2.7 HIGHWAY TRANSPORTATION : TRAFFIC ENGINEERING (TRE) 3150611 GTU

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PREPARED BY : ASST. PROF. VATSAL D. PATEL
MAHATMA GANDHI INSTITUTE OF
TECHNICAL EDUCATION &
RESEARCH CENTRE, NAVSARI.

 Traffic engineering is that branch of engineering which deals
with planning and geometric design of roads and highways,
and with traffic operations thereon, as their use is related to the
safe, convenient and economical transportation of persons and
goods.
 Traffic engineering deals with the regulation, direction and
control of vehicular and pedestrian traffic on a road so as to
ensure safe and free use of the road.
2

 The term Traffic management is sometimes used to express
means and methods adopted to utilize the road systems of a
town to the maximum extent.
3

 Traffic characteristics : Road users characteristics &
Vehicular characteristics
 Traffic studies and analysis : Traffic Census
 Traffic operation – control and regulation : Laws
 Planning and analysis : Major Highways
 Geometric design : Aspects
4

 Human beings, either as pedestrians or drivers, cyclist or
motorist, taken individually and collectively, are an essential
elements to be understood and dealt with in highway traffic.
 Road user behaviour is affected by both external and internal
factors.
 The environmental factors are considered as external factors.
5

ROAD USER
CHARACTERISTICS
Physical Factor
Permanent
Vision
Hearing
Strength
Judgement
power
Reaction time
Temporary
Fatigue
Alcohol,
Drug
Illness,
Disability
Anger
Climate,
Season, Time
Psychological
Factor
Motivation
Intelligence
Learning
Emotion
Individual
differences
PIEV Time
Environmental
Factor
Traffic stream
characteristics
Facility to the traffic
Atmospheric condition
Locality, land use and
activities
6

VISION:
Vision is one of the important factors that affects almost all
aspects of highway design and safety. The human eye is the
sensory organ that enables one to see and evaluate the size,
shape and colour of object and estimate distances and speed of
bodies.
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 Visual acuity (eye sight)
 Peripheral vision
 Eye-movement
 Colour vision
 Glare vision and recovery
 Perception of time and space
8

9
Cone of vision
(horizontal plane)
Clarity of vision
3° to 5° Very clear vision
5° to 7° Clear vision (good)
7° to 12° Satisfactory vision

 The field of view within which an individual can see objects,
but without clear details or colour is called peripheral vision.
It deals with total visual field for the two eyes.
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Speed (km/hr) Angle of peripheral vision (αp)
30 110°
100 40°

 Because the road user’s field of vision is limited, it is
necessary for him to shift his eyes with moment of traffic to
scan areas significant for him. To obtain clear vision in
highway traffic eye makes six different types of movement, all
of which take time and assume travel distance.
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First : 0.1 to 0.3 sec.
Second : 0.125 to 0.235 sec.
Third : Moving Elements
Fourth : 0.3 to 0.5 sec.
Fifth : Movement of the Head
Sixth : Noise and Stimuli
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 Colour is an important factor in perception under good light
many colours can be differentiated, but as light decreases, the
red and blue becomes less visible while yellow remains
visible. The different colours have different wavelengths and
thus have their relative visibility.
 Colour blindness is a condition where one cannot distinguish
between different colours. But, it has not been a significant
factor in traffic accidents.
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 Adaptability to light changes is important factor of vision. Eye
takes more time to adapt when we go from light to dark. Eye
adapts much faster while going from darkness to light.
Because of tunnels, street lighting and head light glare heavy
demands are placed on the road user’s adaptability to light
changes.
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 Glare recovery time is the time required to recover from the
effect of a glare after the light source is passed. It is about 6
seconds when going from light to dark and about 3 seconds
when going from dark to light.
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 Perception of space refers to the ability of the eye to judge the
space, depth and time. Perception of space allow the road
user to form judgements of his own behaviour as well as of the
behaviour of other in the traffic stream.
 Overtaking operations, use of islands, road marking and
delineators, parking guides, clearance lights, etc. require
judgement of space and speed. Increasing frequency of rear
end collision on high speed roads is due to failure of speed
judgement.
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HEARING:
Hearing is an aid to the road-user which can at times be very
vital. The sound of a horn or the sound of the nearing vehicle
itself can alert a pedestrian to safety. Elderly by person with
falling eyesight can perceive better through hearing than
through seeing. Defective hearing is however, not a very
serious handicap.
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STRENGTH:
Through strength is not an important factor in general, lack of
strength may make parking manoeuvres difficult, particularly
for heavy vehicles.
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JUDGEMENT POWER:
Ability to judge the coming situation depends upon
experience and one’s own judgement power. Before the
actual response it is the right judgement of the steps to be
taken to avoid the mishaps. Road user’s judgement as a driver
or pedestrian is therefore important.
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REACTION TIME:
 The time required to perceive and understand the traffic
situation and to take the appropriate action is known as
reaction time. It depends on permanent and temporary
physical factors as well as psychological factors.
 Increase in reaction time increases the complexity of the
situation.
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 Fatigue : Drowsiness or sleep
 Alcohol, Drug : Mental and Physical efficiency
 Disease : Emotional reaction
 Desire : Anger, Fear
 Climate : Polluted
 Season : Summer, Winter, Monsoon
 Weather : Clear, Foggy
 Time of the day : Day, Night
 Altitude : Oxygen supply
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MOTIVATION :
People entre the traffic stream for business, social, recreation,
marketing purposes. They may be intent on going to a regular
place of employment, to market, to rail, water, air or other
terminals. They may be going to school, to visit, to the theatre,
or to dance. They may be going to games, to hunt fish or
weak-end drive. But once the individual enters the traffic
stream he is usually motivated by his desire.
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INTELLIGENCE :
The capacity of the road user to be aware of external factors
relevant to his behaviour in traffic and to adapt and adjust
himself in accordance with his intents and motives requires a
fair degree of intelligence.
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LEARNING :
The learning process, while dependent on motivation,
intelligence, and other modifying factors, develops the skills,
habits and abilities of road user to respond properly to the
total environment of traffic operations.
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EMOTION :
Usually emotion strongly motivates the road user to in
efficient, random adjustment. Fear, anger, worry, and other
similar emotional states tend to create disorganized reactions
and behaviour.
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INDIVIDUAL DIFFERENCES :
Because of the modifying factors of motivation, intelligence,
learning and emotion there is a great variation among users of
the highway. But just as there are limits to the range of
variation in the height, weight and age and other physical
characteristics of human beings, there are limits in the range
and there are central tendencies in the traffic performance
quality of the road users.
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REACTION TIME (PIEV time) :
Reaction time of a driver is the time taken from the instant the
object is visible to the driver to the instant the brakes are
effectively applied. Total reaction time may be split up into
two parts.
1) Perception time
2) Brake reaction time
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 According to PIEV theory,
The total reaction time of driver is split into four parts :
1) Perception time
2) Intellection time
3) Emotion time
4) Volition time
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I-E
BRAIN
Stimulus
P V
Response
Spinal Chord

