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8/6/2019 Unit 11 ( BASIC CHARACTERISTICS OF A ROAD SYSTEM ( Part 1) )
http://slidepdf.com/reader/full/unit-11-basic-characteristics-of-a-road-system-part-1- 1/15
BASIC CHARACTERISTIC ROADHighway Engineering C3010 / UNIT 11
BASIC CHARACTERISTICS OF A ROAD
SYSTEM
( Part 1)
OBJECTIVES
General Objective
To understand the basic characteristic of a road system.
Specific Objectives
At the end of the unit you should be able to :-
• state the characteristics that will influence the system.
• identify the related factors of the system.
• describe the importance characteristics of drivers.
UNIT 11
8/6/2019 Unit 11 ( BASIC CHARACTERISTICS OF A ROAD SYSTEM ( Part 1) )
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BASIC CHARACTERISTIC ROADHighway Engineering C3010 / UNIT 11
11.0 INTRODUCTION
A Road Design includes Geometry and Pavement Design. These designs
are require in providing information on traffic flow. The highway engineer mustdesign for a wide range of vehicle operating characteristics and allow for great
differences in driver and pedestrian characteristics. Most highway facilities must
be designed to accommodate the smallest subcompact automobile as well as the
largest tractor-trailer truck. In may instances, the design must also accommodate
motorcycle and bicycle users and pedestrians. It should be remembered that
within each class of users there is great variability; differences in vehicle sizes,
weights, and operating characteristic ability to comprehend and react to highway
features and traffic events.
11.1 ROAD SYSTEM CHARACTERISTIC
There are several characteristics in the road system.
11.1.1 DRIVERS CHARACTERISTICS
Drivers in Malaysia are licensed to drive under laws. The
differences about age, skill and experience also can produce some impact
to the traffic flow. It is important that highway engineers keep in mind that
street and highway facilities must be designed to accommodate driver with
INPUT
BASIC CHARACTERISTICS OF A ROAD
SYSTEM
8/6/2019 Unit 11 ( BASIC CHARACTERISTICS OF A ROAD SYSTEM ( Part 1) )
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BASIC CHARACTERISTIC ROADHighway Engineering C3010 / UNIT 11
a wide range of ages and skills, the young and the elderly and the novice
as well as the experienced professional.
11.1.2 VEHICLE CHARACTERISTICS
Vehicle characteristics also influence the traffic flow in any road
systems. Vehicles are used for transportation on the road or highway. All
types of vehicles have shapes, characteristics and own usage.
11.1.3 TRAFFIC CHARACTERISTIC
Traffic characteristic are the most important characteristic in the
traffic flow for any road systems.
11.2 IMPORTANT CHARACTERISTIC OF DRIVERS
The driver characteristics must be identified initially before a certain
geometry design and other related road design is implemented or proceed. Thedrivers are also considered as the road user. There are several factors that
influence driver’s, such as physical, environment and psychology factors.
11.3 INFLUENTIAL FACTORS.
There are some factors that would influence the characteristics of a driver.
11.3.1 PHYSICAL FACTORS
The driver’s decisions and actions depend principally on
information received through the senses. This information comes to the
driver through the eyes, ears, and the sensory nerve ending in the
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BASIC CHARACTERISTIC ROADHighway Engineering C3010 / UNIT 11
muscles, tendon, joints, skin, and organ. In general the order of
importance of the senses used by drivers are;
1. Visual ( sight ).
2. Kinesthetic ( movement ).
3. Vestibular ( equilibrium ).
4. Auditory ( hearing ).
Driver perception-reaction time is defined as the interval between
seeing, feeling or hearing a traffic or highway situation and making initial
response to what has been perceived. People generally react more
quickly to very strong stimuli than to weak one.
11.3.2 ENVIRONMENTAL FACTORS
Weather and road condition also influence the characteristics of
drivers. Most of the drivers will take an extra cautious when the road is wet
and the road surface is damaged. This condition will endanger the safety
of driver.
11.3.3 PSHYCOLOGICAL FACTORS.
New drivers become nervous compare to the experienced drives
whenever they are driving in a crowded traffic area. They feel safer driving
through a straight road would speed more.
