirement(placement)
Detached5’
Attached6’vert.curb/
Detached5’others
Attached6’vert.curb/
Detached5’others
N/A Detached5’
BicycleAccom-modation
Onstreetw/sharedlane
Onstreetw/sharedlane
Onstreetw/sharedlane
Onstreetw/sharedlane
TreelawnWidth 7’ 7’-6” 7’ N/A 7’
Parking Allowed TwoSides One-sideparkingonly No Twosides
Access PartialControl
PartialControl
PartialControl N/A Partial
Control
DesignVehicle WB40 SU30 SU30 N/A WB67
SignalizedIntersectionFrequency N/A N/A N/A N/A ½mile
Un-signalizedIntersectionFrequency 600’ 300’max 300’max ½adjacent
streetlength 600’
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Design Element
Collector Residential (Local)
Minor Residential
(Local)Public Alley Industrial
VerticalAlignment
RefertoVerticalCurveDesigninAASHTOGeometricDesignofHighwaysandStreets
HorizontalAlignmentRadius
335’ 200’ 200’ 85’ 335’
Grade(min-max) 1%-10% 1%-10% 1%-10% 1%-10% 1%-8%
IntersectionGrade 1%-3% 1%-4% 1%-4% 1%-4% 1%-3%
IntersectionSightDistance 335’ 280’ 280’ 170’ 335’
StoppingSightDistance(2) 200’ 155’ 155’ 80’ 200’
Note: Alternate design standards may apply when Traditional Neighborhood, Mixed Use, Hillside, or Low-Impact Development are used. (1) Speed refers to the anticipated posted speed. The design speed is 5 mph greater than the posted speed. (2) For level terrain only.
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17.0 Transit Services
Onarterialstreetsthatareadesignatedbusroute,developerswillneedtoworkwithMountainMetropolitanTransittodeterminetheappropriatelocationofbusstopsandbusturnouts.BusturnoutsaretobeconsideredonArterialstreetswherethereisnoon-streetparking,ahighvolumeofvehiculartraffic,andpostedspeedsare40mphorgreater.Busbays,openbusbays,andqueuejumperbusbaysareallacceptabledesignsforbusturnouts.ThegeneralguidelinesandstandarddetailsforbusturnoutsareavailablefromMountainMetropolitanTransit.
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18.0 Definitions, Abbreviations, and Acronyms
AASHTO–AmericanAssociationofStateHighwayandTransportationOfficials
Accesses–Commercialentrancesandexits.
ADT–AverageDailyTraffic
Algebraic Difference in Grades (%)–Thenumberderivedbysubtractingtheapproachanddepartingtangentgrades(%)ofacurve.
Asymmetrical Reverse Curve–Opposingcurvesofthesameradius.
CDOT–ColoradoDepartmentOfTransportation
Design Speed–Safeandcomfortabledrivingspeed.Usually5MPHoverthepostedspeed.
DHV–DesignHourVolume
Driveways–Residentialentrancesandexits.
Fc–FaceofCurb
K Value–Thelengthofaverticalcurvedividedbythealgebraicdifferenceofapproachgrades.
MPH–Milesperhour
Posted Speed–Thespeedlimitplacedonthesignsnexttotheroadway.
TIS–TrafficImpactStudy
VPH–VehiclesPerHour
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19.0 References
- APolicyonGeometricDesignofHighwaysandStreets,AmericanAssociationofStateHighwayandTransportationOfficials(AASHTO)5thEdition,2004
- APolicyonGeometricDesignofRuralHighways,AASHTO,2004
- TransportationandTrafficEngineeringHandbook,InstituteofTransportationEngineers(ITE),1999
- UrbanTransportationOperations–TrainingDesignofUrbanStreets,U.S.DepartmentofTransportationFederalHighwayAdministration(USDOT–FHWA),1982
- ASurveyofUrbanArterialDesignStandards,InstituteforMunicipalEngineering–AmericanPublicWorksAssociation(APWA),1969
- SubdivisionPolicyManual,CityofColoradoSprings,1980Update
- ManualonUniformTrafficControlDevices,USDOT–FHWA,2003
- GuidelinesforDrivewayDesignandLocation,ITE,1985
- GuidelinesforUrbanMajorStreetDesign,ITE,1985
- ResidentialStreets,UrbanLandInstitute(ULI),NationalAssociationofHomeBuilders(NAHB),AmericanSocietyofCivilEngineers(ASCE),1977
- TripGeneration,7thEdition,ITE,2003
- 2010PavementDesignManual,ColoradoDepartmentofTransportation(CDOT)
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Appendix A
Traffic Impact Study Guidelines for Development Projects
Purpose
Thepurposeoftheseguidelinesistoprovideauniformmethodologyforthetrafficengineeringconsultantstouseinconductingtrafficimpactstudiesforproposeddevelopmentprojects.ThecomplianceoftheseguidelineswillresultinthetimelyreviewbyCityEngineeringandreducedrevisions.
Atrafficimpactstudy(TIS)willberequiredforaproposednon-residentialdevelopmentwithapeakhourtripgenerationofover100vehicles,oranyproposedresidentialdevelopmentwith150ormoredwellingunits.TheforecastvolumeshallbebasedontripgenerationratescontainedinthelatesteditionoftheTripGenerationManualpublishedbytheInstituteofTransportationEngineers(ITE)orotherratesasapprovedbyCityEngineering.
AllTISsfornewsubdivisiondevelopmentshallbesubmittedtotheEngineeringDevelopmentReviewDivision(EDRD)ofCityEngineering.EDRDwillreturnreviewcommentstothepreparer.WhenthereviewprocessiscompleteandtheTISisreadyforapproval,EDRDrequirestwocopiesbesubmittedforCitysignature.Additionalcopiescanbesubmittedandwillbereturnedtotheengineer.Thesecopiesshallbeproperlycertified,signed,sealed,anddatedbytheregisteredprofessionalengineerresponsibleforthereport.ThesignatureblockforEDRDshallreadThisTrafficImpactStudyisherebyacceptedbyCityEngineeringwithalinefortheEDRDreviewer’ssignatureanddate.FollowingEDRDapprovaloftheTISascannedPDFversionoftherecordapprovedreportandplansmustbereceivedbyEDRDpriortorecordingtheFinalPlat.
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Thefollowingtypesofsubmittalswhichexceedthetripgeneration/dwellingunitcriteriawillrequireaTIS:
1. Amasterplanordevelopmentplansubmittal.
2. Anyrezoningapplication.
3. Apreliminarymaporfinalplatifthepropertyhasalreadybeenrezonedfortheproposeduseandnotrafficstudywasrequiredfortherezoning,ortheoriginaltrafficstudyismorethantwoyearsold.
