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Chapter5:DesignofSharedUsePaths DRAFTFebruary2010AASHTOGuideforthePlanning,Design,andOperationofBicycleFacilities

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2010

Intersectionsbetweenpathwaysandroadwaysshouldbedesignedtobeaccessibletoallusers,as1

statedinSection5.1.1.ofthischapter.2

5.3.1.SHAREDUSEPATH CROSSINGTYPES 3Sharedusepathcrossingscanbebroadlycategorizedasmidblock,sidepath,orgradeseparated4

crossings.Acrossingisconsideredmidblockifitislocatedoutsideofthefunctionalareaofanyadjacent5

intersection.Insomerespects,amidblocksharedusepathcrossingcanbeconsideredasafourleg6

intersection.7

Asidepathcrossingoccurswithinthefunctionalareaofanintersectionoftwoormoreroadways(see8

Exhibit5.13).Sidepathcrossingsaretypicallyparalleltoatleastoneroadway.Sidepathintersections9

haveuniqueoperationalchallengesthataresimilartothoseofparallelfrontageroadways.Section5.2.210

coverstheseoperationalissuesindetail,andprovidesguidelinesforlocationswheresidepathsmaynot11

beappropriate.12

Insomelocations,roadwayorpathtrafficconditionsmaywarrantconsiderationofagradeseparated13

crossingconsistingofeitherabridgeovertheroadwayoranunderpassbeneaththeroadway.An14

analysisshouldbemadetoassessthedemandforandviabilityofagradeseparatedcrossing.See15

Section5.2.10.andthediscussionofgradeseparatedcrossingsintheAASHTOGuideforthe16DevelopmentofPedestrianFacilities.(9)17


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Chapter5:DesignofSharedUsePaths DRAFTFebruary2010AASHTOGuideforthePlanning,Design,andOperationofBicycleFacilitiesDRAFTFORAASHTOCOMMITTEEREVIEWANDCOMMENT

167AmericanAssociationofStateHighwayandTransportationOfficials,2010

1Exhibit5.13.MidblockandSidepathCrossingsRelativetoIntersectionFunctionalArea2

5.3.2.DESIGN OF MIDBLOCK CROSSINGS 3Thetaskofdesigningamidblockcrossingbetweenapathwayandaroadwayinvolvesanumberof4variables,includinganticipatedmixandvolumeofpathusers,thespeedandvolumeofmotorvehicle5trafficontheroadwaybeingcrossed,theconfigurationoftheroad,theamountofsightdistancethat6canbeachievedatthecrossinglocation,andotherfactors.Geometricdesignfeaturesandtraffic7controlsmustbeusedincombinationtoachievesafeandefficientaccommodationsforallusers.8GEOMETRICDESIGNISSUESAT CROSSINGS9Thedesignapproachfortheintersectionofasharedusepathwitharoadwayissimilartothedesign10approachusedfortheintersectionoftworoadwaysinthefollowingways:11

Theintersectionshouldbeconspicuoustobothroadusersandpathusers.12 Sightlinesshouldbemaintainedtomeettherequirementsofthetrafficcontrolprovided.13 Intersectionsandapproachesshouldbeonrelativelyflatgrades.14 Intersectionsshouldbeasclosetoarightangleaspossible,giventheexistingconditions.15


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Theleasttrafficcontrolthatiseffectiveshouldbeselected.1Itispreferableformidblockpathcrossingstointersecttheroadwayatanangleascloseto2

perpendicularas

practical,

so

as

to

minimize

the

exposure

of

crossing

path

users

and

maximize

sight

3

lines.Acrossingskewedat30degreesistwiceaslongasaperpendicularcrossing,doublingthe4

exposureofpathuserstoapproachingmotorvehicles,andincreasingdelaysformotoristswhomust5

waitforpathuserstocross.Retrofittingskewedpathcrossingscanreducetheroadwayexposurefor6

pathusers.Exhibit5.14depictsapathrealignmenttoachievea90degreecrossing.Aminimum607

degreecrossinganglemaybeacceptabletominimizerightofwayrequirements.(2)8

9

Exhibit5.14.CrossingAngleforMidblockPath10SPECIALISSUESWITHASSIGNMENTOF RIGHTOFWAY 11

