Module 3
CET 206
TRANSPORTATION
ENGINEERING
Reuben Jacob Chacko
Assistant Professor
Department of Civil Engineering
STCET
reuben@stthomascollege.ac.in
Reuben Jacob, Dept. of CE
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SYLLABUS
Module
Contents
Hours
Introduction to Transportation Engineering, Classification of roads, Typical
cross sections of roads in urban and rural area, Requirements and factors
controlling alignment of roads.
1
Introduction to geometric design of highways, Design controls and criteria,
10
Design of highway cross section elements, Design of horizontal alignment Stopping sight distance, Overtaking sight distance, super elevation, transition
curve, length and shift of transition curve, extra widening.
Vertical alignment (introduction only)
Introduction to highway materials, Desirable properties and testing of road
aggregates, bituminous materials and sub grade soil.
2
Introduction of flexible and rigid pavements, Factors influencing the design of
10
flexible pavements, Design of flexible pavements by CBR method and IRC 37:
2018. Construction of bituminous pavements
Introduction to traffic engineering, Traffic characteristics, Capacity and Level
3
of Service, Design Speed, Traffic surveys, Types of road intersections, Traffic
Control devices (introduction only), Design of isolated signals by Webster’s
7
method.
Railway Engineering - Component parts of a railway track - functions, concept
of Gauges, coning of wheels, cant deficiency, compensation of gradients
Tunnel Engineering: Tunnel – sections, tunnel surveying - alignment,
4
transferring centre grade into tunnel.
9
Harbours – classification, features, requirements. Break waters - necessity and
functions, classification.
Docks – Functions and types - dry docks, wet docks ( Introduction only)
Introduction to Airport Engineering, Components of airport, selection of site
5
for airport.
9
Runway orientation, basic runway length and corrections required, Taxiways
and aprons.
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MODULE-3
TRAFFIC ENGINEERING
3.1 TRAFFIC CHARACTERISTICS
It includes:
1) Road user characteristics
2) Vehicular characteristics
1. Road User Characteristics

Road users: Pedestrian, cyclist or driver

The physical, mental and emotional characteristics of human being affect the traffic operation.

The various factors which affect the road user characteristics are
a) Physical
b) Mental
c) Psychological
d) Environmental
a) Physical characteristics
It includes:
•
Vision – eye movement, day vision and night vision and depth of judgment affect
the traffic operation
•
Hearing - Help to gather sound and information. Useful for cyclist and pedestrian
•
Strength - useful for heavy vehicles
•
Reaction time – important in stopping distance
b) Mental characteristics
It includes:
•
Skill – skilled driving reduces traffic problems
•
Knowledge – knowledge about vehicle, traffic behavior, rules of road
•
Intelligence – to understand critical situation and act in emergency situation
•
Experience- experienced drivers can avoid traffic problems
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c) Psychological characteristics
It includes

emotional factors such as fear and anger, impatience and general attitude toward
traffic and regulations
d) Environmental characteristics
It includes

Traffic stream – mixed traffic or heavy traffic

Traffic facilities – overtaking facility, parking facility etc

Atmospheric condition – rain, darkness etc
2. Vehicular Characteristics

It affects the design and traffic performance

It includes
1) Static characteristics
2) Dynamic characteristics
1) Static characteristics

It includes
1. Vehicular Dimensions
2. Weight and Power
3. Turning angle
1. Vehicular dimensions

Height – affects clearance of overhead structures like electric line, over
bridge etc

Width – affects width of traffic lane, shoulder and parking lane

Length – affects capacity, overtaking distance etc
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Table: Maximum values of dimension are given by IRC
Dimensions
Width
Details
Value (m)
All vehicle
Single deck
Height
vehicle
Double deck
vehicle
Length
2.5
38
4.75
Single unit truck
11
Tractor trailer
18
2. Weight and Power of vehicle
•
Affect design of pavement, thickness and gradient
•
Govern the limiting gradient and affect the speed and acceleration
3. Turning angle
•
affects the radius of curve
2) Dynamic characteristics


It includes

Speed

Acceleration

Braking characteristics
Speed of vehicle – affects the stopping distance, super elevation, length and radius of
horizontal and vertical curve, width of road, gradient etc.