4. Priortoissuanceofabuildingpermit,ifthepropertyhasalreadybeenzoned/plattedandnoprevioustrafficstudylessthantwoyearsoldexists.
5. ForaStateHighwayAccessPermit,if:
a. SiteaccessisrequiredoffaStateHighwaypriortoissuingabuildingpermit.
b. AdditionalaccessoffaStateHighwaytoanexistinguseisbeingrequested.
c. AnychangeofuseaffectingaccessfromtheStateHighway.
6. ForanapplicationforannexationintotheCity.
7. Theapplicantwillberequiredtosubmitanewtrafficstudyif,aftersubmittingtheoriginaltrafficstudy,thelanduseintensityandtrafficgenerationisincreasedbymorethan15%.
8. OtherconditionsasdeterminedbyCityEngineering.
9. CityEngineeringmayrequireothermemos,letters,analyses,orotherdocumentationtoaddressspecifictrafficissuesatstaffdiscretion.
ThetrafficstudyshallbeconductedbyaprofessionalengineerregisteredintheStateofColoradowithadequateexperienceintrafficengineeringand/ortransportationplanning.
Methodologies
Thestudyshallbeconductedusingthefollowingmethodologies.
ThepreparerofthetrafficstudyshallmeetwithCityEngineering.Atthismeeting,thefollowingitemswillbeaddressed:
- Establishmentofthestudyarea
- Identificationoftheanalysisperiods(AM,PM,Weekend)tobestudied
- Theforecastyears(openingyearandhorizonyear)
- Tripgenerationassumptions
- Methodologytoobtaintripdistributionandassignmentassumptions
- Identificationofhighaccidentlocationsoroperationaldeficienciestobeaddressedaspartofthestudy
Itisrecommendedthattheapplicantsubmitthecompletedforecastsofbackgroundtraffic,projecttripgeneration,tripdistribution,andtripassignmenttoCityEngineeringforreviewpriortothefulltrafficanalysis.
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Impactsofthedevelopmentontheexistingandproposedroadwaynetworkshallbeidentified.Intersectiontrafficanalyses(includingprojectdriveways)shallbeconductedusingtheoperationalmethodologiesdescribedinthelatesteditionoftheHighwayCapacityManual(HCM).
TrafficanalysisconductedusingSynchroorothercomputersoftwareproductsshallusethefollowingsettingsunlessotherwiseapprovedbyCityEngineering:
- PeakHourFactor(PHF):0.88Rural;0.92Urban
- CycleLength:between60secondsand120seconds;higherandlowercyclelengthsrequirepriorapprovalbyCityEngineering.
- YellowTime:3.0secondsminimum;followITEguidelines
- All-RedTime:2.0seconds
- TheCityrecognizestheHCMlevelofservice(LOS)asthenationallyacceptedstandardforLOS.HCMreportsshallbeusedforLOSresultsinSynchro,notSynchro’sownLOScalculations.
LOSfiguresshouldshowtheLOSresultsforeachintersectionapproachaswellastheoverallintersectionLOS.
Mid-blocktrafficanalysesshallbebasedonvolumetocapacityratiosusingthefollowingcapacityvalues:
Roadway Classification ADT
PrincipalArterials(8Lane) 65,000
PrincipalArterials(6Lane) 50,000
PrincipalArterials(4Lane) 25,000
MinorArterials 25,000
MajorCollectors 10,000
MinorCollectors 3,500
Local 1,500
MinorLocal 300
Industrial-Commercial 10,000
FrontageRoad 5,000
Mid-blockanalysisshallbeusedonlywhereintersectionanalysisdoesnotadequatelyaddresscapacityconcerns.Atlocationswherethe“withproject”scenarioanalysesindicateintersectionapproachLOSDwillbeexceededand/ormidblockLOSCwillbeexceeded,thestudyshallidentifymitigationmeasuresorexplainwhymitigationisnotneeded.ThemitigationmeasuresshallincludeimprovementsthatwillprovideLOSDorbetteratintersectionapproachesandLOSCorbetteratmidblocklocations.Themitigationmeasuresshallbepresentedwithdrawingstoclearlyshowtheexistingandproposedimprovements.
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TheneedfornewtrafficsignalsshallbeevaluatedusingthewarrantsinthelatesteditionoftheManualonUniformTrafficControlDevices(MUTCD).NonewtrafficsignalsshouldbeproposedthatcannotbejustifiedusingMUTCDtrafficsignalwarrants.Trafficprogressionisofparamountimportance.Allpotentialsignalizedintersectionsshouldbeplannedfor½mileintervals.Allotherlocationstobeconsideredshallmeetthefollowingcriteria:
- Theprogressionpatterncalculationshalluseacyclelengthbetween60and120seconds.Efficiency(e)equalsBandwidth(BW)inthatdirectioninsecondsdividedbythecyclelength(C)insecondsandmultipliedby100toobtainapercent.e=BW/Cx100.Aminimumefficiencyof30%shallbeachieved.Thoseintersections,whichwouldreducetheprogressionefficiencytobelow30%ifasignalwereinstalled,shallremainunsignalizedandhaveturningmovementlimitedbydrivewaydesignormedianislands.
- Submittalofatime/spacediagramwithacceptablethroughbands,cyclelengths,andprogressionspeeds.
- InareasthatmayaffectestablishedcomplexcomputerizedprogressionsanydeviationfromexistingconditionsshallbethoroughlyaddressedandapprovedbyCityEngineeringpriortoapproval.
- Thegreentimeallowedtothecrossstreetshallbeconsiderednolessthanthetimethatisrequiredforapedestriantocrossthemainlineatfourfeetpersecond.
Weaveanalysesforpotentiallyaffectedlocationsmayberequiredforthestudy.ThisanalysisshouldbeconductedusingHCMmethodologiesand/ormicro-simulationmodelingbyanapprovedmicro-simulationmodel.
Traffic Study Format
Specificrequirementswillvarydependingonthesitelocation.However,alltrafficstudiesshallcontain,asaminimum,thefollowinginformation.Seethe“RequiredFiguresandTablesMatrix”todeterminetherequiredexhibits.
