Traffic engineering

ALL Basic Component of Traffic Engineering to be covered with example of Signal with suitable figure.

1. 2CI 703 –Highway & Traffic
Engineering
“Traffic
Engineering”

2. What Is Traffic Engineering?
✓TrafficEngineeringisabranchofCivilEngineering
whichdealswiththeSafe&Efficientmovementof
people&goodsonroadways.
✓InstituteofTrafficEngineering,U.S.A.defines,“Traffic
engineeringisthatphaseofengineeringwhichdealswith
planningandgeometricdesignofStreets,Highways,
abuttinglandsandwithtrafficoperationthereon,astheir
useisrelatedtothesafe,convenient&economic
transportationofpersons&Goods”.

3. ✓TrafficEngineeringisthatbranchofengineeringwhich
dealswiththeimprovementoftrafficperformanceof
roadnetwork&terminals.
✓Thisisachievedbysystematictrafficstudies.Scientific
analysis&engineeringapplication.
✓Thismethodincludesplanning&geometricdesignonthe
onehandandregulationandcontrolontheother.
✓Trafficengineeringthereforedealswiththeapplicationof
scientificprinciples,tools,techniques&findingforsafe,
rapid,convenient&economicmovementofpeople&
goods.

4. ✓Trafficengineeringfocusesontheconstructionof
infrastructurewhichnecessaryformovementofpeople&
goodswithgoodlevelofservice,safe,economic,
sustainable&environmentallysafe.
✓MovementofPeople&goodsfromoneplacetoother
placeinvolvemanyactivitieslikepurposeofmovement,
timeformovement,modeformovement.

5. ❑Scope of Traffic Engineering:
✓ThebasicobjectofTrafficengineeringistoachieve
efficientfree&rapidflowoftraffic,withleastnumberof
trafficaccident.
✓Actualstudiesoftrafficoperationsprovidethefoundation
fordevelopingmethodsforimprovementingeneral&for
solvingspecificproblems.
✓Thestudyoftrafficengineeringdividedintoseven
majorsection:
✓TrafficCharacteristics
✓Trafficstudies&Analysis
✓Trafficoperation-control&Regulation
✓Planning&analysis
✓Geometricdesign
✓Administration&Management
✓RoadsafetyAspect

6. ✓StudiesofTrafficcharacteristicisthemostessential
prerequisiteforanyimprovementoftrafficfacilities.
✓Thetrafficcharacteristicsarequitecomplexwithvarious
typesofroadusersintheroadmovingwithdifferent
motives.
✓Thestudyofvehicularcharacteristicsisanessentialpart.
Apartformthesethevariousstudiestobecarriedouton
theactualtrafficincludespeed,volume,capacity,travel
pattern,origin&destination,trafficflowcharacteristics,
parking&accidentstudies.
✓Variousaspectsthatarecoveredundertrafficoperations
areregulations,controlandthewarrantsforapplicationof
controls.

7. ✓Regulationsmaybeintheformoflaws&ordinancesor
othertrafficregulatorymeasuressuchasspeedlimitsetc.
✓InstallationofTrafficcontroldeviceslikesigns,signals&
islandsaremostcommonmeanstoregulate&control
traffic.
✓Trafficplanningisaseparatephaseformajorhighways
likeexpressway,arterialroad,masstransitfacilities&
parkingfacilities.
✓Alltheaspectssuchascrosssection&surfacedetails,
sightdistancerequirement,horizontal&vertical
alignment,intersections&parkingfacilitiesaretobe
suitablydesignforbetterperformance.

8. ✓Thevariousphaseoftrafficengineeringareimplemented
withthehelpof“Engineering,Enforcement&
Education”or“3-Es”.
✓Enforcementisusuallymadethroughtrafficlaws,
regulation&control.
✓Educationispossiblebysufficientpublicity&through
schoolsandtelevision.Itaimsatimprovingthehuman
improvedtrafficperformance.
✓Engineeringphaseistheonewhichisconstructive.This
phasedealswithimprovementofroadgeometrics,
providingadditionalroadfacilities&installationof
suitablydesignedtrafficcontroldevices.

9. ❑TRAFFIC CHARACTERISTICS
✓TrafficEngineeringdealswiththreeelements:
✓RoadUserCharacteristics(Drive,Passenger&
pedestrian)
✓VehicleCharacteristics(Vehicleusedforthemovement)
✓Road(Typeofroad&itsgeometry)
✓Itisveryessentialtoknowthecharacteristicsofallthese
threeelementsforthetrafficengineeringtomakeefficient
management&planningoftrafficflow.

10. ❑ROAD USER CHARACTERISTIC
✓Roaduseristhepersonwhousestheroadbeing
pedestrian,bicyclists,driverorpassenger.
✓Thisisthepartdealsdirectlywithhumanbehaviorand
needstoconsidervaryingsituation,time,ageofthe
person,decisionmakingetc.
✓Thephysical,mentalandemotionalcharacteristicsof
humanbeingaffectstheirabilitytooperatemotorvehicle
safetyorasapedestrian.
✓Hencetheimportancetothetrafficengineertostudythe
characteristics&limitationsoftheroadusers.

11. ✓Thevariousfactorswhichaffecthumancharacteristicsasroad
usersmaybroadlyclassifiedunderfourheads:
✓Physical(Vision,Hearing)
✓Mental(Knowledge,Intelligence)
✓Psychological(Fear,Anger)
✓Environmental(WeatherCondition)
✓PhysicalCharacteristics:
i.VisualFactors
ii.Hearing
iii.Strength
iv.JudgmentPower
v.ReactionTime

12. ✓Visionplaysthemostimportantroleofallthese.These
includetheacuityofvision,peripheralvision,eyemovement
&depthjudgment.
✓Glarevision&glarerecoverytimesofdriversplayimportant
duringnight.
✓Minimumstandardforacuityofvisionareoftenlaiddownby
licensingauthority.
✓Thevisionisfairlysatisfactoryupto10ingeneral&evenup
to20inthehorizontalplane.
✓Asthefiledofclearvisionislimited,theroadusershaveto
oftenshifttheireyeswithintheperipheralfieldtoobtainclear
vision.

13. ✓Eye vision:

14. ✓Thetotaltimetakenfortheeyemovementdependsin
someofthephysicalcharacteristicsincludingthe
response.
✓Thedepthofjudgmentisimportantforadriverin
judgingdistance&speedofvehicles&otherobject
ahead.
✓Theeffectsofglare,adoptabilitytochangesoflighti.e.,
darknesstolight&brightlighttodarkness,shouldalso
bestudied.
✓Hearinghelpsdriverinaway,thoughitismoreimportant
factorforpedestrian&cyclists.