Sharedusepathsareuniqueintermsoftheassignmentoftherightofway,duetothelegal12

responsibilityofdriverstoyieldto(orstopfor)pedestriansincrosswalks.Moststatecodesalso13

stipulatethatapedestrian(andbypresumedextensioninmanystates,acyclistenteringapath14

crosswalk)maynotsuddenlyleaveanycurb(orplaceofsafety)andwalkorrunintothepathofa15

vehiclethatissoclosethatitisimpossibleforthedrivertoyield.Theresultisamutualyielding16

responsibilityamongmotorvehicledriversandpathusers,dependinguponthetimingoftheirarrivalat17

anintersection.Thespeeddifferentialbetweenbicyclistsandpedestriansonthepathwaymustalsobe18

takenintoaccount.Bicyclistsapproachtheintersectionatafargreaterspeedthanpedestrians,andthey19


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desiretomaintaintheirspeedasmuchaspossible.Theresultisaneedtoremindbicyclistsoftheir1

responsibilitytoyieldorstop,whilenotconfusingtheissueofwhohasthelegalrightofwayatmidblock2

crossings.3

Giventhesecomplexities,themostprudentapproachwhendeterminingtheappropriatesafetyand4

controlmeasuresatmidblockpathwayintersectionsistofirstdeterminewhatmeasuresareneededfor5

pedestriansafetyandaccess(asdescribedbelow),asitmaybedeterminedthroughthisprocessthata6

pedestriansignalorbeaconisneeded.Ifasignalorabeaconisnotneeded,thenextstepisto7

determineclearsighttrianglesonthemajorandminorapproaches,soastoevaluateapplicabilityof8

yieldcontrolontheminorapproach.Engineeringjudgmentshouldbeapplied.9

DETERMININGAPPROPRIATE CROSSINGMEASURES10

Pedestrians

amount

to

a

substantial

share

of

users

on

most

paths

and

experience

the

greatest

amount

11

ofexposureatintersections.Uncontrolledpathwaycrossingsdesignedforpedestriansafetywillresult12

inbettersafetyforallusers.13

Highvisibilitymarkedcrosswalksarerecommendedatalluncontrolledpathroadwayintersections.On14

roadwayswithlowtrafficvolumesandspeedswheresightdistancesareadequate,themarked15

crosswalkshouldbesufficienttoaddresspedestriansafety.However,additionalcrossingmeasures16

(suchasreducingtrafficspeeds,shorteningcrossingdistance,enhancingdriverawarenessofthe17

crossing,and/orprovidingactivewarningofcrosswalkuserpresence)areneededatuncontrolled18

locationswherethespeedlimitexceeds40milesperhourandeither:19

TheroadwayhasfourormorelanesoftravelwithoutaraisedcrossingislandandanADTof2012,000vehiclesperdayorgreater;or21

Theroadwayhasfourormorelanesoftravelwitharaisedcrossingisland(eitherexistingor22planned)andanADTof15,000vehiclesperdayorgreater.(10)23

DETERMININGPRIORITYASSIGNMENT24

Inconventionalroadwayintersectiondesign,rightofwayisassignedtothehighervolumeand/orhigher25

speedapproach.Inthecaseofapathroadwayintersection,uservolumesonthepathshouldbe26

considered.Whileinmanycasesroadwayswillhavegreatervolumes,uservolumesonpopularpaths27

sometimesexceed

traffic

volumes

on

minor

crossed

streets.

In

such

situations,

total

user

delay

may

be

28

minimizedifroadwaytrafficyieldstopathtraffic,andgivencyclists'reluctancetolosemomentum,such29

anoperatingpatternoftendevelopsspontaneously.Insuchsituations,YIELDorSTOPcontrolismore30

appropriatelyappliedontheroadwayapproaches(givenananalysisofspeeds,sightdistances,etc.as31

describedbelow).32

Changesinuservolumesovertimeshouldalsobeconsidered.Newsharedusepathsareoftenbuiltin33

segments,resultinginlowinitialvolumes.Inthatcase,assignmentofprioritytoroadwaytrafficis34