11.4 VEHICLE CHARACTERISTICS
The standard of road design is influenced by the characteristic of vehicles
that used the road. The sizes of motor vehicle influence clearances for bridges,
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BASIC CHARACTERISTIC ROADHighway Engineering C3010 / UNIT 11
tunnel, and grade separation structure and the geometric characteristic of
streets, roads, and parking facilities.
11.4.1 RESISTANT
A vehicle’s motion tends to be retarded by at least five types of resistance:
1. Inertia resistance.
2. Grade resistance.
3. Rolling resistance.
4. Curve resistance.
5. Air resistance.
11.4.1.1 Inertia resistance.
It will be recalled from the study of physics that inertia is the
tendency of a body to resist acceleration; the tendency to remain at
rest or to remain in motion in a straight line unless acted upon by
some forces. The forces, Fi, required to overcome a vehicle’s inertiais described by the familiar relationship
Fi = ma = W/g a, kg
Where
m = vehicle mass
a = acceleration ( m/s2)
W = vehicle weight ( kg )
g = acceleration force due to gravity ( 9.81 m/s2)
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BASIC CHARACTERISTIC ROADHighway Engineering C3010 / UNIT 11
When acting to move a vehicle forward, this force is positive.
When the force is slowing or stopping a vehicle, it and the
corresponding acceleration (deceleration) are negative.
11.4.1.2 Grade resistance.
Grade resistance is the component of the vehicle weight
acting down a frictionless inclined surface. As figure illustrates
below, the magnitude of the forces is directly proportional to the
gradient. By similar triangles;
G /100 = Fg/Fn
Fg = FnG/100 = W cos θ G /100
Where
G = gradient ( percent)
W = vehicle weight ( kg )
Fg = grade resistance ( kg )
Fn = normal forces ( kg )
For even the steepest highway gradients encountered in practice,
cos θ ≈ 1.0.
For practical purpose, the gradient resistance is
Fg = WG/100
11.4.1.3 Rolling resistance.
A vehicle does not operate on a smooth friction surface.
There is resistance to motion as the tires roll over irregularities in
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BASIC CHARACTERISTIC ROADHighway Engineering C3010 / UNIT 11
the surface and push through mud, sand or gravel. This resistance,
termed rolling resistance, includes that caused by the flexing of the
tires and the internal friction of the moving part of the vehicle.
11.4.1.4 Curve resistance
As was stated earlier, once a vehicle is set in motion,
it tends to remain in motion in a straight line unless acted on by
some force. The forces changing the direction of a vehicle are
imparted through the front wheels. Components of these forces
tend to impede a vehicle’s forward motion. Curve resistance then is
the force required to cause a vehicle to move along a curve path. It
is a function of the radius or degree of curvature and the vehicle
speed.
11.4.1.5 Air resistance.
Air resistance includes the force required to move air from a
vehicle’s pathway as well as the friction effects of air along its top,
sides, and undercarriage. It is a function of the frontal cross-
sectional area of the vehicle and the square of the vehicle speed.
11.5 VEHICLE OPERATING CHARACTERISTIC
There are various vehicle-operating aspects that considered for geometry
design purpose. The vehicle-operating characteristics that influence are road
geometry design, curves radius, acceleration and braking.
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BASIC CHARACTERISTIC ROADHighway Engineering C3010 / UNIT 11
11.6 ACCELERATION AND DECELERATION
A motor vehicle move according to fundamental laws of motion;
relationships between distance, time, velocity and uniform acceleration are given
by the following equation:
Vf = vo + at
D = vot + ½ at2
V2f = v2
o + 2ad
Where
vf = final velocity ( m/s )
vo = initial velocity ( m/s )
a = acceleration or deceleration
t = time ( sec )
d = distance ( m ).
Maximum acceleration rates vary with the size of the vehicle and itsoperating speed. Vehicles are capable of greatest acceleration at lowest speeds.
From a standing start to a speed of 15 mph, maximum acceleration value range
from about 2 mph/sec for tactor-semitrailer trucks up to about 10 mph/sec for
large cars. For a speed change of 0 to 30 mph, typical maximum acceleration are
for tractor semitrailer truck – 4.57 m/s2, for large car – 3.14 m/s2 and for small
high performance sports car – 4.33 m/s2.