15. ✓Thoughstrengthisnotanimportantfactoringeneral
lackofstrengthmaymakeparkingmaneuversdifficult,
particularlyforheavyvehicles.
✓Thereactiontotrafficsituationdependsonthetime
requiredtoperceive&understandthetrafficsituation&
totakeappropriateaction.

16. ✓TemporaryPhysicalFactors:
i.Alcohol
ii.Fatigue
iii.Illness
iv.Anger
v.ClimaticFactors
✓Psychologicalfactors
i.Motivations
ii.Intelligence
iii.Learning
iv.Emotion
v.PIEVtime(ReactionTime)

17. ✓TemporaryPhysicalfactors
✓Alcoholaffectsonthephysical&mentalabilitytodrive.
Itproducespoorattention,lessselfcontrol,slower
responseofthedriver&latereactiontime.
✓Fatigue(Tired)producessleepiness&reducesthe
judgmentcapacity&increasereactiontime.
✓Ifroaduserhavingillnessoranydisease,itresultsinto
slowerreactiontime.
✓Angereffectsonthementalstability.Itaffectson
judgmentcapacity&reactiontime.
✓Climaticfactorsincludeseasonalchange,timeoftravel,
altitude,light&otherpsychologicaleffects.

18. ✓Psychologicalfactors
✓Motivation:Thepurposeoftravelaffectsonthebehavior
ofthedriver.Ifpurposeoftravelistosavemoney,time
etc.itmayleadtoviolationofsafetynorms.
✓Intelligence:Thecapacityoftheroaduserdependson
theawarenessofthetraffic&adjustmenttothesituation.
✓Learning:Itdependsonhabits,skills,motivation,
intelligenceetc.roadusermaylearnfromthepaststudy
&behaveaccordingly.
✓Emotion:Inincludesfear,anger,worry,behavior,logic
etc.itaffectsdirectlyonthebehaviorofroadusers.

19. ✓PIEVtime:itistimerequiredtoresponse.Itis
summationofPerception,Intellection,Emotion&
Volitiontime.
✓Perception:Itisthetimerequiredtoperceiveanobjector
situation.
✓Intellection:Itisthetimerequiredforunderstandingthe
situation.Italsoincludedthecomparisonofdifferent
thoughts&newsensations.
✓Emotion:Itistimeinwhichtheemotion&disturbances
suchasanger,fearetc.produceswithreferencetosituation.
✓Volition:Itistimetakenfortheaction.
✓Totalreactiontimeofanaveragedriveris3to4seconds.It
mayincreasedependonAgecomplexity,dependingonthe
situation.

20. ✓FactorsaffectingPIEV:
✓Age
✓Fatigue
✓ComplexityofReactions
✓PresenceofDrugsorAlcohol
✓ForbrakingreactiononHighways
✓Perception&Reactiontime:2.5seconds
✓ForreactiontimetotrafficSignal
✓PedestrianFactors:Pedestrianwalkingspeedsrangesfrom
1to1.5mperseconds&theirreactiontimerangesfrom4.0to
5.0seconds.ItdependsinAge,mental,physical&emotional
characteristicsofpedestrianandtraffic&Roadcondition.

21. Vehicle Characteristics
✓Vehicleisanimportantelementoftrafficengineering.
Trafficflowbehaviordependonthetypeofvehicle&its
characteristics.
✓Vehiclecharacteristicscanbeclassifiedinphysical&
operatingcharacteristics.Thisisusefulforgeometric&
pavementdesignofhighway.
✓PhysicalCharacteristics:
✓Trafficstreamconsistofmotorized&nonmotorized
vehicleswiththedifferentweights&dimensionin
developingcountry.

22. ✓Typeofvehicle
✓InIndiaHeterogeneoustrafficisobserved.Itisacombinationof
fastmoving&slowmovingvehicles.
✓FastMovingvehicle:itincludestruck,buses,luxury,jeeps,cars,
autorickshaw,scooters,bikes&othertransportvehicles.
✓SlowMovingvehicle:Itincludesbullockcart,cycles,manpulled
rickshawetc.
✓Dimensions:
✓Dimensionsofthevehiclesarehavingmuchimportanceinthe
geometricdesignoftheroad.
✓Length:
✓ItaffectsonHorizontalalignment,minimumturningradius,extra
wideningofcurve,passingsightdistancecapacityoftheroad&
Parkingspace.
✓Thelengthofsingleunitwithtwoaxlevehicleis10.7m.
✓Themaximumpermissiblelengthis9.5mto18.0m.

23. ✓Width:
✓Itaffectsonlanewidth,widthofshoulders,widthofparking
lots,etc.themaximumpermissiblevalueofwidthis2.44m
formotorvehicleto2.7fortransportvehicle.
✓Weight:
✓Itaffectsonpavementthickness,gradient,superelevation.
✓AsperIRCspecification,themaximumpermissibleloadof
singleaxlevehicleis8165kg,thegrossweightofthevehicle
canbefoundoutbyusingtheequation.
✓??????=[465(24+3.28??????)−1.46??????
2
]
✓WhereW=Grossweightofvehicleinkg
✓L=Distancebetweentheaxleinm.

24. ✓Vehicle Dimension

25. ✓Height:
✓Itaffectsontheclearancetobeprovidedunderbridges,sub
ways&serviceslinesetc.Maximumpermissibleheightis
varyingfrom3.8mto4.75mfordoubledeckedmotorvehicle.
✓TurningRadius:
✓Theminimumturningradiusofslowspeedvehiclesdepend
uponthewheelbase&steeringangle.Forhighspeedvehicles,
turningradiusiscontrolledbysuperelevation&sidefriction.It
affectsontheparkingmaneuver,curvesetc.
✓SpeedofVehicle:
✓Thevehiclespeedaffects(i)SightDistance(ii)super
elevation,lengthoftransitioncurve&limitingradiuson
horizontalcurves(iii)Lengthoftransitioncurvesonvertical
valleycurves&onhumps.(iv)Widthofpavement&
shouldersonstraight&horizontalcurves(v)Designgradient
(vi)capacityoftrafficlane(vii)design&controlmeasureson
intersections.

