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Title: tranportation notes for 3-2 civil b.tech students
Description: to get marks as well aspractical knowledge
Description: to get marks as well aspractical knowledge
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LECTURE NOTES ON
TRANSPORTATION ENGINEERING
JN
TU
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Department of Civil Engineering
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CONTENTS
Highway development in india
Necessity for highway planning
Different road development plans
Classification of roads
Road network patterns
Highway Alignment
Factors affecting alignment
Engineering surveys
Drawing and reports
Highway project
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CHAPTER 4 INTERSECTION DESIGN
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Types of Intersections
Conflicts at Intersections
Requirements of At –Grade intersectionTypes of at-Grade IntersectionsChanalization -Traffic Islands
Types of Grade Separated Intersections
Rotary Intersection –concept of Rotary
Design factors of rotary
Advantages and limitations of rotary intersections
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CHAPTER 1
HIGHWAY DEVELOPMENT AND PLANNING
Overview
History of highway engineering
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Road transport is one of the most common mode of transport
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were used even from the pre-historic times
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Thus road construction became an inseparable part of many civilizations
and empires
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Also we will discuss about the highway planning in India
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Roads in Rome were
constructed in a large scale and it radiated in many directions helping them in military operations
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In this section we will see in detail about Ancient roads,
Roman roads, British roads, French roads etc
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These human pathways would have been developed for speci c
purposes leading to camp sites, food, streams for drinking water etc
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Since these loaded animals required more
horizontal and vertical clearances than the walking man, track ways emerged
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Then it became necessary that
the road surface should be capable of carrying greater loads
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To
provide adequate strength to carry the wheels, the new ways tended to follow the sunny drier side of a path
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After the invention of wheel, animal drawn vehicles were
developed and the need for hard surface road emerged
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The earliest authentic record of road was found from
Assyrian empire constructed about 1900 BC
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They were a remarkable achievement and provided travel times across
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Romans recognized that the fundamentals of good road construction
were to provide good drainage, good material and good workmanship
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Roman roads were always constructed on a rm - formed subgrade strengthened
where necessary with wooden piles
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The next
step was the construction of the agger
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This was then topped with a
sand leveling course
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The pavement
structure on the top of the agger varied greatly
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A typical cross section of roman road is given in Figure 2:1 The
main features of the Roman roads are that they were built straight regardless of gradient and used heavy
foundation stones at the bottom
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Thus concrete was a major Roman road making innovation
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The signi cant
contributions were given by Tresaguet in 1764 and a typical cross section of this road is given in Figure 2:2
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The pavement used 200 mm pieces of quarried stone of a more compact form and shaped such that they had at
least one at side which was placed on a compact formation
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Finally the running layer was made
with a layer of 25 mm sized broken stone
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This created major drainage problems which were counteracted by
making the surface as impervious as possible, cambering the surface and providing deep side ditches
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5 m
Cross slope
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Side drain
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_________________CompactedSubgradeslope1:36
50mm Broken Stones, 100mm thick
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He also enunciated the necessity for continuous organized maintenance, instead
of intermittent repairs if the roads were to be kept usable all times
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British roads
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The British government also gave importance to road construction
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Stone size was an
important element of Macadam recipe
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Thus he introduced an
economical method of road construction
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2
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But the inter particle friction abraded the sharp interlocking faces and partly destroy the e ectiveness
of the course
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Such mixes also proved less permeable and easier to compact
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Modern roads
The modern roads by and large follow Macadam's construction method
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Various advanced and cost-e ective construction
technologies are used
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Many easily
and locally available materials are tested in the laboratories and then implemented on roads for making
economical and durable pavements
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Population of the country is increasing day by day
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The need for travel to various places at faster speeds also increased
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While the above development in public transport sector was taking place,the development in private transport was
at a much faster rate mainly because of its advantages like accessibility, privacy, exibility, convenience and
comfort
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Thus road space
available was becoming insu cient to meet the growing demand of trafficand congestion started
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This has led to the increased attention towards control of vehicles so
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that the transport infrastructure was optimally used
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were implemented
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These were large projects requiring large investment
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This has led to the
emergence of transportation planning and demand management
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Highway planning in India
JN
Excavations in the sites of Indus valley, Mohenjo-dero and Harappan civilizations revealed the existence of
planned roads in India as old as 2500-3500 BC
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Ancient
books like Arthashastra written by Kautilya, a great administrator of the Mauryan times, contained rules for
regulating tra c, depths of roads for various purposes, and punishments for obstructing tra c
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Roads linking North-West and
the Eastern areas through gangetic plains were built during this time
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The
construction of Grand-Trunk road connecting North and South is a major contribution of the British
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Modern developments
The rst World war period and that immediately following it found a rapid growth in motor transport
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For that, the Government of India appointed a committee called Road
development Committee with Mr
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R
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This committee came to be known as
Jayakar committee
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The major recommendations and
the resulting implementations were:
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Committee found that the road development of the country has become beyond the capacity of local
governments and suggested that Central government should take the proper charge considering it as a
matter of national interest
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One of the recommendations was the holding of periodic road conferences to discuss about road
construc-tion and development
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This led to the introduction of a
development fund called Central road fund in 1929
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INTRODUCTION TO HIGHWAY ENGINEERING
A dedicated research organization should be constituted to carry out research and development work
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Nagpur road congress 1943
TU
The second World War saw a rapid growth in road trafficand this led to the deterioration in the condition of
roads
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The result of the conference is famous as the Nagpur plan
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It was the rst attempt
to prepare a co-ordinated road development programme in a planned manner
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B) State highways which would be the other main roads of a state
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According
to the importance, some are considered as major district roads and the remaining as other district
roads
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The committee planned to construct 2 lakh kms of road across the country within 20 years
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One of the objective was that the road length should be increased so as to give a road density of
16kms per 100 sq
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The changed economic, industrial and agricultural conditions in the country
warranted a review of the Nagpur plan
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The highlights of the plan were:
It was the second 20 year road plan (1961-1981)
The total road length targeted to construct was about 10 lakhs
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Scienti c methods of construction was proposed for the rural
roads
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They suggested that the length of the road should be increased so as to give a road density of
32kms/100 sq
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Lucknow road congress 1984
This plan has been prepared keeping in view the growth pattern envisaged in various elds by the turn of the
century
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It is also called Lucknow road plan
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km
The plan has set the target length of NH to be completed by the end of seventh, eighth and ninth ve
year plan periods
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such that no part of country is
farther than 50 km from NH
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Energy conservation, environmental quality of roads and road safety measures were also given due
impor-tance in this plan
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Of these, pavement surface characteristics a ect both of these
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They
are explained brie y in this chapter
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Friction
Friction between the wheel and the pavement surface is a crucial factor in the design of horizontal curves
and thus the safe operating speed
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Lack of adequate friction can cause skidding or slipping of vehicles
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Various factors that a ect friction are:
Type of the pavement (like bituminous, concrete, or gravel),
Condition of the pavement (dry or wet, hot or cold, etc),
TU
Condition of the tyre (new or old), and
Speed and load of the vehicle
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The choice of the value of f is a very complicated issue since it
depends on many variables
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35-0
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Unevenness
It is always desirable to have an even surface, but it is seldom possible to have such a one
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Unevenness a
ect the vehicle operating cost, speed, riding comfort, safety, fuel consumption and wear and tear of tyres
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An unevenness index value less
than 1500 mm/km is considered as good, a value less than 2500 mm
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Light reflection
White roads have good visibility at night, but caused glare during day time
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Drainage
The pavement surface should be absolutely impermeable to prevent seepage of water into the pavement
layers
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Camber
Camber or cant is the cross slope provided to raise middle of the road surface in the transverse direction to
drain o rain water from road surface
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Camber is measured in 1 in n or n% (Eg
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The values suggested by IRC for various
categories of pavement is given in Table 12:1
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Parabolic camber y=2x /nw
w
1 in n
2n
W
b
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Combination of straight and parabolic camber
Figure 12:1: Different types of camber
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Surface
type
Concrete/Bituminous
Gravel/WBM
Earthen
Heavy
rain
2%
3%
4%
Light
rain
1
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5 %
3
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Width of a trafficlane depends on the width of the vehicle and the clearance
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The maximum permissible width of a vehicle is 2
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68 m
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75 m for a single lane road
(Figure 12:2a)
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53 m, on either side and 1
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Therefore, a two lane road require minimum of 3
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The desirable
carriage way width recommended by IRC is given in Table 12:2
TU
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Table 12:2: IRC Specification for carriage way width
Single lane
3
...