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usuallyappropriate.However,pathvolumesmayincreaseovertime,raisingtheneedtoreexamine1

priorityassignment.Trafficflowsatpathroadwayintersectionsshouldbereviewedoccasionallyto2

assurethatthepriorityassignmentremainsappropriate.3

ROUTINEUSEOFSTOPSIGNS 4

Applicationofintersectioncontrols(YIELDsigns,STOPsigns,ortrafficsignals)shouldfollowtheprinciple5

ofprovidingtheleastcontrolthatiseffective.Installingunwarrantedorunrealisticallyrestrictive6

controlsonpathapproachesinanattempttoprotectpathuserscanleadtodisregardofcontrolsand7

intersectionoperatingpatternsthatareroutinelydifferentthanindicatedbythecontrols.Thiscan8

increaseanunfamiliaruser'sordriver'sriskofcollision,andpotentiallyleadtoalossofrespectforthe9

controlatwarrantedlocations.10

Acommon

misconception

is

that

the

routine

installation

of

stop

control

for

the

pathway

is

an

effective

11

treatmentforpreventingcrashesatpathroadwayintersections.PoorbicyclistcompliancewithSTOP12

signsatpathroadwayintersectionsiswelldocumented.Bicycliststendtooperateasthoughthereare13

YIELDsignsattheselocations:theyslowdownastheyapproachtheintersection,lookforoncoming14

traffic,andproceedwiththecrossingifitissafetodoso.Yieldcontrol(eitherforvehiculartrafficon15

theroadwayorforusersonthepathway)canthereforebeaneffectivesolutionatsomemidblock16

crossings,asitencouragescautionwithoutbeingoverlyrestrictive.17

EVALUATINGSIGHTDISTANCETOSELECTTYPEOF CONTROL18

Intersectionsightdistance(sighttriangles)isafundamentalcomponentinselectingtheappropriate19

controlatamidblockpathroadwayintersection.Asdescribedabove,theleastrestrictivecontrolthatis20

effectiveshouldbeused.Asnotedinhorizontalsightdistanceequation(Equation55),thelineofsight21

isconsideredtobe2.3feet(0.7m)abovetheroadwayorpathsurface.22

Roadwayapproachsightdistanceanddeparturesighttrianglesshouldbecalculatedinaccordancewith23

proceduresdetailedintheAASHTOPolicyonGeometricDesignofHighwaysandStreets(11),asmotor24vehicleswillcontrolthedesigncriteria.25

Generally,pathwayapproachsightdistanceshouldbecalculatedutilizingthefastesttypicalpathuser,26

whichinmostcasesistheadulttwowheeledbicyclist.Undercertainconditionsitmaybenecessaryor27

desirableto

use

adifferent

design

user

(therefore

different

approach

speed)

if

they

are

more

prevalent

28

andrepresentafastervalue.Ideally,approachsighttrianglesprovideanunobstructedviewofthe29

entireintersectionandasufficientamountoftheintersectingfacilitytoanticipateandavoidapotential30

collisionwithcrossingtraffic,regardlessofthetrafficcontrol.Approachestouncontrolledandyield31

controlledintersectionsshouldprovidetherecommendedapproachsighttriangle,orelseamore32

restrictivecontrolshouldbeconsidered.33


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Approachsighttrianglesneededforyieldcontroldependonthedesignspeedsofboththepathandthe1

roadway.Ifyieldcontrolistobeusedforeithertheroadwayapproachorthepathapproach,available2

sightdistanceshouldbeadequateforatraveleroneitherapproachtoslow,stop,andavoidatraveler3

ontheotherapproach.Theroadwaylegofthesighttriangleisbasedonbicyclistsabilitytoreachand4

crosstheroadwayiftheydontseeapotentiallyconflictingvehicleapproachingontheroadway,and5

havejustpassedthepointwheretheycanexecuteastopwithoutenteringtheintersection(seeExhibit6

5.15andEquation56).SeeEquation53andExhibit5.7forbicycliststoppingsightdistance.Similarto7

theroadwayapproach,thepathlegofthesighttriangleisbasedonmotoristsabilitytoreachandcross8

thejunctioniftheydontseeapotentiallyconflictingpathuserapproaching,andhavepassedthepoint9

wheretheycanexecuteastopwithoutenteringtheintersection.Thelengthalongthepathlegofeach10

approachisgivenbyEquation571.Ifthisyieldsighttrianglecannotbeprovided,amorerestrictive11

controlisrequired.12

13

14

15

16

Exhibit5.15.YieldSightTriangles17

1Equation57accountsforreducedmotorvehiclespeedsperstandardpracticeintheAASHTOPolicyon