26. Maximum dimension on Road vehicles:
Dim. of Vehicle Details Maxi. Dim. (m)
Width Allvehicles 2.50
Height
(a)Single–deckedvehiclefor
normalapplication
3.80
(b)Double–deckedvehicle 4.75
Length
(a)Singleunittruckwithtwoor
moreaxle
11.00
(b)Singleunitbuswithtwoor
moreaxle
12.00
(c)Semitrailertractor
combination
16.00
(d)Tractor&tailorcombination 18.00

27. ✓BrakingCharacteristics:
✓Thedeceleration&brakingcharacteristicsofvehicles
dependonthedesign&typeofbrakingsystem&its
efficiency.
✓Thesafetyofvehicleoperation,stoppingdistance&the
spacingbetweenthetwoconsecutivevehiclesinatraffic
streamareaffectedbythebrakingcapacity.
✓Thusthehighwaycapacity&overtakingsightdistance
requirementsalsoindirectlygetaffected.
✓Atleasttwoofthefollowingthreemeasurementsare
neededduringthebrakingtestsinordertodeterminethe
skidresistanceofthepavement.
✓(i)BrakingDistance,Lmeters
✓(ii)Initialspeed,um/sec
✓(iii)Actualdurationofbrakeapplication,tseconds.

28. ✓HeadLightofvehicle:
✓Thiswillbeusefulforverticalcurvedesign&designofsign
boardfornightvisibility.

29. Traffic Flow Characteristic:
✓Thetrafficengineersareconnectedwiththeflowofgroupof
vehiclesonthehighwaysystemforplanning,designing&
operationplans.
✓Thecharacteristicsoftrafficflowareinfluencedbytypeofroad
&thevehiclesuperoperatingcharacteristics.
✓Therearethreebasicflowofparameteroftraffic.These
parameterareinterconnected.
✓Speed
✓Volume/flow
✓Density

30. ✓Speed:Itisthedistancetravelledperunittime.Itisexpressed
inkm/hour.
✓Spotspeed:Itisaspeedofvehicleatanyspotonahighway.
✓Timemeanspeed:Itisaarithmeticmeanofthespeedsofall
trafficpassingataspecificpoint.Itisalsoknownasaverage
spotspeed.
✓Runningspeed:Itisthespeedofthevehiclesoveraspecified
stretch,itisdistancetravelleddividedbyrunningtime.
✓Designspeed:Itisthemaximumsafespeedmaintainedover
thespecifiedsectionunderidealconditionsofweather,traffic
&geometricdesign.

31. ✓ModalSpeed:Whenallthespeeddataarearrangedin
ascendingorder,themiddlespeedvalueiscalledModalspeed.
Itisthe50
th
Percentilespeed.
✓OperatingSpeed:Itisthehighestspeedatwhichdrivercan
travelunderexistingconditionwithoutanyexceedingdesign
speed.
✓Spacemeanspeed:Itisthespeedcorrespondingtothe
averageofoveralltraveltimetopassthespecifiedsectionof
road.

32. ✓Volume/Flow:Itisthenumberofvehiclepassingagiven
pointduringthespecifiedperiodoftime.Itisexpressedas
vehicle/Hour.
✓Density:Itisthenumberofvehicleoccupyingtheaunit
lengthofthelaneoftheroadwayatagiveninstant,itis
expressedasvehicles/km/lane.
✓Spaceheadway:Itisthedistanceformheadtoheadof
successivevehicles.
✓Timeheadway:Itisthetimeintervalbetweenheadtoheadof
successivevehiclespassinggivenpointmeasuredfromfrontto
frontofthevehicles.

33. ✓Purposeofspotspeedsurvey:
✓Toestablishthetendsinspeedofvehicles.
✓Togetthespeeddatafortrafficregulationworks.
✓Toestablishthespeedlimitsincities.
✓Tolocatethespeedbreaker.
✓Tolocatethetrafficsign.
✓Todeterminethehazardousspotsinacities.
✓Todeterminethedesignspeedofthevehicles.
✓Todeterminethesuperelevation,sightdistanceetc.

34. ✓TrafficVolumestudies:
✓Trafficvolumestudyisimportantintrafficplanning,
designing,operation&research.Trafficvolumedataareused
for
▪Establishingtrendsintrafficvolume
▪Calculatinganaccidentratepervehicleskm
▪Designingoftrafficelements
▪Geometricdesignoftheroads
▪Calculatingacapacityofroads
▪Justifyingthecontroldevicessuchassignals.

35. ✓MethodsofTrafficvolumecount
✓ManualCount
✓MechanicalMethods
✓Electriccontactdevice
✓Radardevice
✓Magneticdevice
✓Pneumaticdetector
✓PhotographicMethod
✓VideographyMethod.

36. ✓ManualCount:
✓Itisasimplestmethodofcounting.Anobservercountthe
vehiclespassesafixedpointonaroad.Manualcountingcan
bedoneusinghandtallies–adevicewhichispressed&
rotatesthenumberincreasesbyone.
✓Thetotalnumberofvehiclesattheendofeachcounting
periodisobtained.Itisnotsuitableforbadweather.
✓Electriccontactdevice:
✓Itconsistsubsurfacedetector.Itprovidespositivecontact
foreachvehiclecrossingthroughit.Asteelplateoverwhich
rubberpadisprovidedtoholdsuspendedstrips.

37. ✓Radardevice:
✓Vehicleisdetectedcontinuouslybycomparingthe
frequencytransmittedradiosignalwithfrequencyofthe
reflectedsignal.Ifthevehiclespassesthroughlane,
frequencydifferenceoccurs.
✓PhotographicMethod:
✓Itinvolvesthecontinuousstripphotographsfromairplane
overthestretch.Basedontheprinciplesofphotogrammetry,
therelationshipofvolume,speed7otherparametersare
evaluated.

38. ✓Videographymethod:
✓Thevideographyiscarriedoutforthestretchofroadabout
20-30m.theentry&exitofthevehicleontheselected
approachshouldbecoveredinthevideography.Thestart
timeofthevideoissettoZero.
✓Themovementofthevehiclesarerecordedforanhour.
Aftertheendofthevideography,thevehiclesarecountedon
thescreenofthecomputerofDVD.
✓Theentrytimeofthevehicles&exittimeofthevehicleis
recordedforthevehiclesontheselectedapproach,the
distancepassedbythevehicleperunittimeisworkedout.

39. ✓PassengerCarUnit(PCU)
✓Allthevehiclesarehavingwiderangeofcharacteristicslike
length,width,height,power,speed,accelerationetc.inour
country,suchtypeofmixedtrafficmoves.
✓Itisdifficulttoestimatetrafficvolume&capacityofroad
way.
✓Thepassengercarisconsideredasstandardvehicleunitto
converttheothervehicleclasses.Thisunitiscalled
PassengerCarUnits(PCU).

