Traffic Characteristics: (i) Road user’s characteristics - general human characteristics, physical, mental and emotional factors, factors affecting reaction time, PIEV theory. (ii) Vehicular characteristics :( static and dynamic), Characteristics affecting road design-width, height, length and other dimensions. Weight, power, speed and braking capacity of a vehicle

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

2.  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.
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3.  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.
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4.  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
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5.  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.
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6. 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
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7. 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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8.  Visual acuity (eye sight)
 Peripheral vision
 Eye-movement
 Colour vision
 Glare vision and recovery
 Perception of time and space
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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

10.  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°

11.  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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12. 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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13.  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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14.  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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15.  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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16.  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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17. 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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18. 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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19. 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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20. 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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21.  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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22. 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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23. 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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24. 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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25. 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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26. 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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27. 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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28.  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

29. 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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30. 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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31.  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

32. 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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33.  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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34. Length of the vehicle:
 Design of horizontal alignment of road
 Road capacity
 Parking facility
 Overtaking distance
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35. 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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36. Weight of the vehicle:
 Structural design of pavement, its thickness
 Design of bridges
 Ruling and limiting gradients
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37.  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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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

39.  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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40. 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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41. 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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42. 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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43. 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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44. 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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45.  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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46.  Low speed turns:
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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47.  Low speed turns:
off tracking =
Where,
n = no of lanes
l = length of wheel base (m)
R = radius of curve (m)
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48.  High speed turns:
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49.  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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50.  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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51.  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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52.  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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53.  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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54.  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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55.  PAVEMENT SURFACE CHARACTERISTICS:
The important surface characteristics are:
1) Friction
2) Unevenness
3) Light reflecting characteristics
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56.  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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57.  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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58.  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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59.  Type of pavement surface:
Bituminous
Cement concrete
WBM
Earth surface
 Roughness of the surface
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60.  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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61.  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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62.  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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63.  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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