traffic engineering studies

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Traffic Engineering StudiesTraffic Engineering Studies

Chapter 4


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Traffic studies may be grouped

into three main categories:

(1) Inventories,() !dministrative studies, and

(") #ynamic studies$


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(1) Inventories:

provide a listor graphic displayof

existing information, such as: street widths,

parking spaces,

transit routes, traffic regulations.


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() !dministrative studiesuse existingengineering records,

available in government agencies anddepartments.

include the results of surveys, whichmay involve:

field measurementsand/oraerial photography.


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(") #ynamic traffic studies

involve the collection of data under

operational conditionsand

include studies of: speed,

traffic volume,

travel time and delay,

parking, and crashes.

They are described in detail in this chapter.


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4$1 S%&T S%EE# ST'#IES

Spot speed studies are conducted toestimate the distribution of speedsof

vehicles in a stream of traffic at a particular

locationon a highway.

carried out by recording the speedsof asampleof vehicles at a specified location.


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S%&T S%EE# ST'#IES

'sed to:

Establish parameters for

traffic operation and control, such as:speed ones,

speed limits !"#th$percentile speed%


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4$1$1 ocations for Spot Speed Studies&epresent different traffic conditions on a

highway for basic data collection.

'id$blocks of urban highways and straight,level sections of rural highways for speedtrend analyses.

(ny location may be used for solution of a

specific traffic engineering problem.


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4$1$1 ocations for Spot Speed Studies

Shoud be seected to achieve the foo*ing:

)nbiased data*rivers be unaware

E+uipment concealed from the driver,

bservers inconspicuous.


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4$1$1 ocations for Spot Speed Studies

statistical analysis,

statistically ade+uate number of vehicle

speeds be recorded.


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4$1$ Time of #ay and #uration of

Spot Speed Studies

depends on the purposeof the study.

recommended when traffic is free$flowing,

during off$peakhours.

typically:

the duration is at least - hourand the sample sie is at least vehicles.


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4$1$" Sampe Si+e for Spot Speed StudiesThe largerthe sample sie, will give an

estimated meanwithin acceptable error

limits.(verage Speed'edian Speed'odal SpeedThe ith$percentile Spot Speed0aceStandard *eviation of Speeds


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4$1$4 ethods for Conducting Spot

Speed Studies manual and automatic

manual method is seldom used

automatic devices

-. road detectors

1. radar$based

. the principles of electronics.


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&oad *etectors pneumatic road tubes 2 induction loops

collect data on speeds 2 volume at the

same time !dvantage:

3uman errors are considerably reduced

#isadvantages: expensive

may, affect driver behavior,


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0neumatic road tubes laid across the lane in which data are to be

collected.

4hen moving vehicle passes over, an airimpulse is transmitted to the counter.

two tubes are placed across the lane, 1 m

apart.

(n impulse is recorded when the front

wheels of a moving vehicle pass over the

first tube5


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0neumatic road tubes a second impulse is recorded when the

front wheels pass over the second tube.

The time elapsed between the two

impulses and the distancebetween the

tubes are used to compute the speedof

the vehicle.


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inductive loop a rectangular wire loop buriedunder the

roadway surface.

6t operates on the principle that a

disturbancein the electrical field is created

when a motor vehicle passes across it.


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&adar$7ased Traffic Sensors

Electronic$0rinciple *etectors

traffic characteristics, such as speed,volume, +ueues, and headways are

computed.

)sing video image processing


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!a%&T'S *eployed in the 8orward 9ooking 'ode


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!b%&T'S *eployed in the Side$fire 'ode


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!a% Schematic 6llustration

of the (uto scope


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!b% The (uto scope *eployed


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4$1$- %resentation and !naysis of

Spot Speed #ata Statistical methods

(nalying data

fre+uency histogram

cumulative fre+uency distribution curve


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E.ampe 4$ *etermining Speed

haracteristics from a Set of Speed

*ata.

Table ;.1 shows the data collected on a rural

highway in


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-. The arithmetic mean speed

1. The standard deviation

. The median speed

;. The pace

#. The mode or modal speed

=. The "#th$percentile speed


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Soution: The speeds range from ;." to =#. km/h,

giving a speed range of .1.

8or eight classes, the range per class is .>#km/h5

for 1 classes, the range per class is -.#- km/h.

6t is convenientto choose a range of 1 km/h per

classwhich will give -= classes. ( fre+uency distribution table can then be

prepared, as shown in Table ;..


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Tabe 4$ Speed *ata btained on a &ural 3ighway


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/igure 4$4 3istogram of bserved


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Tabe 4$" 8re+uency *istribution Table for Set of Speed *ata


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/igure 4$- 8re+uency *istribution


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/igure 4$0 umulative *istribution


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The median speed ;@ km/h,

the #th$percentile speed.