GeometricDesignofHighwaysandStreets.(10)


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where: where:

= traveltimetoreachandcleartheroad(s)

= traveltimetoreachandcleartheroad(s)

a = lengthoflegofsighttrianglealongtheroadwayapproach(ft) a = lengthoflegofsighttrianglealongtheroadwayapproach(m)

= traveltimetoreachtheroadfromthedecisionpointforapathuserthatdoesntstop(s)

= traveltimetoreachtheroadfromthedecisionpointforapathuserthatdoesntstop(s)

w = widthoftheintersectiontobecrossed(ft)

w = widthoftheintersectiontobecrossed(m)

= typicalbicyclelength=6ft(seechapter3forotherdesignusers) = typicalbicyclelength=1.8m(seechapter3forotherdesignusers)

= designspeedofthepath(mph) = designspeedofthepath(km/h)= designspeedoftheroad(mph) = designspeedoftheroad(km/h)

S = stoppingsightdistanceforthepathusertravelingatdesignspeed(ft) S = stoppingsightdistanceforthepathusertravelingatdesignspeed(m)

USCustomary Metric

gt

at

aL

gt

at

aL

path

aag

V

Lwtt

47.1

path

aV

St

47.1

pathV

roadV

groadtVa 47.1

path

aV

St

278.0

groadtVa 278.0

pathV

roadV

path

aag

V

Lwtt

278.0

1Equation56.LengthofRoadwayLegofSightTriangle234


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where: where:

= traveltimetoreachandclearthepath

(s)

= traveltimetoreachandclearthepath

(s)

b = lengthoflegofsighttrianglealongthe

pathapproach(ft)

b = lengthoflegofsighttrianglealongthe

pathapproach(m)

= travel

time

to

reach

the

path

from

the

decisionpointforamotoristthat

doesntstop(s).Forroadapproach

gradesthatexceed3percent,value

shouldbeadjustedinaccordancewith

theAASHTOGreenBook(10)

= travel

time

to

reach

the

path

from

the

decisionpointforamotoristthat

doesntstop(s).Forroadapproach

gradesthatexceed3percent,value

shouldbeadjustedinaccordancewith

theAASHTOGreenBook(10)

= speedatwhichthemotoristwould

entertheintersectionafterdecelerating

(mph)(assumed0.60xroaddesign

speed)

= speedatwhichthemotoristwould

entertheintersectionafterdecelerating

(km/h)(assumed0.60xroaddesign

speed)

= speedatwhichbrakingbythemotorist

begins(mph)(sameasroaddesign

speed)

= speedatwhichbrakingbythemotorist

begins(km/h)(sameasroaddesign

speed)

= motoristdecelerationrate(ft/s)on

intersectionapproachwhenbrakingtoa

stopisnotinitiated

(assume5.0ft/s)

= motoristdecelerationrate(m/s)on

intersectionapproachwhenbrakingtoa

stopisnotinitiated

(assume1.5ft/s)

w = widthoftheintersectiontobecrossed

(ft)

w = widthoftheintersectiontobecrossed

(m)

= lengthofthedesignvehicle(ft) = lengthofthedesignvehicle(m)

= designspeedofthepath(mph) = designspeedofthepath(km/h)

= designspeedoftheroad(mph) = designspeedoftheroad(km/h)

USCustomary Metric

gt

at

aL

gt

at

aL

pathV

roadVpathV

roadV

road

aag

V

Lwtt

88.0

road

aag

V

Lwtt

167.0

gpathtVb 278.0

i

bea

a

VVt

47.147.1

i

bea

a

VVt

278.0278.0

gpathtVb 47.1

eV

bV

ia

eV

bV

ia

2

2

2

2

1

Equation57.

