Fundamentals of traffic Engg

Subject : Traffic Engineering(TRE)
Subject Code : 22507
Subject Teacher: Prof. K.S.Somase
Semester: Fifth
Year: 3rd (2020-21)
Scheme : I
Department of Civil Engineering
Traffic Engineering (Elective)
Unit 1-
Fundamentals of TrafficEngineering
By
Prof. K. S. Somase
(BE-Civil Engg)

Civil Engineering Department
Gurukul Education Society’s Institute of Engineering & Technology
by : prof: k.s.somase
Unit : 1 (Topics and Subtopics)
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Unit 1 -Fundamentals of Traffic Engineering
What is Traffic Engineering?

Traffic engineering is an important aspect in highway engineering
Due to abundant growth in population and infrastructure
there has become an urgent need to pay attention to traffic issues like
traffic controlling devices, traffic signals ,Signs and Pavement
markings.
Traffic Engineering-It is a branch of engineering of measuring
traffic, planning, designing and operating systems to achieve safe and
efficient movement of peoples and goods.
Traffic engineering includes planning and geometric design on one
hand and regulation. And control on theother.
Traffic Engineering
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The objectives of traffic engineering are :-
 Toprovide easy flow.
 Toensure safety to traffic.
 Toavoid traffic congestion.
 Toreduce road accidents.
 Toincrease the speed of vehicle.
 Toensure safe and convenient transport of goods.
 Toensure safety of pedestrians.
Objects
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The basic objective of traffic engineering is to achieve efficient,
free and rapid flow of traffic with least number of traffic accidents.
❑ Following are the Major area of traffic engineering.
 Traffic characteristics.
 Traffic studies and analysis
 Planning and analysis
 Geometric design
 Traffic operation, regulation and control.
 Administration and management.
Scope of TrafficEngineering
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 The human element is involved in all actions of the road
users either as pedestrian, cyclist, car driver or motorists.
 The various factors which affects road user characteristics of
human beings affect their ability to operate motor vehicle
safely or to service as a pedestrian.
 Following are the road user:
1. Motor Car driver
2. Pedestrian
3. Cyclist
4. Bullock cart driver
5. Rickshaw driver
Road User’s Characteristics
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1. Physical
2. Mental
3. Psychological
4. Environmental
 Most of the accidents are caused by errors of judgment. Hence
it is more essential and challengious to the traffic engineer to
study the various factors which affects the rate of which errors
occur.
The Various Factors Which Affects
Road User Characteristics
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• The physical Characteristics of the road user may be permanent or
temporary
• The permanent Characteristics are vision , hearing, strength and thee
general reaction to trafficsituation.
• Vision plays important role of all these.
• These include the acute of vision, peripheral vision , eye movement
and judgment.
• Minimum standards for acute of vision are often laid down by
licensing authorities.
• The temporary physical Characteristics of the road users affecting their
efficiency are fatigue, alcohol and illness. All this reduces alertness and
increase the reaction time and also affect quality of judgment in some
situation.
1. Physical Characteristics
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• knowledge, skill, intelligence experience and literacy can
affect the road Characteristics.
• knowledge of vehicle Characteristics, traffic behaviour, driving
practice , rules of roads and physicology of road user’s will be
quit useful for safe traffic operation.
• Reaction to certain traffic to certain traffic situation
become more spontaneous with experience.
• understanding the traffic regulation and special instruction to road
users and timely action depend on intelligence and literacy.
2. Mental Characteristics
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• These affect reaction to traffic situation of road users to a
great extent.
• The emotional factors such as attentiveness,
fear,anger,superstition ,general attitude towords traffic and
regulations and maturity also under this category.
• Distraction by non-traffic events and worries reduce
attentiveness to traffic situation,dangerous actions are likely
due to impatience.
• some road users do not pay due regard to traffic regulations
and do not have right attitude towords the traffic
3. Psychological Characteristics
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• The various environmental condition affecting the behaviour of
road traffic stream,roadside features,atmospheric conditions and
the locality.
• The Traffic stream may consist of mixedtraffic or heavy traffic.
• If the percentage of slow moving traffic is high the need for
overtaking increase for the faster vehicles.
• The adaptability to different traffic stream Characteristics
depends on the drivers Characteristics as well as the
motivation.
4. Environmental Characteristics
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 It is important to study the various vehicular characteristics which
affect the design of the road facilities and the traffic performance.
 This is because it is possible to design road for any vehicle but not
for vehicle type.
 It will not be economically feasible to keep on increasing the
geometric standards and thickness of pavements from time to time
to meet the needs of a few vehicles whose dimensions and weight
are increased.
 Hence the vehicle standards should be uniform at least within the
country keeping in view the large percentage of existing vehicles
and those likely to be manufactured in the near future.
Vehicular Characteristics
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 The standers for the dimension and weights of vehicles should be
consistent with the road facilities now available or could be made
available in the near future.
 The various vehicular characteristics affecting the road design may
be
 Classified as-
 Static characteristics.
 Dynamic characteristics
Vehicular Characteristics
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 It Static characteristics of vehicles affecting road design are the