PERCEPTION TIME:
Perception time is the time required for the sensations received
by the eyes or ears to be transmitted to the brain through
the nervous system and spinal chord.
INTELLECTION TIME (Identification):
It is the time required for understanding the situation. It is
also the time required for comparing the different thoughts,
regrouping and registering new sensations.
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EMOTION TIME (Judgement):
It is the time elapsed during emotional sensations and
disturbance such as fear, anger, etc. with reference to the
situation.
VOLITION TIME (Reaction):
Volition time is the time taken for the final action. The “will”
to take some act or produce some action is volition.
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 Physical and psychological characteristics of the driver.
 Type of the problem involved.
 Environmental condition.
 Temporary factors, (e.g. Motive of the trip, travel speed,
fatigue, consumption of alcohol, etc.)
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Stimulus Reaction time (sec.)
Light 0.18
Sound 0.14
Touch 0.14

Vehicular Characteristics
Static
Dimensions (length,
width, height)
Weight(gross vehicular
weight, axle load)
Maximum turning radius/
angle
Dynamic
Speed
Acceleration
Braking
system
Lighting
system
Vehicle body
design
Tyres
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 The static characteristics affecting highway design are the
dimensions, weight and maximum turning angle.
Width of vehicle:
 Lane width
 Width of shoulders
 Width of parking lots
 Speed of vehicle
 Capacity of parking lots
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Length of the vehicle:
 Design of horizontal alignment of road
 Road capacity
 Parking facility
 Overtaking distance
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Height of the vehicle:
 Clearance required under structures such as under bridges,
over bridge, electric service line.
 Height of tunnels
 Height of driver seat affects the visibility distance
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Weight of the vehicle:
 Structural design of pavement, its thickness
 Design of bridges
 Ruling and limiting gradients
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 The gross load of any vehicle or combination of vehicles
should not exceed the value given by the following relation:
 W= 1525 [ L + 7.3 ] – 14.7 L2 ........ When L > 2.44 m
Where,
W = Gross weight of vehicle in kg.
L = Distance between extreme axles in metres.
When L < 2.44 m, the gross weight of vehicle should not
exceed 14515 kg.
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38
Dimension
of
vehicle
Details Maximum
dimensions in m
(excluding front
and rear
bumpers)
Width All vehicle 2.50 m
Height (a) Single decked vehicles for normal application 3.80 m
(b) Double-decked vehicle 4.75 m
Length (a) Single unit truck with two or more axles 11.0 m
(b) Single unit bus with two or more axles 12.0 m
(c) Semi-trailer tractor combination 16.0 m
(d) Tractor and trailer combinations 18.0 m

 Dimensions of road design vehicles
WIDTH:
No vehicle shall have a width exceeding 2.5 m.
HEIGHT:
 No vehicle other than a double-decker bus shall have a height
exceeding 3.8 m for normal application and 4.2 m when
carrying ISO series 1 freight containers. Double Decker
buses may however, have a height not exceeding 4.75 m.
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LENGTH:
 The maximum overall length of a single unit truck, exclusive
of front and rear bumpers, having two or more axles, shall be
11 m.
 The maximum overall length of a single unit bus, exclusive
of front and rear bumpers, having two or more axles, shall be
12 m.
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LENGTH:
 The maximum overall length of a truck-tractor semi-trailer
combination, exclusive of front and rear bumpers, shall be
16 m.
 The maximum overall length of a truck-trailer combination,
exclusive of front and rear bumpers, shall be 18 m.
 No combination of vehicle shall comprise more than 2 vehicle.
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Single Axle Weight:
The total gross weight imposed on the highway by a single
axle fitted with dual wheels shall not exceed 10.2 tonnes, in
the case of axle with single wheels, the axle weight shall not
exceed 6 tonnes.
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Tandem Axle Weight:
The total gross weight imposed on the highway by two axles
in tandem articulated from a common attachment to the
vehicle or individually attached to the vehicles and spaced
not less then 1.2 m but not more than 2.5 m apart, shall not
exceed 18 tonnes.
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Maximum Permissible Gross Weight:
The maximum permissible gross weight for a given vehicle
or vehicle combination would be equal to the sum of the
individual single axle and tandem axle weights.
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 Low speed turns:
The minimum turning radius for low speed vehicles (speed
less than16 km/hr) depends upon the wheel base and steering
angle. The path followed and space required by a vehicle
when making a sharpest possible turn is specially important in
vehicle manoeuvring such as parking.
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When vehicle turns at low speeds, the rear wheel tracks the
front wheel, on a shorter radius. The difference between radii
of rear and front wheels known as “off tracking” or
“mechanical widening” is dependent on the turning radius
and vehicle wheel base. If inner front wheel takes a path on
the inner edge of a pavement at a horizontal curve, inner rear
wheel will be off the pavement on the inner shoulder.
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off tracking =
Where,
n = no of lanes
l = length of wheel base (m)
R = radius of curve (m)
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 High speed turns:
At high speed turns ( at 0.7 times of design speed), as on
intersection curves the turning radius is controlled by amount
of super elevation and by the side friction factor between the
tires and pavements.
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 High speed turns:
It is given by the following formula.
R =
Where,
R = Radius of curve in m
V = Speed of vehicle in km/hr
e = rate of super elevation
f = coefficient of side friction
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 The dynamic characteristics of vehicles affecting highway
design are speed, acceleration, braking system, vehicle body
design, etc.
 The speed and acceleration depends upon the power of the
engine and the resistance to be overcome and are important in
all the geometric design elements.
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 Sight distance
 Super elevation
 Length of transition curve on horizontal curves
 Radius on horizontal curves
 Length of transition curve on vertical curves
 Width of pavement and shoulders
 Design gradient
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 BRAKING SYSTEM:
The braking system of a vehicle is important from the point of
view of safety. The safety of vehicle operation, stopping
distance and the spacing between the two consecutive vehicles
in a traffic stream are affected by the braking capacity.
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 ACCELERATION:
Acceleration characteristics of a vehicle need to be understood
when designing the intersection elements and overtaking sight
distance acceleration rate is governed by the vehicle
transmission system, weight and horse power. The
acceleration rate also varies with speed, being high at lower
speeds and low at higher speeds.
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 PAVEMENT SURFACE CHARACTERISTICS:
The important surface characteristics are:
1) Friction
2) Unevenness
3) Light reflecting characteristics
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 FRICTION:
The friction between the vehicle tyres and pavement surface is
one of the important factors determining the operating speed
of vehicle and distance requirements in accelerating and
stopping the vehicles. The coefficient of friction or skid
resistance offered by the pavement surface is important for
safety.
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 SKID:
Skid occurs when the wheels of the vehicle slide without
revolving or when the wheels partially revolve, i.e. When the
path travelled along the road surface is more than the
circumferential movements of the wheels due to their rotation,
as brakes are applied. When the brakes are applied the wheels
are locked fully or partially, and the vehicle moves forward,
the longitudinal skidding take place which may vary from 0 to
100%.
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 SLIP:
Slip occurs when a wheel revolves more than the
corresponding longitudinal distance along the roads. Slipping
usually occurs in the driving wheel of a vehicle when the
vehicle rapidly accelerates from stationary position on
pavement surface which is wet and slippery.
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 Type of pavement surface:
Bituminous
Cement concrete
WBM
Earth surface
 Roughness of the surface
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 Condition of pavement namely dry, wet, smooth, rough, etc.
 Condition of tyres
 Speed of vehicles
 Break efficiency
 Load and tyre pressure
 Temperature of road surface and tyre, etc.
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 If pavement surface is even and with less undulations,
vehicles can travel at a higher speed. Pavement unevenness
also affects the vehicle operation cost, comfort and safety. Fuel
consumption and wear and tear of types and other moving
parts increases with increase in pavement unevenness.
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 Night visibility is affected by the light reflecting
characteristics of the pavement surface. Light coloured or
white pavement surface gave good visibility at night during
rains, and they produce glare and eye strain during bright
sunlight. Bituminous surface (black top pavement) on the
other hand provides very poor visibility at nights, especially
when the surface is wet.
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 Braking test is used to determine the skid resistance of
pavement surface. If the brakes are applied till the vehicle
comes to stop, it may be assumed that wheels are fully locked
and the brake efficiency is 100%. During braking test at least
two of the following three measurements are needed in order
to determine the skid resistance of the pavement:
[1] Braking distance (L), metres [2] Initial speed (u), m/s
[3] Actual duration of brake application (t) seconds.
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1. Traffic volume study
2. Speed study : (a) Spot speed study (b) Speed and delay study
3. Origin and Destination – O & D study
4. Traffic flow characteristics study
5. Traffic capacity study
6. Parking study
7. Accident study
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1. To analyse the facilities available on road.
2. To suggest measures to increase traffic flow capacity of roads.
3. To analyse road accident & suggest suitable measures to reduce
accidents.
4. To collect information for geometric design of highway.
5. To know the nature of present traffic and forecast future traffic.
6. To provide parking facilities on road.
7. To suggest suitable measures to control speed of vehicle.
65