0
Two lane, raised kerbs 7
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5
Multi-lane
3
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44m
0
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68m
2
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53m
3
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44m
1
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53m
7
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Di erent
types of kerbs are (Figure 12:3):
Low or mountable kerbs : This type of kerbs are provided such that they encourage the trafficto remain
in the through trafficlanes and also allow the driver to enter the shoulder area with little di culty
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This is usually provided at medians and channelization schemes and also helps in
longitudinal drainage
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Their height is
15 cm above the pavement edge
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Barrier type kerbs : They are designed to discourage vehicles from leaving the pavement
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They are placed at a height of 20 cm
above the pavement edge with a steep batter
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semi barrier type
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20 cm
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barrier type
carriageway
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carriageway
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The kerbs are provided at pavement edges between
the pavement edge and shoulders
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The portion of the road beyond the carriageway and on the roadway can be generally called road margin
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Shoulders
Shoulders are provided along the road edge and is intended for accommodation of stopped vehicles, serve
as an emergency lane for vehicles and provide lateral support for base and surface courses
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The shoulder width
should be adequate for giving working space around a stopped vehicle
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6
m for the shoulders
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5 m is recommended for 2-lane rural highways in India
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Parallel parking is preferred because it is safe for
the vehicles moving on the road
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0 m width in the case of
parallel parking
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They are provided so that they do not obstruct
the movement of vehicles in the carriage way
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Service roads
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Service roads or frontage roads give access to access controlled highways like freeways and expressways
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These roads are provided to avoid congestion in the expressways and also
the speed of the trafficin those lanes is not reduced
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Footpath
Footpaths are exclusive right of way to pedestrians, especially in urban areas
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Minimum width is 1
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The footpath should be either as smooth as the pavement
or more smoother than that to induce the pedestrian to use the footpath
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They serve to
prevent the vehicles from running o the embankment, especially when the height of the ll exceeds 3 m
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Guard stones painted in alternate black and white are usually used
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Width of formation or roadway width is the sum of the widths of pavements or carriage way including
separators and shoulders
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The values suggested by
IRC are given in Table 12:3
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5-9
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5
6
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8
4
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75
4
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It should be
adequate to accommodate all the cross-sectional elements of the highway and may reasonably provide for
future development
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Control line is a line which represents the nearest limits of future uncontrolled building activity in
relation to a road
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The right of way width is governed by:
Width of formation: It depends on the category of the highway and width of roadway and road margins
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Side slopes of embankment or cutting: It depends on the height of the slope, soil type etc
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Sight distance considerations : On curves etc
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Reserve land for future widening: Some land has to be acquired in advance anticipating future developments like widening of the road
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Extra width of land is available for the
construction of roadside facilities
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) The normal ROW requirements for built up and open
areas as specified by IRC is given in Table 12:4
Sight distance
Overview
The safe and effcient operation of vehicles on the road depends very much on the visibility of the road ahead of
the driver
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This distance is said to be the sight distance
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Three sight distance
situations are considered for design:
Stopping sight distance (SSD) or the absolute minimum sight distance
Intermediate sight distance (ISD) is de ned as twice SSD
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Overtaking sight distance (OSD) for safe overtaking operation
Head light sight distance is the distance visible to a driver during night driving under the illumination of
head lights
Safe sight distance to enter into an intersection
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The computation of sight distance depends on:
Reaction time of the driver
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Reaction time of a driver is the time taken from the instant the object is visible to the driver to the instant
when the brakes are applied
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In practice, all these times are usually combined into a total perception-reaction time suitable for
design purposes as well as for easy measurement
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5 to 2 secs under normal conditions
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For example, IRC suggests a reaction time of
2
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Speed of the vehicle
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The speed of the vehicle very much a ects the sight distance
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Hence it is evident that, as the speed increases, sight distance also increases
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If the
brakeffciency is 100%, the vehicle will stop the moment the brakes are applied
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Also for safe geometric design, we assume that the vehicles have only
50% brake efficiency
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When the frictional resistance is more, the vehicles stop immediately
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No separate provision for brake e ciency is provided while computing the sight distance
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IRC has speci ed the value of longitudinal
friction in between 0
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4
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Gradient of the road also a ects the sight distance
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Therefore sight distance required is less
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Sight distance required will be
more in this case
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There is a term called safe stopping distance and is one of the important measures in traffic engineering
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Drivers must have adequate time if they are to suddenly respond to a situation
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The
stopping sight distance is the sum of lag distance and the braking distance
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Braking
distance is the distance traveled by the vehicle during braking operation
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If F is the maximum
frictional force developed and the braking distance is l, then work done against friction in stopping the vehicle
is F l = f W l where W is the total weight of the vehicle
...
1)
W
SSD = vt +
2gf
2
where v is the design speed in m=sec , t is the reaction time in sec, g is the acceleration due to gravity and f is the
coe cient of friction
...
When there is an
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Table 13:1: Coe cient of longitudinal friction
Speed, kmph
<30 40
50
60
>80
f
0
...
38 0
...
36 0
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The component of gravity acting parallel to the surface which adds to the the braking force is
equal to W sin W tan = W n=100
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Therefore the general equation is
given by Equation 13
...
2
v
SSD = vt + 2g(f 0:01n)
(13
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The overtaking sight
distance or passing sight distance is measured along the center line of the road over which a driver with his
eye level 1
...
2 m above the road surface
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Spacing between vehicles, which in-turn depends on the speed
Skill and reaction time of the driver
Rate of acceleration of overtaking vehicle
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Gradient of the road
The dynamics of the overtaking operation is given in the gure which is a time-space diagram
...
The trajectory of the slow moving
vehicle (B) is shown as a straight line which indicates that it is traveling at a constant speed
...
The trajectory of the vehicle is shown initially with a steeper
slope
...
The vehicle A slows down to follow
the vehicle B as shown in the gure with same slope from t 0 to t1
...
The time duration T = t3 t1 is the actual duration of the overtaking operation
...
From the Figure 13:1,
the overtaking sight distance consists of three parts
...
Therefore:
OSD = d1 + d2 + d3
(13
...
So d1 is given by:
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d1 = vb t
(13
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The
vehicle A maintains the spacing s before and after overtaking
...
5)
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W
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Let T be the duration of actual overtaking
...
Also, during this time, vehicle A accelerated from initial velocity v b and overtaking is completed while
reaching nal velocity v
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6)
= 2s + vb
a
The distance traveled by the vehicle C moving at design speed v m=sec during overtaking operation is given by:
d3 = vT
(13
...
8)
2
where v b is the velocity of the slow moving vehicle in m=sec , t the reaction time of the driver in sec, s is the
spacing between the two vehicle in m given by equation 13
...
In case the speed of the overtaken vehicle is not given, it can be assumed that it moves 16 kmph
slower the the design speed
...
Note that:
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Table 13:2: Maximum overtaking acceleration at di erent speeds
Speed
Maximum overtaking
2
(kmph) acceleration (m/sec )
25
1
...
30
40
1
...
11
65
0
...
72
100
0
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Overtaking zones
Overtaking zones are provided when OSD cannot be provided throughout the length of the highway
...
The desirable length of overtaking
zones is 5 time OSD and the minimum is three times OSD (Figure 13:2)
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They should be able to perceive a hazard and stop the vehicle if required
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The sight distance should be provided such
that the drivers on either side should be able to see each other
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Design of sight distance at intersections may be used on three possible conditions:
Enabling approaching vehicle to change the speed
Enabling approaching vehicle to stop
Enabling stopped vehicle to cross a main road
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Horizontal alignment
Design Speed
The design speed, as noted earlier, is the single most important factor in the design of horizontal alignment
...
For e
...
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The design speed also depends on the type of terrain
...
Therefore, the design speed is normally reduced for terrains
with steep slopes
...
Based on the type of road and type of
terrain the design speed varies
...
The recommended design speed is given in Table 14:2
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Centrifugal force depends on speed and radius of the horizontal curve and is
counteracted to a certain extent by transverse friction between the tyre and pavement surface
...
For proper design of the curve, an understanding of the forces acting on a vehicle taking a horizontal curve
is necessary
...
CG
W/2
P
W/2
b/2
A
B
W
Ra
Rb
Figure 14:1: E ect of horizontal curve
W
They are the centrifugal force (P) acting outward, weight of the vehicle (W) acting downward, and the
reaction of the ground on the wheels (RA and RB )
...
Let the wheel base be assumed as b units
...
1)
gR
TU
where W is the weight of the vehicle in kg, v is the speed of the vehicle in m=sec, g is the acceleration due to
2
gravity in m=sec and R is the radius of the curve in m
...
2)
gR
The centrifugal force has two e ects: A tendency to overturn the vehicle about the outer wheels and a tendency for
transverse skidding
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The second tendency of the vehicle is for transverse skidding
...
e
...
The transverse skid resistance (F) is given by:
F=
FA + FB
f (RA + RB )
fW
or
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where FA and FB is the fractional force at tyre A and B, RA and RB is the reaction at tyre A and B, f is the
lateral coe cient of friction and W is the weight of the vehicle
...
2)
P
W
=f= v
2
gR
and for safety the following condition must satisfy:
v
2
f>
(14
...
3 and 14
...
If equation 14
...
4 is violated, the vehicle will skid at the horizontal curve
Analysis of super-elevation
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TU
Super-elevation or cant or banking is the transverse slope provided at horizontal curve to counteract the centrifugal force, by raising the outer edge of the pavement with respect to the inner edge, throughout the length
of the horizontal curve
...
In order to nd out how much this raising should
be, the following analysis may be done
...
2
Forces acting on a vehicle on horizontal curve of radius R m at a speed of v m=sec are:
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P cos
P sin
P
or
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W cos
Fb
FA
W
W sin
Figure 14:2: Analysis of super-elevation
P the centrifugal force acting horizontally out-wards through the center of gravity,
W
W the weight of the vehicle acting down-wards through the center of gravity, and
F the friction force between the wheels and the pavement, along the surface inward
...
2
...
2
...
Dividing by W cos , we get:
JN
P cos
W cos
P
W
P
W (1 f tan )
2
...
3
...
