chapter 650 sight distance - wsdot.wa.gov
TRANSCRIPT
Design Manual M 21-01.03 Sight Distance May 2008 Page 650-1
Chapter 650 Sight Distance650.01 General650.02 References650.03 Definitions650.04 StoppingSightDistance650.05 PassingSightDistance650.06 DecisionSightDistance650.07 Documentation
650.01 GeneralThedriverofavehicleneedstoseefarenoughaheadtoassessdevelopingsituationsandtakeactionsappropriatefortheconditions.Forthepurposesofdesign,sightdistanceisconsideredintermsofstoppingsightdistance,passingsightdistance,anddecisionsightdistance.
Foradditionalinformation,seethefollowingchapters:
Chapter Subject
910 Sightdistanceatintersectionsatgrade
915 Sightdistanceatroundabouts
920 Sightdistanceatroadapproaches
930 Sightdistanceatrailroadcrossings
1020 Sightdistanceforpathsandtrails
650.02 References
(1) Design GuidanceManual on Uniform Traffic Control Devices for Streets and Highways,USDOT,FHWA;asadoptedandmodifiedbyChapter468-95WAC“Manualonuniformtrafficcontroldevicesforstreetsandhighways”(MUTCD)
(2) Supporting InformationA Policy on Geometric Design of Highways and Streets,AASHTO,2004
650.03 DefinitionsFordefinitionsofdesignspeed,roadway,ruraldesignarea,suburbanarea,andurbandesignarea,seeChapter440.
decision sight distance Thedistanceforadrivertodetectanunexpectedordifficulttoperceivecondition,interpretandrecognizethecondition,selectanappropriatemaneuver,andcompletethemaneuver.
passing sight distance Thedistance(onatwolanehighway)foravehicletoexecuteanormalpassingmaneuverbasedondesignconditionsanddesignspeed.
sight distance Thelengthofhighwayvisibletothedriver.
stopping sight distance Thedistancetostopavehicletravelingatdesignspeed.
Sight Distance Design Manual M 21-01.03 Page 650-2 May 2008
Sight Distance Chapter 650
650.04 Stopping Sight Distance
(1) Design CriteriaStoppingsightdistanceisprovidedwhenthesightdistanceavailabletoadriverequalsorexceeds thestoppingdistanceforapassengercartravelingatthedesignspeed.Stoppingdistancefordesign iscalculatedinaconservativefashionwithlowerdecelerationandslowerperceptionreactiontime thannormallyexpected.
Note:Providedesignstoppingsightdistanceatallpointsonallhighwaysandonallintersectingroadways.
(a) Stopping distanceisthesumoftwodistances:thedistancetraveledduringperceptionandreactiontimeandthedistancerequiredtostopthevehicle.Theperceptionandreactiondistanceusedindesignisthedistancetraveledin2.5secondsatthedesignspeed.Thedesignstoppingdistanceiscalculatedusingthedesignspeedandaconstantdecelerationrateof11.2feet/second2.(Forstoppingdistancesongradeslessthan3%,seeFigure650-1;forgrades3%orgreater,seeFigure650-3.)
(b) Sight distanceiscalculatedforapassengercarusinganeyeheight(h1)of3.50feetandanobjectheight(h2)of0.50foot.Theobjectheightistheheightofthelargestobjectinvisibletothedriveratthestoppingdistance.Inurbandesignareas,withjustification,theobjectheight(h2)maybeincreasedto2.00feet.Also,the2.00-footobjectheight(h2)isusedwhenthesightlineobstructionisbarrier.
(c) Design stopping sight distance. Figure650-1givesthedesignstoppingsightdistancesforgradeslessthan3%,theminimumcurvelengthfora1%gradechangetoprovidethesightdistance(usingh2=0.50feet)foracrest(KC)andsag(KS)verticalcurve,andtheminimumlengthofverticalcurveforthedesignspeed(VCLm).Forsightdistanceswhenthegradeis3%orgreater,see650.04(2).