 Traffic volume (flow) is variable. It is of great importance to
the traffic engineer. It is essentially the quantity of movement
per unit of time at a specified location. The quantity of
movement may be either of single traffic unit – pedestrians,
cars, buses or goods vehicles, etc. Time period will depend on
the purpose of study.
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 Traffic volume :
 The number of vehicle crossing a section of road per unit time
at any selected period is called traffic volume.
 The unit of traffic volume is vehicles per hour or vehicles per
day.
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 Objects and uses of traffic volume study :
 Traffic volume is accepted as a true measure of the relative
importance of roads and in deciding the priority to
improvement and expansions.
 Traffic volume study is used in planning, traffic operation and
control of existing facilities.
 Used in planning and designing the new facilities.
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 For the analysis of traffic patterns and trends.
 Classified volume study is useful in structural design of
pavements, in geometric design and in computing roadway
capacity.
 For planning side walks, cross walks, subways, etc.
 Turning movement study used in design of intersections in
planning signal timings, etc.
 To know the various types of vehicles using the road.
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 Classification of traffic, i.e. Buses, trucks, cars, bullock carts,
pedestrians, etc.
 Number of vehicle in each class.
 The direction of each class of traffic flow is also noted.
 At intersections the traffic flow in each direction of flow
including turning movements are recorded.
 Peak traffic period is also noted.
70

 Hourly traffic volumes, and average daily volumes are those
commonly used in planning, design and operation of highway
facilities.
 Traffic demands in vehicle per hour per lane are of great
significance in dealing with practical traffic problems.
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 The highest hourly volume in a day is called peak hour
volume. It is the maximum number of vehicles that pass a
point on a highway during one hour.
 There is one peak in the morning and another in the evening
referred as “morning peak hour” and “evening peak hour”
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 Functional classification of highways (like arterial, sub-
arterial, collector and local streets for urban roads)
 Geometric design of highway (like number of lanes,
intersection signalization, channelization, etc.)
 Capacity analysis
 Parking demands and regulations
 Planning and location of traffic control devices.
 Location of interchanges.
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 It is the average of 24 hours volume count collected every day
in the year.
 AADT =
 Planning major streets
 Improvement, construction or reconstruction of roads
 Computing accident rates
 Estimating highway user revenue
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 The total volume during certain number of days, divided by
that number of days is called average daily traffic.
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 Geometric design with respect to minimum turning paths,
clearance, grade
 Structural design of pavements, bridges
 Estimating highway user revenues
76

 Analysing maximum rates of flow and variation within peak
hour
 Providing economical means of obtaining volume data
 Determining capacity limitations in urban areas
77

 Planning parking facilities
 To obtain accumulation of vehicles inside the cordon area
78

 These are utilized in planning the cross walks and signals for
pedestrians.
79

 Design of intersection and interchanges
 Planning of signal timings
 Planning turn prohibitions
 Channelization, etc.
80

81
TRAFFIC
VOLUME
COUNTS
MANUAL
DIRECT
METHOD
INDIRECT
METHOD
AUTOMATIC
CONTACT
SYSTEM
CONTACT –
LESS SYSTEM

 These may be either fixed (permanent) type or portable type.
 The mechanical counter can automatically record the total
number of vehicles crossing a section of the road in a desired
period.
 The working may be by the effect of impulse or stimuli caused
by traffic movements on a pneumatic hose placed across the
roadway.
82

 It can works throughout the day and night for the desired
period, recording the total hourly volume.
 It does not require any supervision.
 It is suitable for long counts.
83

 It is not possible to get the traffic volume of various classes of
traffic.
 It does not give the details of turning movements.
 The impulses caused by light vehicles may not be enough in
some cases to acute the counter.
 It is not possible to record the pedestrian traffic.
84

 Pneumatic tube (road tube)
 Electric contact device
 Co-axial cable
 Photo-electric device
 Radar
 Infra-red device
 Magnetic device
 Ultrasonic device
85

 A thick walled flexible tube (10-12 mm diameter, 3 mm thick)
with one end sealed is clamped to the road surface at right
angles to the pavement. The other end of the tube is connected
to a diaphragm or counter.
86

 At the sealed end a small air release hole is provided to avoid
bounced impulses. As a vehicle wheel crosses the tube it
compresses it, causing an air “shock wave” to travel along the
tube, operating a simple “make and break” circuit of the
counter.
87

 A pair of steel strips are contained in a rubber pad which is
burried beneath the road surface. On being passed by the
weight of a moving axle the steel strips come into contact with
each other and cause the electric current to flow. Electric
contacts are installed in each lane.
88

 A co-axial cable is clamped across the road surface with the
capability of generating signals with the passage of axles.
These signals actuate a transistorised counter. The advantages
associated with this type of detectors are their better reliability
and performance on inferior type of surfaces and their lesser
susceptibility to damage.
89

 On one end of the road is a source of light which emits a beam
across the road. At the other end is a photo cell which can
distinguish between the light beam and absence of the light
beam.
90