Without braking, a vehicle will decelerate when the driver release the
accelerator due to the drag of the engine, air resistance, grade resistance and so
forth. A passenger car operating in the range of 50 to 60 mph will decelerate
about 0.91 m/s2 without braking; in the range of 20 to 30 mph, and automobile
will decelerate about 0.46 m/s2.
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BASIC CHARACTERISTIC ROADHighway Engineering C3010 / UNIT 11
Under normal braking conditions, the levels of deceleration developed
usually do not reach the limit of vehicle’s braking capability nor that of the
pavement-tire interface. The deceleration may be limited by either the condition
of the brakes or that of the tires and roadway surface. In panic situations, most
drivers tend to apply the brakes to the extent that a locked wheel skid develops,
even though a greater frictional force is developed before skidding occurs.
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BASIC CHARACTERISTIC ROADHighway Engineering C3010 / UNIT 11
TEST YOUR UNDERSTANDING BEFORE YOU CONTINUE WITH THE NEXT
INPUT
1. The motion of the vehicle tends to be retarded by at least five types of
resistance. State the type of vehicles resistance.
2. Describe the grade resistance.
3. This formula is to determine acceleration or deceleration velocity. Find the
meaning of this formula,
V2f = v2
o + 2ad
Where;V2
f = _____________________
v2o = _____________________
a = _____________________
d = ______________________
ACTIVITY 11
Question
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BASIC CHARACTERISTIC ROADHighway Engineering C3010 / UNIT 11
1. A vehicle’s motion tends to be retarded by at least five types of
resistance:
i. Inertia resistance.
ii. Grade resistance.
iii. Rolling resistance.
iv. Curve resistance.
v. Air resistance.
2. Grade resistance is the component of the vehicle weight acting
down a frictionless inclined surface. As figure illustrates below, the
magnitude of the forces is directly proportional to the gradient. Bysimilar triangles;
G /100 = Fg/Fn
Fg = FnG/100 = W cos θ G /100
Where
G = gradient ( percent)
W = vehicle weight ( kg )
Fg = grade resistance ( kg )
Fn = normal forces ( kg )
For even the steepest highway gradients encountered in practice,
cos θ ≈ 1.0.
FEEDBACK ON
Answer
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For practical purpose, the gradient resistance is
Fg = WG/100
3. V2f = v2
o + 2ad
Where
vf = final velocity ( m/s )
vo = initial velocity ( m/s )
a = acceleration or deceleration
t = time ( sec )
d = distance ( m ).
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Describe briefly the factors that would influence the characteristics of a driver.
Describe the following aspects: -
a. Curve resistance.
b. Air resistance
Question
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BASIC CHARACTERISTIC ROADHighway Engineering C3010 / UNIT 11
1. There are some factors that would influence the characteristics of a
driver.
PHYSICAL FACTORS
The driver’s decisions and actions depend principally on
information received through the senses. This information comes to
the driver through the eyes, ears, and the sensory nerve ending in
the muscles, tendon, joints, skin, and organ. In general the order of
importance of the senses used by drivers are;
a. Visual ( sight ).b. Kinesthetic ( movement ).
c. Vestibular ( equilibrium ).
d. Auditory ( hearing ).
Driver perception-reaction time is defined as the interval
between seeing, feeling or hearing a traffic or highway situation and
making initial response to what has been perceived. People
generally react more quickly to very strong stimuli than to weak
one.
ENVIRONMENTAL FACTORS
Answer
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Weather and road condition also influence the
characteristics of drivers. Most of the drivers will take an extra
cautious when the road is wet and the road surface is damaged.
This condition will endanger the safety of driver.
PSHYCOLOGICAL FACTORS.
New drivers become nervous compare to the experienced
drives whenever they are driving in a crowded traffic area. They
feel safer driving through a straight road would speed more.
2. Curve resistance
As was stated earlier, once a vehicle is set in motion, it tends
to remain in motion in a straight line unless acted on by some force.
The forces changing the direction of a vehicle are imparted through
the front wheels. Components of these forces tend to impede avehicle’s forward motion. Curve resistance then is the force
required to cause a vehicle to move along a curve path. It is a
function of the radius or degree of curvature and the vehicle speed.
Air resistance.
Air resistance includes the force required to move air from a
vehicle’s pathway as well as the friction effects of air along its top,
sides, and undercarriage. It is a function of the frontal cross-
sectional area of the vehicle and the square of the vehicle speed.