40. PCU values as per IRC:106-1990 (For Urban Area)
Sr.No. VehicleType
Equivalent PCUfactors %
composition of vehicle type in
traffic stream
5% 10% andMore
1
Two wheelers,Motor
cycle or scooter
0.5 0.75
2
Passenger car, pick up
van
1.0 1.0
3 Auto rickshaw 1.2 2.0
4 LCV 1.4 2.0
5 Truck or Bus 2.2 3.7
6 TractorTrailer 4.0 5.0
7 Cycle 0.4 0.5
8 Hand Cart 2.0 3.0

41. PCU values as per IRC:64-1990 (For Rural Area)
Sr.No. VehicleType
Equivalent
Factors
1
Two wheelers,Motor
cycle or scooter
0.5
2
Passenger car, pick up
van
1.0
3 Tractor,LCV 1.5
4 Truck or bus 3.0
5 Cycle 0.5
6 Cycle-rickshaw 2.0
7 Handcart 3.0
8 Bullock cart 8.0

42. PARKINGSTUDIES:
✓Citiesaredevelopingtremendously.Productionofvehicles&
ownershipofalltypesofvehiclesincreases.
✓Itismandatorytoprovideparkingareaforthevehicles.Itis
importanttostudyabouttheparkingarea&itsrequirements.
✓Weneedtounderstandtheterminologyusedinparking
study:
✓ParkingAccumulation:Itisthetotalnumberofvehicles
parkedinthedefinedareaataspecifiedtime.
✓ParkingVolume:Itisthenumberofvehiclesparkedina
specifiedareaovergivenperiodoftime.Itismeasuredin
vehicles/day.
✓ParkingLoad:Itistotalnumberofparkingspacehoursused
bythevehicleduringagivenperiodoftime.

43. ✓ParkingDuration:Itistheaveragetimespentinaparking
space.
✓TurnOver:Itisaveragenumberoftimesaparkingspaceis
usedbyvehiclesduringagivenperiodoftime.
✓PurposeofParkingStudy:
✓Todeterminethesupply&demandoftheparkingfacilities.
✓Toknowthepurposeofparkingfacilities.
✓Todeterminethedemandforparkingspace.
✓Tofinalizethelocationofparkingarea.
✓Tostudylegal,financial&administrativefactorsrelatedto
parkingarea.

44. TypesofParkingSurvey:
✓Inventoryofparkingspace
✓Parkingusagesurvey
✓Questionnairestypeparkingspacesurvey
✓CordonCount
InventoryofParking:
✓Inthismethod,thedetailsofexistingfacilitiessuchaslanes,
streets,kerbetc.arelocated.Thedataincludesthelocation,
capacity&featuresofthesurroundingarea.Alldataare
summarized&planningismadeaccordingly.
ParkingUsageSurvey:
✓Inthismethod,thewholestudyareaisdividedintoblocks,
actualparkingspaceutilizedisrecorded.Thetimeforwhich
thevehicleisparkedarerecorded.Theinventoryofbothon
streetparking&offstreetparkingisrecorded.

45. QuestionnairetypeParkingspacesurvey:
✓Inthismethod,thevehicleusersareaskedtogivethedetailsof
hisorigin,destination,journeytime,parkingfeesexpected,
parkingspaceavailability,timeofarrival&departurefrom
parkingetc.basedonthedatacollected,thedemand&supply
oftheparkingisworkedout.Theplanningoftheparkingis
done.
CordonCount:
✓Inthismethod,thecountingofvehiclescominginorgoingout
fromthestreet&crossingofthestudyareaarerecorded.Itis
carriedouttodeterminethevolume,classificationoftraffic,
parkingloadetc.

46. Types Of Parking:
On Street Parking
Off Street Parking
✓OnStreetParking:
Thefollowingarethetypesof
onStreetParking
✓Parallelparking
✓30Angleparking
✓45AngleParking
✓60AngleParking
✓RightAngleParking
✓OffStreetParking
Thefollowingarethetypesof
OffStreetParking
✓SurfaceParking
✓MultiStoreyParking
✓RoofParking
✓MechanicalParking
✓UnderGroundParking

47. Types of On Street Parking

48. Accident Studies:
✓Roadaccidentscanbeclassifiedas:
✓Fatal
✓Major
✓Minor&Propertydamage
✓Fatal:Thevictimofaccidentisdeadonthespot.
✓Major:Thevictimoftheaccidentishospitalizedformore
than48hours.
✓Minor:Thevictimoftheaccidentgoestohiswork
immediatelyaftergettingfirstaidtreatment.

49. Purpose of Accident Studies:
✓Toidentifytheaccidentpronezoneinthecity.
✓Toimprovethegeometricdesignoftheaccidentpronezone.
✓Tocalculatethefinanciallossesofaccidents.
✓Tocreatetheawarenessaboutthesafetyinroadusers.
✓Togivethedataofaccidenttotheplanningstagetoconsider
thesuggestion.
Causes of An Accident:
Accidentoccurredonroadduetocombinationofseveralfactors
likeunsafedrivingorwalking,badwhetheretc.followingare
thecausesofaccidents.
✓DuetotheDriver:Excessspeed,violatingtherules,fatigue,
sleep,alcoholetc.
✓Duetopedestrian:Carelessness,Illiteracy,crossingofthe
roadatwronglocationetc.

50. ✓DuetoPassenger:Causinginattentionofdriversbytalking&
joking,projectingpartofthebodyoutside.
✓Vehicles:Duetotyreburst,failureofbrakes,improper
lightingorothermechanicalfactors.
✓ConditionofRoads:Slipperysurface,impropersurface,pot
holes,damagedroads.
✓RoadDesign:impropergeometricdesign,impropercross
slope,impropersuperelevation,improperdesignofcurvesetc.
✓WeatherConditions:Rainyseason,snowfall,dust,improper
visibility.

51. COLLISIONDIAGRAM:
✓Itisapictorialrepresentationofdifferenttypesofaccidents
occurredattheIntersection.
✓Itisusefultodisplay&identifytheaccidentpatterns.
✓ItishelpfulforstudyingtheaccidentpatternonParticular
intersection.
✓Itprovidestheinformationonthetype&numberof
accidents,includingconditionsuchastimeofday,dayof
week,climaticconditions,pavementconditions&other
informationcriticaltodeterminingthecausesofsafety
problems.

52. ✓Thecollisiondiagramincludesthefollowing
information:
✓PeriodofObservation
✓Directionofvehiclemovement
✓Availabilityoffixedproject
✓Positionofvehiclesatthetimeofaccident
✓Headoncollision
✓RearEndcollision
✓Typesofcollisionlikerightanglecollision,rightturn
collision
✓TheCollisiondiagramispreparedforequalperiods.After
theproperstudyofcollisiondiagram,thecorrective
measurescanbeplanned.

53. Collision Diagram

54. ConditionDiagram:
✓Theobjectoftheconditiondiagramistoshowthe
intersection&theconditionwithinthesurroundingareaas
itaxis.
✓Theconditiondiagramisthepictorialpresentationof
physicalconditionpresentattheintersectionunderstudy.
✓Therequiredvisibilityforthe85
th
percentilespeedonthe
road&theactualvisibilitytrianglearedeterminedfromthe
conditiondiagram.