 The passage of vehicle in the path of the light beam obstruct
the beam and causes detection by the photo cell. The difficulty
is that obstruction can be caused by pedestrians and that more
than one vehicle in the different traffic lanes, will register only
one vehicle.
91

 When a moving object approaches or recedes from the source
of a signals, the frequency of the signal received back from the
moving object will be different from the frequency of the
signal emitted by the source. The difference in the two
frequencies causes detection of a moving vehicle.
92

 This device utilises a pick-up cell, which is similar to a
photoelectric cell, but is sensitive to infrared (heat) radiation,
rather than to visible light. The unit is mounted above the road
surface on a bridge or sign structure etc.
93

 In this, detection is done by a signal or impulse caused by a
moving vehicle and disturbing a magnetic field. The unit is
installed in each lane immediately blow the road surface. It is
more durable but more expensive than pneumatic detector.
94

 This is similar in its operation to a radar unit.
 A beam crosses the road and is broken by the passage of a
vehicle.
95

 In this method, the members of field team collect the
necessary information on the prescribed record sheet at the
selected points of roadway.
96

 It gives classified volume of each category of traffic, namely,
buses, cars, trucks, auto rickshaws, cycles, scooters,
pedestrians, etc. Which can not be collected by mechanical
counters.
 The direction of each class of traffic at intersection is also be
recorded.
 The number of occupants in vehicles are also recorded in this
method.
97

 It is not possible to have manual counts for all the 24 hours of
the day and on all days round the year.
 It is tedious, laborious and costly.
98

 This method is also known as Wardrop Charlesworth method.
It was developed in England.
 This method consists in counting the number of cars met,
numbers of cars overtaken, and the time taken to travel by the
observer, once moving against the traffic and once moving
along with the traffic.
99

 The floating car method is generally followed in India.
 Here we have a test car with four observers in it which is
floating, i.e. Which is travelling at approximately the same
speed at that of the traffic.
10
0

 The first observer equipped with two stop watches is an
observer to record delays. At strategic locations such as
bridges, intersections, roads in vicinity of markets etc.
 He observes with the help of two stop watches the time
required to negotiate these focal points, i.e. He observes the
delay time.
10
1

 The second observer in the car notes the cause of this delay
either in the tabular form or with vivid descriptions.
 The third observer record the number of vehicles overtaken
by the floating car or the number of vehicles that overtakes the
floating car, in specified time.
 The fourth observer notes the number of vehicles travelling
in opposite direction in each trip.
10
2

 The moving observer method gives an unbiased estimate of
the flow.
 As compared to the stationary observer method, the moving
observer method is equivalent to a stationary count over twice
the single journey time. Hence it is economical in manpower.
 It gives mean values of flow and speed over a section, rather
than at a point. Thus it gives directly the space mean speed,
whereas spot speed studies gives the time mean speed.
10
3

 It gives additional information of stops at intersection, delays,
parked vehicles etc.
 It enables data on speed and flow to be collected at the same
time.
10
4

 The videography is carried out for the stretch of road about 20
to 30 m. The entry and exit of the vehicle on the selected
approach should be covered in the videography. The start time
of the video is set to zero. The movement of the vehicles are
recorded for an hour.
10
5

 The movement of the vehicles are recorded for an hour. After
the end of the videography, the vehicles are counted on the
screen of the computer or DVD. The entry time of the vehicle
and exit time of the vehicle is recorded for the vehicles on the
selected stretch. The distance passed by the vehicle per unit
time is worked out. Video photography gives a permanent
record of volume counts. Its analysis can be done conveniently
in the office by replaying the cassette on a TV monitor.
10
6

 Different classes of vehicles such as cars, buses, trucks, auto
rickshaws, scooters, cycles, bullock carts, etc. Are found to
use the common roadway facilities without segregation on
most of the roads. Such a traffic flow is called heterogeneous
traffic flow or mixed traffic flow.
10
7

 The different vehicles classes have a wide range of static
characteristics such as length, width, etc. and dynamic
characteristics such as speed, acceleration, etc. It is rather
difficult to estimate the traffic volume and traffic capacity of
roadways under mixed traffic flow.
 It is a common practice to consider the passenger car as the
standard vehicle unit to convert the other vehicle classes and
this unit is called Passenger Car Unit (PCU).
10
8

 PCU =
 PCU indicates the space required for a vehicle on a road.
 PCU indicates the space required for a vehicle on a road. For
example, PCU for car is 1 and that for bus is 3, it means the
space required for a bus on the road is three times more than
that required for a car.
10
9

 PCU values for different classes of vehicle as per IRC : 64-
1990 are given in table.
11
0
SR.NO CLASS OF VEHICLE PCU
1. Passenger car 1.0
2. Auto rickshaw 1.0
3. Bus, Truck 3.0
4.. Tractor – Trailer unit 3.0
5. Motor cycle, Scooter, Pedal cycle 0.5
6. Horse drawn vehicles 4.0
7. Small bullock cart 6.0
8. Large bullock cart 8.0

 Vehicle characteristics :
 Dimensions (length, width etc.)
 Power
 Speed
 Acceleration and braking characteristics
11
1

 Traffic stream characteristics :
 Gap (transverse and longitudinal) between moving vehicle
 Composition of different vehicle classes
 Mean speed and speed distribution
 Ratio of volume to capacity of the road
11
2

 Roadway characteristics :
 Road geometries (including gradient and curves)
 Access control
 Rural/urban
 Intersections (number and type)
11
3

 Control of traffic :
 Speed limit
 One-way street operation
 Traffic control devices (signs, markings, signals etc.)
11
4

 Traffic flow at intersection
11
5

 The data collected during the traffic volume studies are sorted
out and are presented in any of the following forms depending
upon the requirements.
 Average Annual Daily Traffic (AADT or ADT) :
 The average of traffic of 365 days of the year is called ADT.
 It helps in deciding the relative importance of a route and in
phasing the road development programme.
11
6

 Volume charts :
 Variation charts showing hourly, daily and seasonal variations
are prepared. These help in deciding the facilities and
regulation needed during peak traffic periods.
 Volume flow diagram at intersection :
 Volume flow diagrams at intersection showing the details of
crossing and turning traffic are prepared. Traffic volume is
also indicated in the diagram.
11
7

 Trend charts :
 These charts show the volume changes over a period of years.
 Traffic flow maps :
 These maps show volume along various routes by using bands
proportional to the traffic volume carried. On a long route,
annual average daily volume and in cities, where congestion
occurs, average peak hour volumes will be more informative.
11
8

 The 30th highest hourly volume is the hourly volume that will
be exceeded only 29 times in a year and all other hourly
volumes of the year will be less than this value.
 The highest (peak) hourly volume of the year will be too high
that it will not be economical to design the facilities according
to this volume.
11
9

 The 30th highest hourly volume is found from the plot between
hourly volume and the number of hours in an year the traffic
volume is exceeded.
12
0

 The facilities designed with capacity for 30th highest hourly
traffic volume in the assumed year is found to be satisfactory
from both facility and economic considerations.
 Thus the 30th highest hourly volume is generally taken as the
hourly volume for design.
12
1