"#th$percentile speed is #; km/h


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4$ &'E ST'#IES

1$ !verage !nnua #aiy Traffic!((*T%

the average of 1;$hour counts collected

every day of the year.

$ !verage #aiy Traffic !(*T%

the average of 1;$hour counts collected

over a number of days greater than onebut less than a year.


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4$ &'E ST'#IES

"$ %ea2 3our oume!03


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4$$1 ethods of Conducting

oume Counts 'anual 'ethod

(utomatic 'ethod


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/igure 4$Aamar Traffic *ata ollector T*$- 1 3ooked to a omputer


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8igure ;.@ (pollo Traffic ounter/lassifier


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/igure 4$15 Example of ounters that &e+uire the 9aying of Subsurface *etectors


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/igure 4$11 Traffic Eye )niversal System


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/igure 4$1Example of Station 9ocations for a ordon ount


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4$$ Types of oume Counts *epending on the anticipated use of the

data to be collected.

6ntersection ounts vehice cassifications,

through movements,

turning movements$


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4$$ Types of oume Counts 0edestrian


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4$$" Traffic oume

#ata %resentation

Traffic /o* aps:

volume of traffic oneach route is

represented by the

width of a band.

Figure 4.13 shows a

typical traffic flow map.

/igure 4$1" Example of a Traffic 8low 'ap


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/igure 4$14 6ntersection Summary Sheet

Intersection Summary

Sheets:

Figure 4.14shows atypical intersection

summary sheet.


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4$$" Traffic oume #ata

%resentation Time$7ased *istribution harts:

see 8igure ;.-#


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/igure 4$1- Traffic


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/igure 4$1- Traffic


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Tabe 4$4 Summary of Traffic


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(dBustment of 0eriodic ounts

Expansion 8actors from ontinuous

ount Stations.

3ourly expansion factors !3E8s% are

determined by the formula


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*aily expansion factors !*E8s% are

computed as

'onthly expansion factors !'E8s% are

computed as


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Tabe 4$- 3ourly Expansion 8actors for a &ural 0rimary &oad


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Table ;.= *aily Expansion 8actors for a &ural 0rimary &oad


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Tabe 4$ 'onthly Expansion 8actors for a &ural 0rimary &oad


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4$" T6!E TIE !7# #E!8

ST'#IES Travel time: time re+uired to travel from

one point to another on a given route. the locations, durations, and causes of

delays.

good indication of the level of service identifying problem locations,


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4$"$1 !ppications of Trave Time and#eay #ata efficiency of a route

locations with relatively high delays causes for delays before$and$after studies

relative efficiency of a route travel times on specific links economic studies


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4$"$ #efinition of Terms 6eated toTime and #eay Studies

1$ Trave time: time taken by a vehicle totraverse a given section of a highway.

$ 6unning time: time a vehicle is actually inmotion


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;..1 *efinition of Terms &elated to Time and*elay Studies

"$ #eay time lost due to causes beyond thecontrol of the driver.

4$ &perationa deay: delay caused by theimpedance of other traffic.

!for example, parking or unparkingvehicles%,


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-$ Stopped9time deay0$ /i.ed deay: caused by control devices

such as traffic signals, regardless of the

traffic volume

$ Trave9time deay: differencebetween the

actual travel time and the travel time

obtainedby assuming that a vehicle

traverses at an average speed e+ual tothat for an uncongestedtraffic flow


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4$"$" ethods for Conducting Trave

Time and #eay Studies 'ethods &e+uiring a Test


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Tabe 4$ Speed and *elay 6nformation

T ffi E i i St di


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Moving-Vehicle Technique(moving observer)

the observer makes a round trip on a test

section 8igure ;.-=, The observer starts at section C$C, drives

the car eastward to section D$D,

turns the vehicle around

drives westward to section C$C again

T ffi E i i St di


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/igure 4$10 Test Site for 'oving$


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Moving-Vehicle Technique. foo*ing data are coected as The time it takes to travel east from C$C to

D$D !Te%, in minutes The time it takes to travel west from D$D to

C$C !Tw%, in minutes

The number of vehicles traveling west in

the opposite lane while the test car is

traveling east !Ne%

T ffi E i i St diT ffi E i i St di


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/igure 4$10 Test Site for 'oving$


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Moving-Vehicle Technique.