3
...
5)
W
1 f tan
We have already derived an expression for P/W
...
5, we get:
v
2
gR
tan + f
= 1 f tan
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(14
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But normally, f = 0:15 and < 4 , 1 f tan 1 and for small , tan sin
= E=B = e, then equation 14
...
7)
gR
where, e is the rate of super elevation, f the coe cient of lateral friction 0:15, v the speed of the vehicle in
2
2
m=sec , R the radius of the curve in m and g = 9:8m=sec
...
7 are as follows:
v2
or
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If there is no friction due to some practical reasons, then f = 0 and equation 14
...
This
results in the situation where the pressure on the outer and inner wheels are same; requiring very high
super-elevation e
...
4 If there is no super-elevation provided due to some practical reasons, then e = 0 and equation 14
...
This results in a very high coe cient of friction
...
7 is given by v b = f gR where vb is the
restricted speed
...
e
...
For slow moving
vehicles, providing lower superelevation considering coe cient of friction is safe, i
...
centrifugal force is
counteracted by superelevation and coe cient of friction
...
e e1 =
(0:75v)
Step 2 If e1
0:07, then e = e1 =
gR
(0:75v)2
...
2
v
TU
Step 3 Find f1 for the design speed and max e, i
...
2
v
gR
0:07
...
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Maximum and minimum super-elevation
Depends on (a) slow moving vehicle and (b) heavy loaded trucks with high CG
...
The minimum super elevation is 2-4 percent for drainage purpose,
especially for large radius of the horizontal curve
...
2
...
2
...
shifting the position of the crown: This method is also known as diagonal crown method
...
2
...
6 Rotation of the pavement cross section to attain full super elevation by:There are two methods of
attaining superelevation by rotating the pavement
W
rotation about the center line : The pavement is rotated such that the inner edge is depressed and
the outer edge is raised both by half the total amount of superelevation, i
...
, by E=2 with respect
to the centre
...
TU
Radius of Horizontal Curve
The radius of the horizontal curve is an important design aspect of the geometric design
...
Although it is possible to design
the curve with maximum superelevation and coe cient of friction, it is not desirable because re-alignment
would be required if the design speed is increased in future
...
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Rruling =
2
v
g(e + f )
(15
...
However, very large curves are also not
desirable
...
In addition, it also enhances driving strain
...
This widening is done due to two reasons: the rst and most important
is the additional width required for a vehicle taking a horizontal curve and the second is due to the
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tendency of the drivers to ply away from the edge of the carriageway as they drive on a curve
...
These are
discussed in detail below
...
5
...
Therefore, to
provide the same clearance between vehicles traveling in opposite direction on curved roads as is provided on
straight sections, there must be extra width of carriageway available
...
Trailor trucks also need extra carriageway, depending on the type of
joint
...
The expression for extra width can be derived from the simple geometry of a vehicle at a
horizontal curve as shown in gure 15
...
Let R1 is the radius of the outer track line of the rear wheel, R2 is the
radius of the outer track line of the front wheel l is the distance between the front and rear wheel, n is the number
of lanes, then the mechanical widening W m (refer gure 15:1) is derived below:
2
R2
2
= R1 + l
2
2
(R2
=
R2 2R2W m + W m + l
2
2
2
2
W
2
Wm ) + l
2
=
2R2W m
Wm
= l
Therefore the widening needed for a single lane road is:
l2
TU
Wm = 2R2 Wm
(15
...
Therefore, the extra widening of
a road with n lanes is given by,
2
nl
Wm = 2R2
Please note that for large radius, R2
Wm
(15
...
4)
JN
15
...
Psychological widening
Widening of pavements has to be done for some psychological reasons also
...
Some extra space is to be provided for more clearance for the
crossing and overtaking operations on curves
...
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Therefore, the total widening needed at a horizontal curve W e is:
We
= W m + W ps
2
nl
v
=
+
2R
(15
...
A national highway passing through a rolling terrain has two horizontal curves of radius 450 m and 150
m
...
TU
Solution
Assumptions The ruling design speed for NH passing through a rolling terrain is 80 kmph
...
15
...
07
...
e e1 =
2
e1 = (0:75 22:22)
= 0:0629
(0:75v)
gR
2
V
3:6
= 3:6 = 22:22m=sec
V
3:6
...
Hence the design is su cient
...
06
...
e e1
e1 =
Step 3
(0:75 22:22)2
2
= (0:75v)
...
e to be provided = 0:07
9:81 150
2
2
v
Find f1 for the design speed and max e, i
...
p
0:22gR =
2
...
Given R=100m, V=50 kmph, f=0
...
Find:
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p
0:22 9:81 150 =
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(a) e if full lateral friction is assumed to develop [Ans: 0
...
197]
(c) Find equilibrium super-elevation if pressure on inner and outer outer wheel should be equal
(Hint: f=0) [Ans: 0
...
3
...
5 m
...
(ii) By how much the outer edge of the pavement is to be
raised with respect to the centerline, if the pavement is rotated with respect to centerline
...
059 (ii) 0
...
4
...
[Ans: e=0
...
087 and with in limits]
5
...
(Hint: f=0
...
75 kmph and e=0
...
5
...
(Hint: Vruling =100kmph, Vmin =80kmph
...
07, f=0
...
6
...
(Hint: n=2)
[Ans:0
...
7
...
Assume all
W
data
...
0m, n=2, l=6
...
07, f=0
...
[Ans:
Rruling =230m, We=0
...
71m]
Horizontal Transition Curves
TU
Transition curve is provided to change the horizontal alignment from straight to circular curve gradually and has a
radius which decreases from in nity at the straight end (tangent point) to the desired radius of the circular curve at
the other end (curve point) There are ve objectives for providing transition curve and are given below:
12
...
1
to introduce gradually the centrifugal force between the tangent point and the beginning of
the circular curve, avoiding sudden jerk on the vehicle
...
to enable the driver turn the steering gradually for his own comfort and security,
12
...
3
to provide gradual introduction of super elevation, and
12
...
4
to provide gradual introduction of extra widening
...
2
...
JN
12
...
2
Type of transition curve
Di erent types of transition curves are spiral or clothoid, cubic parabola, and Lemniscate
...
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Length of transition curve
The length of the transition curve should be determined as the maximum of the following three criteria: rate of
change of centrifugal acceleration, rate of change of superelevation, and an empirical formula given by IRC
...
Rate of change of centrifugal acceleration
At the tangent point, radius is in nity and hence centrifugal acceleration is zero
...
The rate of change of centrifugal acceleration should be adopted such
that the design should not cause discomfort to the drivers
...
1)
cR
where c is the rate of change of centrifugal acceleration given by an empirical formula suggested by by IRC
as below:
W
Ls1 =
80
= 75 + 3:6v ;
c
(16
...
Rate of introduction of super-elevation
Raise (E) of the outer edge with respect to inner edge is given by E = eB = e(W + W e )
...
Therefore, the length of the transition curve Ls2 is:
Ls2 = N e(W + W e )
(16
...
By empirical formula
IRC suggest the length of the transition curve is minimum for a plain and rolling terrain:
L =
35v
2
(16
...
5)
2
Ls
24R
The length of the transition curve Ls is the maximum of equations 16
...
3 and 16
...
5, i
...
s=
Ls = Max : (Ls1 ; Ls2 ; Ls3 )
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...
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Setback Distance
Setback distance m or the clearance distance is the distance required from the centerline of a horizontal
curve to an obstruction on the inner side of the curve to provide adequate sight distance at a horizontal
curve
...
4 sight distance (OSD, ISD and OSD),
15
...
6 length of the curve
...
8)
(16
...
10)
(16
...
4
...
4
...
m=R
For multi-lane road
180Lc
=
2
m=R
R cos( =2) +
(S
Lc)
sin( =2)
2
(16
...
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D
SD
m
C
A
B
or
ld
__________
__________
__________
__________
__________
__________
__________
__________
__________
R
R
W
a/2
JN
TU
Figure 16:1: Set-back for single lane roads (Ls < Lc)
centre line of the road
d
m’ m
line of sight
centre line
of inner lane
R
2
Figure 16:2: Set-back for multi-lane roads (Ls < Lc)
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L
m2
(S−L)/2
(S−L)/2
m1
=2
or
ld
R
=2
Figure 16:3: Set back for single lane roads (Ls < Lc)
S Q
T cos
T
C
D
W
P
A
B
TU
Figure 16:4: Curve resistance
Curve Resistance
JN
When the vehicle negotiates a horizontal curve, the direction of rotation of the front and the r ear wheels are di
erent
...
This
is illustrated in gure 16:4
...
The tractive force available
on the front wheels is T cos in the PS direction as shown in the gure 16:4
...
Hence, the loss of tractive force for a vehicle to negotiate a horizontal curve is:
CR = TT cos
(16
...
While aligning a
highway, the gradient is decided for designing the vertical curve
...
Usually steep gradients are avoided as far as possible because of the di culty to climb and increase in the
construction cost
...
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Effect of gradient
The e ect of long steep gradient on the vehicular speed is considerable
...
Due to restrictive sight distance at uphill gradients the speed
of trafficis often controlled by these heavy vehicles
...
Further, due to high di erential speed between
heavy and light vehicles, and between uphill and downhill gradients, accidents abound in gradients
...
