unit 12 ( basic characteristics of a road system ( part 2 ) )

8/6/2019 Unit 12 ( BASIC CHARACTERISTICS OF A ROAD SYSTEM ( Part 2 ) )

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BASIC CHARACTERISTIC ROADHighway Engineering C3010 / UNIT12

BASIC CHARACTERISTICS OF A ROAD

SYSTEM

( Part 2 )

OBJECTIVES

General Objective

To understand the basic characteristic of a road system.

Specific Objectives

At the end of the unit you should be able to: -

describe the traffic characteristics.

identify the term of volume flow.

describe the speed, traffic volume and density.

UNIT 12


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12.0 INTRODUCTION

A knowledge of traffic characteristic is useful to the highway engineer indeveloping highway and transportation plan, performing economic analyses

establishing geometric design criteria, selecting and implementing traffic control

measures, and evaluating the performance of transportation facilities. Dozens of

measures have been employed to describe the quality and quantity of traffic flow.

12.0.1 TRAFFIC VALUME

Traffic volume is defined as the number of vehicles that pass a point

along a roadway or traffic lane per unit of time. A measure of the quantity of

traffic flow, volume is commonly measured in units of vehicles per day,

vehicle per hour.

12.0.2 SPEED

Speed of travel is a simple and widely used measuring the quality of

traffic flow. Basically, speed is the total distance traversed divided by the

time of travel.

INPUT

TRAFFIC CHARACTERISTICS


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12.0.3 DENSITY

Traffic density also referred to as traffic concentration, is defined as

the average number of vehicle occupying a unit length of roadway at a given

instant.

12.1 TERM OF VOLUME FLOW

The first basic characteristic of traffic is volume. Traffic volume study were

made to get accurate information about quantity vehicle movement characteristic

and pedestrian in an area, in a specific places in connection.

Volumes can be definition as a number of cars which post at a certain

point, a short road section in a certain time. If N were a number of vehicle

crossing a line at a road in a duration of time; T, so the volume traffic is

q = N/T

The unit of volume is vehicle/hour. The unit of time duration that were made not

necessary on hour or consistent to an hour. In a certain case, like peak time

study, time duration that were taken is 15 minute. So the volume unit is

vehicle/15 minute. Besides the general definition of volume that was discussed

earlier, there was more phase of volume that were used for a specific road

design.


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12.1.1 ANNUAL AVERAGE DAILY TRAFFIC. (AADT)

To obtain the average traffic per day, count the number of vehicles

over the duration of more than a day. Then divided the total number of

vehicles by number of days.

12.1.2 DAILY AVERAGE TRAFFIC

Daily average is a unit of vehicles per day and is calculated as the

time duration is more a day and than a year traffic divided by the number

of days in that period of time.

12.1.3 PEAK HOUR VOLUME

1) Geometric design considering numbers and width of with of lane,

intersection design, and other road characteristic.

2) Determine insufficient payload of the road.3) To plan and determining the location of the traffic control such as traffic

light, traffic sign and others.

4) To design a traffic operation program.

5) Planning and enforcing law.

12.1.4 VOLUME HOUR DESIGN.

The traffic flow is a dynamic phenomenon. The traffic characteristic

and the traffic flow always changes from time to time. Thus, an average

value should be obtained in designing purpose. For geometrical design,

traffic volume is calculated base on every hour. This volume is called


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volume per hour. For the purpose of design, the volume per hour should

be as close as possible value of the volume peak hour. The highest

volume per hour will not be used in road designing because it will result in

over design.

The identify volume per hour is known volume per hour design.

One criterion to determine the volume per hour design is congested rate

that were allowed in peak hour.

12.1.5 VOLUME HOUR DESIGN RATIO

In the proceeding sections of this chapter, consideration was given

to some predetermined, congested, or peak hour, and the temporal non-

uniformity of traffic flow over this hour was accounted for by using the

peak hour factor. However, there is a larger question that looms: How is

the peak hour determined for either highway design (i.e., determining thenumber of lanes required, and so on) or congestion analysis? This

question is complicated by two concerns. First, there is considerable

variability in traffic volumes by time of day, day of week, time of year, and

type of highway.

Current design practice in the United States generally uses a peak

hour between the 10th 50th highest volume hour of the year, depending on

the type and location of the road ( e.g., urban freeway, rural multilane

highway, and so on ), local traffic data, and engineering judgment.

Perhaps the most common hourly volume used for roadway design in the

30th highest hourly volume of the year. In practice, the K factor is used to


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convert average annual daily traffic (AADT ) to the 30 th highest annual

hourly volume.

K = DHV

AADT

12.1.6 PEAK TIME FACTORS.

In determining the level of service of a highway segment, a few key

definitions and associated notations must be well understood.

Hourly volume is the actual hourly demand volume for the

highway in vehicle per hour, given the symbol V. Generally, the highest

24-hour hourly volume ( i.e., peak hour volume ) is used forVin traffic

analysis computations.

Peak Hour Factoraccounts for the non-uniformity of traffic flow

over the peak hour. It is denoted PHF and is typically defined as the ratioof the hourly volume ( V) to the maximum 15 min rate of flow ( V15 )

expanded to an hourly volume. Therefore,

4xPHF

15v

v

=

Equation obove indicates that the further the PHF is from unity, the

morepeakedor non-uniform the flow. For example, consider two roads

both of which have a peak-hour volume, v, of 2000 veh/hr. However, the

first road has 1000 vehicles arriving in the highest 15-mm interval and the


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second road has 600 vehicles arriving in the highest 15-mm interval.

Clearly, the first road has a more non-uniform flow, and this is

substantiated by the fact that is PHF of 0.5 (i.e,2000/(1000 X 4 )) is further

from unity than the second roads PHF OF ( i.e, 2000/(600 X 4).