Braking characteristics – affects the stopping distance, capacity and overtaking
distance
3.2 TRAFFIC STUDIES

To analyses the traffic characteristics, designing pavement and planning
traffic systems traffic studies should be conducted

Various studies that are conducted:
1. Traffic volume study
2. Speed study
3. Origin and destination study
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4. Traffic flow characteristics
5. Traffic capacity study
6. Parking study
7. Accident study
1. Traffic volume study

Number of vehicles crossing a station per unit time – vehicles per day or vehicles per
hour

It represents the flow of traffic

Traffic volume vary hourly, daily or seasonally

Studied by counting the vehicle by:
1) Mechanical counter – automatically record the number
2) Manual counting
2. Speed study

It studies the speed of vehicle in the traffic – by enoscope method, graphic record
method or electronic meter method

It studies delay of vehicles and its causes – by floating car method, license plate
method or by interview method
3. Origin and Destination study

It studies the number of vehicles and their origin and destination

It gather information about number of passenger, purpose of trip, intermediate stop
and reason

Studied by – road side interview method, license plate method, tag on car method or
home interview method
4. Traffic flow characteristics

It studies the traffic maneuver like diverging, merging, crossing and weaving 
5. Traffic capacity study

It gives the maximum capacity of a road section

Capacity depends on lane width, width of shoulder, presence of commercial vehicle etc
6. Parking study
It studies the

Parking demand – number of vehicles accumulated over an area
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
Parking characteristics– parking practice, parking pattern and parking problem

Parking space – location and space required for parking 
7. Accident study
It studies

Causes of accident

Zone of accident

Report of each accident – it includes
•
Location of accident
•
Details of vehicle
•
Nature of accident
•
Road and traffic condition
•
Causes of accident
•
Accident costs
3.3 ROAD INTERSECTION

Type of intersections:
1) Intersection at grade
2) Grade separated intersection
1) Intersection at grade

Road meet at same level

Merging, diverging and crossing involved 

Types of intersection at grade
1) Un-channelized intersection
2) Channelized intersection
3) Rotary intersection
a) Un-channelized intersection

Lanes are not separated by channel divider

Vehicles have no restriction to use any part of intersection

One of the crossing vehicle have to stop while other proceeds

More conflicts
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Un-channelised intersection
b) Channelized intersection

Lanes are separated by channel divider

Vehicles have restriction to use any part of intersection

One of the crossing vehicle have to stop while other proceeds

Less conflicts than un-channalised
Channelized intersection
c) Rotary intersection

All converging vehicle are forced to move around a large central island in
clockwise direction and they can move out of flow into their respective
direction

Eliminate stopping of vehicle

Reduce conflict
Rotary intersection
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2) Grade separated intersection

Intersecting roads are separated by over pass or under pass

Overpass – when highway is taken above ground level by an over bridge

underpass – when highway is taken below ground level by an under bridge
3.4 FUNDEMENTALS OF TRAFFIC ENGINEERING

Spot speeds can be divided into
1) Time mean speed
2) Space mean speed
1) Time mean speed (𝑣𝑡 ):

It is defined as the average speed of all the vehicles passing a point on a highway
over some specified time period. This is average of spot speeds.
𝒗𝒊
𝒗𝒕 =
𝒏
2) Space mean speed (𝑣𝑠 ):

Space mean speed (𝑣𝑠 ) is defined as the average speed of all the vehicles
occupying a given section of a highway over some specified time period.