The number of vehicles that overtake the

test car while it is traveling west from D$D

to C$C, that is, traveling in the westbounddirection !Ow%

The number of vehicles that the test car

passes while it is traveling west from D$Dto C$C, that is, traveling in the westbound

direction !Pw%



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Moving-Vehicle Technique. The volume !Vw% in the westbound

direction can then be obtained from the

expression:



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where !Ne Ow Pw% is the number ofvehicles traveling westward that cross

the line C$C during the time !TeTw%.

Similarly, the average travel time in thewestbound direction is obtained from



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T ffi E i i St diTraffic Engineering St dies


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T ffi E i i St diTraffic Engineering Studies


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ethods 7ot 6e;uiring a Test

ehice

!icense-"late#bservations

observers at the beginning and end ofthe test section.

Each observer records the last three or

four digits of the license plate of eachcar that passes, together with the time

at which the car passes.

T ffi E i i St diTraffic Engineering Studies


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in the office by matching the times of

arrival at the beginning and end of the

test section for each license plate

recorded. difference between these times is the

traveling time of each vehicle.

average of these is the averagetraveling time on the test section.

Traffic Engineering St diesTraffic Engineering Studies


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a sample sie of # matched license

plates.

$nterviewsobtaining information from

people who drive on the study siteregarding their travel times, experience

of delays, re+uires the cooperation of

the people.



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$T% &'vance' Technologies (dvanced technologies

ell phones

0S satellite system

technology is used to determine average

speeds and travel times along highways



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4$4 %!6


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0roviding ade+uate parking space to

meet the demand for parking in the

entral 7usiness *istrict !7*%

This problem usually confronts a citytraffic engineer.

solution is not simple, 0arking studies

are used to determine the demandforand the supplyof parkingfacilities.



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4$4$1 Types of %ar2ing /aciities

n$Street 0arking 8acilities also known as curb facilities. 0arking bays

are provided alongside the curb on one orboth sides of the street.

unrestricted parking

unlimited and free &estricted parking facilities



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n$Street 0arking 8acilities limited to specific times for a maximum

duration.

may or may not be free. handicapped parking

bus stops

loading bays.



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ff$Street 0arking 8acilities privately or publicly owned5

surface lots and garages.

Self$parking garages

attendant$parking garages



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4$4$ #efinitions of %ar2ing Terms

1$ !space9houris a unit of parking that

defines the use of a single parking

space for a period of - hour.

$ %ar2ing voumeis the total number of

vehicles that park in a study area

during a specific length of time, usuallya day.



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"$ %ar2ing accumuationis the number ofparked vehicles in a study area at any

specified time.

4$ par2ing oadthe number of space$hoursused during the specified period of time.

-$ %ar2ing durationlength of time a vehicle is

parked at a parking indication of how

fre+uently a parking space becomesavailable.



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0$ %ar2ing turnoverrate of use of aparking space.

btained by dividing the parking

volume for a specified period by the

number of parking spaces.



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4$4$" ethodoogy of %ar2ing Studies

6nventory of Existing 0arking 8acilities detailed listing of the location and all other

relevant characteristics of each legalparking facility, private and public.

The study area includes both on$ and off$

street facilities.



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Type and number of parking spaces at each

parking facility

Times of operation and limit on duration of parking,

if any

Type of ownership !private or public%

0arking fees, method of collection &estrictions

ther restrictions, loading and unloading ones,

bus stops, taxi ranks

0ermanency The inventory should be updated at regular

intervals of about four to five years.



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4$4$" ethodoogy of %ar2ing Studies

ollection of 0arking *ata &ccumulation

by checking the amount of parking during

regular intervals on different days of the week.

arried out on an hourly or 1$hour basis

used to determine hourly variations of parking

and peak periods of parking demand.



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ollection of 0arking *ata Turnover an' uration

collecting data on a sample of parking spaces

in a given block. recording the license plate of the vehicle

parked on each parking space in the sample at

the ends of fixed intervals during the study

period. The length of the fixed intervals depends on

the maximum permissible duration.



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Turnover an' uration 8or example, if the maximum permissible

duration of parking at a curb face is - hour, a

suitable interval is every 1 minutes.

6f the permissible duration is 1 hours, checking

every minutes would be appropriate.

Turnover is then obtained from the e+uation



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/igure 4$1 0arking (ccumulation at a 0arking 9ot



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%ar2ing #emand by interviewing drivers at the various parking

facilities

6nterview all drivers using the parking facilities

on a typical weekday between ": a.m. and

-: p.m.

6nformation include !-% trip origin, !1% purpose

of trip, !% driverFs destination after parking.

the location of the parking facility, times of

arrival and departure, vehicle type.



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%ar2ing #emand 0arking interviews also can be carried out

using the postcard techni+ue,

about to # percent of the cards distributed

are returned.



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