Traffic Characteristics
General
I Study of traffic characteristics include
I Vehicular characteristics
I Road user's characteristics
I Traffic engineer has to design and operate the traffic facilities that will be used by
pedestrian, cyclists and motorists. As such a proper understanding of the behavior of
the road user and the vehicle characteristics is necessary for this purpose.
D Vehicular and traffic characteristics affect highway planning, design, iinprovement or
operational aspects of traffic engineering. As such design/improvement/control and
I.e,gulations of roadway features should be compatible with its users for safe and
effici'ent movements.
Vehicular Characteristics
I It would be impracticable and uneconomical if roadway is designed to ace,ommodate
all t}'pes of \'ehicles. Generall}'. roadwa}' is designed for desigri vehicle that will enjoy
safe driving and full le`.e! of seivice a.OS) -``-herean extreme users \`-ill get lo``er
satiety and LOS.
I .+`L \Jchicle that represents the design standards is eermed as drsigB `drle "ha
pTopeTtiesarefixedbasedonstetis(icalanabrrisOffxxpquhatin-5Ofpr±{nmanu
`.aiue: 8i.+ percentile or marimum `alue etc. depending on de pupae of tre i.e.
fixing luming oa`Lh. parking lot desigr. etc. Characteristics of design vehicle actually
fix all Lhc dimensions of the road.
L~j i iic vat.ious v``,hi.uiar c}-iaractei.isiics aifcciiiig -ilie foaci design can be classified a,s
LJ St.:t.lie charcict.ei.istics artd
I D}liamic characteristics
Static/physical Characteristics
1] .4jc/c foc[4J -Weight of vehicle affects
H structural design of
E pavement - numbci. of layei.s, thickness of each la}'er, material requiremeiits
ctc.
I bridge/fly-over/grade sepai.ator
n fixing gradient of roads in rolling terrain, ramp, bridge approach etc. and it
depends on Vehicles weight/power ratio
D Wz.4/J/I -Width of vehicle affects
I lanewidth
I shoulder width
I width of parking bay
I fc/tgJ/j -Length of vehicle affects
_.--
dffi
I design of horizontal alignment i.e. determination of extra widening and minimum
turning radius
I passing sight distance
I parking facility (bay & isle)
I roadway capacity
I JJci.g/€f -Height of vehicle affects
I clearance to be provided under the structures e.g. under-bridge, over-bridge, sign-
post gantry, electric services lines etc.
Dynamic Characteristics
H Speed - It is such a factor that controls most of the geomethe standards of the
highway viz.
I . horizontal and vertical alignment design
I limiting radius
I grade
I length oftTansition cLirve
I] ±====;uni±iiiHig
sFch- sir E=E=
- ri-mH===::== H9raa-iqT-
I ujiiiigivrm
I \ma ququn ~m dHi? all edllnd #Eril€ allb HEEL co-± qu dEri
ap*ee-
I SEL resisaaurs
FI Acceleration/Deceleratton apraking) performance
I acceleration capability influences junction capacity, safe passing distance etc.
I maximum deceleration rate is required to know safe stopping distance.
Road User's Characteristics
General
I Road users e.g. pedestrians and drivers are inost complex and least understood
element of roadway system
I As road users are a major part of the system, human limitations and behavior must be
understood and taken into account in all trafric engineering and design maters
I It has been found that over 90 per cent of all highway accidents are due to errors of
judgment.
I As such it is of paramount importance for a traffic engineer to study the factors which
directly or indirectly influence the manner and rate at which errors occur
I The behavior of a rood user depends upon the factor like education, environment and
training
I Di.ivel.'s driving education/road sense can be improved by strict licensing/road safety
education policy
I As for pedestrians there is no scope for formal education and they are most exposed
vulnerable group comprising largest road users group especially within urban area -
they need protection by law. Priority on right-of-way is given to pedestrian.
Therefore, it is the driver's responsibility for safety of pedestrian and as such his
behavior in this 1.egard is very important.
Driver Characteristics
Drivers' characteristics are involved in
D accommodating roadway environment during driving or adopting safe speed
according to roadway environment
I curved/straight
I poor surface condition
D .lane width
I poor acce-ss controlled
I density oftriric
I approaching towards priority junction
E--gil-
I q[=(g|nilrilqg bouLppc][± iErmsE€± st tr€ahai txxigfa pedEa[iaD
I dDfty -qlElilm-iffiEREwmBripDF
.a-d-
I grF±-
],qmHilgjl-in-qbdiedgpRIpirimp«agrqmringrmdmFTHngvi
I keeping headraor- "th the kite
D roadway sign design (letter height/size and placement - color perceptioD depth o
vision, speed)
D street lighting design (fixing level of illumination - depending on drivers' ability to
see)
Droadwaymarkingsdesign(colorandintensityofretro-reflectivemarkings)
H licensing control
Factors affecting t he road user characteristics
The factors which affect behavior of road users are:
I P/®jJsl.c¢//acfors - this includes
I eye-sight/vision
I hearing power
I other defects/.disabilities
I fatigue, alcohol or drugs, illness etc. are the temporary physical characteristics
whichaffectreactiontime,judgmenttime,alertness
I MeHfoJ/¢cfors - this includes
H intelligence
I education, skill, knowledge
I experience/training of the drivers
I Pryc/!o/ogJ.c¢//¢cfors - this includes
I impatience
I attentiveness
I ability of follow regulation and
I maturity
Reaction Time
The time interval betwieen seeing, hearing, or feeling, and the starting to do something in
responsetothestimulusofatrafficorhighwaysituationiscalled"reactiontime",ideally,this
responseofthedriverrequirestimeforthefollowingpsychologicalprocess:
General
DPerccpfz.o«-whichinvolvesseeingthestimulialongwithotherperceivedobjects
DJdefflfl#c¢fj.oftor!.#feJfecf..o#-whichinvolvestheidentificationandunderstandingof
the stimuli.