1.0 Introduction
% Purposeofthereport
% Studyobjectives
2.0 AreaConditions
% StudyAreaLandUse
• Existinglandusesonthesiteandinthevicinity
• Existingzoningonthesite
• Approvedfuturedevelopmentonothersitesinthevicinity
% SiteAccessibility
• Arearoadwaysystem
– Existing–withcurrentroadwayclassificationdesignation
– Future–IntermodalTransportationPlan(ITP)designation
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• Trafficvolumesandconditions
– Ifpractical,allreportedcountsshouldbeactualcountsandnotbasedonfactoredpeakhoursampling.LatestavailablecountsfromtheCityand/orCDOTmaybeacceptableiftakenwithinareasonabletime(typically2years).
– PeakHourFactor(PHF)forexistingconditions.LOSanalysiscanmatchrecordedcounts
– Describeanyexistinghighaccidentlocationsinthestudyarea
• Transitservice
• Existingrelevanttransportationsystemmanagementand/orTrafficDemandManagement(TDM)programs(ifany)
• Otherasapplicable
3.0 ProposedDevelopment
% Descriptionofthesizeoftheparcel,generalterrainfeatures,andthelocation
% Vicinitymapshowingthesiteinrelationtothesurroundingtransportationsystem
% Siteplanshowingproposedproject
• Descriptionofeachproposedlanduseincludingtheunitsize(area,#ofworkers,etc.)
• Phasing(ifany)andconstructiontiming
% Sightdistanceexhibitsforproposedprojectaccesslocations
• SightdistanceshouldbebasedonspeedlineofsightasdescribedelsewhereinCityguidelines
• Ifverticalalignmentimpactssightdistance,thentheexhibitshouldincludeaverticalprofiledemonstratingthatverticalcurvesdonotinterferewiththeaccesslineofsight,orappropriatefielddata.
• Ifsightdistanceisnotanissue;explaintherationalewithinthetextofthereport.
4.0 ProjectedTraffic
% Sitetraffic
• Tripgenerationtable–ShouldfollowITE,TripGenerationguidelinesonwhentouseaverageratesandwhentouseequations.Thepeakhourofadjacentstreettrafficshouldbeusedwhenavailable.Also,includeITEorotherreferencematerialsintheappendixofthereportforanytripratesusedand/ortripreductionfactorsused.
• TripDistribution–Mayneedmultipletripdistributionsdependingonprojectphasingandtimingofsurroundingroadwaynetworkbuild-out
• Modalsplit(ifappropriate)
• Pass-bytrafficshouldnotexceed10%ofadjacentstreettrafficduringthepeakhour.
• Tripassignment
% Backgroundtraffic
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• Openingyear(s)–UsecombinationoflatestPikesPeakAreaCouncilofGovernments(PPACG)model,otheradjacenttrafficstudies,existingcounts,NationalCooperativeHighwayResearchProgramReport(NCHRP)255methodology,andinterpolationtodetermine
• Horizonyear–NeedstomatchlatestPPACGtraveldemandmodelhorizonyear
% Totaltraffic
• Openingyear(s)–Sumofsitetrafficandbackgroundtraffic
• Horizonyear–Sameasabove
5.0 Trafficanalysis
% Existingconditions(withoutproject)–ifnotalreadypresentedinSection2.0
% Openingyear(s)
• Withoutproject
• Withproject
% Horizonyear
• Withoutproject
• Withproject
6.0 EquivalentSingleAxleLoads(ESAL)Projections
% Ifneededtoprovideadetailedpavementdesign,ESALprojectionsshouldbedevelopedusingthetechniqueprovidedintheCDOTPavementDesignManual
7.0 FindingsandconclusionswithPEcertificationandCitysignatureblocks.
% Siteaccess
% Accidenttrendsandcauses
% Trafficimpacts
% Parking–discussifproposedparkingmeetsCityrequirementsandifnot,howtheshortagewillbeaccommodated.Ifreciprocaland/orsharedparkingiscontemplated,aparkingaccumulationstudyforexistingfacilitiessimilartoproposeduseswillbenecessary.
8.0 Recommendations
% Siteaccess/circulationplan
% Improvements–AnadditionalLOSanalysistodemonstratethatproposedimprovementswillmitigatetheimpacts
• Canincludeaccessturnrestrictionsaswellasaccessspeedchangelanes.Ifspeedchangelanes(acceleration/decelerationlanesintoandoutofprojectaccesses)areproposed,depictgraphicallydemonstratinghowproposedspeedchangelaneconformstoCity’sguidelinesand/orqueuesproducedfromLOSanalysis(whicheverisgreater)
9.0 Appendix
% Inadditiontothetables/figuresshownintheattached“RequiredFiguresandTablesMatrix”whichcanbeincludedineithertheappendixorwithinthetextofthereport,thefollowingitemsneedtobeincludedintheappendixofthereport
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• Trafficcounts
• Tripgenerationsources–eitherITEorotheracceptedsource
• Forecastcalculations/data
– IncludePPACGorothersourcedataandcalculationsonhowopeningyearandhorizonyearbackgroundforecastsweredetermined
• LOSAnalyses(forallscenariosstudied)
– Intersections
– Roadways
– Queues
– Weaves
• Parking
– Counts
– Calculations
Required Figures and Tables Matrix
Table or Figure Description
VicinityMapAreamapshowingsitelocationandareaofinfluence.Includeexistingroadwaysystemshowingmajorandminorstreetsadjacenttositeandsiteboundaries.
SiteDevelopmentPlan Planshowingtheproposeddevelopmentunderstudyincludingaccesslocations,buildingsizes,andlandusezones.
SiteLandUseTable Tabledescribingthedifferentsitelanduses,thedescribingunit(area,workers,etc…)andtheITEtripgenerationcode.
SiteTrafficGenerationTable
TableshowingtheestimateddailytripsandA.M.andP.M.peakhour(orweekend)tripsgeneratedbyeachcomponentoftheproposeddevelopment.Peakhourtripsmustbeshownseparatelyforinboundandoutbounddirections.ITELandUsecodeusedshouldbedisplayed.
InternalCaptureTable Tableshowingtripreductionsforinternalcaptureofamulti-usedevelopment.
Pass-byTripTableandFigure
Tableshowingthepass-bytripreductionandfigureshowingtheturningmovementsofthepass-byvehiclesenteringandexitingthesite.
TripDistributionandAssignmentFigure
Maportableshowing(bypercentages)theportionofsitetrafficapproachinganddepartingtheareaoneachroadway;maydifferbylandusewithinmulti-usedevelopment.
AverageDailyTrafficVolumeFigure Dailyvolumesonroadsinthestudyarea.
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AMandPMPeakHourTurningVolumeFigure
Peakhourturningvolumesateachlocationcriticaltositeaccessorservingmajortrafficvolumesthroughthestudyarea.
