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TRAFFIC ENGINEERING STUDIES

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Generally the duration is calculated based from 1 hour,1 day or 1 year.Unit of traffic volume is either no. of vehicle or

passenger car unit (PCU).Traffic can be divided into types and class of vehicles,such as cars, motorcycle, lorries, truck, van, taxi andbus.

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2.1.1: Passenger Car Unit (PCU)The standard unit of measurement which is designedto give the effect of an equivalent numbers ofpassengers cars.Basically passenger carrying vehicle is the large sizeof traffic on the road.Size of transportation involved influence the numberof traffic on a stretch of road hence the number ofpassenger.

The PCU for a particular year of transport is differentin stretch of road and at junction.


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Convert the traffic volume veh/hr to passenger carunit/hr. Say the traffic volume along a road in a town is600 veh/hr.


Vehicle No. of vehicle /hr

PCU Value PCU/ hr

Motorcycle 150

Buses 50

Lorries 40 Van 60

Car/taxi 300

Total

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2.2.1 Traffic Survey Methods for Volume and SpeedStudies.

Information from traffic survey data may be used forintersection design, evaluate the effectiveness ofbefore-and-after up grading program of the road(road safety and delay), and economic justificationfor new road construction or upgrading.

Choice of traffic data collection technique depends on

data usage and the accuracy required and the costoccur (economic). Method of data gatheringindirectly indicated by the sizze of traffic study, which may be done manually or automatically.


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Period of count use of traffic data dictates thedurations of count requirement:

1. 12 hour counts start from 7a.m to 7p.m

2. 16 hour counts start from 6a.m to 10p.m3. 24 hour counts start from midnight to midnight


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2.2.2: Methods of MeasurementTraffic volume counts are conducted using two basicmethods i.e manual and automatic. A description of

each counting method follows.1. Manual Method- Manual counting involves one or more personsrecording observed vehicles using a counter.

- The main advantages and disadvantages of manualcounts are:


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2. Pressure contact strip Method- Usually two pneumatic tubes (lay across the

carriageway at a fixed distances)- When a vehicle passes over the first tube, an air

impulse is sent instantly along the tube.- When the same wheels depress the second tube thetimer is automatically stopped.

- The reading noted either by observer or by automatic

data recorder.

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AdvantagesInexpensive

PortableNot required specialised Accurate results

Long life on low volume road

Disadvantages. Wear and tearStreet cleaners VandalismMay disrupts traffic during installation

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Loop detector usually hexagon shaped wires buried inroadways, are the primary source of quantitative trafficdata. When a vehicle passes over a detector, itsmetallic mass causes fluctuations in the detectors inductance.

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3. Manual method of spot speed data- To observe the time required by a vehicle to cover a

short distances- With the direct timing procedure- To reference points where located at a roadway at a

fixed distance apart- Observer starts and stops a stopwatch as a vehicle

enters and leaves the test section.

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Other traffic flow apparatus/methods- Radar speed meter method

- Sonic-detector method- Time-laps camera method

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2.2.4: Spot Speed studies

A spot speed study is a study of speed of traffic at onepoint or spot on a traffic way.To determine enforceable speed limitsThe locations should be at minimum influence of theobserver and measuring equipment.If not possible to measure all vehicle speed, select only atrandom for example for every 10 vehiclesIt consists of a series or a sample of observation of theindividual speeds at which vehicle are approaching anintersection.The observations are used to estimate the speeddistribution of the entire traffic stream at that locationunder the conditions prevailing at the time of the study.

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2.2.5 : Application of spot speed dataSpeed is a primary factor in all modes of transportation

and it is a basic measure of traffic performance. Spotspeed data have many application such as:

1. For trends in the operating speeds of the different

vehicles types which are obtained from datecollected through periodic sampling at the selectedlocations.

2. For speeds at the problems locations, to determine

whether speeds are too high and if complaintsreceived are justified.