55. Condition Diagram :

56. ConditionDiagramincludesthefollowing
information:
✓NorthDirection
✓Pavementedges,kerb&shoulders
✓WidthofRoad
✓Existingparkingcondition
✓Busstops
✓Availabilityofexistinglightningpoles
✓Trees
✓Signs
✓FencesorCompoundwalls
✓Existingbuilding
✓Distancetoadjacenttrafficsignal
✓Pavementmarking
✓Cycletrack

57. PreventivemeasuresforAccidents:
✓Geometricaspectslikeroadwidth,alignment&designof
intersectionshouldbeproperlydone.Provisionofbyepass,
flyoversetc.mayhelpinpreventionofaccident.
✓Allvehicleofpublicservices&goodsmovementshouldbe
maintainedproperly.
✓Provisionsofadequatelightingsystemonroadmayhelpin
preventionofaccidents.
✓Excessivespeedistheprimefactorsforaccident.Speed
breakersshouldbeproperlyprovided.

58. ✓Trafficcontroldeviceslikesign,marking,signaletc.should
beappropriatelyprovided.
✓Beforeissuinglicense,visibility,reactiontime&other
medicaltestshouldbeconductedfordrivers.
✓Exclusivelaneforpedestrian&cyclistshouldbeprovided.
✓Pedestrian,drivers&otherroadusersshouldbeproperly
trainedthroughfilm,slides,posteretc.

59. Conflict at Two-Way Traffic

60. Traffic Control Devices:
TrafficControldevicesareclassifiedasshownbelow:
Traffic Control Devices
Signs
Regulatory
Warnings
Informatory
Markings
Pavement
Kerb
Object
Reflectors
Signals
Fixed Time
Manually
Operated
Pedestrian
Special Traffic
Islands
Divisional
Channelizing
Rotary
Pedestrian
Loading
Lights

61. ✓Thedevicesusedtocontrol,regulate&guidetrafficis
calledtrafficcontroldevices.
TrafficSign:
✓Trafficsignisadevicemountedonafixedorportable
supportwherebyaspecificmessageisconveyedbymeans
ofwordsorsymbolofficiallyerectedforthepurposeof
regulating,warningorinformingtraffic.
✓SizeofSign:Therecommendedsizesforthetrafficsign
areshowninTable.Thenormalsizeisusedinimportant
roads&smallersizeisusedinlessimportantroads.On
expressways,biggerthannormalsizesmaybeused.
✓ColourofsignsshouldbeasshowndetaildrawingIRC:67.

62. Size of Sign Boards
Sign Normal size (cm)Small Size (cm)
Mandatory:Stop Sign
(Octagonal)
90 60
Mandatory:Give way
(Inverted Triangle)
90 (Side) 60
Mandatory: Other
(Circular)
90 (Dia) 60 (Dia)
Warning (Triangular) 90 (Side) 60 (Side)
Informatory
(Rectangular)
80 *60 60

63. ✓RegulatoryorMandatorySignaremeantoinformtheroad
userofcertainlaws,regulation&prohibition.Theviolationof
thissignisthelegaloffence.Theregulatorysignsare
classifiedunderthefollowingsubheads:
✓StopandGive-waysigns
✓Prohibitionsigns
✓NoParking&NoStoppingsigns
✓Speedlimit&VehicleControlSigns
✓RestrictionEndsSign
✓CompulsoryDirectioncontrol&othersigns
✓ThissigniswhiteColourwitharedborder.
✓TheNoStopping/standingsigniscircularinshapewithblue
background,redborder&twoobliqueredbarsat45&right
angletoeachother.

64. ✓Regulatory or Mandatory Sign

65. ✓WarningSignareusedtowarntheroadusersofcertain
hazardousconditionthatexistonoradjacenttotheroadway.
✓Thewarningsignsareintheshapeofequilateraltrianglewith
itsapexpointingupward.Theyhavewhitebackground,red
border&blacksymbol.
✓Thewarningsignsaretobelocatedatsufficientdistancein
advanceofthehazardwarnedagainst;thisdistanceare
120,90,60&40mrespectivelyonNational/StateHighway,
MDR,ODR&VRonurbanroadsthisdistanceis50m.
✓ThecommonlyusedwarningsignsareRightHand/Lefthand
curve,SteepAscent/Descent,Narrowbridge/RoadAhead,Gap
inMedian,SlipperyRoad,Cyclecrossing,Pedestrian
Crossing,SchoolZone,UnguardedRailwayCrossing,
GuardedRailwayCrossing.

66. ✓Warning Sign are used

67. ✓InformatorySignareusedtoguidetheroadusersalongthe
travelroutetomaketraveleasier,safe&pleasant.Thesesign
informtoroaduserthenameofhighway,distances&the
directionoftheplaces&otheramenitieslikehotels,fuelpump
etc.
✓Thedirection&placeinformationsignsarerectangularwith
whitebackground,blackborder&blackarrow&letters.
✓Thefacilityinformationsignsarerectangularwithblueback
ground&white/blackletters/symbols.Someofthesesign
indicatepublictelephone,petrolpump,hospital,eatingplace.

68. Informatory Sign

69. Road Marking
✓Markingontheroadcarriageway&ontheobjectwithinan
adjacenttoroadwaysareusedasmeanstoguiding&
controllingthetraffic.
✓Theypromoteroadsafety&ensuresmoothflowoftrafficin
totherequireddirectionorpathoftravel.
✓Themarkingaremadebywhite,black&yellowcolors
paints.Usethesecolorsareforspecificmarkingapplications.
✓Yellowmarkingareusedtoindicateparkingrestriction,
continuousCentreline&barrierlinemarking.
✓Whitecolorsmarkingprovideatintersectionforpedestrian
crossing.
✓Thenightvisibilityisimprovedbytheuseofminuteglass
beadsembeddedinthepavementmarkingmaterialtoproduce
aretroreflectivesurface.

70. ✓TypesofRoadMarking
✓LongitudinalLines:
✓Theselinemarkingsareusedas
✓Lanelines–Toseparatethelanes
✓BarrierLines–Tokeepthedistancefromvehicle
✓Separationline–Singlebrokenline
✓Guidelines–Toguidethedriveraboutthelane
✓Continuityline–Toshowthecontinuityoflane
✓Edgeline–Toshowtheedgeofthelaneonroad
✓Centreline–ToshowtheCentreoftheroad

71. TransverseLines:
✓StopLine–Toshowthestopvehicle
✓HoldingLine–Toshowthesafepositionforvehicletobeheld
✓ZebracrossingLine–Topermitthepedestrianforcrossingthe
road
✓OtherMarking:
✓TurnLines–Toguidethevehiclesduringturning
✓GivewayLines–Togivewaytovehiclesattheentranceof
theintersection
✓ParkingcontrolLine–Normallyyellowincolorsfor
temporaryparkingonroad.

