CE 434 : Lecture 3

Traffic Studies :

Traffic Volume Study

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Traffic studies

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Types of Studies

ü Volume studies

ü Speed studies

ü Travel-time & Delay studies

ü Accident studies

ü Parking studies

ü Origin and Destination Study

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Volume studies and characteristics

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Traffic counts are the most basic of traffic studies and arethe primary measure of demand.

All aspects of traffic engineering require volume as aninput , including highway planning and design, decisionson traffic control and operations, detailed signal timing andothers.

Volume Studies

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Volume—the total number of vehicles that pass over a givenpoint or section of a lane or roadway during a given timeinterval; volumes may be expressed in terms of annual,daily, hourly, or sub hourly periods.

Rate of flow—the equivalent hourly rate at which vehiclespass over a given point or section of a lane or roadwayduring a given time interval less than 1 hr, usually 15 min.

Volume and Rate of Flow

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The following examples further illustrate the difference between hourly volumes and flow rates.

Volumes were observed for four consecutive 15-min periods. Thetotal volume is 400 vehicles, or the sum of the four counts. The rateof flow, however, is zero in two 15-min intervals and 800 vph in thetwo other 15-min intervals. Thus, a design based on the hourlyvolume (400 vph) would not prove adequate.

Time Period Volume (Veh) Rate of Flow (vph)

5.00-5.15 0 0

5.15-5.30 200 800

5.30-5.45 200 800

5.45-6.00 0 0

5.00-6.00 400

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Peak rates of flow are related to hourly volumes through the use of the peak-hour factor. This factor is defined as the ratio of total hourly volume to the peak rate of flow with in the hour.

PHF = Hourly Volume / Peak rate of flow (with in the hour)

If 15-mins periods are used, the PHF may be computed as

PHF = V / (4 x V15 )

V= hourly volume (vph)

V15 = volume during the peak 15 min of the peak hour (veh/15 min)

Peak Hour Factor

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Basic Measurements

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Volume, Demand and Capacity

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Flow

• Average Annual Daily Traffic (AADT)– The average 24-hour traffic volume at a given

location over a full 365-day year

– Total number of vehicles passing the site in a year divided by 365

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Flow

• Average Daily Traffic (ADT)

– An average 24-hour traffic volume at a given location for a period of time less than a year• Six months or a season

• A month or week

– ADT is a valid only for the period over which it was measured

• Variations of Volume with time

– Monthly

– Weekly

– Daily

– Hourly

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Seasonal and monthly variations

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• Measurement Techniques

– Manual counting

– Mechanical counters

– Video photography

– Loop detectors and Sensors

Time Bus Truck LCV Car Motorised Three-

Wheeler

Motorised Two –Wheeler

Bicycle Tri cycle ADV2 Axle > 2

Axle

TRAFFIC SURVEYDate : Name of the Surveyor:

Day : Location: Traffic Flow Direction : From…….……………….…………. To … …..…………..….………… Weather Condition:

LCV – Light Commercial Vehicle ADV- Animal Drawn VehicleDr.PV Lecture Notes

Eastbound Traffic

Westbound Traffic

Southbound Traffic

Northbound Traffic

NOT TO SCALE

813

543

818

581

768

619

649

719

100

416

103

121

388

140

8157068

8459787

2755TOTAL

1124N / S

1631E / W

TOTAL TRAFFIC ENTEREING

INTERSECTION

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Expressing traffic volume as number of vehicles passing agiven section of road per unit time will be inappropriatewhen several types of vehicles with widely varying staticand dynamic characteristics are present in the road traffic.

The problem of measuring volume of such heterogeneoustraffic has been addressed by converting the differenttypes of vehicles into equivalent passenger cars andexpressing the volume as Passenger Car Unit (PCU) perhour.

Passenger Car Unit (PCU)

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The following definition of PCU, which is based on theperformance measure, speed, proposed by Transport andRoad Research Laboratory (TRRL, 1965), London, UKhas been adopted for this study:

“on any particular section of road under particulartraffic conditions, if the addition of one vehicle of aparticular type per hour will reduce the average speed ofthe remaining vehicles by the same amount as theaddition of, say x cars of average size per hour,….then,one vehicle of this type is equivalent to x PCU.

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Factors Affecting PCU Values

Vehicle characteristics

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Traffic Stream characteristics

Roadway characteristics

Simulation Technique:Simulation is an innovative tool used to study the behaviourof complex real world systems like heterogeneous traffic flowand facilitates conduct of experiments under controlledsituations over a wide range of operational conditions.

A limited number of simulation studies have been conductedfor estimating PCU values taking the speed as theperformance measure.

For highly heterogeneous traffic conditions simulation hasbeen found a versatile tool to model complex systems forstudy of the system characteristics over a wide range ofoperating conditions.

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PCU Estimation Method

Indian Road Congress (IRC) Guidelines for capacity of urban roads inplain areas. IRC:106, New Delhi, India.1990.

Vehicle Type PCU Factors

% composition of vehicle 5% (up to 9%)

% composition of vehicle 10% and Above

Two Wheelers, Motor cycles or scooter

0.5 0.75

Passenger car 1.0 1.0

Auto rickshaw 1.2 2.0

Light commercial Vehicle 1.4 2.0

Truck or Bus 2.2 3.7

Agricultural Tractor-Trailer 4.0 5.0

Cycle 0.4 0.5

Cycle rickshaw 1.5 2.0

Hand Cart 2.0 3.0

*Horse drawn vehicle – 4.00 *Small Bullock cart – 6.00 *Bullock cart - 8.00* Rural Roads Dr.PV Lecture Notes

Vehicle Type Volume (Veh/hr)

Bus 220Truck 105Light Commercial Vehicles 185

Car 1259

Motorized Three Wheeler (M.Th.W.) 984

Motorized Two Wheeler (M.T.W) 4008

Bicycle 350

Convert the field observed Traffic Flow (Veh/hr) into PCU/h. (Using IRC PCU values.)

Example 1

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