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3. For traffic operation:- establish speeds limits

- Determining safe speeds at curves

4. For geometric design features

5. Research studies

Factors that influence spot speed are:

1. The driver including his trip, numbers ofpassengers, residence

2. The vehicle including type, age, weight and horsepower

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Definitions

1. Speed rate of movement of a vehicles expressed inkilometer per hour.

2. Average spot speed the arithmetic mean of speedsof all traffic at a specified point.

3. Overall travel time the time of travel includingstop and delays

4. Overall travel speed the speed over a specifiedsection of highway

5. Running speed the average speed maintain over aparticular distance which the vehicle is in motion

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Arithmetic mean speed,

x = fvn

Where:

f = frequency of observation v = mean speedn = number of observation

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9. Time mean speed the arithmetic mean of speedsof all vehicles passing a point during specifiedinterval of time

10. Space mean speed the arithmetic mean of speedsof vehicles occupying a relatively long section ofstreet or highway at a given instant

11. Median speed middle value when all speed valuesare arrayed in ascending order

12. Modal speed value with the highest frequency ofobservations

13. The roadway geographic location

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Median speed = L + [n/2 f L] x c[f m]

Where:n= total number of observationL = Lower bound of the group in which the medianin

f L = cumulative number of observation up to thelower bound of the group in which median hasf m = number of observation in the group whichmedian liesc = speed interval of the group

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14. The traffic include volume and density15. The environment season whether

16. Standard deviation which measure of the spread ofthe individual speeds.

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Standard deviation,s = (fv 2) - (fv)2

(n-1) n(n-1)

Where:f = frequency of observation v = mean speedn = number of observation

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SpeedGroup

MeanSpeed, v

Frequency,f

v 2 f.v f.v 2

10-14.9 12.5 0

15-19.9 17.5 6

20-24.9 22.5 8

25-29.9 27.5 29

30-34.9 32.5 60

35-39.9 37.5 63

40-44.9 42.5 74

45-49.9 47.5 29

50-54.9 52.5 19

55-59.9 57.5 10

60-64.9 62.5 2

65-69.9 67.5 0

TOTAL

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From the table find the following:1. Arithmetic mean speed2. Median

3. Standard deviation

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Speed

Group

Mean

Speed, v

Frequency,

f

v 2 f.v f.v 2

10-14.9 12.5 0 156.25 0 015-19.9 17.5 6 306.25 105 1837.520-24.9 22.5 8 506.25 180 405025-29.9 27.5 29 756.25 797.5 21931.2530-34.9 32.5 60 1056.25 1950 6337535-39.9 37.5 63 1406.25 2362.5 88593.7540-44.9 42.5 74 1806.25 3145 133662.545-49.9 47.5 29 2256.25 1377.5 65431.25

50-54.9 52.5 19 2756.25 997.5 52368.7555-59.9 57.5 10 3306.25 575 33062.560-64.9 62.5 2 3906.25 125 7812.566-69.9 67.5 0 4556.25 0 0

TOTAL 300 22775 11615 472125

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1. Arithmetic mean speed,x = fv

n= 11615 / 300= 38.72 km/h

2. Median speed = L + [n/2 f L] x c[f m]

= 35 + [300/2 103] x 4.963

= 38.66 km/h

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3. Standard deviation,s = (fv 2) - ( fv)2

(n-1) n(n-1)= [472125 / 299] - [(11615)2 / 300(299)]= 8.66 km/h

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Parking Studies

Any vehicle traveling on a highway will at one time or anotherbe parked for either a relatively short time or a much longertime, depending on the reason for parking.

The provision of parking facilities is therefore an essentialelement of the highway mode of transportation.

The need for parking spaces is usually very great in areas where land uses include business, residential, or commercialactivities.

The growing use of the automobile as a personal feeder serviceto transit systems (park -and- ride) has also increased thedemand for parking spaces at transit stations.

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Types of

ParkingFacilities

On-Street ParkingFacilities Off-Street Parking

Facilities

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On-Street Parking Facilities These are also known as curb facilities. Parking bays are

provided alongside the curb on one or both sides of the street. These bays can be unrestricted parking facilities if the

duration of parking is unlimited and parking is free, or theycan be restricted parking facilities if parking is limited tospecific times of the day for a maximum duration.

Parking at restricted facilities may or may not be free.Restricted facilities also may be provided for specificpurposes, such as to provide handicapped parking or as busstops or loading bays.

Off-Street Parking Facilities These facilities may be privately or publicly owned; theyinclude surface lots and garages. Self-parking garages requirethat drivers park their own automobiles; attendant-parkinggarages maintain personnel to park the automobiles.

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