Design Speed (mph)
Design Stopping Sight Distance (ft) Kc Ks VCLm (ft)
25 155 18 25 7530 200 30 36 9035 250 47 49 10540 305 70 63 12045 360 98 78 13550 425 136 96 15055 495 184 115 16560 570 244 136 18065 645 313 157 19570 730 401 180 21075 820 506 206 22580 910 623 231 240
Design Stopping Sight DistanceFigure 650-1
Design Manual M 21-01.03 Sight Distance May 2008 Page 650-3
Chapter 650 Sight Distance
(d) Existing stopping sight distance.Thecosts,environmentalimpacts,andtrafficimpactstoincreasesightdistanceonexistingroadwaysareoftenhigherthantoprovidethatsightdistancewhenbuildinganewroadway.Theexistingroadwaycanbeanalyzedtodeterminewhetherthereisacorrectablecollisiontrend.Thelessconservativeexistingstoppingsightdistancecriteriamaybeusedwhentheverticalandhorizontalalignmentsareunchanged,thesightlineobstructionisexisting,thesightdistancewillnotbereduced,andthereisnoidentifiedcorrectablecollisiontrend.Thestoppingdistanceforexistingcriteriaisbasedonatravelspeedlessthanthedesignspeed.Also,the2.00-footobjectheight(h2)isusedforexistingcriteria.Foradditionalinformation,see650.04(7).
(e) Stopping sight distance design criteria selection. Figure650-2givesguidance fortheselectionofstoppingsightdistancedesigncriteria.
Type Stopping Sight Distance Object HeightRural Figures 650-1 & 650-3 0.50 ftUrban desirable Figures 650-1 & 650-3 0.50 ft Urban[1] Figure 650-1 2.00 ftExisting[2] Figures 650-1 & 650-3 2.00 ftTraffic Barrier Figure 650-13 2.00 ft[1] Justification required.[2] See 650.04(1)(d).
Stopping Sight Distance: Design Criteria SelectionFigure 650-2
(2) Effects of GradeThegradeofthehighwayhasaneffectonthevehicle’sstoppingsightdistance. Thestoppingdistanceisincreasedondowngradesanddecreasedonupgrades. Figure650-3givesthestoppingsightdistancesforgradesof3%andsteeper.Whenevaluatingsightdistancewithachanginggrade,usethegradeforwhichthelongest sightdistanceisneeded.
Sight Distance Design Manual M 21-01.03 Page 650-4 May 2008
Sight Distance Chapter 650
Design Speed (mph)
Stopping Sight Distance (ft)Downgrade Upgrade
-3% -6% -9% 3% 6% 9%25 158 165 173 147 143 14030 205 215 227 190 184 17935 258 271 288 237 229 22240 315 333 354 289 278 26945 378 401 428 345 331 32050 447 474 508 405 389 37555 520 553 594 470 450 43360 599 638 687 539 515 49565 683 729 786 612 585 56170 772 826 892 690 658 63175 867 928 1004 773 736 70580 966 1037 1123 860 818 782
Design Stopping Sight Distance on GradesFigure 650-3
Forstoppingsightdistancesongradesbetweenthoselisted,interpolatebetweenthevaluesgivenorusetheequationinFigure650-4.
±
+=
1002.3230
47.1
2
G
VVS
a
t
Where:S = Stopping sight distance on grade (ft)V = Design speed (mph)t = Perception/reaction time (2.5 sec)a = Deceleration rate (11.2 ft/sec2)G = Grade (%)
Stopping Sight Distance on GradesFigure 650-4
(3) Crest Vertical CurvesUseFigure650-5ortheequationsinFigure650-6tofindtheminimumcrestverticalcurvelengthtoprovidestoppingsightdistancewhengiventhealgebraicdifferenceingrades.WhenusingtheequationsinFigure650-6,useh1=3.50feetandh2=0.50foot.Figure650-5doesnotusethesightdistancegreaterthanthelengthofcurveequation.Whenthesightdistanceisgreaterthanthelengthofcurveandthelengthofcurveiscritical,theS>LequationgiveninFigure650-6maybeusedtofindtheminimum curvelength.