relevant dimensions, maximum turning angle and the total
weight.
 The dimension of vehicle significantly control the design of
highway geometric elements are the overall width, length and
height of different vehicles, particularly of larger ones.
Width of vehicle
 The width of vehicle affect the width of traffic lane , shoulder
and parking facilities.
 If the width of lane is not adequate due to wider vehicles using
the roads the capacity of road will decrease significantly.
Static Characteristics
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Length of vehicle
 The length of the vehicle and length of wheel base are important
factors in the design of horizontal alignment as they affect the
extra width of pavement at horizontal curves, the minimum
turning radius, safe overtaking distance, capacity of the road and
parking facilities.
 The length of vehicle should also be considered in the design of
valley curves and dips.
 The minimum turning radius depends on the length of wheel base
and the features of the steering system and this affects design of
sharp curves.
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Height of vehicle
• Height of vehicle affects the clearance to be provided under
structures such as over bridges, electric and other service
lines and overhead gantries for sign boards.
Weight of loaded vehicles
• The Maximum weight of loaded vehicle and the load on the
wheels and axles affect the design of pavement thickness and
gradients.
• In fact the limiting gradients are governed by both the
weights and pulling power of the heavy vehicles.
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Power of vehicle
 The power of heaviest vehicles and their loaded weights
govern the permissible and limiting values of gradient on road.
 In this regards the total resistances to traction consisting of
inertia. rolling resistance and grade resistance are considered.
 From the total hauling capacity and the power required to
overcome the total tractive resistance it is possible to determine
the speed and acceleration of the vehicle which in turn are
useful in planning, design of road geometries and traffic
regulation.
Dynamic Characteristics
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Speed of vehicle
 The vehicle speed affects design of sight distance, super
elevation, length of transition curve and limiting radius on
horizontal curves, width of each traffic lane and shoulder on
straight and on horizontal curve, design gradient, design and
control measures at intersection.
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Braking characteristics
 The deceleration and breaking characteristics of vehicle depend on
the design and type of braking system and its efficiency.
 The consecutive vehicles in traffic stream are affected by the
efficiency of the braking system.
 Thus the highway capacity and overtaking sight distance
requirement also indirectly get affected by the acceleration and
deceleration characteristics as well as the braking characteristics
of vehicle.
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 While aligning a road way the general topography is followed.
But the natural ground may have plain topography or uneven
surface having different magnitude. So vertical profile has
certain gradient or slope. In order of smooth functioning of
vehicle on roads the changes in the gradient should be made
and the surface should be leveled.
 Gradient.
 Curve of road.
 Design speed.
 Friction between road and tyre surface.
Road Characteristics
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 Gradient is the rate of rise or fall along the length of the road
with respect to horizontal.
 The gradients are divided into four categories:
1. Ruling gradient.
2. Limiting gradient.
3. Exceptional gradient.
4. Minimum gradient.
Gradient
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 Ruling gradient:-
Ruling gradient is the maximum gradient within which the designer
attempts to design the vertical profile of road. Gradient up to ruling
gradient are adopted as a normal course in design of vertical alignment
and accordingly the quantities of cut and fill are decided. Ruling gradient
are known as design gradient.
 Limiting gradient:-Where topography compels adopting steeper gradient
than the ruling gradient limiting gradient is used in view of enormous
increase in cost in constructing rods with gentler gradient On hill roads it
may be frequently necessary to exceed ruling gradient and adopt limiting
gradient.
Types of gradient
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 Exceptional gradient
In some extra ordinary situation it may not be unavoidable to provide still
steeper gradients than the limiting gradient at least for short stretches and in
such cases the steeper gradient up to the exceptional gradient may be
provided. However the exceptional gradient should be strictly limited only
for short stretches not exceeding about 100 m at a stretch.
 Minimum gradient
The road can be level with little or no gradient in such case their will be
problem of drainage. Hence from the drainage point of view it is desirable
to have certain minimum gradient. It depends upon the amount of rainfall,
type of soil, run off and other site condition.
Types of gradient
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 Curves:-The bends in road to bring change in direction for
regular movement of traffic is known as curve. Due to change in
grade in the vertical alignment of highway it is necessary to
introduce vertical curve at the intersection of different grades to
smoothen out the vertical profile and ease off the changes in
gradient for the fast moving vehicle.
 The vertical curves used in highway are classified as:
1. Summit curves.
2. Valley curve.
Curves
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 Types of curve
• Summit curves:-The summit curve have convexity upward they are formed
in one of the following ways.
A rising gradient intersecting a falling gradient (Fig-a).
A rising gradient meeting another rising gradient (Fig-b).
A rising gradient meeting at horizontal road (Fig-c).
Types of curves
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Types of curves
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1. Summit curves