LaneGeometryFigure Exhibitshowingtravellanesandmovementsateachlocationshownontheturningvolumefigure.
LevelofServiceFigure Levelsofservicecomputedforeachturningmovement,approach,intersectionandroadwayinthestudyarea.
QueueLength Scaleddrawingshowingqueuelengthsortablecomparingqueuelengthtostoragelengthandaccessspacing.
Note:Theabovetablesandgraphsmaybecombinedaslongastheinformationisunderstandable.
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Appendix B
Standard Utility Locations
Thisappendix,whichwilldefinethestandardutilityandstormsewerplacementinthevariousstreetclassifications,isstillunderconsideration.
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Appendix CRoundabout Design Guide
1.0 Introduction to Roundabout Design Guide
Roundaboutsareasafeandefficientformoftrafficcontrol,whichcanbeusedatmanyofthesamelocationsastrafficsignalsorstopcontrols.BasedonUSandinternationalstudies,roundaboutsreduceaccidentsformotorvehiclesandpedestriansand,duetotheslowerspeedsandthereducedangles,theseverityofaccidentsareless,withfewerinjuries.Becauseoftheadvantagesofroundabouts,itisthepolicyoftheCitytouseroundaboutsasasubstituteforothertypesofintersectioncontrol,includingintersectionswithnocontrol,2-wayorall-waystop.Theyshouldbeusedinsteadofatrafficsignalatalllocationswherearoundaboutisshowntooperateaswellorbetterthanasignalwherevertheroundaboutcanbeconstructedtomeetthesestandards.Roundaboutsareallowedonlocalstreets,minorandmajorcollectors,minorandprincipalarterials,butarelimitedtonomorethantwoapproachlanes.
Standardsincludedhereinwillbeused,alongwithengineeringjudgmentandinformationfromothersources,forthedesignofallroundaboutswithintheCityofColoradoSprings,andforthereviewofdesignsbycitystaffandprivateconsultants.Whereconflictingstandardsexist,thisdesignguideshallgovern.
Whendesigningroundabouts,thereareseveralcharacteristicsthatcanbestandardized,suchassigningandmarking;whileothersmustbeadaptedwithinthedesignstandardstofitthedemandsofthelocation,suchasapproachanglesandrightofwayrestrictions.Thisdesignguidehasbeencreatedtoallowengineerstheflexibilitytodesignaroundabouttofitaparticularsite,whilestillmaintainingconsistencywithotherroundaboutscitywidetoenhancedriverexpectancy.
Allroundaboutdesignswillrequireatwostepprocess:apreliminarydesigninitiallysubmittedthatmeetsdesigncriterialistedunderbothgeneraldesigncriteriaandspecific/geometricdesignelementsasnoted,anduponapprovaloftheoverallpreliminarydesign,afinaldesignshowingallconstructiondetailsandanyphasedconstructionsigningandmarking.
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2.0 General Design Criteria
2.1 Appropriate Roadways / Locations
Roundaboutsshouldbeusedwherephysicalconditionssuchasapproachgradesandadequaterightofwayallow.Theyarelimitedtouseonaroadwaywithfourorfewerthroughlanesresultinginnomorethantwoapproachlanes.Theyarenotappropriatewhenthecapacityrequiresmorethantwocirculatinglanes.Roundaboutsarealsonotappropriateiftheuseofaroundaboutisexpectedtoproducegreatervehicledelayorincreaseddifficultyforpedestrians.
Designoftheapproachroadandroundaboutmustprovideadequatevisibilityoftheroundaboutfromadistancethatwillallowapproachingdriverstoseetheroundabout,bothdaytimeandnighttime.Thisdecisionsightdistance(DSD)istheminimumdistancerequiredthatwhichwillallowdecelerationfromthe85%travelspeed(orpostedspeedlimit,whicheverisgreater)tothemaximumentryspeedof20MPH(singlelane)or25MPH(multilane)withoutexceedingadecelerationrateof10’/s/s.Thisisgenerallythesamedistanceasthe“intersectionsightdistance”notedinAASHTOstandards,variablebyapproachspeed.
2.2 Approach and Circulatory Speeds
Thecenterlinesoftheapproachingroadwaysshouldgenerallymeetnearthecenteroftheroundabout,withsomeoffsetallowedaslongasthefastestpathcriteriaaremet.However,roundaboutsoffsetsignificantlyfromthiscriteriawillcreateadifficultdesign,withthefastestpathrequiringartificialrestrictionsordifficulttotraverseapproaches.Thiscanresultinvehiclescrossinglanesand/orfailingtofollowthelanelinesontheapproachorexit.Roundaboutsmayhavethree,fourorfiveapproaches.Approachroadwaysmaybesinglelane,singlelanewithaflareouttoprovideanaddedlaneatthecirculatingroadway(usedtoprovidealeft-onlylane),singlelanewithaby-passrightturnlane,ortwolaneswithoutaddedlane.Theconfigurationisbasedontheturningmovementvolumes.
Theapproachroadwaysectionincludestheroadwayfromthepointwheretrafficistravelingatthespeedlimittotheyieldpointwheretheenteringvehiclesentertheinscribedcircle(seefigureIforexplanationoftheroundaboutelements).Thissectionextendstothelimitsofthedecisionsightdistance(Exhibit3-3,Section3AASHTOGeometricDesignofHighways&Streets,2001,avoidancemaneuverB–Stoponurbanroadway).
Thecentralislandshallbevisiblefromtheintersectiondecisionsightdistancebothdayandnightwithouttheinstallationofanylightingthatwoulddistractorshinedirectlyatanyvehicleoperators.Theminimumdistancevarieswiththeroadwayclassification,butgenerallyisthesameasapproachinganyotherintersectionlistedintheintersectionstandards.Thedistancewherethedrivershouldbeabletotelltheyareapproachingaroundaboutrangesfrom450’priortotheyieldpointforalocalroadwayto750’forahigherspeedarterial.
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Approachspeedscalculatedat50’and150’priortotheyieldpointorentrancetothecirculatingroadwayarecriticaltothesafeoperationoftheroundabout.Thedesignshouldmeetthemaximumdesirableapproachspeedof20MPH(singlelane)or25MPH(multilane)at50’,and5MPHfasterthanentryspeedatthe150’point.Actualoperatingspeedmaximumsarecontrolledbythe“fastestpath”asnotedinFigureII,whicharetheradiimeasuredalongthevehiclepath,notalongthecurbflowlines.Reversecurves,landscaping,roadwaynarrowing,andotherformsofpsychologicalspeedreductionmayberequiredwhereapproachspeedsarehigh.