72. Road Marking

73. Traffic Signal
✓Signalisadeviceprovidedatintersectiontocontrolthetraffic.
✓Itprovidesfororderlymovementofvehicle,reducesthe
frequencyofaccidents&warns&controlthetraffic.
✓Itmaybeoperatedmanually,electricallyormechanically.
✓SignalshowstheRED,GREEN&YELLOW.
✓RedIndicates–VehiclemustSTOP
✓GreenIndicates–VehicleCanGO
✓Yellow/AmberIndicates–LightisgoingtoChange,Itvaries
from2to4seconds

74. Traffic Signal

75. ✓Types of Traffic Signal
✓FixedTimeSignals
✓VehicleactuatedSignal
✓PedestrianSignal
✓FlashingSignal
✓BusPrioritySignal
✓FixedTimeSignal:ThetimePeriodforeachphaseisfixed.
ThesignalindicatesRed-Green-Yellowlightatfixedinterval
foreachphase.
✓Inthissystem,trafficflow&itsfluctuationisnotconsidered.
Thecyclelengthmayveryfrom40to120seconds.
✓Thistypeofsignalischeap&easytoinstall&Maintain.

76. ✓VehicleActuatedSignal:Inthistypeofsignalsystem,the
signaltimingarechangedaccordingtotheactualtraffic
volumeoneachlegoftheintersection.
✓ThedetectingdevicesareplacedintotheRoad.Vehicleis
recordedasitcrossesthedetector.
✓Signalareautomaticallyadjustedasperthetiminginterval
betweenthevehiclesontheleg.
✓Thistypeofsignalareusefulwhentrafficflowatthe
intersectionvariesontermbasis.
✓BusPrioritySignal:Thistypeofsignalisprovided,where
thepriorityistobegiventopublictransport.Whenthereisbus
inthetrafficstream,signalindicates‘Green’tothebuslaneto
reducethedelaytoPassengers.

77. ✓PedestrianSignal:Inthebusytrafficarea,signalsare
providedforcrossingtheroadsbypedestrians.
✓Thesignalsindicates“Red”lightfortraffictostop&permit
thepedestriantocrosstheintersection.
✓FlashingSignal:Sometimes“Yellowflashingsignalsare
providedonthemainroad”&“Redflashingsignalsare
providedtowarnthedrivers”.Itindicatesslowdownthe
vehicles&proceedwithcaution.
✓Thistypeofsignalsareprovidedatsharphorizontalcurves,
Railwaycrossing&otherimportantcrossroads.

78. ✓OneWaystreets:
✓Incongestedstreetsoneofthemethodstoreduceaccidents&
toensuresmoothflowoftrafficalongonewaystreet.
✓Thetrafficisallowedtomoveonlyinonespecifieddirection.
✓Themainadvantagesofonewaystreetsmaybegreater
capacity,increasedaveragespeed,improvedpedestrians
movement&reductioninaccident.
✓Thevarioustypesofconflictatanintersectionare
✓CrossingConflicts
✓MergingConflicts
✓DivergingConflicts

80. Various Types of Intersection :
✓AnintersectionisaJunctiononaroadwheretwoormore
roadseithermeetorcrossatgrade.
✓Intersectionmaybe3-leg,4-leg,5-legasperthenumberof
roadsmeetatparticularjunction.
✓Thisjunctioncontrolledbyprovidingtrafficlights&maybe
roundabout.
✓Theintersectionfurtherclassifiedasun-controlled&
controlled.
✓AnUncontrolledintersectioniswherenotrafficlightorsigns
areusedtoindicatetherightofway.
✓Controlledintersectioniswheresignalorothermeansto
indicatetheRight-of-way.

81. ✓Intersectionareclassifiedundertwobroadheadsnamely,At-
Grade&GradeSeparated.
✓Ingradeseparatedintersection,oneormorecrossingconflicts
arereducedbyoverbridgeorunderpass.
✓Atgrade&Gradeseparatedintersectionsmaybesub-divided:
✓Byshape:“T”,“Y”,scissor,crossstaggered.
✓ByseparationoftravelPath:ChannelizedIntersection.
✓BytypeofControl:Uncontrolled&Prioritycontrolled.
✓Byconversionofcrossingintoweavingmaneuver:Rotaryor
Roundabout.
✓Byseparationintime:Signalcontrolled.
✓Byspaceseparation:Gradeseparation:Flyover,Roadover
bridges,Roadunderbridges,Interchanges.

82. ✓Types Of Intersection

83. ✓AtGradeIntersection:
✓Allroadintersectionswhichmeetataboutthesamelevel
allowingtrafficmaneuverslikemerging,diverging,crossing&
weavingarecalledatgradeintersection.
✓Theseintersectionclassifiedasunchannelized,channelized&
rotaryintersection.

84. ✓AtGradeIntersection:

85. ✓BasicRequirementsofIntersectionAtGradeare:
✓Attheintersectiontheareaofconflictshouldbeassmallas
possible.
✓Suddenchangeofpathshouldbeavoided.
✓Adequatevisibilityshouldbeavailableforvehicles
approachingintersection.
✓Geometricfeaturesliketurningradius&widthofpavement
shouldbeadequateprovided.
✓Propersignshouldbeprovidedontheroadapproaching
intersectiontowarnthedrivers.
✓Goodlightningatnightisdesirable.
✓Ifthenumberofpedestrians&cyclistarelargeseparate
provisionshouldbemadefortheirsafepassageinintersection
withhighvolumeoffastmovingtraffic.

86. ✓GradeSeparatedIntersection:
✓Theintersectingroadsareseparatedbydifferenceinlevel,thus
eliminatingthecrossingmaneuvers.
✓Gradeseparatedintersectiondesignisthehighestformof
intersectiontreatment.Thistypeofintersectioncausesleast
delay&hazardtothecrossingtraffic&ingeneralismuch
superiortointersectionatgradefromthepointofviewof
trafficsafety&efficientoperation.
✓Ahighwaygradeseparationisachievedbymeansofvertical
level.

87. ✓Grade Separated Intersection :

88. ✓AdvantagesofGradeSeparation:
✓Maximumfacilityisgiventothecrossingtraffic.Astheroads
areseparate,thisavoidsnecessityofstopping&avoidaccident
whilecrossing.
✓Thereisoverallincreaseincomfort&conveniencetothe
motorists&savingintraveltime&vehicleoperatingcost.
✓Gradeseparationisanessentialpartofcontrolledaccess
highwaylikeexpressway&freeway.
✓Itispossibletoadoptgradeseparationforalllikelyangles&
layoutofintersectingroads.