This is the harmonic mean of spot speed.
𝒗𝒔 =
𝒏
𝟏
𝒗𝒊
Relation between 𝑣𝑡 & 𝑣𝑠 :
𝒗𝒕 = 𝒗𝒔 +
𝝈𝟐
𝒗𝒔
where 𝝈 = standard deviation
Both mean speeds will always be different from each other except in the unlikely
vehicles are traveling at the same speed.
Example: Three vehicles pass a mile stone at 50, 40 and 35.3 kmph, respectively. What is
the time mean speed and space mean speed of three vehicles?
Sol: Average time mean speed,
𝒗𝒕 =
𝒗𝒕 =
Reuben Jacob, Dept. of CE
𝒗𝒊
𝒏
𝟓𝟎+𝟒𝟎+𝟑𝟓.𝟑
𝟑
= 41.77 kmph
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Average space mean speed,
𝒏
𝒗𝒔 =
𝟏
𝒗𝒊
𝒗𝒔 =
𝟑
𝟏 𝟏
𝟏
+ +
𝟓𝟎 𝟒𝟎 𝟑𝟓.𝟑
= 40.91 kmph
Traffic Density (k):

The number of vehicles occupying a unit length (1km) of a lane of road way at a
given instant.

Relation between Traffic volume (q), Traffic density (k) and Speed(v)
q=k v
Derived characteristics

From the fundamental traffic flow characteristics like flow (volume)"q", density "k",
and speed "v", few other parameters of traffic flow can be derived.

Significant among them are the time headway, distance headway and travel time.

Time Head way: Time gap between two successive vehicles which are
crossing a section on a road
𝑯𝒕 =
𝟑𝟔𝟎𝟎
𝒒
where Ht is time head way in seconds,
q = traffic flow in vehicles / hr

Distance headway: The average distance between two successive vehicles or
inverse of density and is sometimes called as 'spacing' or 'space headway’.
𝑺=
𝟏
𝒌
Traffic Capacity

It is the ability of road way to accommodate traffic volume

Capacity is maximum traffic volume or traffic now.
𝑪=
𝟏𝟎𝟎𝟎𝑽
𝑺
Where, V =speed in kmph and S -distance headway in m

Basic Capacity (Theoretical or Ideal Capacity): The maximum number of
vehicles that pass a given point on a lane or road way during one hour under
ideal road way and traffic conditions.
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
Two roads of same physical features will have same basic capacities.
S = vt +L, for theoretical capacity
where v is design speed in m/s:
t=reaction time of driver= 0.7 sec:
L= length of rigid wheel base

Practical Capacity (Design Capacity): The maximum number of vehicles that
can pass a given point so that they may not cause unreasonable delay, hazards
and restriction to driver's freedom to maneuvers under the prevailing road
conditions. It is of primary interest to the designers.
Capacity of single lane road is
S = SSD+L ; for practical capacity
where SSD= stopping sight distance
Example: The design speed of traffic lane is 80 kmph. Average length of the vehicle
6m. The capacity of the when reaction time of driver is 2sec. Coefficient of
longitudinal friction is 0.35.
Sol: S = SSD + L
SSD = 116m
S = 116 + 6 = 122 m
𝟏𝟎𝟎𝟎𝑽
𝑺
1000 × 80
=
122
𝑪=
= 656 𝑣𝑒ℎ/ℎ𝑟
Example: Traffic in a congested multilane highway lane is observed to have an
average spacing of 50 m, and an average headway of 3.6 s. Estimate the rate of flow,
density and speed of traffic in this lane.
Soln: s = 200 ft
Ht = 3.6s
𝑯𝒕 =
𝑞=
3600
𝐻𝑡
=
𝟑𝟔𝟎𝟎
𝒒
3600
3.6
= 1000 𝑣𝑒ℎ/ℎ𝑟
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𝑺=
𝒌=
=
𝟏
𝒌
𝟏
𝒔
1000
(in m)
𝑠
=
1000
50
= 20 𝑣𝑒ℎ/𝑘𝑚
q=kv
1000 = 20 x v
So v = 50 kmph
Fundamental diagrams of Traffic flow
Fundamental diagrams of Traffic flow
3.5 TRAFFIC CONTROL DEVICES

Traffic control devices includes:
1. Traffic signs
2. Traffic signals
3. Markings
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1. Traffic signs

Three types
i.
Regulatory signs
ii.
Warning signs
iii.
Informatory signs
i. Regulatory signs

These are mandatory signs

It inform certain laws, regulations and prohibitions

Violation of regulatory sign is an legal offence

Regulatory signs are classified as:
a) Stop and give way signs

Stop sign – to stop the vehicle. Octagonal in shape and red in color with a white
border