DesignspeedlimitationsandtheirrespectiveradiithroughtheroundaboutareshownonFigureII,includedinSection3.0–Specific/GeometricDesignElements,identifiedasR1,R2,R3,R4,andR5.Themaximumradiusandrespectivespeedsatvariouslocationsonthetravelpaththroughtheroundaboutarecriticaltothesafeoperationoftheroundabout.Curbandgutter,splitterislands,andthecentralislandplacementcontrolthefastestvehiclepath,butarenotthesameradii.Inadditiontotheoverallspeedlimitationforoperation,themaximumspeeddifferentialbetweenanytwopartsofthetraveledpathis12MPHtoreducethepotentialforrear-endaccidentsforvehiclesturningleftorexiting.
Allalignmentparameters,includingsightdistancerestrictionsforlandscapingshallbeincludedinthepreliminarydesigndrawings.SeeFigureIIIforsightdistancerestrictions.
2.3 Design Vehicle
Allroundaboutsshallbedesignedtoallowsinglepassengercars,pickups,SUtrucksandcitybusoperationwithouttheuseofatruckapron.Largertruckswillrequiretheuseofatruckapron,especiallyonsinglelaneroundabouts.Amovingvan,firetruck,and/orWB50truckshallbeusedtocheckfortheabilitytonavigatetheroundaboutusingtruckaprons,butwithoutstrikinganyoftheoutsidecurbs,signs,utilitystructures,orsplitterislands.
Operationofallroundaboutsshallbecheckedusingtheturningcharacteristicsforthedesignvehiclesinthefollowingchart,exceptforstatehighways,orarterialsnearindustrialareas,otherareasofhightruckusage,oralongestablishedtruckroutes,whereaWB67truckshallapply.Theturningtrucksmayberequiredtouseatruckapronmeetingthesestandards,butwithoutcausinganydamagetoanypartoftheroundabout.Generally,amultilaneroundaboutwillnotneedatruckapron,aslargervehicleswillusebothlanes.
Road Classification Circulatory Lanes Design Vehicle Roundabout Type
Local 1 SU Singlelane
Collector 1 WB40 Singlelane
MinorArterial 1 WB50 Singlelane
MinorArterial 2 WB50 Multilane
MajorArterial 2 WB50 Multilane
Areasnotedabove,regardlessofclass 1-2 WB67 Singleormultilane
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Theuseofeithervehicleturningtemplates,orplotfromAutoturnsoftwareisallowed.Allpreliminarydesigndrawingsmustincludethisturningpath.
2.4 Pedestrian/Bicycles
Allroundaboutsshallbedesignedtoallowpedestriancrossingswheneversidewalksareexistingorplannedattheintersection.Pedestriancrossingsshallbemarkedandsignedwhenever20yearprojectedpedestrianusageisequaltoorexceeds20pedestriansperhouratanytimeoftheday.Markedandsignedcrosswalksarealsorequiredforallroundaboutcrossingsonaschoolrouteorborderingapark,shoppingarea,orotherareawherepedestrianactivityisexpected.Lightingshallbedesignedtoilluminatethepedestrianareawithoutbacklightingpersonswithinthecrosswalk.
Inareasofunusuallyhighpedestrianusage,supplementalactivewarningdevicesmayberequired,suchasflashingbeaconsorLEDsupplementedsignage.Thewarningdevicesmaybeactivatedeithermanuallybytheuserorautomaticallybyanyapproveddetection/actuationtechnology.Whereblindpedestriansareexpected,theflashingbeaconsmustbeactivatedmanuallybytheuseofatactileorsoundemittingpushbutton.
Iftheroundaboutisonastreetwithbicyclelanesoraroadwaywithdesignatedorplannedbicyclelanes,theapproachshallallowfortheconnectionfromthebicyclelanetothesidewalk,allowingthebicyclistthechoicetoeither“claimthelane”andproceedthroughtheroundaboutasavehicle,orexittheroadwaypriortotheroundaboutontothesidewalkandusethepedestrianfacilities.Theroadwayshouldbereducedinwidthatthepointwherethebicyclelaneexitsfromtheroadway.
SeeFigureIVfordetailsofconstruction,signingandmarkingforpedestriansandbicyclists.Detailsofmarkingandsigningshallbeincludedinthefinaldesign.
2.5 Design Software
Theappropriatedesignsoftwareshallbeusedtoensureproperdesignandcapacity.Localstreetorminorcollectorintersections,wheretheroundaboutisusedforaestheticsorspeedcontrol,andvolumesarelowdonotrequireacapacityanalysis.OtherclassificationsmayrequiresomeanalysisbyeitherAASidraorRodeltoanalyzetheroundaboutincomparisonwithothertrafficcontroldevices.Forcapacityanalysisordesignvariablesonmajorcollectors,minororprincipalarterials,theuseofRodelsoftwareisrequired.
AllpreliminarydesignsshallbeaccompaniedbyAMandPMpeakhourturningmovecountsforexisting(ordevelopmentopening)volumesandfora20yearprojection,includingtheelectronicfilefromRodelwhenrequired.Wheretheroundaboutisnearaschool,shoppingcenter,orothermajortrafficgenerator,thepeakhourforlocaltrafficwiththetrafficgeneratorfullydevelopedshallbeused.
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2.6 Utilities & Drainage
Designofundergroundandoverheadutilitiesshallbeincludedonthefinaldesign.Designofwater,sewer,electric,andgaslinesshallmeettheappropriateColoradoSpringsUtility(CSU)standards.StreetlightingshallfollowCSUstandardsforpole,lightfixture,andtypeoflighting.Lightingshallbedesignedtoilluminateanypedestrianswithinthecrosswalkswithoutcausingabacklighteffect.Lightingshallbesituatedtohelpthedriveridentifythegeneralshapeoftheintersectionandtohighlightconflictpointsorareasofentry,andexitfrombeyondthestoppingsightdistanceasidentifiedinFigureIII.
Thefollowingdrainagestandardsapplytoroundabouts:
1. DrainageshallcomplywiththeCityDrainageCriteriaManual.Roundaboutsshouldbegenerallydesignedtoslopeawayfromthecentralislandwithdrainageinletslocatedontheoutercurbline.Placementofanyinletsshallincludeconsiderationofthewheelpathtravelingthroughtheroundaboutwiththedesirablelocationbetweentheentranceandexit,notalongtheroundaboutentrance,thecentralisland,theexit,orthesplitterislands.Inletswithintheroundaboutshallbeconstructedwitha6inchcurbheightandnoextensionofthegutterpan.AnalternatetothestandardCityinletdesign,suchastheCDOTTypeRinlet,isallowedtomeetthiscriterion.