The
deviation angle N is: when two grades meet, the angle which measures the change of direction and is given
o
by the algebraic di erence between the two grades (n1 ( n2)) = n1 + n2 = 1 + 2
...
33% 2
is a steep gradient, while 1 in 50 = 2% 1 100 is a atter gradient
...
n
1
N
W
100
Figure 17:1: Representation of gradient
Ruling
3
...
0
6
...
0
6
...
0
Exceptional
6
...
0
8
...
On the contrary, the speeds of the heavy vehicles are considerably reduced when long
gradients as at as two percent is adopted
...
Therefore, IRC has speci ed the desirable gradients for each terrain
...
Di erent types of grades are discussed below and the recommended type of
gradients for each type of terrain and type of gradient is given in table 17:1
...
Ruling gradient
The ruling gradient or the design gradient is the maximum gradient with which the designer attempts to design the
vertical pro le of the road
...
In atter terrain, it may be possible to provide at gradients, but in hilly terrain it
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is not economical and sometimes not possible also
...
But our country has a
heterogeneous trafficand hence it is not possible to lay down precise standards for the country as a whole
...
Limiting gradient
This gradient is adopted when the ruling gradient results in enormous increase in cost of construction
...
But the length of the limiting
gradient stretches should be limited and must be sandwiched by either straight roads or easier grades
...
They should be limited for
short stretches not exceeding about 100 metres at a stretch
...
At hairpin bends,
the gradient is restricted to 2
...
Critical length of the grade
The maximum length of the ascending gradient which a loaded truck can operate without undue reduction in
speed is called critical length of the grade
...
This value depends
on the size, power, load, grad-ability of the truck, initial speed, nal desirable minimum speed etc
...
Camber will take care of the lateral
drainage
...
Therefore minimum gradient is provided for drainage purpose and it depends on the rain fall, type of soil and
other site conditions
...
TU
Creeper lane
JN
When the uphill climb is extremely long, it may be desirable to introduce an additional lane so as to allow
slow ascending vehicles to be removed from the main stream so that the fast moving vehicles are not
Affected
...
There are no hard and fast rules as when to
introduce a creeper lane
...
When there is no restrictive sight distance to
reduce the speed of the approaching vehicle, the additional lane may be initiated at some distance uphill
from the beginning of the slope
...
Also the creeper lane should
end at a point well beyond the hill crest, so that the slow moving vehicles can return back to the normal lane
without any danger
...
Grade compensation
While a vehicle is negotiating a horizontal curve, if there is a gradient also, then there will be increased resistance
to traction due to both curve and the gradient
...
For the design, in some cases this maximum value is limited to the ruling gradient
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N = n1 n2
+n2
N = n1n
=0
2
+n1
+n
1
(a)
(b)
N = n1 + n 2
n1
n2
+n1
N=nn
2
(d)
n2
or
ld
(c)
1
Figure 17:2: Types of summit curves
and in some cases as limiting gradient
...
Thus grade compensation can be de ned as the reduction in
gradient at the horizontal curve because of the additional tractive force required due to curve resistance (T T
cos ), which is intended to o set the extra tractive force involved at the curve
...
1
...
30+R
%, where R is the radius of the horizontal curve in meters
...
Grade compensation is
R
3
...
TU
Summit curves are vertical curves with gradient upwards
...
3
...
2
...
5 when positive gradient meets a at gradient [ gure 17:2b]
...
3
...
JN
2
...
7 when a descending gradient meets another descending gradient [ gure 17:2d]
...
This is primarily because of the ease with it can be laid out as well as allowing a
comfortable transition from one gradient to another
...
Furthermore, the use of parabolic curves was found to give excellent riding comfort
...
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Length of summit curve greater than sight distance(L > S)
The situation when the sight distance is less than the length of the curve is shown in gure 17:3
...
1)
p
2 p h1 + h 2
2
Valley curve
JN
Valley curve or sag curves are vertical curves with convexity downwards
...
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...
when a descending gradient meets another descending gradient [ gure 18:1a]
...
when a descending gradient meets a at gradient [ gure 18:1b]
...
when a descending gradient meets an ascending gradient [ gure 18:1c]
...
when an ascending gradient meets another ascending gradient [ gure 18:1d]
...
But visibility is reduced during night
...
Hence
valley curves are designed taking into account of headlight distance
...
This will result in jerking of the vehicle and cause discomfort to the passengers
...
JN
For gradually introducing and increasing the centrifugal force acting downwards, the best shape that
could be given for a valley curve is a transition curve
...
See gure 18:2
...
The head light sight distance should be at least equal to the
stopping sight distance
...
Length of the valley curve
The valley curve is made fully transitional by providing two similar transition curves of equal length The
transitional curve is set out by a cubic parabola y = bx
3
where b =
2N
The length of the valley transition curve
2
3L
is designed based on two criteria:
1
...
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...
2
...
Comfort criteria
The length of the valley curve based on the rate of change of centrifugal acceleration that will ensure comfort: Let
c is the rate of change of acceleration, R the minimum radius of the curve, v is the design speed and t is
the time, then c is given as:
or
ld
2
c
v
R
=
0
t
2
v
R
=
0
L
v
3
L
v
=
LR
3
v
=
cR
(18
...
2)
3
cLs
N
=
Ls
r
Nv
3
c
L
=
Nv
2r
(18
...
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...
Safety criteria
Length of the valley curve for headlight distance may be determined for two conditions: (1) length of the
valley curve greater than stopping sight distance and (2) length of the valley curve less than the stopping
sight distance
...
The sight distance
available will be minimum when the vehicle is in the lowest point in the valley
...
The case is shown in gure 18:3
...
4)
2h1
W
+ 2S tan
where N is the deviation angle in radians, h1 is the height of headlight beam, is the head beam inclination in
degrees and S is the sight distance
...
A
h
E
F C
Stan
G
h1
TU
1
B
D
S
I
N
JN
Figure 18:3: Valley curve, case 1, L > S
h
S
L
A
D
C
S tan
B
N
h
L=2
S
L=2
Figure 18:4: Valley curve, case 2, S > L
Case 2 Length of valley curve less than stopping sight distance (L < S)
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The length of the curve L is less than SSD
...
The important points are the beginning of the curve and the bottom most part of the curve
...
Therefore, the length of the curve is derived by assuming the vehicle at the beginning of the curve
...
From the gure,
h1 + s tan = S2
N
L
= 2S
2h1 + 2S tan
N
(18
...
We will not be able to know prior to which case to be
adopted
...
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CHAPTER III
Traffic Engineering & Regulation
Overview
Data requirements
or
ld
Unlike many other disciplines of the engineering, the situations that are interesting to a trafficengineer cannot
be reproduced in a laboratory
...
Therefore, trafficstream characteristics need to be
collected only from the eld
...
Measurements at a point
W
The most important trafficcharacteristics to be collected from the eld includes sped, travel time, ow and
density
...
In addition, the occupancy, ie percentage
of time a point on the road is occupied by vehicles is also of interest
...
In each category, numerous data collection are
there
...
TU
The most important point measurement is the vehicle volume count
...
In manual method, the observer will stand at the point of interest and count the vehicles with
the help of hand tallies
...
and
for each types of vehicles like cars, two wheelers, three wheelers, LCV, HCV, multi axle trucks,
nonmotorised trafficlike bullock cart, hand cart etc
...
JN
Modern methods include the use of inductive loop detector, video camera, and many other technologies
...
In video cameras, data is collected
from the eld and is then analyzed in the lab for obtaining results
...
Since no length is involved, density cannot be obtained by
measuring at a point
...
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...
Manual methods include the use of
enoscope
...
Enoscope is placed at
one end and observer will stand at the other end
...
Then he stops the stop watch when the vehicle passes in front of him
...
W
An alternative method is to use pressure contact tube which gives a pressure signal when vehicle moves
at either end
...
Road will be cut and a small magnetic loop is placed
...
The advantage of this detector is that the counts can be obtained throughout the life time of the road
...
When dual loops are used and if the spacing between them is known then speed
also can be calculated in addition to the vehicle cost
...
Usually the stretch will be having a
length more than 500 metres
...
Most traditional method uses aerial photography
...
In time lapse photography,
several frames are available
...
JN
Moving observer method for stream measurement
Determination of any of the two parameters of the trafficow will provide the third one by the equation q = u:k
...
In this method, the observer moves in the trafficstream unlike all other
previous methods
...
Two di erent cases of motion can be
considered
...
If no is
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or
ld
www
...
in
W
l
Figure 32:2: Illustration of moving observer method
n
the number of vehicles overtaking the observer during a period, t, then ow q is t0 , or
n0 = qt
TU
(32
...
If np is the
number of vehicles overtaken by observer over a length l, then by de nition, density k is np , or
l
np = kl
(32
...
3)
or
JN
where v 0 is the speed of the observer and t is the time taken for the observer to cover the road stretch
...
In that case m o vehicles will overtake the
observer and mp vehicles will be overtaken by the observer in the test vehicle
...
5 and equation 32
...
4)
This equation is the basic equation of moving observer method, which relates q; k to the counts m, t and v o
that can be obtained from the test
...
For
generating another equation, the test vehicle is run twice once with the trafficstream and another one against
traffic stream, i
...
mw
= q:tw + k:vw
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= q:tw + k:l
ma
= qtak:va:ta
= q:tak:l
or
ld
where, a; w denotes against and with trafficow
...