89. ✓PresentationonSpotspeeddata:
(a)Averagespeedofvehicles:Fromthespotspeeddataofthe
selectedsamples,frequencydistributiontablesareprepared
byarrangingthedataingroupcoveringvariousspeedranges
&thenumberofvehiclesinsuchrange.
✓Thearithmeticmeanistakenastheaveragespeed.Thetable
givesthegeneralinformationofthespeedsmaintainedonthe
section&alsoregardingthespeeddistributionpattern.
(b)Cumulativespeedofvehicles:Agraphisplottedwiththe
averagevaluessuchofeachspeedgroupontheX-axis&the
cumulativepercentofvehiclestravelledatorbelowthedifferent
speedofY-axis.
✓Fromthisgraph,the85
th
percentilespeedisfoundoutwhich
givesthatspeedatorbelow85percentofthevehiclesare
passingthepointonthehighwayoronly15%ofthevehicles
exceedthespotspeed.

91. ✓Thedriversexceeding85
th
percentilespeedareusually
consideredtodriverfasterthanthesafespeedunderexisting
conditions&hencethisspeedisadoptedforthesafespeed
limitatthiszone.Howeverforthepurposeofhighway
geometricdesignthe98
th
percentilespeedistaken.
✓The15
th
percentilespeedrepresentstheslowerspeedlimitifit
isdesiredtoprohibitslowmovingvehiclestodecreasedelay&
congestion,as85%percentofvehiclestothesteamtravelas
speedshigherthanthisvalue&thereforeneedovertaking
opportunities.
(c)ModalAverage:Afrequencydistributioncurveofspot
speedsisplottedwithspeedofvehiclesoraveragevaluesofeach
groupofvehiclesontheX-axis&thepercentageofvehiclesin
thatgroupontheY-axis.
✓Thespeeddistributioncurveishelpfultodeterminethespeed
atwhichthegreatestproportionofvehiclesmove,givenby
modalspeed.

92. ✓Allvehiclesdonottravelatthesamespeedatalocationalong
aroad.Theamountofspeeddispersionorthespreadfromthe
averagespeedaffectsbothcapacity&safety.
✓Thismaybejudgedbyseveralmethodssuchas(85
th
Minus
15
th
percentilespeeds)standarddeviationofspeedsorthe
coefficientofvariationinspeed.

93. ✓Example:spotspeedstudieswerecarriedoutatacertain
stretchofhighway&theconsolidateddatacollectedaregiven
below.
✓Determine(i)theupper&lowervaluesorspeedlimitsfor
regulationofmixedtrafficflow(ii)thedesignspeedfor
checkingthegeometricdesignelementsofhighway.
Speed Range
kmph
No.of
vehicles
observed
Speed Range
kmph
No.of
vehicles
observed
0 to 10 12 50 to 60 255
10 to 20 18 60 to 70 119
20 to 30 68 70 to 80 43
30 to 40 89 80 to 90 33
40 to 50 204 90 to 100 9

94. Speed
Range kmph
Midspeed
kmph
Frequency, f
Frequency,
%
Cumulative
Frequency,
%
0 to 10 5 12 1.41 1.41
10 to 20 15 18 2.12 3.53
20 to 30 25 68 8.00 11.53
30 to 40 35 89 10.47 22.00
40 to 50 45 204 24.00 46.00
50 to 60 55 255 33.00 76.00
60 to 70 65 119 14.00 90.00
70 to 80 75 43 5.06 95.06
80to 90 85 33 3.88 98.94
90 to 100 95 9 1.06 100.00
Total 850 100.00
SOLUTION:

95. ✓Usingthevaluesofmidspeed&cumulativefrequency%
column2&5oftable,cumulativespeeddistributioncurveus
plottedfromthisgraphthefollowingresultareobtained.
✓(i)Upperspeedlimitsforregulation=85
th
percentilespeed
=60kmph
✓(ii)Lowerspeedlimitforregulation=15
th
percentilespeed=
30kmph
✓(iii)Speedtocheckdesignelements=98
th
percentilespeed=
84kmph

96. ✓SPEED&DELAYSTUDY:
✓Thespeed&delaystudiesgivetherunningspeed,overall
speeds,fluctuationsinspeed&thedelaybetweentwostations
ofaroadspacedfarapart.
✓Theyalsogiveinformationsuchastheamount,location
durationfrequency&causesofthedelayinthetrafficstream.
✓Thestudiesarealsoutilizedinfindingthetraveltime&in
benefitcostanalysis.
✓Therearevariousmethodsofcarryingoutspeed&delay
study:
✓FloatingcarorRidingbackmethod
✓Licenseplateorvehiclenumbermethod
✓Interviewtechniquemethod
✓Elevatedobservationmethod
✓Photographicmethod

97. ✓Infloatingcarmethodatestvehicleisdrivenoveragiven
courseoftravelatapproximatelytheaveragespeedofthestream,
thustryingtofloatwiththetrafficstream.
✓Anumberoftestrunsaremadealongstudystretch&groupof
observerrecordthevariousdetails.
✓Oneobserverseatedinthefloatingcarwithtwostopwatches.
Oneofthestopwatchesisusedtorecordvariouscontrolpoints
likeintersection,bridgesoranyotherfixedpointineachtrip.
✓Theotherstopwatchisusedtofindthedurationofindividual
delays.
✓Theaveragejourneytimet(minute)forallthevehiclesinatraffic
streaminthedirectionofflowqisgivenby:
✓ҧ�=
??????�−�??????
??????
✓q=
�??????+�??????
????????????+??????�
✓Where,
✓q=flowofvehicle,inonedirectionofthestream

98. ✓na=averagenumberofvehiclecountedinthedirectionofthestream
whenthetestvehicletravelsintheoppositedirection
✓ny=theaveragenumberofvehicleovertakingthetestvehicleminus
thenumberofvehicleovertakenwhenthetestinthedirectionofq
✓tw=averagejourneytime,inminutewhenthetestvehicleis
travellingwithstreamq
✓ta=averagejourneytime,inminutewhentestvehicleisrunning
againstthestreamq
✓Inthelicenseplatemethodsynchronizedstopwatchesor
voicerecordingequipmentareused.Observerarestationedat
theentrance&exitofatestsectionwhereinformationof
traveltimeisrequired.
✓Thetiming&vehiclenumberarenotedbytheobserverofthe
selectedsample.
✓Butthemethoddoesnotgivesuchascausesofdelays&the
duration&numberofdelayswithinthetestsection

99. ✓Intheinterviewtechnique,theworkcanbecompletedina
shorttimebyinterviewing&collectingdetailsfromtheroad
usersonthespot.Howeverthedatacollectedmaynotprovide
withallthedetailscorrectly.
✓Elevatedobservation&photographictechniqueusefulfor
studyingshorttestsectionlikeintersectionetc.
✓Suchstudiesateachintersectionwillhelpinevaluatingthe
efficiency&effectivenessofthecontroldevicelikesignal
system,theremedialmeasureforaccidentsetc.