2. If the8inchcurbheightisusedwiththestandardCityinletdesign,theinletmustbelocatedoutsideoftheroundaboutandapproachestolimitinfluenceonthedrivers’paththroughtheroundabout.Allinletguttersectionswillbelimitedinwidthto24inchesfromliptoflowline.
2.7 Landscaping
Landscapingisanimportantpartofthedesign,especiallyinthecenterislandtoprovidevisualawarenessoftheroundabout.Landscapingdesignsmustconsiderpedestrianandvehiclesafety,providingyeararoundamenitiesfortheroundaboutuserswithoutcausinganysightdistanceproblems,especiallyonapproachtopedestriancrossings.
Allfinaldesignsshallincludealandscapingdesignsheetidentifyingplanttypes,heightfromthetopofthematureplanttotheroadwaysurface,includingtheheightofplanterarea,andminimumpruningheightforthelowerbranchesofanytreestobeplanted.SeeFigureIIforareaswhereheightisrestrictedforsightdistancereasons.Withinthecentralisland,outsideoftherequiredstoppingsightdistanceline,theuseoflargermaterialsisencouragedtoimprovethedriver’sperceptionoftheroundaboutlocationandshape.Avoiddistractingdisplays,suchassigns,intricatesculpturesoranimateditemsorglarefromlightsthatcouldincreasethepotentialforaccidents.
2.8 Other
Otherdesigncriteriainclude,butarenotlimitedto:
1. The exitoftheroundaboutshouldbenosmallerthantheentryandincludetransitiontothefullwidthcross-section,includinganyon-streetparking.
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2. Transitstopsshouldbelocateddownstreamoftheroundaboutclearoftheexitarea,andbuiltwithapullout,ortheymaybecombinedwiththeon-streetparkingarea.
3. Priortosubmittingthepreliminarydesign,apre-designmeetingisrecommendedwithCityEngineeringtoidentifyanyunusualorlocation-specificdesigncriteriaordesignelementsorotherissuesuniquetothelocation.
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3.0 Specific/ Geometric Design Elements
3.1 Approach Roadway
Theapproachroadwaydesignelementsincludecurbalignment,medianwidthandtransition,approachflare,crosswalklocation,horizontalandverticalalignmentoftheapproachlane(s),intersectionandstoppingsightdistancecalculations,approachspeed,fastestpathradii,andotherassociatedelementsidentifiedinFiguresIthruVI.
Minimum/maximumstandardsincludethefollowing:
Fastest PathSingle Lane Multilane Roundabout
R Max Speed (MPH) R Max Speed (MPH)
R1 Entry 86-99’ 20 152-178’ 25
R2 Circulating 99-116’ 20 178-210’ 25
R3 Exit 152-178’ 25 152-178’ 25
R4 Leftturn 99-116’ 15 178-210’ 25
R4 Minimum* 18-20’ 10 33-37’ 13
R5 Rightturn 152-178’ 20 152-178’ 25
*R4hasaminimumrequirementtoreducerearendaccidentscausedbyexcessivespeeddifferential
Note–radiiaregivenasarangeforvarioussuperelevationratesfrom0%to4%,positiveforR1,R3&R5,andnegativeforR2andR4.
CalculationsforeachspecificroadwaysegmentandcorrespondingcrossslopeshouldfollowAASHTOGeometricDesignofHighways&Streets,2001orlater
Maximumapproachgrade 2%for200’onminorandprincipalarterials4%for100’onminorandmajorcollectors4%for50’onlocalstreets
ApproachDecisionSightDistance(“DSD”onfigureWW)
375’for25MPHorless450’for30MPH525’for35MPH600’for40MPH675’for45MPH750’for50MPH
Note–ApproachDecisionSightDistance,DSD,isthedistanceatwhichthedriverisawareofthechangeinalignmentcausedspecificallybytheroundabout.IftherequiredDSDisnotavailableduetotopographiclimitations,advancewarningsignswillberequired.VerticalalignmentmustbecheckedaswellashorizontalalignmentforrestrictionstoDSD.
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MinimumApproachTangent(approachcenterlinetoyieldline)
300’onprincipalarterial200’onminorarterial100’onallcollectors50’onlocalaccess
Min.distancetonearestaccess(distancefromsplitterisland)
600’onprincipalarterial300’onminorarterial100’onallcollectors30’onlocalaccess
3.2 Circulating Roadway
Thecirculatingroadway,thatportionoftheroundaboutbetweenthecentralislandandtheinscribedcircleistheportionoftheroadwayusedbyvehiculartraffic.Theinscribedcircleoftheroundabout,whichenclosesthecirculatingroadway,shallbelargeenoughtoaccommodateallroaduserswithoutexceedingthefastestpathmaximumradii.Generally,thedesignoftheinscribedcirclewillbefrom130’to200’formultilaneroundabouts,andfrom80’to130’forsinglelaneroundabouts.Theoutsideedgeofthecirculatingroadwayiswithinandgenerallythesamesizeastheinscribedcircle.
Thecirculatingroadwayshallbefrom1.0to1.2timestheapproachroadwaywidthattheentrytotheroundabout.Super-elevationforthecirculatoryroadshouldgenerallybenogreaterthan-0.02,althoughasuper-elevationofupto-0.04maybeapprovedifconditionswarrant.Adversesuperelevationispreferredforthecirculatoryroadasitprovidesasmoothertransitionformotorists,betterdrainage,andhelpskeepspeedstoanacceptablelevel.
Roundaboutsmaybedesignedandbuiltinstages,withtheinitialsizeoftheinscribedcirclelargeenoughforamultilaneroundabout,withanoversizedcentralislandthatrestrictsthecirculatingroadwaytoonelane.Inthiscase,itislikelythatatruckapronwillbeneeded.
Bypasslanesshouldbeavoidedifpossible,duetothedifficultyforpedestrians(especiallysightimpaired)tosafelycrossthreeroadwaysinsteadoftheusualtwoinotherroundabouts.IfthecapacityanalysiswithRodelindicatesthattheexistingandshorterrangeprojectedvolumeswilloperateatlevelDorbetter,theroundaboutshouldbebuiltwithoutabypass.Ifthe20yearprojectedvolumesshowtheneedforabypass,adequaterightofwayshallbeincludedtoaccommodatethefutureexpansionandthebypasswillbebuiltwhentheoperatingLOSexceedslevelC.