5 is negative,
because test vehicle moving in the opposite direction can be considered as a case when the test vehicle is
moving in the stream with negative velocity
...
In other words, when the test vehicle moves in the opposite direction, the
observer simply counts the number of vehicles in the opposite direction
...
5 and 32
...
5,
mw
tw = qk:vw :t
q=
(32
...
Therefore,
vs
t
avg
= tw (1
mw
TU
t
avg
l
=
tw
tw ) = t w
l
q
tavg
=v ;
Rewriting the above equation, we get the second parameter of the traffic ow, namely the mean speed vs and
can be written as,
l
vs =
JN
(32
...
Knowing the two parameters the third parameter of
trafficow density (k) can be found out as
k= q
(32
...
Example 1
The length of a road stretch used for conducting the moving observer test is 0
...
Given that the number of vehicles encountered in the stream while the test
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Sample no
...
025
0
...
025
0
...
025
0
...
025
0
...
03
15
...
14
171
129
20
70
or
ld
vehicle was moving against the trafficstream is 107, number of vehicles that had overtaken the test vehicle
is 10, and the number of vehicles overtaken by the test vehicle is 74, nd the ow, density and average speed
of the stream
...
025 hr Time taken by the observer to reach the other end of the stream while it is
20
107+(10 74)
moving against the trafficis ta = tw = 0
...
Column 1 gives the sample
number, column 2 gives the number of vehicles moving against the stream, column 3 gives the number of
vehicles that had overtaken the test vehicle, and last column gives the number of vehicles overtaken by the
test vehicle
...
Also plot the fundamental
diagrams of trafficow
...
1
2
3
4
1
107
113
30
79
2
10
25
15
18
3
74
41
5
9
JN
Solution From the calculated values of ow, density and speed, the three fundamental diagrams can be
plotted as shown in gure 32:3
...
Unlike
other modes of transportation, there is no control on the drivers using the road
...
The major types of trafficcontrol devices used are- trafficsigns, road
markings , traffc signals and parking control
...
Di erent types of
trafficsigns are regulatory signs, warning signs and informatory signs
...
The control device should ful ll a need : Each device must have a speci c purpose for the safe and
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e cient operation of trafficow
...
6
...
For commanding
attention, proper visibility should be there
...
The sign
should be placed in such a way that the driver requires no extra e ort to see the sign
...
It should convey a clear, simple meaning: Clarity and simplicity of message is essential for the
driver to properly understand the meaning in short time
...
The legend should be kept short and simple so that even a less
educated driver could understand the message in less time
...
Road users must respect the signs: Respect is commanded only when the drivers are conditioned
to expect that all devices carry meaningful and important messages
...
9
...
The sign boards should be placed at a
distance such that the driver could see it and gets su cient time to respond to the situation
...
Communication tools
W
A number of mechanisms are used by the trafficengineer to communicate with the road user
...
Messages are conveyed through the
following elements
...
2
...
Usage of di erent
colors for di erent signs are important
...
These are used to code certain devices and to reinforce speci c messages
...
18
...
3
Shape : It is the second element discerned by the driver next to the color of the device
...
Two
exceptional shapes used in trafficsigns are octagonal shape for STOP sign and use of inverted triangle
for GIVE WAY (YIELD) sign
...
JN
18
...
4
Legend : This is the last element of a device that the drive comprehends
...
For the easy understanding by the driver, the legend
should be short, simple and speci c so that it does not divert the attention of the driver
...
There is no need of it in the case of trafficsignals and road markings
...
2
...
Generally solid, double solid and dotted lines are used
...
The frequent and consistent use of pattern to convey information is recommended so that the drivers
get accustomed to the di erent types of markings and can instantly recognize them
...
They can be
classi ed into three main categories
...
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Warning signs:These signs are for the safety of oneself who is driving and advice the drivers to obey these
signs
...
These type of signs are
used to give warning to the road users when some construction work is going on the road
...
The rst three signs will be discussed in detail below
...
If the
driver fails to obey them, the control agency has the right to take legal action against the driver
...
These signs have generally black legend on a white
background
...
The regulatory signs can be further classi ed into :
W
1
...
They are the STOP sign and GIVE WAY sign For example, when one
minor road and major road meets at an intersection, preference should be given to the vehicles
passing through the major road
...
In case
two major roads are meeting, then the trafficengineer decides based on the trafficon which approach
the sign board has to be placed
...
TU
2
...
They
include typical speed limit signs, truck speed, minimum speed signs etc
...
Separate truck speed limits are
applied on high speed roadways where heavy commercial vehicles must be limited to slower speeds
than passenger cars for safety reasons
...
where safety is again a predominant reason
...
JN
3
...
These include turn
signs, alignment signs, exclusion signs, one way signs etc
...
Lane use signs make use of arrows to specify the movements which all vehicles in the lane
must take
...
4
...
5
...
These signs are meant for the safety
of pedestrians and include signs indicating pedestrian only roads, pedestrian crossing sites etc
...
Miscellaneous: Wide variety of signs that are included in this category are: a "KEEP OF MEDIAN"
sign, signs indicating road closures, signs restricting vehicles carrying hazardous cargo or substances,
signs indicating vehicle weight limitations etc
...
They include a stop sign, give way sign,
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signs for no entry, sign indicating prohibition for right turn, vehicle width limit sign, speed limit sign etc
...
They advice
the driver to obey the rules
...
They call for extra vigilance from
the part of drivers
...
The shape used is upward triangular or diamond shape with red borders
...
JN
Informative signs
Informative signs also called guide signs, are provided to assist the drivers to reach their desired
destinations
...
The guide signs
are redundant for the users who are accustomed to the location
...
Route markers are used to identify numbered
highways
...
They are written black letters on yellow background
...
Distance in kilometers are sometimes marked to the right side of the destination
...
They are color coded as
white letters with green background
...
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Classification of road markings
The road markings are de ned as lines, patterns, words or other devices, except signs, set into applied or attached
to the carriageway or kerbs or to objects within or adjacent to the carriageway, for controlling, warning, guiding
and informing the users
...
Longitudinal markings
W
or
ld
Longitudinal markings are placed along the direction of tra c on the roadway surface, for the purpose of
indicating to the driver, his proper position on the roadway
...
Longitudinal markings are provided for separating tra c ow in the same direction and the predominant color
used is white
...
The lines can be either broken, solid or double solid
...
Solid lines are restrictive in character and does not
allow crossing except for entry or exit from a side road or premises or to avoid a stationary obstruction
...
There can also
be a combination of solid and broken lines
...
Vehicles from the opposite directions are not
permitted to cross the line
...
150
3m
TU
4
...
5m
3m
3m
4
...
Usually no centre line is
provided for roads having width less than 5 m and for roads having more than four lanes
...
On urban roads with less than four lanes, the centre line
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may be single broken line segments of 3 m long and 150 mm wide
...
5 m
gaps ( gure 37:1)
...
On undivided urban
roads with at least two tra c lanes in each direction, the centre line marking may be a single solid line of 150
mm wide as in gure 37:2, or double solid line of 100 mm wide separated by a space of 100 mm as shown in
gure 37:3
...
1
...
5m
W
150 mm
3m
TU
3
...
5m
JN
100
Figure 37:4: Centre barrier line marking for four lane road
Figure 37:5: Lane marking for a four lane road with solid barrier line
Traffic lane lines
The subdivision of wide carriageways into separate lanes on either side of the carriage way helps the driver
to go straight and also curbs the meandering tendency of the driver
...
Thus traffic lane markings help in increasing the
capacity of the road in addition ensuring more safety
...
Some examples are shown in figure 37:5 and figure 37:6
...
alljntuworld
...
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...
It may be marked by a solid yellow line
along the centre or a double yellow line
...
These solid lines are also called barrier
lines
...
0 m
100
1
...
5 m
or
ld
3
...
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...
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...
Some typical examples are shown in gure 37:7 and gure 37:8
...
Warning lines
JN
Warning lines warn the drivers about the obstruction approaches
...
They are
broken lines with 6 m length and 3 m gap
...
A typical
example is shown in gure 37:9
Edge lines
Edge lines indicate edges of rural roads which have no kerbs to delineate the limits upto which the driver can
safely venture
...
They are painted in
yellow or white
...
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...
Improved
night visibility may also be obtained by the use of minute glass beads embedded in the pavement marking
materials to produce a retrore ective surface
...
They are marked at intersections etc
...
The type of road marking for a particular intersection depends on several
variables such as speed characteristics of tra c, availability of space etc
...
are some of the markings on approaches to intersections
...
They should be placed either parallel to the intersecting
roadway or at right angles to the direction of approaching vehicles
...
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Figure 37:11: Pedestrian marking near an intersection
Pedestrian crossings
Directional arrows
W
Pedestrian crossings are provided at places where the con ict between vehicular and pedestrian tra c is severe
...
At intersections, the pedestrian crossings should be preceded by a stop line at a distance of
2 to 3m for unsignalized intersections and at a distance of one metre for signalized intersections
...
A
typical example of an intersection illustrating pedestrian crossings is shown in gure 37:11
...
Because of the low angle
at which the markings are viewed by the drivers, the arrows should be elongated in the direction of tra c for
adequate visibility
...
A typical example of a
directional arrow is shown in gure 37:12
...
cause serious hazard to the ow of tra c and should be adequately marked
...