 Valley curves- Valley curves are also called as sag curves with convexity
downwards are formed in any one of the case.
A falling gradient intersecting a rising gradient (Fig-a).
A falling gradient meeting another falling gradient (Fig-b).
A falling gradient meeting a horizontal road (Fig-c).
Types of curves
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2. Valley Curve
Types of curves
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 Design speed is the most important factor taken in
consideration for geometric designing of highway.
The geometric details of a highway mainly depend on
the design speed. All the important geometric
elements such as sight distance, extra widening of
pavement at horizontal curve, rate of super elevation,
radius of horizontal curve, length of summit and
valley curves are dependent on the design speed.
Design speed
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 Friction force is important factor in vehicle speed. It helps in to
determine speed of operation and distance requirements in
retarding and accelerating vehicle.
 The coefficient of friction offered between road and tyre
surface is important with reference to the safety.
 Lack of sufficient friction can cause the vehicle to skid or slip.
 The factors affecting friction are pavement type, pavement
condition, tyre condition, vehicle load and speed.
Friction between road & tyre surface
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 Reaction time:-reaction time is a time taken by a driver
from the instant the object is visible to the driver to the instant
the brakes are effectively applied. The actual time gap or the
reaction time of the driver depends upon several factors.
 During this period of time the vehicle travels a certain distance
at the original speed which may be assumed to be designed
speed of the road.
 The stopping distance increases with increase in reaction time
of driver.
Reaction Time
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The reaction time may be split up into two parts:
1. Perception time.
2. Brake reaction time.
Reaction Time
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 Perception time: the time required for a driver to
realize that break must be applied is called as perception
time. It is the time from instant the object comes on the
line of sight of the driver to the instant he realizes that
the vehicle needs to be stopped. The perception time
varies from driver to driver and also on several other
factors such as distance of object and other
environmental condition.
Reaction Time
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• Brake reaction time:-The brake reaction time is
the amount of time that elapses between the
recognition of an object or hazard in the roadway
and the application of the brakes. The brake
reaction time also depends on several factors
including the skill of the driver, type of problem and
various other environmental condition.
Reaction Time
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 Generally total reaction time of driver is taken together as this is
found vary considerably depending on several factors. The total
reaction time ma be explained with the help of PIEV Theory.
 According to PIEV theory reaction time of driver is split into
four parts.
1. Perception.
2. Intellection.
3. Emotion.
4. Volition.
PIEV Theory
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• Perception Time:- It is the time required for the sensation
received by the eyes or ears of the driver to be transmitted to
the brain through the nervous system and spinal cord.
• Intellection Time:- It is the time required for the driver to
understand the situation. It is also the time required for
comparing the different thoughts, regrouping and registering
new situation.
PIEV Theory
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 Emotion Time:- It is the time elapsed during emotional
sensations and other mental disturbances such as fear, anger or
any other emotional feeling like superstition etc with reference
to the situation. The emotional time varies for different drivers
but even for a particular driver the emotional time is likely to
vary considerably depending upon the situation or the actual
problem.
 Volition Time:- It is the time taken by driver for the final
action such as break application.
PIEV Theory
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Reaction Time & PIEV Process
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Thank You !!!
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Fundamentals of traffic Engg

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