Whenanewcrestverticalcurveisbuiltoranexistingoneisrebuiltwithgradeslessthan3%,providedesignstoppingsightdistancefromFigure650-1.Forgrades3%orgreater,providestoppingsightdistancefrom650.04(2).
Design Manual M 21-01.03 Sight Distance May 2008 Page 650-5
Chapter 650 Sight Distance
The minimum length can also be determined by multiplying the algebraic difference in grades by the KC value from Figure 650-1 (L=KC*A). Both the figure and the equation give approximately the same length of curve. Neither use the S>L equation.
* This chart is based on a 0.50-foot object height. When a higher object height is allowed (see 650.04(3) for guidance), the equations in Figure 650-6 must be used.
Stopping Sight Distance for Crest Vertical CurvesFigure 650-5
Sight Distance Design Manual M 21-01.03 Page 650-6 May 2008
Sight Distance Chapter 650
Inurbandesignareas,withjustification,anobjectheight(h2)of2.00feetmaybeusedwiththeequationsinFigure650-6.
Whenevaluatinganexistingroadway,see650.04(7).
When S>L
( )A
2002SL
2
21 hh +−=
( )A
100
A
LS
2
21 hh ++=
( )2
21
2
hh +
=
200
ASL
( )A
200LS
2
21 hh +=
( )A
2002SL
2
21 hh +−=
( )A
100
A
LS
2
21 hh ++=
( )2
21
2
hh +
=
200
ASL
( )A
200LS
2
21 hh +=
When S<L
( )A
2002SL
2
21 hh +−=
( )A
100
A
LS
2
21 hh ++=
( )2
21
2
hh +
=
200
ASL
( )A
200LS
2
21 hh +=
( )A
2002SL
2
21 hh +−=
( )A
100
A
LS
2
21 hh ++=
( )2
21
2
hh +
=
200
ASL
( )A
200LS
2
21 hh +=
Where:L = Length of vertical curve (ft)S = Sight distance (ft)A = Algebraic difference in grades (%)h1 = Eye height (3.50 ft)h2 = Object height—see text (ft)
Sight Distance: Crest Vertical CurveFigure 650-6
(4) Sag Vertical CurvesSightdistanceisnotrestrictedbysagverticalcurvesduringthehoursofdaylight.Therefore,headlightsightdistanceisusedforthesightdistancedesigncriteriaatsagverticalcurves.Insomecases,alesserlengthmaybeallowed.Forguidance,seeChapter630.
UseFigure650-7ortheequationsinFigure650-8tofindtheminimumlengthforasagverticalcurvetoprovidetheheadlightstoppingsightdistancewhengiventhealgebraicdifferenceingrades.ThesightdistancegreaterthanthelengthofcurveequationisnotusedinFigure650-7.Whenthesightdistanceisgreaterthanthelengthofcurveandthelengthofcurveiscritical,theS>LequationgiveninFigure650-8maybeusedtofindtheminimumlengthofcurve.
Whenanewsagverticalcurveisbuiltoranexistingoneisrebuiltwithgradeslessthan3%,providedesignstoppingsightdistancefromFigure650-1.Forgrades3%orgreater,providestoppingsightdistancefrom650.04(2).
Whenevaluatinganexistingroadway,see650.04(7).
Design Manual M 21-01.03 Sight Distance May 2008 Page 650-7
Chapter 650 Sight Distance
The minimum length can also be determined by multiplying the algebraic difference in grades by the KS value from Figure 650-1 (L=KS*A). Both the figure and equation give approximately the same length of curve. Neither use the S>L equation.