Objects within the carriageway
The obstructions within the carriageway such as tra c islands, raised medians, etc
...
The stripes should slope forward at an angle of 45 with respect to
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...
2
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3
...
5m
3
...
25m
...
2m
0
...
5 m0
0
...
3m
Figure 37:12: Directional arrow marking
the direction of tra c
...
Objects adjacent to carriageway
TU
W
Sometimes objects adjacent to the carriageway may pose some obstructions to the ow of tra c
...
are some examples for such obstructions
...
Poles close to the carriageway should be painted in alternate black and white up to a height of 1
...
Other objects such as guard stones, drums, guard rails etc
...
Kerbs of
all islands located in the line of tra c ow shall be painted with either alternating black and white stripes of 500
mm wide or chequered black and white stripes of same width
...
Word messages
JN
Information to guide, regulate, or warn the road user may also be conveyed by inscription of word message
on road surface
...
The legends should be as brief as
possible and shall not consist of more than three words for any message
...
Therefore, only few and important ones
are usually adopted
...
The character of a road message is also elongated so that driver looking at the road surface at a
low angle can also read them easily
...
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W
Figure 37:13: Marking for objects adjacent to the road way
JN
TU
313 260 1250
78
Figure 37:14: Typical dimension of the character T used in road marking
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L
L
L
Parking
or
ld
Figure 37:15: Approach marking for obstructions on the road way
The marking of the parking space limits on urban roads promotes more e cient use of the parking spaces
and tends to prevent encroachment on places like bus stops, re hydrant zones etc
...
Such parking space limitations should be indicated with markings that are solid white lines 100
mm wide
...
may also be written if the parking area is speci c for any
particular type of vehicle
...
Hazardous location
TU
Parking
W
Wherever there is a change in the width of the road, or any hazardous location in the road, the driver should
be warned about this situation with the help of suitable road markings
...
Converging lines shall be 150 mm wide and shall
have a taper length of not less than twenty times the o -set distance
...
In the gure, the driver is
warned about the position of the pier through proper road markings
...
It is an impact of transport
development
...
This a ects the mode choice also
...
Parking studies
JN
Before taking any measures for the betterment of conditions, data regarding availability of parking space,
extent of its usage and parking demand is essential
...
Parking surveys are intended to provide all these information
...
Parking statistics
Parking accumulation: It is de ned as the number of vehicles parked at a given instant of time
...
Accumulation curve is the graph obtained by
plotting the number of bays occupied with respect to time
...
This
does not account for repetition of vehicles
...
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Parking load : Parking load gives the area under the accumulation curve
...
It is expressed as vehicle hours
...
parkingload
parkingduration =
parkingvolume
Parking turnover: It is the ratio of number of vehicles parked in a duration to the number of parking
bays available
...
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Parking index: Parking index is also called occupancy or e ciency
...
It gives an aggregate measure of how e
ectively the parking space is utilized
...
1)
____
1
__
2
_______
_
3
or
ld
To illustrate the various measures, consider a small example in gure 38:1, which shows the duration for
which each of the bays are occupied(shaded portion)
...
minutes ias shown in the gure
...
of vehicles
Bays and occupancy
3
2
1
0
15 30
45 60
75
90 105
110
Time
W
Parking accumulation curve
Figure 38:1: Parking bays and accumulation curve
The various measures are calculated as shown below:
Parking volume= 5 vehicles
...
75 veh hour
...
5veh
= 0
...
3bays
TU
2:75 veh hour
15
Parking index =
100= 45
...
The most common parking
surveys conducted are in-out survey, xed period sampling and license plate method of survey
...
2
...
Then the number of vehicles that enter the parking lot for a particular time interval is
counted
...
The nal occupancy in the
parking lot is also taken
...
Only one person may be enough
...
Parking duration and turn over is not obtained
...
2
...
6 Fixed period sampling: This is almost similar to in-out survey
...
Then after a xed time interval that may vary between 15 minutes to i hour, the
count is again taken
...
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2
...
7 License plate method of survey: This results in the most accurate and realistic data
...
This will give the data regarding the duration for which a particular vehicle
was using the parking bay
...
If the time interval is shorter, then there are less chances of
missing short-term parkers
...
or
ld
Ill effects of parking
Parking has some ill-effects like congestion, accidents, pollution, obstruction to re- lighting operations etc
...
Hence, speed will be reduced, journey time and delay will also subsequently increase
...
Accidents: Careless maneuvering of parking and unparking leads to accidents which are referred to as
parking accidents
...
W
Environmental pollution: They also cause pollution to the environment because stopping and starting of
vehicles while parking and unparking results in noise and fumes
...
TU
Obstruction to relighting operations: Parked vehicles may obstruct the movement of relighting vehicles
...
Parking requirements
JN
There are some minimum parking requirements for di erent types of building
...
m require only community parking space
...
m,
minimum one-fourth of the open area should be reserved for parking
...
m as parking area
...
Thus, the parking requirements
are di erent for di erent land use zones
...
This will be usually
controlled by government agencies itself
...
This classi
cation is based on the angle in which the vehicles are parked with respect to the road alignment
...
5 metres and that for a truck is 3
...
5 metres
...
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...
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...
9
2
...
0
Figure 38:2: Illustration of parallel parking
A B
O
1Q
5m
L
4
...
25 m
or
ld
1
...
5
n
4
...
2
Figure 38:3: Illustration of 30 parking
W
Parallel parking: The vehicles are parked along the length of the road
...
Hence, it is the most safest parking from the accident
perspective
...
This method of parking produces least obstruc-tion to the ongoing tra c on the road since least road width is used
...
The length available to park N number of vehicles, L =
N
5:9
TU
30 parking: In thirty degree parking, the vehicles are parked at 30
with respect to the road
alignment
...
Also there is better
maneuver-ability
...
An example is
shown in gure 38:3
...
58+(N-1)5 =0
...
Hence
compared to parallel parking and thirty degree parking, more number of vehicles can be
accommodated in this type of parking
...
54 N+1
...
More number of vehicles can be
accommodated in this parking type
...
89N+2
...
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1
...
31 m
5
0
...
5
2
m
Figure 38:4: Illustration of 45 parking
or
ld
L
60
2
...
Although it consumes maximum width kerb length required is very little
...
This
arrangement causes obstruction to the road tra c particularly if the road width is less
...
An example is shown in gure 38:6
...
5N
...
Such a parking is referred to as o -street parking
...
A typical layout of an o -street parking is shown in gure 38:7
...
5
Figure 38:6: Illustration of 90 parking
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__ _
__ _
__ _
__ _
___
___
___
___
___
___
______
______
______
______
ENTRY
________________________
________________________
______________
________________________
________________________
________________________
________________________
________________________
____________
__________
EXIT
___
___
___
___
___
___
______
______
______
______
or
ld
______
_______
_______
_______
Figure 38:7: Illustration off-street parking
Example 1
W
From an in-out survey conducted for a parking area consisting of 40 bays, the initial count was found to be
25
...
The number of vehicles coming in and out of the parking lot for a
time interval of 5 minutes is as shown in the table 38:1
...
JN
TU
Table 38:1: In-out survey data
Time In Out
5
3
2
10
2
4
15
4
2
20
5
4
25
7
3
30
8
2
35
2
7
40
4
2
45
6
4
50
4
1
55
3
3
60
2
5
Solution
The solution is shown in table 38:2
Accumulation can be found out as initial count plus number of vehicles that entered the parking lot till
that time minus the number of vehicles that just exited for that particular time interval
...
It is being tabulated in column 4
...
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...
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...
5
135
7
3
31
77
...
5
185
2
7
32
80
160
4
2
34
85
170
6
4
36
90
180
4
1
39
97
...
5
195
2
5
36
90
180
Total
1735
or
ld
Time
(1)
5
10
15
20
25
30
35
40
45
50
55
60
column 5
...
The occupancy for the remaining time slot is similarly calculated and is tabulated in
Average occupancy is the average of the occupancy values for each time interval
...
63%
...
It is obtained by multiplying accumulation with the time interval
...
TU
Total parking load is the summation of all the values in column 5 which is equal to 1935 vehicle
minutes or 32
...
Find the average occupancy, average turn over, parking load, parking capacity and e ciency of the parking lot
...
Columns 1 to 5 is the input data
...
If a vehicle occupies that bay for that time interval, then it has a code 1
...
Turn over is computed as the number of vehicles present in that bay for that particular hour
...
Similarly, for the second bay, one vehicle is present throughout that hour
and hence turnout is 1 itself
...
Average turn over =
Sum of turn over
Total number of bays
= 2
...
alljntuworld
...
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...
Accumulation for rst time interval of 15 minutes = 1+1+1+1+1+0+0+1+1+1+1+1 = 10
Parking volume = Sum of the turn over in all the bays = 27 vehicles
Average duration is the average time for which the parking lot was used by the vehicles
...
78 minutes/vehicle
...
For rst time interval of 15 minutes, occupancy = (10 100)/12 = 83% Average occupancy is found out as
the average of total number of vehicles occupying the bay for each time interval
...
Average occupancy =
Parking capacity = number of bays
0:83+0:92+0:75+0:92
4
100 = 85
...
number of hours = 12 1 = 12 vehicle hours
(10+11+9+11) 15
Parking load = total number of vehicles accumulated at the end of each time interval time = 60 =
10
...