a Ji`«fo/7.oi7 or /.«irgm"" - which involves the decision making process, in which a
determination is made as to the proper course of action ;(to stop, pass, merge, cross:
qrm€ ]aDeralb-T or blouir hon cm.)
I I--nE---imhade cErmnin ofdr decisin.
ELermdEgEq-qbedqriqb'q=i-iDcllEHEmag-si--
prqprinofad-Bsi--BED-I-HdEdllnEErqiB-tr
__, --1 ----, I-= I--l=
.4LstisLdbuldreapolEEEismTqlEckdg-a-
in-menigsngOfi- n~ in de fine of a hupuEEi±~L .. _.:
Teflex-like, ofro
:=`T3RE i-`=,+. situation. -+T=i~T=
PIIIV
DThetotaltimerequiredtoperceiveandcompleteareactiontoastimulusisthesumof
the times necessary for perception, identification, emotion, and violation. This total
reaction time is often referred to as the PIEV time,
D The time required for reacting properly and safely (after making proper evaluation of
allpertainingfactors)canvaryfromabout0.5secforsimplesituationstoasmuchas
3 or 4 sec for more complex situations.
I PIEV time is required to determine
I safe-stopping sight distance
I safe approach speeds at intersection
I amber/clearance time interval for traffic signals
D PIEV time increases with
I complexity of situation
ngravityoftheevent®eoplegenerallyreactquickertoverystrongstimulithanto
weak ones)
I vehicle speed
I drivers' age
Hifi5
EE=
I physical deficiencies
I mental/emotional state/psychological conditions - which temporary distract
attention/concentration/alertnessofdrivingormakelessresponsivetostimuli.
I Besides above factors PIEV time depends on
I speed of vehicle
Devenlocationofroadsetc.-withinbuilt-updriversremainextravigilant/alertand
alwaysexpectsurprisesituation,incontrastdrivinginopenruralhighwayisvery
relaxed and less attentive.
I PIEV design value
Ddesignvalueisusuallybaseduponthenormalrangeofroadusers(85thpercentile
group) and not upon the abnormal. (design would be uneconomical if extreme
values are consideied)
DbrakereactiontimerecommendedbyAASHTOforperceptiontime=1.5sec)
D rural area - 1.0 sec (PIEV = 2.5 sec)
a urban ar.ea -0.75 or 1.0 sec (PIEV = 2.25 -2.5 sec)
pt-chJ-
ieirrd
I illlrdn€pdBirty il -4-
BgHdE---hii-nL-dbdidbin-dqquillEHmin
.ngriflrq±luriEdLEhriniqEHd-
I qbfty acbaDdtoc±
B]xpst[IausnoreOfmdisobeytrafficorfuuldevkrsdhod[ETF:
EiiiE5--
Crossing Characteristics
Dingeneralpedestrianstendtowalkinapaththatrepresentstheshortestdistanceor
most
|L|\JJ, convenient route between two points.
\,\,I ,,--- _ _ __ ,,__
theyoftencrossatmid-blockinsteadofusingcrosswalks
pedestriansalsohaveabasicresistancetochangegradeswhencrossingroadways
theydon'tvoluntarilymakeuseofspecialpedestrianfacilitiessuchasunderpassesor
overpasses.
Bangladesh
D Dearth of qualified traffic engineers
DTrafficengineeringprofessionhasnotbeenrecognizedattheinstitutionallevel
D Little importance of data/monitoring system
a No systematic collection of comprehensive data
DLackofdatabasedplarmingandprogramimplementation-manyimprovementsdone
without benefit/cost analysis
Traffic Volume Study
Introduction
Volume data are needed in research, planning, designing and regulation phases of traffic
engineeringandarealsousedinestatilishingprioritiesandschedulesoftrafficimprovements.
Thetrafficengineermustacquiregeneralknowledgeoftrafficvolumecharacteristicsinorder
tomeasureandunderstandthemagnitudes,composition,andtimeandroutedistributionsof
volume for each area under his jurisdiction.