3.3 Sight Distance
StoppingSightDistance(SSD)isthedistancebetweenthehazardandtheapproachingdriver,measuredalongthevehiclepath.Itisusedtoassesssafetyforvehicletovehicleandvehicletopedestrianorbicyclehazards.Everyconflictpointattheintersectionmustbechecked,basedonvehiclespeedneartheconflictareaforobstructionsoftherequiredvisibilityarea–seeFigureIII.
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SSDfortheapproachandyieldattheroundaboutarebasedonAASHTOstandardsforurbanroadways,Section9ofthe2001geometricdesignmanual,CaseAforsightdistancetotheleft,andSection3,Ex3-1forSSDrelatingtopedestrians.Horizontalandverticalalignmentmustbechecked.
StoppingSightDistance 15MPH80’ 20MPH 115 25MPH 155 30MPH 200 35MPH 250 40MPH 305 45MPH 360
3.4 Splitter Islands
Splitterislandsprovideproperdeflectionofvehiculartrafficforspeedcontrolandpedestrianrefugearea.Theyarerequiredonallroundabouts,withpaintonlyallowedasanoptiononmini-roundaboutsand6”highmountablecurbonallotherroundabouts.Theyshallbeaminimumof50’long(measuredfromtheoutsideedgeofthecirculatorroad)ifthereisapedestriancrossing.Thealignmentofthesplitterislandshouldincorporateatangentextensionofthesplitterislandflowlinemeetingtheoutsideflowlineofthecentralisland.SeeFigureV
Splitterislandswherecrosswalksexistorareprojectedshallhaveaminimum6’x6’pedestrianrefuge(an8’x8’refugeispreferable).Crosswalksshouldbe25’fromtheyieldlineforsinglelaneroundabouts,and45–50’formultilaneroundabouts.Onmultilaneapproaches,thecrosswalksshouldberadialtothetraveledwaytoimprovevisibilityforpedestrians.
Thecurbfacealongthecirculatingroadwayshouldbeoffsetfromthetraveledwayadistanceof3’ontheapproachsidenexttothecirculatingroadwaytaperingto1.5’attheintersectionoftheentryandtheapproach.IslandnoseradiishallmeetthedimensionsasshowninFigureV.
3.5 Central Island
Centralislandsarethemostvisiblepartoftheroundaboutforapproachingvehiclesandestablishtheshapeandsizeoftheroundabout.Theirsizeiscriticaltothecorrectoperationoftheroundabout.
Centralislanddiameterforamultilaneroundaboutshouldbedesignedforeachcasetoassurethatthedeflectionforenteringvehiclesresultsinmeetingthemaximumfastestpathrequirements.Generally,thecentralislanddiameterwillbebetween65’and135’foramultilaneroundaboutandbetween50’and100’forasinglelaneroundabout.
Requiredtruckapronsshallnotexceed-0.08superelevations.Theyshallbeconstructedwitha4”highmountablecurbslopedbackata60degreeangleandroundedatthetop,with12”spillgutterfornewroundabouts.Key-incurbonlywithoutgutterpanwillbeallowedforretrofitofexistingintersectionsforthecentralislandwithdrainageawayfromthecurb.
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Truckapronsshouldbeconstructedofconcrete,contrastingintextureandcolorfromtheroad,easytomaintain,andabletowithstandloadsofturningtrucks(i.e.minimum6”decorative,contrastingconcrete,suchasexposedaggregate,colored,and/orpatternedconcrete,etc.).Brick,cobblestone,orotherindividuallyplacedpavingmaterialsarenotallowed.
Elevationdrawingsofthecentralislandshallbeincludedwiththepreliminaryplansforreview.Thecentralisland,notincludinganytruckapron,shallbeaminimumof2’abovethesurroundingroadwayoutsideofthesightdistancerestrictedareas,andshallbeofcontrastingtextureandcolorstotheroadwayandthebackground.Theyshallbedesignedforlowmaintenance(restricttheuseofsodorotherhighmaintenancesurfaces).
3.6 Signing and Marking 1. Signing-SeeFigureIVforsignlocations.AllsignsshallconformtoManualonUniform
TrafficControlDevices(MUTCD)asmodifiedbythelatestrecommendedroundaboutsigningstandardsandbythesedesignstandards.
a. Advanceroundaboutwarningsignswithadvisoryspeedplaquesarerequiredwhenevertopographyordriverdistractionprecludesadequateadvancevisibilityoftheroundabout–seeApproachDecisionSightDistanceinparagraph3.1fordistances.Theymayalsobeusedtemporarilyorpermanentlywheneveraroundaboutismodifiedoranewroundaboutconstructedasaretrofittoanexistingintersection.
b. Yieldsignsshallbeplacedontherightsideoftheroadatthepointwherevehiclesaretoyieldwhenenteringtheroundabout.Supplementalyieldsigninginthesplitterislandmayberequiredduetoalignmentorsightdistanceproblemswhereasingleyieldisnotadequate.Supplementalsignsnoting“ToTrafficinCircle”mayberequiredtobeaddedtotheyieldsignsonmultilaneroundabouts.“YIELD”pavementmarkingmayberequiredwherefieldobservationwarrants.
c. Laneassignmentsignsdepictingthelanesmaneuveringaroundtheroundabout(asinthefollowingfigure)shallbeprovidedonallmulti-laneapproaches.
1. Note–thissigntobereplacedwiththenewsignwith“Roundabout”atthetopinBlack/Yellow,and“LeftLane”and“RightLane”belowthesymbols.Also,examplesofsignswithonlyoneturnata“T”intersectionwillbegiven,andasignforasinglelaneentrywithanauxiliaryleftturnlaneontheflaredapproach.
d. Streetnamesignswithaminimumof6”letteringshallbeplacedonthesplitterislandsorientedtowardtrafficonthecirculatoryroadway.Flagtypesignsindicatingtheexitstreetnamearerequiredforarterialsonanymultilaneroundabout.
e. Advanceddirectionalguidancesigns(asdepictedinthefollowingfigure)shallbeusedasnotedintheintersectionguidelines.
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f. Seeparagraph2.4forrequiredpedestriancrossings.Pedestriansignageisrequiredwherepedestrianusagemeetsminimumrequirements.Allmarking,signing,andsupplementalwarningdevicesshallmeetMUTCDstandardsasmodifiedandshowninthedetaildrawingsinthisdesignguide.
