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Lec 8, Ch4, pp.99-115:Volume StudiesPowerPoint Presentation

Lec 8, Ch4, pp.99-115:Volume Studies

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Lec 8, Ch4, pp.99-115:Volume Studies

- Know the definitions of typical volume study terms
- Know typical volume count methods (through reading)
- Be able to state the purpose and methods of typical volume counts
- Know how to present volume count data (through reading)
- Know how to determine the number of count stations
- Know how to adjust periodic counts

What we cover in class today…

- Terminology
- Types of volume counts
- Determination of number of count stations
- Adjustment of period counts

Terminology

- Traffic volume studies are conducted to collect data on the number of vehicles and/or pedestrians that pass a point on a highway facility during a specified time period.

- Average Annual Daily Traffic (AADT): the average of 24-hour counts collected every day in the year.
- Average Daily Traffic (ADT): the average of 24-hour counts collected over a number of days greater than 1 but less than a year.
- Peak Hour Volume (PHV): the maximum number of vehicles that pass a point on a highway during a period of 60 consecutive minutes.

Terminology (cont)

- Vehicle Classification (VC): Records volume with respect to the types of vehicles.
- Vehicle Miles (Kilometers) of Travel (VMT, VKT): A measure of travel along a section of road. A product of roadway in miles to which the volume is applicable.
- Hourly Flow Rate: An hourly volume expanded from a counter taken in a period shorter than 60 minutes. The typical one is Peak hourly flow rate which is 4 times the peak 15-minute count.

Vpeak = 4*Vpeak 15-min

Volume count by microwave sensors

RTMS Box

Multiple-lane sensing by one microwave sensor

Firing example

Determination of number of count stations

Common precision level for volume counts: 95-5, which means 95% confidence level and the precision level (tolerance) expressed as 5% of the estimated mean volume.

Where,

n = minimum number of count locations required

t = value of the student’s t distribution with (1 - /2) confidence level (N – 1) degree of freedom

(Review Example 4.4)

Adjustment of periodic counts

HEF = (total volume for 24-hr period)/(volume for particular hour)

DEF = (average total volume for week)/(avg. volume for particular day)

MEF = AADT/(ADT for particular month)

(Review Example 4-5)

Finding truck adjustment factors

This adjustment is needed when we make volume counts by checking the number of axles

Manual count result (for obtaining the truck factor value for the site under study)

Type

No. of Axles

No. of vehicles

No. of axles

7700

3850

Passenger cars

2

4110

1370

Trucks

3

2080

4

520

Trucks

5740

13890

Total

Truck adjustment factor = 13890/5740 =2.42 axles/vehicle

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