Definitions
Volume/foow
Thetotalnumberofvebiclesthatpassoveragivenpointorsectionofalaneorroadway
duringagiventimeinterval.Itmaybeexpressedintermsofannual,daily,hourly,orsub-
houi-lyperiods;usuallyinvphorvpd.Volumeisanactualnumb\erofvehiclesobservedor
predictedtopassingapQintduringagiveninterval.
BJBBE Of ftoRP
TheeTiquHLqrtyralB-Rrfu`thirksprsotaagivenpointorsectionofalaneor
------ I-ihiL I IID -]s in b dip-the
Tqltry,die.givtii-ilndb-]bi- Dmha
blf-LDlb
ITqE±dHEfingdrfeaqilBi-he-ILu
•++ rty r
.-"ngng Dde Trrfe I.sot)
Thevolumeduringagiventimeperiod(inthewholedaysgreaterthanonedaybutlesthan
one year) divided by the number of days in that time period and expressed in terms of
veh/day or vpd.
AverageAnnualDallyTraffl?.(4fr:I)
Itisthetotalyearlyvolumedividedbythenumberofdaysinayearandexpressedinterms
of veh/day or vpd.
Design Hourly Volume
ltistheeconomichourlyflowoffutureyear,whichisusedfordesigninggeometricfeatures
of roadway.Itischoseninsuchawaythatduringthedesignperioditshouldnotbeexceeded
too often or too much.
ScopeofTrafricVolumeStudies
ThetrafficVolumecountstudyiscarriedouttogetfollowingusefulinformation:
Dmagnitudes.classiflcationsandthetime&directionalsplitofvehicularflows
I proportions of vehicles in the traffic stream
DhourLy,daily,yearlyandseasonalvariationsofvehicularflows
D flow fluctuation on different approaches at a junction or different parts of a I-oad
network system
Objectives
Thepurposesforcarryingouttrafficvolumecountareasfollows:
Design purposes
D sti-uctural and geometric design of pavements, bridge, and other highway facilities
I intersection design including minimum turning path, channelization, flaring, traffic
control devices viz. trafflc signs, markings, signals based on approach volume and
turning proportions
D pedestrian volume study is useful for designing side walks, pedestrian crossing etc.
Inaprovement purposes
a to allocate limit:d maintenance budget rationally it is important to know the traffic
`-olume carded b}- a particular roadway section in order to decide the importance of
-t-
*nddfiriBisrdfroprfu-.
I in -Ib b ill- A indap ap=nling em.dinim in is inponam to know the
] D eB-u Gririil€qr-iqddroqll-of& mHaD 9Bdin
I nD ,dLck * rd fr€-IIrty-Oqrd dhiH
]pdrmmirdet}peofirbprut--ieDedtDbeqED
a to measpe dpe-ed5EfHae¥=gffi
-T`T_=
Planning purposes
D accurate information on the amount of traffic on the roads in vital for the planning of
both road maintenance and improvement policies
H traffic volume network analysis helps in deciding/planning if there is need for
I improvement or
H expansion in terms of constructing missing links, by-pass, alternative road etc.
Dy namic Traf f ilc Management Purposes
HUptodateandcontinuousflow/congestioninformationisessentialforoptimizing
I traffic signal design and thereby improving junction performance
D network productivity by providing information to the road users
Other Purposes
D estimation of highway use
D measurement of current demand of a facility
I estimation of trends
I economic feasibility evaluation
I computation of accident rates -accidents/loom vehicle-miles
Types of Flow/Volume
IIiterruptedfoow Flow at stopped and go situation
Uninterruptedfoow When the flow is smooth
Saturation f oow The maximum hourly rate of an approach at a signalized
junction
Serv.lee f oow rate The maximum hourly rate of a roadway section during a given
period under prevailing roadway condition
Free foow When drivers face no restriction in driving and can maintain
their desired speeds
Forced foow When lane changing opportunity decreases with increasing
traffic volume and drivers are forced to follow slow leaders
Stable/steadyfoow When demand in well below the roadway capacity and the
average rate of flow remains almost constant with time.
Unstable foow When demand is at or near or exceed the roadway capacity and
the a`.erage rate of flow fluctuates largely with time.
rFTE= Fha- aB peak periods
qE=-
f-Jh, The-drHElthFEinds
-frnrf±-ji±enaEng in.dtp uich
-rfeLUG±-aiibqEsil[=qriLEnd
fruilBiiife=-srERI 0 idlBma a- H±
wH cmfty he -B5 aimdred to, .co in appo=iE dindiin
Iiunf lee Tqse Who haife flows in both direction exhlbit unbalanced
characteristics at peak periods viz. morning rush at in-bound
lanes due to commuter traffic and in the evening the same is true
for the out-bound lanes.
Induced foow Flow that is generated because of new or improved roadway
facility
Methods of Counting
I Manual Counting Method -following are the most common forms of manual counting
methods:
Direct Method- data is collected by using hand tally and manual
counters/enumerators
Advantages
H besides traffic volume, vehicle classification and turning proportions can be obtained
I data can be use immediately after collection
Disadvantages
I not practicable for long duration count and when flow is high
I counts become ei.ror prone specially when volume is high