Stopping Sight Distance for Sag Vertical CurvesFigure 650-7
Sight Distance Design Manual M 21-01.03 Page 650-8 May 2008
Sight Distance Chapter 650
Where S>L
A
3.5S400-2SL
+=
3.52A
400LAS
−
+=
3.5S400
2AS
L+
=
( )
2A
1600AL2
3.5L3.5LS
+±=
A
3.5S400-2SL
+=
3.52A
400LAS
−
+=
3.5S400
2AS
L+
=
( )
2A
1600AL2
3.5L3.5LS
+±=
Where S<L
A
3.5S400-2SL
+=
3.52A
400LAS
−
+=
3.5S400
2AS
L+
=
( )
2A
1600AL2
3.5L3.5LS
+±=
A
3.5S400-2SL
+=
3.52A
400LAS
−
+=
3.5S400
2AS
L+
=
( )
2A
1600AL2
3.5L3.5LS
+±=
Where:L = Curve length (ft)A = Algebraic grade difference (%)S = Sight distance (ft)
Sight Distance, Sag Vertical CurveFigure 650-8
(5) Horizontal CurvesUseFigure650-10ortheequationinFigure650-11tocheckforadequatestoppingsightdistancewheresightlineobstructionsareontheinsideofacurve.Astoppingsightdistancesightlineobstructionisanyroadsideobjectwithinthehorizontalsightlineoffset(M)distance(suchasmedianbarrier,guardrail,bridges,walls,cutslopes,woodedareas,andbuildings),2feetorgreaterabovetheroadwaysurfaceatthecenterlineofthelaneontheinsideofthecurve(ho).Figure650-10andtheequationinFigure650-11areforusewhenthelengthofcurveisgreaterthanthesightdistanceandthesightrestrictionismorethanhalfthesightdistancefromtheendofthecurve.Whenthelengthofcurveislessthanthestoppingsightdistanceorthesightrestrictionisneareitherendofthecurve,thedesiredsightdistancemaybeavailablewithalesserMdistance(seeFigure650-9).Whenthisoccurs,thesightdistancecanbecheckedgraphically.
Sight Distance Area on Horizontal CurvesFigure 650-9
Design Manual M 21-01.03 Sight Distance May 2008 Page 650-9
Chapter 650 Sight Distance
A sightline obstruction is any roadside object within the horizontal sightline offset (M) distance, 2 feet or greater above the roadway surface at the centerline of the lane on the inside of the curve. For additional information, see 650.04(5).
Horizontal Stopping Sight DistanceFigure 650-10
Sight Distance Design Manual M 21-01.03 Page 650-10 May 2008
Sight Distance Chapter 650
Whentheroadgradeislessthan3%,providedesignstoppingsightdistancefromFigure650-1. Whenthegradeis3%orgreater,providestoppingsightdistancefrom650.04(2).
Inurbandesignareas,withjustification,orwhenthesightlineobstructionisatrafficbarrier,a2.00footobjectheight(h2)maybeused.Whenh2=2.00feet,roadsideobjectswithaheight(ho)between2.00feetand2.75feetmightnotbeastoppingsightdistancesightlineobstruction.Whenh2=2.00feet,objectswithanhobetween2.00feetand2.75feetcanbecheckedgraphicallytodeterminewhethertheyarestoppingsightdistancesightlineobstructions.
Whereasightlineobstructionexistsandsitecharacteristicsprecludedesignmodificationstomeet criteria,consultwiththeRegionTrafficEngineerandAssistantStateDesignEngineerforadeterminationofappropriateaction.
Whenevaluatinganexistingroadway,see650.04(7).