2. Marking-AllpavementmarkingsshallconformtoMUTCDasmodifiedbythelatestrecommendedroundaboutguidelinesandthesedesignstandards.
a. Laneusepavementmarkings,includingarrowsandsolidordashedlinesshallbeusedonallmultilaneroundabouts.SeeFigureIVfortheircorrectplacement.
b. Yieldtrianglesshallbeusedtomarkthelocationatwhichdriversmustyieldtocirculatingtraffic.Theyieldmarkingsshallbecurvedalongtheoutlineofthecirculatoryroadandshallhavetrianglesorientedtowardapproachingdriversasdepictedinthefollowingfigure.Supplemental“YIELD”pavementmarkingmayberequiredwherefieldobservationsindicateasignificantnumberofvehiclesdonotyield.
c. Yellowedgelinesshallbeplacedalongtheleftedgeoftheapproachroadwayalongtheedgeofthesplitterislandsifthesplitterislandisinstalledwithinapaintedmedian.Formultilaneroundaboutsonly,yellowedgelinesarerequiredaroundthecentralisland,andwhiteedgelinesarerequiredalongtherightsideofthesplitterislandoutliningthecirculatingroadway.
d. Pedestriancrossingsshouldbemarkedwithladderstylemarkingsconsistingof2’x8’markings.
e. Retroreflectiveraisedpavementmarkers(RRPM)mayberequiredonthecentralislandandsplitterislandswheresightdistanceand/orlightingindicatesimprovedwarningisneededfornighttimeoperation.
3.7 Landscaping Design Elements
Splitterislandsshallbehardscapeorcontainlowlevelvegetationwithamaximumheightofthecurb,splitterislandstructure,andlandscaping,atmaturity,of30”abovetheroadway(seeFigureIII).
Thecentralislandshouldcontainverticalfeaturesoutsideofthestoppingsightdistancerestrictionarea,visibletoapproachingtrafficbothdayandnight,toreduceapproachspeeds.
NewroundaboutswithlandscapingshallhaveamaintenanceagreementwiththeCityParksDepartment,providingformaintenance,ortheyshallhaveguaranteedfundingformaintenanceofthelandscapingbyprivateorganizations(i.e.homeownersassociations,propertymanagementagencies,etc.).Retrofitroundaboutsshallhavelow-maintenancelandscapingoramaintenanceagreementsimilartonewroundabouts.
Landscapinganddesignelementsshallbeaestheticallypleasing,shallfitwithinthecontextofthesurroundingarea,shallnotdistractdrivers,andshallnotinterferewithpedestriansafety.
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4.0 Definitions
Central Island–theraisedareainthecenterofaroundaboutaroundwhichtrafficcirculates
Fastest Path Radius–theminimumradiusonthefastestthroughpatharoundthecentralislandmeasured5’fromanyflowline
Circulating Volume–thetotalvolumeinagivenperiodoftimeonthecirculatoryroadwayimmediatelypriortoanexit
Circulatory Roadway Width–thewidthbetweentheouterflowlineofthecirculatoryroadwayandthecentralisland,notincludingthewidthofanyapron
Deflection–thechangeintrajectoryofavehicleimposedbygeometricfeaturesoftheroadway
Departure Width–thewidthoftheroadwayusedbydepartingtrafficdownstreamoftheroundabout.Thedeparturewidthistypicallynomorethanthetotalroadwaywidth
Decision Sight Distance–fromAASHTOGeometricDesignmanual,Section3,thedistancefromtheintersectionwherethedriverrecognizesthattheyareapproachinganobstaclethatwillrequireamaneuverorstop
Design Vehicle–thelargestvehiclethatcanreasonablybeanticipatedtouseafacility
Entry Flare–thewideningofanapproachtoprovideadditionalcapacityattheyieldlineandstorage
Entry Path Radius–theminimumradiusonthefastestthroughpathpriortotheyieldline,measured5’fromanyflowline,notedasR1
Entry Radius–theminimumradiusofcurvatureoftheoutsideorrightcurbattheentry
Entry Speed–thespeedavehicleistravelingatasitcrossestheyieldline
Entry Width–thewidthoftheentrywhereitmeetstheinscribedcircle,measuredperpendicularlyfromtherightedgeoftheentrytotheintersectionpointoftheleftedgelineandtheinscribedcircle
Exit Path Radius–theminimumradiusonthefastestthroughpathintotheexit,measured5’fromanyflowline,notedasR3
Exit Radius–theminimumradiusofcurvatureoftheoutsiderightcurbattheexit
Exit Width–thewidthoftheexitwhereitmeetstheinscribedcircle,measuredperpendicularlyfromtherightedgeoftheexittotheintersectionpointoftheleftedgelineandtheinscribedcircle
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Inscribed Circle–thecircleformingtheouteredgeofthecirculatoryroadwayusedtodefinethesizeofaroundabout,measuredbetweentheouteredgesofthecirculatingroadway.Itisthediameterofthelargestcirclethatcanbeinscribedwithintheoutlineoftheintersection
Multilane Roundabout–aroundaboutthathasatleastoneentrywithtwoormorelanes,andacirculatoryroadwaythatcanaccommodatemorethanonevehicletravelingside-by-side
Right-Turn Bypass Lane–alaneprovidedadjacentto,butseparatedfrom,thecirculatoryroadway,thatallowsright-turningmovementstobypasstheroundabout.Alsoknownasaright-turnsliplane
Roundabout–anintersectionwith3ormoreapproachlegs,generallycircularinshapewherecontinuousflowoftrafficisallowedthroughtheuseoftheyieldandmergemaneuvers
Sight Triangle–anarearequiredtobefreeofobstructionstoenablevisibilitybetweenconflictingmovements
Single-Lane Roundabout–aroundaboutthathassinglelanesonallentriesandonecirculatorylane
Splitter Island–araisedorpaintedareaonanapproachusedtoseparateenteringfromexitingtraffic,deflectandslowenteringtraffic,andprovidestoragespaceforpedestrianscrossingthatintersectionapproachintwostages
Stopping Sight Distance–thedistancemeasuredalongthecenterlineoftravelonaroadwayrequiredforadriverusingthesighttriangleorsightlinetoperceiveandreacttoanobjectintheroadwayandtobraketoacompletestopbeforereachingthatobject
Truck Apron–araised,coloredand/ortexturedconcretesurfacenexttotheoutsidecurbofthecentralislanddesignedtoallowlargetruckstoturnwiththeirrearwheelsleavingtheroadwayandridingupontotheapronarea
Two-Stage Crossing–aprocessinwhichpedestrianscrossaroadwaybycrossingonedirectionoftrafficatatime,waitinginapedestrianrefugebetweenthetwotrafficstreamsifnecessarybeforecompletingthecrossing