 Spot speed :
 This is the instantaneous speed of a vehicle at a specified
section or location.
 Average speed :
 Average speed is the average of the spot speeds of all the
vehicles passing a given point on the roadway.
12
2

 Running speed :
 It is the average speed maintained by a vehicle over a
particular stretch of road, while the vehicle is in motion.
 Running speed =
12
3

 Travel speed (Overall speed) :
 It is the effective speed with which a vehicle traverse a
particular route between two stations.
 It is also called journey speed.
 Travel speed =
12
4

 Location :
 At all major highways.
 At all high accident frequency points
 At all points where installation of traffic signals and stop signs
are contemplated.
 At other representative locations for collecting basic data for
future planning.
12
5

 Time of study :
 One hour between 9 to 12 a.m.
 One hour between 3 to 6 p.m.
 One hour between 6 to 10 p.m.
12
6

 To use in planning traffic control and in traffic regulation.
 For highway geometric design.
 To use in accident study.
 To study the traffic capacity.
 To decide the speed trends.
12
7

Measurement of spot speed
By measuring time required to
travel known distance
Long base methods :
- Direct timing procedure
- Enoscope
-Pressure contact tube
Short base
methods
Radar speed meter
Photographic
method
12
8

 Enoscope is a mirror box supported on a tripod stand. In its
simplest principle, the observer is stationed on one side of the
road and starts a stop watch when a vehicle crosses that
station.
12
9

 An enoscope is placed at convenient distance of say 50 m in
such a way that the image of the vehicle is seen by the
observer when the vehicle crosses the section when the
enoscope is fixed and at this instant the stop watch is stopped.
13
0

 The time required for the vehicle to cross the known length is
found and is converted to the speed in kmph. The main
advantage of this method is that it is a simple and cheap
equipment and is easy to use.
 The main disadvantage of this method is that the progress is so
slow as it is difficult to spot out typical vehicles and the
number of samples observed will be less. There is also a
possibility of human error.
13
1

 In this method, the observer stand between two enoscopes.
When the image of vehicle is seen in the enoscope at A, stop
watch is started and the instant, when image of vehicle is seen
at B, stop watch is stopped.
13
2

 The spot speed data can be presented graphically in the
following ways :
1. Histogram and frequency distribution curve
2. Cumulative frequency curve
13
3

 Histogram is a plot between speed interval (speed range) and
frequency %.
 A frequency distribution curve, of spot speeds is plotted with
average values of each speed group of vehicles on x-axis and
% of vehicle (frequency %) on y-axis.
 Thus, frequency distribution curve is found by rounding off
the histogram so that the area of the frequency curve is equal
to the area of the histogram.
13
4

 Modal speed :
 The speed corresponding to peak of the frequency distribution
curve is called modal speed.
 The modal speed indicate the speed at which the greatest
proportion of vehicle travel.
13
5

 Cumulative frequency curve :
 The cumulative frequency curve is plotted between cumulative
frequency percentage and upper limit of speed in each speed
group.
 It is used for determining the number of vehicles travel above
or below given speed.
13
6

 The speed corresponding to 85% cumulative frequency in the
cumulative speed distribution graph is known as 85th
percentile speed.
 85th percentile speed is the speed at or below which 85% of
the vehicles are passing the point on the highway or only 15%
of the vehicles exceed the speed at that spot.
13
7

 85th percentile speed is also known as safe speed limit.
 15th percentile speed is the minimum speed.
 98th percentile speed is taken as the design speed for a
highway.
13
8

 Time mean speed (Vt) :
 The average speed of different vehicles measured at a
particular section of the road is called time mean speed.
13
9

 Space mean speed (Vs) :
 It is the speed of vehicles on a road length measured at
different sections but at the same time.
14
0

 A travel time and delay study measures average travel time
and running time along sections of a route, while at the same
time information regarding location, cause and duration of
delay is collected.
 The difference in running speed and journey speed is due to
delay in the traffic. A delay study measure stopped time delay
at specific locations such as intersection, crossings, etc.
14
1

 Information on amount, cause and location of delays helps in
locating “congestion spots” , where proper remedial measures
can be taken.
 Sufficiency ratings or quality indices methods based on travel
time, are used to compare different roads and assess the
quality.
 Travel time being a good indication of efficiency of roadway.
14
2

 Economic studies such as cost-benefit analysis utilise travel
time and delay data.
 To determine the need for traffic signals.
 Traffic assignment is based on speed-delay characteristics.
 Before and after studies, utilizing data on travel time and
delay, are used to determine effectiveness of a traffic
improvement, such as parking regulation, signal timing, new
one way street, etc.
14
3

 It is the delay which traffic is subjected to regardless of the
amount of traffic volumes and interferences present on the
highway. This delay is not due to the characteristics of traffic
streams.
 This includes : Traffic signals, Stop signal, Railroad crossings,
etc.
 This delay can occur even with only one vehicle on the
highway.
14
4

 This is known as congestion delay.
 This delay is caused by interference with other components of
traffic.
 The difference between travel time over a route during an
extremely low and during very high traffic volume indicates
the amount of operational delay.
14
5

 Example of operational delay are :
 Interference with the stream flow by parking or imparking
vehicles, turning vehicles, pedestrian, etc.
 Congestion due to high traffic volume, lack of capacity of
road, waiting for a gap to cross street traffic.
14
6

 Stopped time delay :
 This is the time period that a vehicle is actually standing still
due to any factor.
 Travel time delay :
 This the delay caused by acceleration and deceleration in
addition to stopped time delay.
14
7

 Moving observer method or floating car method
 Registration number method
 Elevated observer method
 Interview method
 Test car method
 Photographic method
14
8

 This method is also called Licence Plate Method.
 In this method, observers are stationed at the ends of a
measuring section, about 0.5 – 1.0 km long. The time and
registration number of the vehicles entering and leaving the
section are noted using synchronized watches.
 By matching the registration numbers later, the journey times
and speed can be determined.
14
9

 If the traffic is too heavy for being recorded, some method of
sampling can be adopted. For instance, noting down only
numbers ending with an odd number will yield 50 percent
sample. The vehicle classification can also be noted in this
method thus yielding this additional information.
15
0

 Two observers are normally employed for each direction of
travel, one for noting the registration number and calling the
same, the other for recording it along with time.
15
1

 No sophisticated instruments are needed except stop watches.
 Analysis can be done by the help of computers.
15
2

 It requires large number of man power.
 It does not give important details such as causes, duration and
number of delays.
 The method can be used on highway sections having minor or
no intersections.
 Method is suitable only on rural highway sections.
15
3

 In urban areas, it is sometimes possible to station observers in
high buildings or other elevated points from which a
considerable length of route may be observed. The observers
stationed on top of an elevated building select vehicle at
random and follow their course along the road, noting the time
of entering the test section, duration and nature of delays
suffered and the time of leaving.
15
4

 The test section has to be short such as a street in the central
area of a city. It is difficult to secure suitable points for
observation through the length of the route to be studied.
15
5