42%
...
alljntuworld
...
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...
Essentially all the major con icts at an intersection namely
the collision between through and right-turn movements are converted into milder con icts namely merging
and diverging
...
They then weave out of the rotary to the desired direction
...
will be discussed in this chapter
...
2
...
W
12
...
7
All the vehicles entering the rotary are gently forced to reduce the speed and continue to
move at slower speed
...
12
...
8
Because of lower speed of negotiation and elimination of severe con icts, accidents and
their severity are much less in rotaries
...
2
...
TU
12
...
10
They are ideally suited for moderate tra c, especially with irregular geometry, or intersections
with more than three or four approaches
...
All the vehicles are forced to slow down and negotiate the intersection
...
JN
Even when there is relatively low tra c, the vehicles are forced to reduce their speed
...
The vehicles do not usually stop at a rotary
...
Therefore, they are not suitable when there are high pedestrian movements
...
alljntuworld
...
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...
There are few guidelines that
help in deciding the suitability of a rotary
...
2
...
8 Rotaries are suitable when the trafficentering from all the four approaches are relatively equal
...
2
...
TU
2
...
10
A rotary is very bene cial when the proportion of the right-turn tra c is very high; typically if it
is more than 30 percent
...
2
...
Rotaries are ideally suited if the intersection geometry is complex
...
All the other con
icts are converted into these three less severe con icts
...
5 Diverging: It is a tra c operation when the vehicles moving in one direction is separated into di erent
streams according to their destinations
...
6 Merging: Merging is the opposite of diverging
...
2
...
These movements are shown in gure 40:1
...
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splitterisland
exit radius
radius of the central
island
entry
radius
entry
length
weaving
circulation
width
weaving
width
exit width
approach
width
GIVE WAY
line
or
ld
radius of the
inscribed
circle
width
Figure 40:2: Design of a rotary
Design elements
Design speed
W
The design elements include design speed, radius at entry, exit and the central island, weaving length and
width, entry and exit widths
...
A typical rotary and the important design elements are shown in gure 40:2
TU
All the vehicles are required to reduce their speed at a rotary
...
Although it is possible to design roundabout without much speed
reduction, the geometry may lead to very large size incurring huge cost of construction
...
Entry, exit and island radius
The radius at the entry depends on various factors like design speed, super-elevation, and coe cient of friction
...
This will force the driver to reduce the
speed
...
JN
The exit radius should be higher than the entry radius and the radius of the rotary island so that the
vehicles will discharge from the rotary at a higher rate
...
5 to
2 times the entry radius
...
The radius of the central island is governed by the design speed, and the radius of the entry curve
...
The radius of the central island which is about 1
...
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d
d
c
c
b
or
ld
b
a
a
Figure 40:3: Weaving operation in a rotary
Width of the rotary
W
The entry width and exit width of the rotary is governed by the tra c entering and leaving the intersection and
the width of the approaching road
...
IRC suggests that a two lane road of 7 m
width should be kept as 7 m for urban roads and 6
...
Further, a three lane road of 10
...
5 m respectively for urban and rural roads
...
Normally this will be
one lane more than the average entry and exit width
...
1)
TU
where e1 is the width of the carriageway at the entry and e 2 is the carriageway width at exit
...
It is decided based on many
factors such as weaving width, proportion of weaving tra c to the non-weaving tra c etc
...
A ratio of 4 is the minimum
value suggested by IRC
...
Capacity
JN
The capacity of rotary is determined by the capacity of each weaving section
...
280w[1 +
Qw =
where e is the average entry and exit width, i
...
2)
, w is the weaving width, l is the length of weaving, and
2
p is the proportion of weaving tra c to the non-weaving tra c
...
Therefore,
p=
b+c
a+b+c+d
This capacity formula is valid only if the following conditions are satis ed
...
Weaving width at the rotary is in between 6 and 18 metres
...
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N
1433
400
W
375
408
600
650
1405
505
350
510
1260 E
500
250
370
or
ld
420
1140
S
Figure 40:4: Trafficapproaching the rotary
37
...
1
The ratio of average width of the carriage way at entry and exit to the weaving width is in the
range of 0
...
The ratio of weaving width to weaving length of the roundabout is in between 0
...
4
...
5
...
The proportion of weaving trafficto non-weaving trafficin the rotary is in the range of 0
...
5
...
W
37
...
2
Example
TU
The width of a carriage way approaching an intersection is given as 15 m
...
The tra c approaching the intersection from the four sides is shown in the gure 40:4 below
...
Solution
The traffic from the four approaches negotiating through the roundabout is illustrated in gure 40:5
...
5 m
2
JN
Weaving length, l is calculated as = 4 w = 54 m
The proportion of weaving traffic to the non-weaving trafficin all the four approaches is found out rst
...
Let the proportion of weaving tra c to the non-weaving tra c in West-North
direction be denoted as pW N , in North-East direction as pN E , in the East-South direction as pES ,
and nally in the South-West direction as pSW
...
Then using equation,pES
510+650+500+600
=
= 2260 =0
...
718
505+510+350+600+400+370
2735
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N
400
600 650
408
505 350 375 505
+
+
+
+
510 370
W
510 370
420
E
375
500+600
or
ld
500+375 600
350
+
370
510
+
650
250
S
Figure 40:5: Trafficnegotiating a rotary
d
510+650
c
W
b
c
d
375
a
250
b
500+600
a
TU
Figure 40:6: Trafficweaving in East-South direction
pN E =
650+375+505+370
650+375+505+370+510+408
pSW =
350+370+500+375
350+370+500+375+420+600
= 1900 =0
...
6099
Thus the proportion of weaving trafficto non-weaving trafficis highest in the East-South direction
...
From equation,
280 13:5[1 +
QES =
10 ][1
13:5
1 + 13:5
54
0:783
3
]
= 2161:164veh=hr:
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(40
...
alljntuworld
...
The entry and exit width at the rotary is 10 m
...
Find the capacity of
the rotary
...
Weaving width is calculated as, w = [
e1 +e2
] + 3:5 = 13
...
JN
It is clear from equation,that the highest proportion of weaving tra c to non-weaving tra c will give the
minimum capacity
...
Then using equation,pES =
= 2220 =0
...
69
350+370+550+500+520+420
2510
420+500+700+300
pN E =
= 1920 =0
...
630
550+450+400+370+420+350
2540
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CHAPTER 5
HIGHWAY MATERIAL, CONSTRUCTION AND MAINTENANCE
Overview
or
ld
A highway pavement is a structure consisting of superimposed layers of processed materials above the natural
soil sub-grade, whose primary function is to distribute the applied vehicle loads to the sub-grade
...
The ultimate aim is to ensure that the transmitted stresses due to
wheel load are su ciently reduced, so that they will not exceed bearing capacity of the sub-grade
...
This
chapter gives an overview of pavement types, layers, and their functions, and pavement failures
...
Requirements of a pavement
An ideal pavement should meet the following requirements:
Su cient thickness to distribute the wheel load stresses to a safe value on the sub-grade
W
soil, Structurally strong to withstand all types of stresses imposed upon it,
Adequate coe cient of friction to prevent skidding of vehicles,
Smooth surface to provide comfort to road users even at high
speed, Produce least noise from moving vehicles,
Dust proof surface so that tra c safety is not impaired by reducing visibility,
TU
Impervious surface, so that sub-grade soil is well protected, and
Long design life with low maintenance cost
...
In exible pavements, wheel loads are transferred by grain-to-grain contact of the aggregate through
the granular structure
...
g
...
alljntuworld
...
alljntuworld
...
On the contrary, in rigid pavements, wheel loads are transferred to sub-grade soil by
exural strength of the pavement and the pavement acts like a rigid plate (e
...
cement concrete roads)
...
A thin layer of exible pavement over rigid
pavement is an ideal pavement with most desirable characteristics
...
JN
TU
W
Flexible pavements will transmit wheel load stresses to the lower layers by grain-to-grain transfer through the
points of contact in the granular structure (see Figure 19:1)
...
Taking advantage of this stress
distribution characteristic, exible pavements normally has many layers
...
Based on this, exible pavement may be constructed in a
number of layers and the top layer has to be of best quality to sustain maximum compressive stress, in
addition to wear and tear
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Flexible pavements are constructed using bituminous materials
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Flexible pavement layers re ect the deformation of the lower layers on to the surface layer (e
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, if
there is any undulation in sub-grade then it will be transferred to the surface layer)
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Tack Coat
Seal Coat
Prime coat
Surface Course (25−50 mm)
Binder Course (50−100 mm)
Base Course (100−300 mm)
Subbase Course (100−300 mm)
Compacted Subgrade (150−300 mm)
Natural Subgrade
2
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Types of Flexible Pavements
or
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Figure 19:2: Typical cross section of a flexible pavement
The following types of construction have been used in flexible pavement:
Conventional layered flexible pavement,
Full - depth asphalt pavement, and
Contained rock asphalt mat (CRAM)
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Full - depth asphalt pavements are constructed by placing bituminous layers directly on the soil subgrade
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Contained rock asphalt mats are constructed by placing dense/open graded aggregate layers in between
two asphalt layers
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Typical layers of a flexible pavement
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Typical layers of a conventional exible pavement includes seal coat, surface course, tack coat, binder course,
prime coat, base course, sub-base course, compacted sub-grade, and natural sub-grade (Figure 19:2)
...