=
R
28.65Scos-1RM
−
=−
R
MRcos
28.65
RS
1
=
R
28.65Scos-1RM
−
=−
R
MRcos
28.65
RS
1
Where:M = Horizontal sightline offset measured from the centerline of the inside lane of the curve to the sightline obstruction (ft)R = Radius of the curve (ft)S = Sight distance (ft)
Sight Distance, Horizontal CurvesFigure 650-11
(6) Overlapping Horizontal and Vertical CurvesAverticalcurveonahorizontalcurvewillaffectwhicharoadsideobjectswillbecomesightlineobstructions.Acrestverticalcurvewillmakeroadsideobjectsmorelikelytobecomesightlineobstructions.Asagverticalcurvewillmakeroadsideobjectslesslikelytobesightlineobstructions.
Figure650-12canbeusedtodeterminethesightdistanceforcrestverticalcurvesonhorizontalcurveswith:• SightlineobstructionsinsidetheMdistance.• Sightlineobstructionheight(ho)of2.00feetorless.• Objectheight(h2)of2.00feet.
Forotherlocations,thesightdistancecanbecheckedgraphically.
(7) Existing Stopping Sight DistanceFigure650-13givesthevaluesforexistingstoppingsightdistanceandtheassociatedKCandKS values.Useanobjectheight(h2)of2.00feetwithexistingstoppingsightdistancecriteria.
Design Manual M 21-01.03 Sight Distance May 2008 Page 650-11
Chapter 650 Sight Distance
( ) ( )[ ]A
LS
2
21 22100 oo hhhh −+−=
The following equation may be used to determine the sight distance for roadside sightline obstructions inside the horizontal sightline offset (M) distance (see Figure 650-11) with a height of 2.00 feet or less above the centerline of the lane on the inside of the curve on overlapping horizontal and crest vertical curves.
( ) ( )[ ]A
LS
2
21 22100 oo hhhh −+−=
Where:L = Length of vertical curve (ft)S = Sight distance (ft)A = Algebraic difference in grades (%)h1 = Eye height (3.50 ft)h2 = Object height (0.50 ft or 2.00 ft) (see 650.04(1))ho = Height of roadside sightline obstructions above the centerline of the inside curve lane (ft)
Note: The above equation cannot be used for sightline obstruction height (ho) more than 2 feet above the centerline of the lane on the inside of the curve. The available sight distance must be checked graphically for these sightline obstructions.
Overlapping Horizontal and Crest Vertical Curves: Stopping Sight DistanceFigure 650-12
Sight Distance Design Manual M 21-01.03 Page 650-12 May 2008
Sight Distance Chapter 650
(a) For crest vertical curveswherethereisnoidentifiedcorrectablecollision trend,theexistingverticalalignmentisretained,andtheexistingroadwaypavementisnotreconstructed,existingstoppingsightdistancevaluesinFigure650-13maybeused.Theminimumlengthofanexistingcrestverticalcurvemaybefoundusing theequationsinFigure650-6andh2=2.00feet,orusingtheKCvaluesfrom Figure650-13.
(b) For sag vertical curveswherethereisnoidentifiedcorrectablecollisiontrend,theexistingverticalalignmentisretained,andtheexistingroadwaypavementisnotreconstructed,existingstoppingsightdistancevaluesinFigure650-13maybeused.TheminimumlengthofanexistingsagverticalcurvemaybefoundusingtheequationsinFigure650-8,orusingtheKSvaluesfromFigure650-13.Insomecases,whencontinuousilluminationisprovided,alesserlengthmaybeallowed. Forguidance,seeChapter630.
(c) For horizontal curves,existingstoppingsightdistancevaluesfromFigure650-13maybeusedatlocationswhereallofthefollowingaremetatthecurve:• Thereisnoidentifiedcorrectablecollisiontrend• Theexistingverticalandhorizontalalignmentisretained• Theexistingroadwaypavementisnotreconstructed• Theroadwaywillnotbewidened,exceptforminorshoulder wideningrequiringnoworkpastthebottomoftheditch
• Thesightlineobstructionisexisting• Roadsideimprovementstosightdistancedonotrequireadditionalrightofway
Asightlineobstructionisanyroadsideobjectwithinthehorizontalsightlineoffset(M)distancefromtheequationinFigure650-11withaheight(ho)of2.00feetormoreabovethecenterlineoftheinsidelane.Roadsideobjectswithanhobetween2.00feetand2.75feetmightnotbeasightlineobstruction.Objectswithanho between2.00feetand2.75feetcanbecheckedgraphicallytodeterminewhether theyaresightlineobstructions.