 In this method selected individuals are interviewed for their
travel time and delays experienced on the trip.
 Sometimes they are asked in advance to record their
experience.
 With good cooperation the results may be satisfactory and
required minimum time.
15
6

 In this method a test car is driven along the study route using
one of the following operation techniques.
 The test car is driven according to the driver’s judgement of
the average peed of the traffic on the route.
 The test car is driven at the legal speed limit unless impeded
by actual traffic condition.
15
7

 The observer record the time as the test car passes pre-
determined control points and also notes the location, cause
and length of any delay that occurs.
 Normally 8 to 12 runs are required for reasonably accurate
results.
15
8

 Time zone map :
 A time zone map graphically depicts the travel time of any
section of the area from the central focal point.
 The time zone map is especially useful in comparing rotes
leading to a common destination or origin, for comparing
facility of travel for different types of vehicles, or for
comparing travel facilities for different periods of the day.
15
9

 Travel time counters (isochrones) are shown in the map.
16
0

 The various aids and devices used to control, regulate and
guide traffic are :
1. Signs
2. Signals
3. Marking
4. Islands
1
6
1

 The function of traffic sign are :
1. They give timely warning of hazardous situations, when
they are not evident.
2. Traffic signs are helpful in regulating traffic by imparting
messages to the drivers about the need to stop, give way, speed
limit, etc.
3.They give information about highway routes, directions and
points of interest.
1
6
2

 Various traffic signs have been recognized by the government
of India through motor vehicle act, 1939.
1
6
3
TRAFFIC SIGNS
REGULATORY SIGNS
(Mandatory Signs &
Prohibitory Signs)
WARNING SIGNS
(Cautionary signs)
INFORMATORY SIGNS
(Indication, Direction,
Route Identification)

 Regulatory or mandatory signs are meant to inform the road
user of certain laws, regulations and prohibitions. The
violation of these signs is a legal offence.
 All mandatory or regulatory signs are circular in shape. They
are with red circular ring and diagonal bars with white/black
symbols or arrows or letters on white/blue background.
1
6
4

 The regulatory signs are classified under the following sub-
heads :
 Stop and give-way sign
 Prohibitory signs
 No Parking sign and No stopping signs
 Speed limit and vehicle control signs
 Restriction end signs
 Compulsory direction control signs
1
6
5

1
6
8
VEHICLES
PROHIBITED IN
BOTH DIRECTIONS
LEFT/RIGHT TURN
PROHIBITED

169
U-TERN PROHIBITED OVERTAKING PROHIBITED

171
PEDESTRIAN PROHIBITED HORN PROHIBITED

 Warning or cautionary signs are used to warn the road user of
certain hazardous conditions that exists on or adjacent to the
roadway.
 The warning signs are in the shape of a equilateral triangle
with its apex pointing upwards. They have a white
background, red border and black symbols.
174

 The side of triangle is 45 cm.
 The triangular plate is fixed to the vertical post with its lower
side 2.75 m above the ground level.
 About 15 cm below the triangular plate an explanatory plate of
size 45 cm X 40 cm is fixed.
175

176
RIGHT HAND CURVE LEFT HAND CURVE

178
PEDESTRIAN CROSSING NARROW BRIDGE

180
STEEP ASCENT GAP IN MEDIAN

 These signs are used to guide the road user along routes,
inform them of destination and distance and provide with
information to make travel easier, safe and pleasant.
 Information signs are rectangular in shape and are also used
with destination names and distances with arrows indicating
the direction.
181

 These signs are placed at distance 0.6 m from the kerb and at
2.0 to 3.0 m from the edge of carriage way in case of roads
without kerb.
 Various informatory signs are :
1. Direction and place identification signs
2. Facility information signs
3. Parking signs
4. Flood gauge
182

183
ADVANCE DIRECTION DIRECTION

184
REASSURANCE PLACE IDENTIFICATION

186
PETROL PUMP FIRST AID POST

187
LIGHT REFRESHMENT RESTING PLACE

188
NO THROUGH ROAD NO THROUGH SIDE ROAD

18
9
PARK THIS SIDE PARKING LOT MOTOR
CYCLE & SCOOTER

190
PARK LOT CYCLE PARKING LOT CARS

 The design of route marker signs for national highways has
been standardized in India by the IRC. It consists of a shield
painted on a rectangular plate 450 mm X 660 mm. The sign
has a yellow background and all letters, sign and border are
painted in black.
192

 Location of signs :
 In India, traffic signs should be located on the left side of the
road.
 On multi-lane carriage ways, they may be repeated on the
other side of the carriage way.
 On wide expressways, overhead signs may also be provided.
 On hill roads, traffic signs are normally fixed on the valley
side of the road. The signs are usually mounted on posts.
193

 As per IRC: 67 -2012, for all roads, the extreme edge of the
ground mounted sign adjacent to the roadway shall be at a
distance of 600 mm to 3 m from the carriageway or paved
shoulder edge. For road with curbs, it shall not be less than
300 mm from the curb line.
194

 As per IRC: 67 -2012, for kerbed roads, the bottom edge of
the lowest sign shall not be less than 2.1 m and not more than
2.5 m. On roads without kerbs, the bottom edge of the lowest
sign shall not be less than 2.0 m and not more than 2.5 m
above the crown of the pavement. To improve the visibility of
the signs on multi lane roads, the minimum height of the lower
edge of the sign should be kept as 2.5 m above carriageway.
195

 Table gives distances at which signs should be fixed on rural
roads, in advance of the hazards warned against.
19
6
Plain and rolling
terrain
Hilly or mountainous
terrain
On National and state
Highways
120 m 60 m
On Major District roads 90 m 50 m
On other district roads 60 m 40 m
On village roads 40 m 30 m

 Colour for signs :
 Signs shall be provided with retro-reflective sheeting and/or
overlay film as given in IRC-67. The reverse side of all signs
shall be painted grey.
 The sign post shall be painted in 250 mm wide bands,
alternatively white and black. The lowest band next to the
ground shall be in black.
197

 The mandatory and warning signs shall be provided with
white background and red border.
198

 Colour pattern for direction information signs is given in table.
199
Road type Background Arrow/Border/Letters
Expressway Blue White
National Highway (NH) Green White
State Highway (SH) Green White
Major District Road (MDR) Green White
Other District Road (ODR)
Village Road (VR)
White Black
Urban/City Road Blue White

 Material for signs :
 Concrete shall be of M 25 grade
 Reinforcing steel shall conform to IS : 1786 requirements
 The plates and support sections for the sign posts shall
conform to IS : 226 and IS : 2062
 The plate thickness of shoulder mounted ground signs with a
maximum side dimension not exceeding 60 mm shall not be
less than 1.5 mm for aluminim sheet and 3 mm for ACM sheet
200

 Road markings are the lines, patterns, words of other devices
for control, warning and guidance of information of road
users.
 IRC has standardized these markings in IRC : 35-1970.
201

 Controlling and guiding traffic.
 They promote road safety and bring about smooth and
harmonious flow of traffic.
 They serve to supplement the messages conveyed by road
signs and signals.
 They convey the required information to the driver without
distracting his attention from the carriage way.
202