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Tack Coat: Tack coat is a very light application of asphalt, usually asphalt emulsion diluted with water
...
Prime Coat: Prime coat is an application of low viscous cutback bitumen to an absorbent surface like
granular bases on which binder layer is placed
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Unlike tack coat,
prime coat penetrates into the layer below, plugs the voids, and forms a water tight surface
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They are usually constructed with dense graded asphalt concrete(AC)
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Also it will prevent the entrance
of excessive quantities of surface water into the underlying base, sub-base and sub-grade,
It must be tough to resist the distortion under tra c and provide a smooth and skid- resistant riding
surface,
It must be water proof to protect the entire base and sub-grade from the weakening e ect of water
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It's chief purpose is to distribute load to the
base course The binder course generally consists of aggregates having less asphalt and doesn't require
quality as high as the surface course, so replacing a part of the surface course by the binder course results
in more economical design
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Sub-Base course
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The sub-base course is the layer of material beneath the base course and the primary functions are to
provide structural support, improve drainage, and reduce the intrusion of nes from the sub-grade in the
pavement structure If the base course is open graded, then the sub-base course with more nes can serve as
a ller between sub-grade and the base course A sub-base course is not always needed or used
...
In such situations, sub-base course may not be provided
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It
is essential that at no time soil sub-grade is overstressed
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Failure of flexible pavements
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The major exible pavement failures are fatigue cracking, rutting, and thermal cracking
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The failure
criterion relates allowable number of load repetitions to tensile strain and this relation can be determined in
the laboratory fatigue test on asphaltic concrete specimens
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Two design methods have been
used to control rutting: one to limit the vertical compressive strain on the top of subgrade and other to limit
rutting to a tolerable amount (12 mm normally)
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Portland Cement Concrete
150 − 300 MM
Base or Subbase Course
100 − 300 MM
Figure 19:3: Typical Cross section of Rigid pavement
or
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Elastic plate
Viscous foundation
Contact Pressure
Figure 19:4: Elastic plate resting on Viscous foundation
Rigid pavements
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Rigid pavements have sufficient flexural strength to transmit the wheel load stresses to a wider area below
...
Compared to exible pavement, rigid
pavements are placed either directly on the prepared sub-grade or on a single layer of granular or stabilized
material
...
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In rigid pavement, load is distributed by the slab action, and the pavement behaves like an elastic plate
resting on a viscous medium (Figure 19:4)
...
Plate theory is a simplified version of layer theory that assumes the concrete slab as a
medium thick plate which is plane before loading and to remain plane after loading
...
Types of Rigid Pavements
Rigid pavements can be classified into four types:
1
...
Jointed reinforced concrete pavement (JRCP),
JN
3
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Jointed Plain Concrete Pavement: are plain cement concrete pavements constructed with closely spaced
contraction joints
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They
normally has a joint spacing of 5 to 10m
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Dowel bars are required for load
transfer
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Continuous Reinforced Concrete Pavement: Complete elimination of joints are achieved by reinforce-ment
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The allowable number of load repetitions to cause fatigue cracking depends on the stress ratio between
flexural tensile stress and concrete modulus of rupture
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Pumping is the ejection of soil slurry through the joints and cracks of cement concrete pavement,
caused during the downward movement of slab under the heavy wheel loads
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Bituminous materials or asphalts are extensively used for roadway construction, primarily because of their
excellent binding characteristics and water proo ng properties and relatively low cost
...
Tars are residues from the destructive distillation of organic
substances such as coal, wood, or petroleum and are temperature sensitive than bitumen
...
Production of Bitumen
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bitumen is the residue or by-product when the crude petrolium is re ned
...
may be used to produce bitumen of
different consistency and other desirable properties
...
Vacuum steam distillation of petroleum oils
TU
In the vacuum-steam distillation process the crude oil is heated and is introduced into a large cylindrical still
...
The volatile constituents are collected, condensed, and the
various fractions stored for further re ning, if needed
...
The bottom fraction
from this unit is the vacuum-steam-re ned asphalt cement
...
Normally, asphalt produced by this process is softer
...
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Different forms of bitumen
Cutback bitumen
Normal practice is to heat bitumen to reduce its viscosity
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In cutback bitumen suitable solvent is used to lower the viscosity of the
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Bitumen
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The solvent from the
bituminous material will evaporate and the bitumen will bind the aggregate
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The distillates used for preparation of cutback
bitumen are naphtha, kerosene, diesel oil, and furnace oil
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RC is recommended for surface dressing and
patchwork
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SC is used for premix with
appreciable quantity of ne aggregates
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Normally cationic type emulsions are used in India
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When the emulsion is applied on the road it
breaks down resulting in release of water and the mix starts to set
...
The viscosity of bituminous emulsions can be measured as per IS: 8887-1995
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Bitumen
emulsions are ideal binders for hill road construction
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Rapid
setting emulsions are used for surface dressing work
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Slow setting emulsions are preferred in rainy season
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The absorption
therefore depends on the porosity of the surface
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Bituminous primers are generally prepared on road sites by mixing
penetration bitumen with petroleum distillate
...
Bitumen treated with these modifiers is known as modified bitumen
...
The detailed specifications for modified bitumen have
been issued by IRC: SP: 53-1999
...
The advantages of using modified bitumen are as follows
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Lower susceptibility to daily and seasonal temperature
variations Higher resistance to deformation at high pavement
temperature Better age resistance properties
Higher fatigue life for mixes
Better adhesion between aggregates and binder
Prevention of cracking and reflective cracking
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Requirements of Bitumen
The desirable properties of bitumen depend on the mix type and construction
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The bitumen should not be highly temperature susceptible: during the hottest weather the mix should
not become too soft or unstable, and during cold weather the mix should not become too brittle causing
cracks
...
This can be
achieved by use of cutbacks or emulsions of suitable grades or by heating the bitumen and aggregates
prior to mixing
...
Tests on bitumen
There are a number of tests to assess the properties of bituminous materials
...
37
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7 Softening point test
37
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9 Viscosity test
Flash and Fire point test
TU
37
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5 Penetration test
37
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12
Water content test
37
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BIS had standardised the equipment and test
procedure
...
The bitumen is softened to a pouring consistency, stirred thoroughly
and poured into containers at a depth at least 15 mm in excess of the expected penetration
...
It may be noted that penetration value is largely in uenced
by any inaccuracy with regards to pouring temperature, size of the needle, weight placed on the needle and
the test temperature
...
In hot climates, a lower penetration grade is preferred
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4
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Penetration
or
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Figure 23:1: Penetration Test Setup
Ductility test
Ductility is the property of bitumen that permits it to undergo great deformation or elongation
...
Dimension of the briquette thus formed is exactly 1 cm square
...
These samples with moulds are cooled in the air and then in water bath at 27
o
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C temperature
...
Then the mould with
assembly containing sample is kept in water bath of the ductility machine for about 90 minutes
...
The distance up to the
point of breaking of thread is the ductility value which is reported in cm
...
A minimum ductility value of 75 cm has been
speci ed by the BIS
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4
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Ductility
TU
Starting Point
End Point
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Figure 23:2: Ductility Test
Softening point test
Softening point denotes the temperature at which the bitumen attains a particular degree of softening under
the speci cations of test
...
A brass ring containing test
sample of bitumen is suspended in liquid like water or glycerin at a given temperature
...
Temperature is noted
when the softened bitumen touches the metal plate which is at a speci ed distance below
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Figure 23
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3
shows Softening Point test setup
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In most cases bitumen is weighed, but
when used with aggregates, the bitumen is converted to volume using density values
...
Increase in aromatic type mineral impurities cause
an increase in speci c gravity
...
The speci c gravity can be measured using either pycnometer
or preparing a cube specimen of bitumen in semi solid or solid state
...
97 to 1
...
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Viscosity test
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Viscosity denotes the uid property of bituminous material and it is a measure of resistance to ow
...
Low or
high viscosity during compaction or mixing has been observed to result in lower stability values
...
And at low viscosity instead of providing a uniform lm over aggregates, it will lubricate the aggregate
particles
...
The viscosity expressed in seconds is the time taken by the 50 ml bitumen material to pass
through the ori ce of a cup, under standard test conditions and speci ed temperature
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0 mm ori ce at 25 C or 10 mm ori ce at 25 or 40 C
...
And these volatiles
catches re which is very hazardous and therefore it is essential to qualify this temperature for each bitumen grade
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The re point is defined as the lowest temperature under
specified test conditions at which the bituminous material gets ignited and burns
...
But for certain range of consistencies, these tests are not applicable and Float test is used
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The specimen in the mould is
o
cooled to a temperature of 5 C and screwed in to oat
...
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Water content test
It is desirable that the bitumen contains minimum water content to prevent foaming of the bitumen when it is
heated above the boiling point of water
...
The weight of the
water condensed and collected is expressed as percentage by weight of the original sample
...
2% by weight
...
About 50gm of the sample is weighed
0
and heated to a temperature of 163 C for 5hours in a specified oven designed for this test
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Bitumen used in pavement mixes should not indicate more than 1% loss in weight, but
for bitumen having penetration values 150-200 up to 2% loss in weight is allowed
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Title: tranportation notes for 3-2 civil b.tech students
Description: to get marks as well aspractical knowledge
Description: to get marks as well aspractical knowledge