Give way sign – control the vehicle on a road so as to assign right of way to other
roadways. Triangle in shape with apex downward – white in colour with red border
b) Prohibitory sign

To prohibit certain traffic movement, use of horn or entry of certain vehicle

Circular in shape – white in colour and red border
c) No parking – no stopping sign

No parking – to prohibit parking at that place. Circular in shape – blue
background, red border and an oblique red bar at an angle of 45o

No stopping – prohibit stopping of vehicle at that place. Circular in shape – blue
background, red border and two oblique red bar at 45o and right angle to each other
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d) Speed limit and vehicle control sign

To restrict the speed of vehicle on a stretch of road

Circular in shape – white background, red border and black numerals indicating
the speed limit

Vehicle control signs – control load, length, height etc.

Circular in shape – white background, red border and black symbols
e) Restriction end sign

Indicate the point at which all restrictions indicated by signs ends here

Circular in shape with white background and a black diagonal band at 45 degree
f) Compulsory direction control signs

To direct the vehicle in appropriate direction

Circular in shape with blue background and white direction arrows
ii. Warning signs

To warn about certain hazardous conditions

Equilateral triangle in shape with apex pointing upwards.
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
White background red border and black symbols

Example: curve, hair pin bend, narrow bridge, pedestrian crossing, school zone
iii. Informatory signs

To guide the user along the roads, inform about destination, distance and provide
information to make travel easier. The information sign are grouped under the
following heads:
i.
Direction and place identification signs
ii.
iii.

Rectangle with white background, black border with black arrows and letters

Example: destination sign, place identification sign
Facility information sign

Rectangle with blue background, white or black letters or symbol

Example: public telephone, petrol pump, hospital
Parking sign

Square shape with blue background and white colored letter “P‟
2. Traffic Signals

Signal assigns right of way to one or more traffic streams

Most important and effective methods of controlling traffic
Type of traffic signal
i.
Traffic control signals
a. Fixed time signals
b. Manually operated signals
c. Traffic actuated (automatic)signals
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ii.
Pedestrian signals
iii.
Special traffic signals
i.
Traffic control signal

Traffic control signals have 3colours.

Red light: STOP

Yellow or amber: clearance time for vehicles which enter the intersection
area by the end of green time to clear-off

Green: GO

a. Fixed time signals or pre-timed signals

Set to repeat a cycle of red, amber and green lights

Timing is predetermined using traffic studies
b. Manually operated signals

In countries like India traffic police are assigned to watch and regulate the
traffic during the peak hours
c. Traffic actuated signals