 Pavement or carriage way markings may generally be of white
paint.
 Yellow colour marking are used to indicate parking
restrictions and for continuous centre line marking.
203

 Centre line :
 These are meant to separate the opposing streams of traffic on
undivided two-way roads on NH and SH, with two or three
lanes, single broken lines of width 0.1 m, and 3.0 m segments
and 4.5 m gaps may be painted on straight stretches.
204

 Lane lines :
 These markings divide the carriageway into separate lanes on
either side of the centre line. This helps to guide the traffic and
regulate it.
205

 Stop lines :
 These are meant for vehicles to stop near the pedestrian
crossing, signalized intersection etc. where vehicles have to
stop and proceed.
206

 Cross walk lines :
 These markings are provided at important intersections to
facilitate pedestrians to cross a road. The width of pedestrian
crossing may be between 2.0 and 4.0 m.
20
7

 Such type of markings are provided on horizontal curves and
summit curves on two and three lane highways where
overtaking maneuvers are prohibited.
 The marking for a “no overtaking zone” consists of a
combination line along the centre line.
 The combination line consists of a double line, the left hand
element of which shall be a solid barrier line.
208

 The right hand element will be either a normal broken centre
line or solid barrier line. Where a solid barrier line is to the
right of the broken line the overtaking restriction shall apply
only to the opposing traffic. If both the lines are solid lines, no
overtaking is permitted in both directions.
20
9

 Usually pavement edge line marking is done for pavement
without kerbs. They serve as a visual guidance for the drivers,
indicating to them the limit up to which the driver can safely
venture.
21
0

 Marking on the kerb indicate certain regulation like parking
regulation. Marking on the kerb and edges of islands with
alternate black and white line increase the visibility from a
long distance.
211

 Physical obstruction on or near the roadways are hazardous
and hence should be properly marked. Typical obstruction are
supports for bridge, level crossing gates, signs and signals,
traffic island, narrow bridges, culvert head walls, etc.
212

 Reflector markers are used as hazard markers and guide
markers for safe driving during night. Hazard markers
reflecting yellow light should be visible from a long distance
of about 150m.
213

 Traffic signals are provided at road intersection. These are
control devices which could alternatively direct the traffic to
stop and proceed at intersections using red and green traffic
light signals automatically.
 The main requirements of traffic signals are to draw attention,
provide meaning and time to respond and to have minimum
waste of time.
21
4

 Maintain orderly flow of traffic.
 Reduce certain types of accidents.
 Improves safety and efficiency of movement of vehicles.
 Pedestrians can cross the roads safety.
 Provides nearly continuous movement of traffic.
 More economical than manual control.
 Stop heavy traffic to allow slow moving traffic to cross the
road safely.
215

 The rear end collision may increase.
 Improper design and location of signals may lead to violations
of the control system.
 Failure of the signal due to electric power failure or any other
defect may cause confusion to the road users.
216

 The traffic signals are classified into the following types :
 1. Traffic control signals
◦ A. Fixed time signals
◦ B. Traffic actuated signals
 2. Pedestrian signals
 3. Special traffic signals
217

 Generally a traffic signal is composed of three lenses, arranged
vertically one above the other with red lens on top, yellow or
amber in the middle and a green lens at bottom. The normal
sequence of traffic signal is red, amber, green, amber, red and
so on.
 Red : Vehicle must stop
 Amber : Light about to change
 Green : Vehicles can proceed
218

 The Indian standard on traffic signals prescribes the following
symbols for pedestrian.
 The RED standing man represent the don’t cross indication.
 The GREEN walking man represent cross indication.
219

 The fixed time signals are set to repeat regularly a cycle of red,
amber and green lights.
 The timing of each phase of the cycle is predetermined based
on the traffic studies.
 These signals are the simplest type of automatic traffic signals
which are electrically operated.
 These signals are also called Pre-timed signals.
220

 Simple in construction.
 Relatively inexpensive.
 Most successfully used in linked systems requiring a fixed
cycle length for a given pattern and speed of progression.
221

 Inflexible and hence may cause avoidable delay.
 Required careful setting.
 Sometimes the traffic flow on one road may be almost nil and
traffic on the cross road may be quite heavy. Yet as the signal
operates with fixed timings, the traffic in the heavy stream will
have to stop at red phase.
222

 Traffic actuated signals are those in which the timings of the
phase and cycle time are changed according to traffic demand.
 The vehicles on any intersection approach are sensed by a
detecting device (e.g. magnetic tape, loops or pneumatic pads)
placed in the road. By recording the timing the vehicles as
they cross the detector and by timing the interval between
vehicles, the signals are automatically adjusted to give
preference to the approach with the heaviest flow.
223

 Usually reduces the delay.
 Usually increases the capacity.
 It is adaptable to short-term fluctuation in traffic.
 It provides continuous operation under low volume condition.
 It is most efficient for isolated intersections.
224

 They are uneconomical. The cost is about two to three times
the cost of a fixed time signals.
 Detectors are very costly to install and present very difficult
maintenance problems.
 The actuated controller (complete electronic mechanism) is
much more complicated than fixed time controllers.
225

 Fully actuated signals:
 These have detectors located on each approach and assign the
right of way to the various traffic movements on the basis of
demand.
226

 Semi-actuated signals:
 Where traffic on heavy volume of high speed arteries must be
interrupted for relative light class traffic, semi-actuated traffic
signals are often installed.
 For these signals the detectors are placed only on the minor
street.
227

 Cycle :
 A signal cycle is one complete rotation through all of the
indications provided.
228

 Cycle length (C):
 The time required for one complete sequence of signal
indications (i.e. Red-Red/Amber-Green-Amber) is called cycle
length or time cycle. It may vary from 40 to 60 seconds
depending upon :
 1. Volume of traffic on approaches
 2. Width of the roads and intersection.
229

 Interval:
 It indicates the change from one stage to another. There are
two types of intervals.
 1. Clearance amber interval
 2. Initial amber interval
230

 Clearance amber interval :
 It is also called the amber time indicates the interval between
the green and red signal indications for an approach.
 They are normally have a value of 3 to 6 seconds.
231

 Initial amber interval :
 It is also called all red and is provided after each amber
interval indicating a period during which all signal faces show
red and is used for clearing off the vehicles in the intersection.
 It is the interval between red and green signal.
232

 Green interval :
 It is the green indication for a particular movement. This is the
actual duration the green light of a traffic signal is turned on.
 It is denoted by Gi
233

 Red interval :
 It is the red indication for a particular movement. This is the
actual duration the red light of a traffic signal is turned on.
 It is denoted by Ri
234

 Phase :
 A phase is the green interval plus the change and clearance
intervals that follow it.
235

 Lost time :
 It indicates the time during which the intersection is not
effectively utilized by any movement.
 For example, when the signal for an approach turns from red
to green the driver of the vehicle will take some time to
perceive the signal and some time will be lost before vehicle
moves.
236

 The main purpose of street lighting is to enable the road user
to see accurately the carriageway and the immediate
surroundings in darkness. Majority of road accidents are
caused in the night and poor lighting is the main cause of
accidents.
2
3
7