100. ✓EXAMPLE:
✓Theconsolidatedarecollectedfromspeed&delaystudiesby
floatingcarmethodonastretchofurbanroadoflength3.5km,
runningNorth-Southaregivenbelow.Determinetheaverage
valuesofvolume,journeyspeed&runningspeedofthetraffic
streamalongeitherdirection.
Trip
No.
Direction of
Trip
Journey Time
Min.Sec
Total
stopped
delay
Min.sec
No.of
vehicle
overtaking
No.of
vehicle
overtaken
No.of
vehicle
from opp.
Direction
1 N –S 6 -32 1 -40 4 7 268
2 S –N 7 –14 1 –50 5 3 186
3 N –S 6 –50 1 –30 5 3 280
4 S –N 7 –40 2 –00 2 1 200
5 N –S 6 –10 1 –10 3 5 250
6 S –N 8 -00 2 –22 2 2 170
7 N –S 6 -28 1 –40 2 5 290
8 S –N 7 -30 1 -40 3 2 160

101. ✓Solution:
Direction of
Trip
Journey Time
Min.Sec
Total
stopped
delay
Min.sec
Number of vehicles
No.of
vehicle
overtaking
No.of
vehicle
overtaken
No.of
vehicle
from opp.
Direction
N –S 6 -32 1 -40 4 7 268
6 –50 1 –30 5 3 280
6 –10 1 –10 3 5 250
6 -28 1 –40 2 5 290
Total : 26 –00 6 –00 14 20 1088
Mean : 6 –30 1 –30 3.5 5.0 272
S –N 7 –14 1 –50 5 3 186
7 –40 2 –00 2 1 200
8 -00 2 –22 2 2 170
7 -30 1 -40 3 2 160
Total : 30 –24 7 –12 12 8 716
Mean 7 –36 1 -40 3.0 2.0 179

102. ✓(i)North–SouthDirection:
✓ny=averageno.ofvehiclesovertakingminusovertaken=3.5-5.0
=-1.5
✓na=averageno.ofvehiclesduringtripsinoppositedirection(from
S–N)=179
✓tw=averagejourneytime=6min30sec=6.5min
✓ta=averagejourneytimeduringtripsagainststream=7min36
sec=7.6min
✓q=averagevolume=
179−1.5
7.6+6.5
=12.59veh/min
✓Averagejourneytime(t)=6.5-
(−1.5)
12.59
=6.62�??????�
✓Averagejourneyspeed=
3.5
6.62
??????�/min
=
3.5∗60
6.62
=31.7??????�??????ℎ

103. ✓Averagestoppeddelay=1.5min
✓Averagerunningtime=Averagejourneytime–Averagestopped
delay
✓=6.621–1.50=5.12min
✓AverageRunningspeed=
3.5∗60
5.12
=41.0??????�??????ℎ
✓(ii)South–NorthDirection
✓ny=3.0–2.0=1.0
✓tw=7.6min
✓ta=6.5min
✓na=(fromN–Sstrips)=272
✓q=
272+1.0
6.5+7.6
=19.36
�??????ℎ
�??????�
✓Journeyspeed=
3.5∗60
7.55
=27.8??????�??????ℎ
✓Averagestoppeddelay=1.8min

104. ✓Averagerunningtime=7.55–1.8=5.75min
✓Averagerunningspeed=
3.5∗60
5.75
=36.5??????�??????ℎ

105. ✓TrialCycleMethodforSignal:
✓The15Minutes-trafficcountsn1&n2onroad1&2arenoted
duringdesignpeakhourflow.
✓SomesuitabletrialcycleC1secondsisassumed&thenumberof
theassumedcyclesinthe15minutesor15*60secondsperiodis
foundtobe(15*60)/C1.
✓Assumingaveragetimeheadway2.5seconds,thegreenperiodG1
&G2roads1&2arecalculatedtoclearthetrafficduringthetrial
cycle.
✓G1 =
2.5n1C1
900
??????��??????2=
2.5�2??????2
900
✓TheambertimeperiodsA1&A2areeithercalculatedorassumed
suitably(3to4seconds)&thelengthC1’iscalculated,equalto
(G1+G2+A1+A2)seconds.
✓IfthecalculatedcyclelengthC1’worksouttobeapproximately
equaltotheassumedcyclelengthC1,thecyclelengthisaccepted
asthedesigncycle.
✓Otherwisethetrialsarerepeatedtillthecyclelengthworksout
approximatelyequaltothecalculatedvalue.

106. ✓Example:The15minute-trafficcountsonroad1&2duringpeakhourare
observedas178&142vehiclesperlanerespectivelyapproachingthe
intersectioninthedirectionofheaviertrafficflow.Iftheambertimesrequired
are3&2secondsrespectivelyfortwoloadsbasedonapproachspeeds,design
thesignaltimingbytrailcyclemethod.Assumeanaveragetimeheadwayof
2.5secondsduringgreenphase.
✓Solution:
Trail(i)
✓AssumeatrailcycleC1=50Sec
✓Numberofcyclein15min=900/15=18
✓GreentimeforRoad1,allowinganaveragetimeheadwayof2.5secper
vehicle.
✓G1 =
178∗2.5
18
=24.7sec
✓Green time for Road 2, G2 =
142∗2.5
18
=19.7���
✓AmbertimeA1&A2are3&2Sec
✓TotalCyclelength=24.7+19.7+3.0+2.0=49.4sec
✓Asthisislowerthantheassumedtrialcycleof50sec,anotherlowercycle
lengthmaybetried.

107. Trail(ii):
✓AssumetrailcycleC2=40sec
✓Numberofcyclein15minutes=900/40=22.5
✓Green time for Road 1, G1 =
178∗2.5
22.5
=19.8���
✓Green time for Road 2, G2 =
142∗2.5
22.5
=15.8���
✓Totalcyclelength=19.8+15.8+3+2=40.6sec
Trial(iii):
✓AssumetrialcycleC3=45sec
✓Numberofcyclein15minutes=900/45=20
✓Green time for Road 1, G1 =
178∗2.5
20
=22.25���
✓Green time for Road 2, G2 =
142∗2.5
20
=17.75���
✓Totalcyclelength=22.25+17.75+3+2=45.0sec
✓Thereforethetrailcycleof45secadopted.