Signals in which the timing of the phase and cycle are changed according to
the traffic demand.
Design of traffic signal by Webster’s method
Optimum signal cycle (The duration of signal) Co is given by
𝐶0 =
1.5𝐿 + 5
1−𝑌
Where, L is the total lost time per cycle in second
𝐿 = 2𝑛 + 𝑅
n- No of phase
R – All red time
𝑌 = 𝑦1 + 𝑦2
Where y1 and y2 are the critical flow ratio and are given by
𝑦1 =
𝑞1
𝑠1
and
𝑦2 =
𝑞2
𝑠2
q1 and q2 – Normal flow in 1st and 2nd road PCU/hr
S1 and S2 - Saturated flow in 1st and 2nd road PCU/hr
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Green time is given by
𝑦1
(𝐶0 − 𝐿)
𝑌
𝑦2
𝐺2 =
(𝐶0 − 𝐿)
𝑌
𝐺1 =
Provide amber time 2 to 4 second
Example 1: Normal flow of a traffic cross road A and B are 400 and 250 PCU/hour.
The saturated flow is 1250 and 1000 PCU/hour. The red time is 12 seconds. Design a
two phase traffic signal
Solution: Critical flow ratio
Optimum signal cycle (The duration of signal) Co is given by
𝐶0 =
1.5𝐿+5
1−𝑌
= 𝐶0 =
1.5𝑥16+5
1−0.57
= 68 sec
Green time is given by
𝐺1 =
𝐺2 =
𝑦1
𝑌
𝑦2
𝑌
0.32
(𝐶0 − 𝐿)=0.57 (68 − 16)= 29 sec
0.25
(𝐶0 − 𝐿) = 0.57 (68 − 16)= 23 sec
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Provide amber time as 2 second
Example 2: A fixed time 2-phase signal is to be provided at an intersection having
four arms. The design hour traffic and saturation flow are
North
South
East
West
Design Hour flow (pcu/hr)
800
400
750
600
Saturation flow (pcu/hr)
2400
2000
3000
3000
Time lost per phase due to starting delay is 2 sec and All red period is 4 sec. Design
two phase traffic signal using Webster`s method. Draw the phase diagram also.
The maximum value of critical flow ratio (y) in N-S direction = 0.33
The maximum value of critical flow ratio (y) in E-W direction = 0.25
Total critical ratio
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𝑌 = 𝑦𝑁𝑆 + 𝑦𝐸𝑊 = 0.33 + 0.25 = 0.58
Total lost time per cycle in second
𝐿 = 2𝑛 + 𝑅 = 2 𝑋 2 + 4 = 8 𝑠𝑒𝑐
Optimum signal cycle (The duration of signal) Co is given by
𝐶0 =
1.5𝐿+5
1−𝑌
= 𝐶0 =
1.5×8+5
1−0.58
= 40 sec
Green time is given by
𝐺1 =
𝐺2 =
𝑦 𝑁𝑆
𝑌
𝑦 𝐸𝑊
𝑌
0.33
(𝐶0 − 𝐿)=0.58 40 − 8 =18 sec
0.25
(𝐶0 − 𝐿) = 0.58 40 − 8 =14 sec
Provide amber time as 2 second
The phase diagram is as follows
3.5
ROAD MARKING

Markings made of lines, patterns, words, symbols or reflectors

It is used to control, warn, guide or regulate the traffic

Markings are made using paints in contrast with the pavement
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
Types of marking
1. Pavement marking
2. Kerb marking
3. Object marking
4. Reflector marking
1. Pavement marking

White or yellow paints are used

Some common types are center line, lane line, walk line, parking space, bus stop
etc.
2. Kerb marking

Parking regulation or any other
3. Object marking

Physical obstruction which are hazardous should be marked
4. Reflector marking

Marking for safe driving during night
3.6 TRAFFIC SURVEY

Precise surveys, studies, and scientific analysis of traffic is necessary for traffic
engineering and find wide applications in anticipating future requirements of roads,
the advancement of existing facilities, design aspects, pavement design, and traffic
guidelines and control.

Traffic surveys, better-called traffic census, covers all kinds of traffic, size, and
weight, traffic flow, traffic volume per hour, and per day, including seasonal
variations/annual variations, distribution in different parts of a road network, and
distribution in different directions at intersections.

Traffic volume counts can be obtained by the following methods:
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1) Manual Method
2) Automatic Counters
3) Pneumatic Counters
4) Electrical Counters
5) Photo-Electric Cell Counters
6) Moving Observer Method

The traffic surveys are done in three stages namely
1) Household Interview Survey
2) Traffic Survey

Roadside Interview (Origin Destination) Survey

Traffic Count Survey

Screen Line Survey

Traffic Count Survey of Major Intersection

Travel Speed Survey

Parking Survey
3) Bus Transport Survey

Bus Traffic Count Survey

Bus Origin Destination Survey

Bus Passenger Interview Survey

Public Transport Firm Interview Survey
3.7 HIGHWAY CAPACITY

Capacity is the maximum traffic flow that can be accommodated in a highway
facility during a given time period under prevailing roadway, traffic and control
conditions. (While traffic volume represents the actual rate of flow and responds to
variations in traffic demand, capacity indicates the maximum rate of flow when
exposed to a certain level of service characteristics or a number of prevailing
roadway and traffic conditions)

This is usually expressed in vehicle per hour

Highway capacity is associated with traffic volume and traffic density.
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
Traffic volume is the number of vehicles passing a given point on a roadway
during a specified time period. This is usually expressed as vehicles per hour

Traffic density is defined as the number of vehicles occupying a unit length of a
lane of a roadway at a given instant of time. This is usually expressed in vehicles
per kilometer.