12.2 TRAFFIC VOLUME CHARACTERISTIC

A knowledge of traffic characteristic is useful to highway engineer in

developing highway and transportation plans, performing economic analyses,

establishing geometric design criteria, selecting and implementing traffic control

measures, and evaluating the performance of transportation facilities. Dozens of

measures have been employed to describe the quality and quantity of traffic flow.

In this unit, information is presented on those flow characteristics that

fundamentally bear on the planning, design, and operation of highway section on

highway capacity, we will consider ways of estimating the ability of various

highway facilities to accommodate traffic flow.

12.2.1 TRAFFIC VOLUME FLOW CHANGGING - DAILY

The flow in each hour has been expressed as a percentage of the

daily flow since this most convenient way of studying such patterns and

permits easy comparison. Weekdays, Saturdays and Sunday usually have

distinctive patterns but, comparing day with day, patterns for routes of a

similar nature often show a marked similarity, which is useful in enabling

predictions to be made.

Especially significant in the design of roads and control of traffic is

the peak hours volume, which is usually 8-10% of total daily flow or 2-2 1/2


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times the average hourly volume. There are a morning and an evening

peak with the latter generally predominant. These include many work trips,

which are relatively, stable in time and fairly insensitive to charge from day

to day and weather and other travel conditions.

12.2.2 TRAFFIC VOLUME FLOW CHANGGING - WEEKLY

Variations are shown, which given a typical weekly flow pattern with

volumes expressed as a percentage of the total flow for the week. Traffic

flow for the weekly, Monday to Friday, remains fairly contents, but

weekend flows are more variable and depend to a large extent on season

and weather. On the average weekend, flows in the center of a large city

will be considerably lower than for weekdays, but main routes out of city.

12.2.3 TRAFFIC VOLUME FLOW CHANGING - SEASONAL

VARIATIONS

Volumes, in general are above in the more pleasant motoringmonths of summer, but this is more pronounced in rural urban areas. This

monthly average flow is usually at a maximum for most rural roads in

August and at its lowest in January. A number of central urban areas show

a dip in midsummer flows but remain fairly consistent during the remainder

of the year. Seasonal patterns for a given type of route are the most

consistent of all the variation patterns and represent the economic and

social conditions of the traffic are served. It is only this condition change,

usually by a gradual process, than the patterns change.


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12.3 CALCULATION FOR TRAFFIC VOLUME

The traffic volume in one direction for each section of the route and for

each class of vehicle is obtained from the following formula.

Q = x + y

Ta +Tw

Where;

Q = Vehicles ( of the appropriate class) per minute in the direction of the

stream.

X = Number of vehicles (of the same class) met travelling.

Y = Number of vehicle ( of the same class) overtaking the test vehicle

traveled with the stream.

Ta = Journey time, in minute, of the vehicle travelling against the

stream.

Tw = Journey time, in minutes, of the test vehicle travelling with the

stream.

The average journey in minutes of the particular class of vehicle in the

stream is given by,

T = Tw - y

q


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TEST YOUR UNDERSTANDING BEFORE YOU CONTINUE WITH THE NEXT

INPUT

1. What is the meaning of these items?

a. Traffic volume.

b. Speed

2. How to determine the traffic volume value using a formula.

ACTIVITY 12

Question


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1.

TRAFFIC VALUME

Traffic volume is defined as the number of vehicles that pass a point

along a roadway or traffic lane per unit of time. A measure of the

quantity of traffic flow, volume is commonly measured in units of

vehicles per day, vehicle per hour.

SPEED

Speed of travel is a simple and widely used measuring the quality of

traffic flow. Basically, speed is the total distance traversed divided by

the time of travel.

2. Q = x + y

Ta +Tw

Where;

Q = Vehicles ( of the appropriate class) per minute in the direction of the

stream.

X = Number of vehicles (of the same class) met travelling.

FEEDBACK ON

Answer


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Y = Number of vehicle ( of the same class) overtaking the test vehicle

traveled with the stream.

Ta = Journey time, in minute, of the vehicle travelling against the

stream.

Tw = Journey time, in minutes, of the test vehicle travelling with the

stream.

The average journey in minutes of the particular class of vehicle in the

stream is given by,

T = Tw - y

q

Traffic volume value will be determined with using this formula.


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1. Describe briefly the traffic volume changing daily.

2. Give the definition on these items.

a. Hourly volume.

b. Peak-hour factor

Question


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1.

TRAFFIC VOLUME FLOW CHANGGING - DAILY

The flow in each hour has been expressed as a percentage of the

daily flow since this most convenient way of studying such patterns and

permits easy comparison. Weekdays, Saturdays and Sunday usually have

distinctive patterns but, comparing day with day, patterns for routes of a

similar nature often show a marked similarity, which is useful in enabling

predictions to be made.

Especially significant in the design of roads and control of traffic is

the peak hours volume, which is usually 8-10% of total daily flow or 2-2 1/2

times the average hourly volume. There are a morning and an evening

peak with the latter generally predominant. These include many work trips,

which are relatively, stable in time and fairly insensitive to charge from day

to day and weather and other travel conditions.

2.

Hourly volume is the actual hourly demand volume for the

highway in vehicle per hour, given the symbol V. Generally, the highest

Answer


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24-hour hourly volume ( i.e., peak hour volume ) is used forVin traffic

analysis computations.

Peak Hour Factoraccounts for the non-uniformity of traffic flow

over the peak hour. It is denoted PHF and is typically defined as the ratio

of the hourly volume ( V) to the maximum 15 min rate of flow ( V15 )

expanded to an hourly volume.

unit 12 ( basic characteristics of a road system ( part 2 ) )

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