Design Speed (mph)
Existing Stopping Sight Distance (ft) KC KS
20 115 6 1625 145 10 2330 180 15 3135 220 22 4140 260 31 5245 305 43 6350 350 57 7555 400 74 8960 455 96 10465 495 114 11570 540 135 12775 585 159 14080 630 184 152
Existing Stopping Sight Distance
Figure 650-13
Design Manual M 21-01.03 Sight Distance May 2008 Page 650-13
Chapter 650 Sight Distance
650.05 Passing Sight Distance
(1) Design CriteriaPassingsightdistanceisthesumofthefollowingfourdistances:• Thedistancetraveledbythepassingvehicleduringperceptionandreactiontimeandinitialaccelerationtothepointofencroachmentontheopposinglane
• Thedistancethepassingvehicletravelsintheopposinglane• Thedistanceanopposingvehicletravelsduringtwo-thirdsofthetimethepassingvehicleisintheopposinglane
• Aclearancedistancebetweenthepassingvehicleandtheopposingvehicleattheendofthepassingmaneuver
Sightdistanceforpassingiscalculatedforapassengercarusinganeyeheight(h1)of3.50feetandanobjectheight(h2)of3.50feet.Figure650-14givesthepassingsightdistancesforvariousdesignspeeds.
Design Speed (mph) Passing Sight Distance (ft)
20 71025 90030 109035 128040 147045 162550 183555 198560 213565 228570 248075 258080 2680
Passing Sight Distance
Figure 650-14
Ontwo-lanetwo-wayhighways,providepassingopportunitiestomeettrafficvolumedemands.Thiscanbeaccomplishedwithsectionsthatprovidepassingsightdistanceorbyaddingpassinglanesatlocationsthatwouldprovidethegreatestbenefittopassing(seeChapter1010).
Inthedesignstage,passingsightdistancecanbeprovidedbyadjustingthealignmenteitherverticallyorhorizontallytoincreasepassingopportunities.
Theseconsiderationsalsoapplytomultilanehighwayswherestagedconstructionincludesatwo-lanetwo-wayoperationasaninitialstage.Whetherauxiliarylanesareprovided,however,dependsonthetimelagproposedbetweentheinitialstageandthefinalstageofconstruction.
Sight Distance Design Manual M 21-01.03 Page 650-14 May 2008
Sight Distance Chapter 650
(2) Vertical CurvesFigure650-15givesthelengthofcrestverticalcurveneededtoprovidepassingsightdistancefortwolanehighways.ThedistancefromFigure650-14andtheequationsinFigure650-6,using3.50feetforbotheyeheight(h1)andobjectheight(h2),mayalsobeusedtodeterminetheminimumlengthofverticalcurvetomeetthepassingsightdistancecriteria.
Sagverticalcurvesarenotarestrictiontopassingsightdistance.
(3) Horizontal CurvesPassingsightdistancecanberestrictedontheinsideofahorizontalcurvebysightlineobstructionsthatare3.50feetormoreabovetheroadwaysurface.UsethedistancefromFigure650-14andtheequationinFigure650-11todeterminewhethertheobjectiscloseenoughtotheroadwaytobearestrictiontopassingsightdistance.Theequationassumesthatthecurvelengthisgreaterthanthesightdistance.Wherethecurvelengthislessthanthesightdistance,thedesiredsightdistancemaybeavailablewithalessersightlineoffset(M)distance.