It is easy to understand that traffic volume is the product of traffic density and
speed.
Importance of the Concept of Highway Capacity:
1. The capacity of a highway should be adequate to serve the needs of the projected
traffic
2. The class of highway, lane width, number of lanes and intersections are dependent on
capacity
3. Improvements on geometric elements, traffic control devices and traffic management
measures can be effectively planned based on the studies of highway capacity.
4. The adequacy of the existing highway network for the existing traffic volume can be
assessed by capacity studies; transportation planning can be done effectively using
this information.
Factors Affecting Highway Capacity
• Lane width
• Width of shoulder
• Lateral clearance
• Commercial vehicles
• Road alignment and geometry (curves, Super elevation etc)
• Existence of intersections.
• One way or two way traffic and number of lanes
• Drivers and vehicular characteristics
• Single type or mixed traffic
• Flow speed
• Weather condition
• Parking
• Presence of pedestrians
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3.8 Design Speed

Design speed, as noted earlier, is the single most important factor in the design of
horizontal alignment. The design speed also depends on the type of the road. For
e.g, the design speed expected from a National highway will be much higher than a
village road, and hence the curve geometry will vary significantly.

Design speed also depends on the type of terrain. A plain terrain can afford to have
any geometry, but for the same standard in a hilly terrain requires substantial
cutting and filling implying exorbitant costs as well as safety concern due to
unstable slopes. Therefore, the design speed is normally reduced for terrains with
steep slopes.

For instance, Indian Road Congress (IRC) has classified the terrains into
four categories, namely plain, rolling, mountainous, and steep based on the cross
slope as given in table. Based on the type of road and type of terrain the design
speed varies. The IRC has suggested desirable or ruling speed as well as
minimum suggested design speed and is tabulated in table.
Table: Terrain Classification
Terrain
Cross slope
Classification
(%)
Plain
0-10
Rolling
10-25
Mountainous
25-60
Steep
60
Table: Design speed as per IRC
Type
Plain
Rolling
Hilly
Steep
NH & SH
100-80
80-65
50-40
40-30
MDR
80-65
65-50
40-30
30-20
ODR
65-50
50-40
30-25
25-20
VR
50-40
40-35
25-20
20-15
3.9 Level of service

Level of service (LOS) is a qualitative measure used to relate the quality of motor
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vehicle traffic service.

LOS is used to analyze roadways and intersections by categorizing traffic flow and
assigning quality levels of traffic based on performance measure like vehicle speed,
density, congestion, etc.

A qualitative term that describes how good is the present traffic situation.

It can be derived from
• V/C ratio
• Mean passenger car speed
• Density

As per the HCM the LOS is divided into six categories based on the above
performance characteristics starting from LOS -A to LOS- F.

The value of v/c ratio can vary between 0 and 1.

Depending upon the travel speed and v/c ratio

HCM has defined six levels of service, level A to level F based on a graph between
operating speed and v/c ratio
• LOS A- complete free flow
• LOS B- free flow with the notice of other vehicles
• LOS C- density begins to influence traffic operation
• LOS D- speed started reducing
• LOS E- vehicles operate at minimum spacing
Reuben Jacob, Dept. of CE
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Module 3
• LOS F- operations are highly unstable
1. LOS-A

Low Volume

Low Density

High Speed

Freedom to choose speed and lane

No restrictions
2. LOS-B

Zone of stable flow

Operating speed is slightly restricted

Driver still have freedom to select their speed and lane operation
Reuben Jacob, Dept. of CE
Page 25
Module 3
3. LOS-F

Low speed

High Density

Forced or breakdown flow
Factors affecting Level of Service

Speed and travel time

Traffic interruptions/restrictions

Freedom to travel with desired speed

Driver comfort and convenience

Operating cost.

Lane width

Lateral clearance

Surface conditions

Alignment

Grades

Shoulders
Reuben Jacob, Dept. of CE
Page 26