 Driving in the night is facilitated by the head lights, but it is
always not possible to depend on head lights. Improved
visibility at night by means of artificial lighting lessens the
strain on driving and ensures comfort.
2
3
8

 Highway lighting is particularly more important at
intersections, bridge site, level crossing and places where there
is restriction of traffic to movements.
2
3
9

 1. Amount and distribution of light flux from the lamps
2
4
0

 3.Brightness of object and background
2
4
2

 4.Reflecting characteristics of the pavement surface
2
4
3

 5.Glare on the eyes of the driver
2
4
4

 6.Time available to see an object
245

 Luminous flux (Ф):
 This is the radiant power given by light source.
 It’s unit is lumen.
246

 Lumen (lm):
 This is the SI unit of luminous flux.
 It is equal to the amount of flux received on surface area of
one square meter of sphere, when a light source of one candle
power placed at its centre.
 Lumen = candle power X solid angle
247

 Steradian:
 A steradian is the unit measure of a solid angle.
 Solid angle = ω
 It is equal to the solid angle subtended at the centre of a sphere
by unit area of its surface. The whole space surrounding a
point subtends a solid angle of 4π.
24
8

 Luminous Intensity (I):
 Luminous flux emitted per unit solid angle is called luminous
intensity.
 I =
249

 Candela:
 It is the unit of luminous intensity. Luminous intensity
expressed in candelas is called candle power.
 Metre Candela:
 It is the normal incident illumination produced by unit candle
power at a distance of one meter.
250

 Illumination (E):
 It is the measure of the amount of light flux which falls on a
surface. It is independent of the direction from which the light
comes or the size of light sources or their positions.
Illumination is same if surface is white or black.
 E = ………….. Lumen/m2
 1 lumen/m2 = 1 lux
251

 Luminance (Brightness):
 The luminous intensity emitted or reflected per unit area of a
surface is called luminance.
 B =
252

 Glare:
 Condition of vision in which there is discomfort or a reduction
in the ability to see significant objects or both, due to an
unsuitable distribution of luminance or to extreme contrasts in
space or time.
253

 Luminare (Lantern):
 A house for one or more lamps, comprising a body and any
refractor, reflector, diffuser or enclosure associated with the
lamps.
254

 Lighting installation:
 The entire equipment provided for lighting a street section,
and consists of lanterns, means of support and the electrical
auxiliaries.
25
5

 The total output of a point light source will naturally radiate
uniformly from the point with equal intensity in all direction.
 It is evident that such light distribution would be insufficient
and uneconomical when the purpose is to direct the light
toward a relatively limited area, such as pavement of a street.
25
6

 There are mainly three type of Distribution of Light like,
1. Glare
2. Vertical Distribution of light
3. Lateral Distribution of light
257

 The amount of glare present is dependent on,
1. Brightness of glare Source
2. Angle of incidence with respect to the normal line of
vision
3. General level of illumination
4. Area of glare Source
5. Distance of Glare source from the observer.
258

 The glare from luminaries may be controlled by:
1. Increasing the height of mountings
2. Shielding the light source
3. Reducing the brightness contrast of the light source
259

1. Cut-off :
 In cut-off system, the light is reduced as completely and as
rapidly as possible above a 70° angle with the downward
vertical, the main beam being usually at this angle. This
system eliminates glare.
26
0

2. Non-cut-off (high angle beam) :
 In non-cut off high angle beam system, the peak intensity is at
about 80° and there is considerable output near the horizontal
plane. With this system, a certain amount of glare is inevitable,
and the modern lighting practice does not favor this system.
26
1

3.Semi-cut-off (medium angle beam) :
 The non-cut-off medium angle beam system is in between
above two systems, with a peak intensity directed at an angle
of 75°.
26
2

 The distribution of light in the horizontal direction is equally
important.
 It is not enough that the pavement alone is lighted from
aesthetic considerations.
 The pedestrian footways and the kerbs are also need to be
adequately lighted.
263

 There are three types of horizontal distribution:
1. Symmetrical distribution
2. Axial distribution
3. Non-axial distribution
264

 1. Contrast :
 When the brightness of the object is less than that of the
background, that is when the object appears darker than the
road surface.
265

 2.Glare :
 The disturbing influence when viewing a difficult visual task
under low brightness conditions is known as glare. There are
two types of glare:
1.Disability glare 2.Discomfort glare
266

 3. Lamps :
 The lamps commonly used for highway lighting are :
Tungsten filament lamps Fluorescent lamps
26
7

 3. Lamps :
 The lamps commonly used for highway lighting are :
Sodium vapour lamps Mercury vapour lamps
268

 4. Luminaire distribution of light :
 It should cover the pavement between the kerbs.
 It should make prominent the traffic signs and other objects
on the road.
 It should illuminate the pavement and the adjacent area to the
extent of about 3m to 5m beyond the pavement edge.
 It should produce maximum uniformity pavement brightness
269

 5. Lateral placement of lighting poles :
 The lighting poles should not be installed very close to the
pavement edge, because in that case, the capacity of the
roadway is decreased and the free movement of traffic is
obstructed.
270

 5. Lateral placement of lighting poles :
 IRC has specified the following horizontal clearances for
lighting poles.
For roads with raised kerbs
(as in urban roads)
Min. 0.3 m and desirable 0.6 m from the
edge of raised kerb.
For roads without raised kerbs
(as in rural roads)
Min. 1.5 m from the edge of the
carriageway, subject to min. 5.0 m from
the centre line of the carriageway.
271

 6. Height and overhang of mounting :
 The distribution of light, shadow and the glare effect from
street lamps depends also on the mounting height.
 The glare on eyes from the mounted lights decreases with
increases in the height of mounting. Usually, mounting height
range from 6 to 10m.
272

 6. Height and overhang of mounting :
 Overhangs on the lighting poles would keep the poles away
from the pavement edges, but still allow the lamp to be held
above the kerb or towards the pavements.
273

 7. Spacing of lighting units :
 The spacing between lamps on straight roads is about 3 to 5
times the mounting height.
 For sharp curves, the spacing between lamps is closer for
better visibility conditions.
274

 8. Lighting layouts :
 Single side lighting
275

 Both side lighting-opposite
276

 Both side lighting-staggered
277

 Central lighting
278

 For various types of luminaire distribution, the utilization
coefficient charts are available for determination of average
lux of intensity over the roadway surface when lamp lumen,
mounting height width of pavement, and spacing between
lighting poles are known.
279

 Spacing between lanterns (m) :
 =
280

 Due to proper street lighting, the police can do better patrol
during night and their job becomes easier and more
manageable.
 Increase in business in city or downtown, are as during night
which would otherwise have been totally not accepted.
 The architects and town planners have found lighting to be a
major source for beautification of their projects.
281

 Due to good street lighting, there is a considerable reduction in
accident rate during night.
 The illegal action and anti-social activities on the roads are
certainly discouraged by the improved lighting techniques.
 It gives a pleasant atmosphere during night.
282

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