(4) No-Passing Zone MarkingsKnowledgeofthepracticesusedformarkingnopassingzonesontwolaneroads ishelpfulindesigningareasonablysafehighway,consultwiththeregiontrafficengineerasappropriate.ThevaluesinFigure650-14arethepassingsightdistancesstartingwherethepassingmaneuverbegins.ThevaluesintheMUTCDareregulatoryfornopassingzonemarkinglimitsandstartwherepassingmustbecompleted.ThevaluesintheMUTCDarelowerthantheFigure650-14values.
650.06 Decision Sight DistanceDecisionsightdistancevaluesaregreaterthanstoppingsightdistancevaluesbecausetheygivethedriveranadditionalmarginforerrorandaffordsufficientlengthtomaneuveratthesameorreducedspeedratherthantojuststop.
Providedecisionsightdistanceatlocationswherethereishighlikelihoodfordrivererrorininformationreception,decisionmaking,orcontrolactions.Examplesincludeinterchanges;intersections;majorchangesincrosssection(suchasattollplazasanddroplanes);andareasofconcentrateddemandwheresourcesofinformationcompete(forexample,thosefromroadwayelements,traffic,trafficcontroldevices,andadvertisingsigns).Ifsitecharacteristicsallow,locatethesehighwayfeatureswheredecisionsightdistancecanbeprovided.Ifthisisnotpracticable,usesuitabletrafficcontroldevicesandpositiveguidancetogiveadvancedwarningoftheconditions.
UsethedecisionsightdistancesinFigure650-16atlocationsthatrequirecomplexdrivingdecisions.
Design Manual M 21-01.03 Sight Distance May 2008 Page 650-15
Chapter 650 Sight Distance
A
2800-2SL =
A
1400
2
LS +=
2800
ASL
2
=
A
2800LS =
Where S>L
A
2800-2SL =
A
1400
2
LS +=
2800
ASL
2
=
A
2800LS =
A
2800-2SL =
A
1400
2
LS +=
2800
ASL
2
=
A
2800LS =
Where S<L
A
2800-2SL =
A
1400
2
LS +=
2800
ASL
2
=
A
2800LS =
A
2800-2SL =
A
1400
2
LS +=
2800
ASL
2
=
A
2800LS =
Where:L = Curvelength(ft)A = Algebraicgradedifference(%)S = Sightdistance(ft)
A
2800-2SL =
A
1400
2
LS +=
2800
ASL
2
=
A
2800LS =
Passing Sight Distance for Crest Vertical CurvesFigure 650-15
Sight Distance Design Manual M 21-01.03 Page 650-16 May 2008
Sight Distance Chapter 650
Design Speed (mph)Decision Sight Distance for Maneuvers (ft)A B C D E
30 220 490 450 535 62035 275 590 525 625 72040 330 690 600 715 82545 395 800 675 800 93050 465 910 750 890 103055 535 1030 865 980 113560 610 1150 990 1125 128065 695 1275 1050 1220 136570 780 1410 1105 1275 144575 875 1545 1180 1365 154580 970 1685 1260 1455 1650
Decision Sight DistanceFigure 650-16
ThemaneuversinFigure650-16areasfollows:A.RuralstopB.UrbanstopC.Ruralspeed/path/directionchangeD.Suburbanspeed/path/directionchangeE.Urbanspeed/path/directionchange
Decisionsightdistanceiscalculatedusingthesamecriteriaasstoppingsightdistance:h1=3.50feetandh2=0.50foot.UsetheequationsinFigures650-6,8, and11todeterminethedecisionsightdistanceforcrestverticalcurves,sagverticalcurves,andhorizontalcurves.
650.07 DocumentationForthelistofdocumentsrequiredtobepreservedintheDesignDocumentationPackageandtheProjectFile,seetheDesignDocumentationChecklist: www.wsdot.wa.gov/design/projectdev/