Length

of

Path

Leg

of

Sight

Triangle

2

3

Determiningsufficientstopandsignalcontrolledapproachsightdistanceissimplerthanyield4

controlled.Regardlessofwhichapproachhasstopcontrolorwhethertheintersectionissignal5

controlled,theroadwayandpathapproachestoanintersectionshouldalwaysprovideenoughstopping6

sightdistancetoobeythecontrol,andexecuteastopbeforeenteringtheintersection.7


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Departuresightdistanceforthepathshouldbebasedontheslowestuserwhowillhavethemost1

exposuretocrossingtraffic.Thisistypicallythepedestrian.However,becausepathcrossingsalso2

functionaslegalcrosswalks,akeysightdistanceconsiderationisstoppingsightdistancefortheroadway3

approachtoprovideadequatedistanceforthemotorvehicletostopifthepathuseriseitheralreadyin4

thecrosswalk,orisjustbeginningtoenterit.Ideally,departuresightdistanceprovidesstopped5

pathwayuserswithenoughsightdistanceoftheintersectingroadwaytojudgeadequategapsin6

oncomingtraffictocrosstheroadsafely.Thistypeofdeparturesightdistanceisdesirableforyieldand7

stopcontrolledpathapproaches.Undercertainconditionsitmaybenecessaryordesirabletousea8

differentdesignuser(andthereforedifferentdeparturespeed)iftheyaremoreprevalentandrepresent9

aslowervalue.10

Regardlessofintersectionsighttrianglelengths,roadwayandpathapproachestoanintersectionshould11

alwaysprovideenoughstoppingsightdistancetoavoidhazardsorpotentialconflictswithinthe12

intersection.

13

Multiway(i.e.,allway)stopsatpathroadwayintersectionsarenotrecommended.14

Atanintersectionofasharedusepathwithawalkway,aclearsighttriangleextendingatleast15ft(4.615

m)alongthewalkwayshouldbeprovided(seeExhibit5.16).Theclearsightlinewillenablepedestrians16

approachingthepathwaytoseeandreacttooncomingpathtraffictoavoidpotentialconflictsatthe17

pathwalkwayintersection.Ifasharedusepathintersectsanothersharedusepath,sighttriangles18

shouldbeprovidedsimilartoayieldconditionatapathroadwayintersection.However,bothlegsof19

thesighttriangleshouldbebasedonthestoppingsightdistanceofthepaths.UseEquation56forboth20

legsof

the

sight

triangle.

21


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1

Exhibit5.16.MinimumPathWalkwaySightTriangle2

MIDBLOCKSIGNALIZEDINTERSECTIONS3

Iftrafficandroadwaycharacteristicsmakecrossingdifficultforthepathuser,theneedforasignalor4

activewarningdevice(suchasabeacon)shouldbeconsideredbasedontrafficvolumes,speed,number5

oflanes,andavailabilityofarefuge.Guidanceontheneedforadditionalcrossingmeasuresisprovided6

inFHWAsSafetyEffectsofMarkedversusUnmarkedCrosswalksatUncontrolledLocations:FinalReport7andRecommendedGuidelines(10).Theuseofpathuservolumetodeterminetheneedforasignalized8crossingmaynotbeappropriate.Insomesituationsthepathusermaynothaveaccesstoanother9

appropriatecrossinglocation.10

MoreinformationonsignalsatpathroadwayintersectionsisprovidedinSection5.4.3.11

5.3.3.EXAMPLES OF MIDBLOCK INTERSECTION CONTROLS 12Exhibits5.17,5.18,5.19and5.20illustratevariousexamplesofmidblockcontroltreatments.Theyshow13

typicalpavementmarkingandsigncrossingtreatments.Thesediagramsareillustrativeandarenot14

intendedtoshowallsignsandmarkingsthatmaybenecessaryoradvisable,oralltypesofdesign15

treatmentsthatarepossibleattheselocations.Eachgraphicassumestheappropriateminimumsight16

distancesareprovidedfortheroadwayandthepath.17


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1Exhibit5.17.ExampleofMidblockPathRoadwayIntersectionPathisYIELDControlled2


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1Exhibit

5.18.

Example

Midblock

Path

Roadway

Intersection

Roadway

is

YIELD

Controlled

2


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1Exhibit5.19.ExampleofMidblockPathRoadwayIntersectionPathisSTOPControlled2


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179

1Exhibit

5.20.

Example

Midblock

Path

Roadway

Intersection

Roadway

is

STOP

Controlled

2

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