This document describes the typical components and layers of a road model, including: - An embankment to support the road structure above the surrounding ground. - A sub-grade layer of compacted soil to evenly support the layers above. - A base layer of crushed rock to further support and allow for drainage. - A pavement surface layer of either asphalt or concrete to bear traffic loads and protect underlying layers.

1. TYPICAL ROAD
MODEL
TRANSPORTATION ENGINEERING

2. TYPICAL ROAD
MODEL
TRANSPORTATION ENGINEERING
SUBMITTED BY:
SAAD ULLAH UW-11-CE-BSC-026
SHEHZAD KHAN UW-11-CE-BSC-035
HAMZA ANWAR UW-11-CE-BSC-033
MUHAMMAD KAMRAN UW-11-CE-BSC-040
ARSALAN KHAN UW-11-CE-BSC-025
WASEEM AHMAD UW-11-CE-BSC-R-27
SUBMITTED TO:
MADAM BUSHRA ATTA
Wednesday, June 11, 2014

3. Introduction:
• A road is a thorough fare, route, or way on land between two places, which has
been paved or otherwise improved to allow travel by some conveyance, including a
horse, cart, or motor vehicle.
• The Organization for Economic Co-operation and Development (OECD) defines a road
as "a line of communication (travelled way) using a stabilized base other than rails or air
strips open to public traffic, primarily for the use of road motor vehicles running on their
own wheels," which includes "bridges, tunnels, supporting structures, junctions,
crossings, interchanges, and toll roads.
•

4. Functions :
• One of the primary functions of a pavement is load distribution which can be
characterized by the tire loads; tire configurations; repetition of loads; distribution of
traffic across the pavement; and vehicle speed.
• Several elements make up the roadway.
• Each layer represents one of the elements of the pavement system.
• All these elements work together to provide a quality durable pavement.

5. Embankment:
 When roads are built higher than the surrounding ground, a structure of compacted earth
called an embankment is built.
 The embankment is built to support the other three layers of the pavement system.
 Embankments can be made from almost any common type of deposit except topsoil.
Sub-grade:
 The sub-grade is made of soils that have been specially prepared to meet the requirements to
support the other two layers.

6.  The sub-grade is a selected soil material that is carefully compacted to provide uniform support to
the pavement.
 The sub-grade lies directly on either the embankment or the native soil.
Base:
 The base is a mixture of crushed rock.
 The base layer provides uniform support to the pavement and allows water that
penetrates any joints or cracks in the pavement to move quickly to the sub-drain without
saturating and softening the sub-grade.
 The base layer lies directly on top of the sub-grade and is built of clean sand or rock.
Pavement:
 The top layer is the pavement.
 The pavement materials can either be Hot Mix Asphalt (HMA) and Portland Cement
Concrete (PCC).
 The pavement itself resists bending, and distributes vehicle weights over a large area.
Sub-Drain:
 The sub-drain collects water from the base and the sub-grade and drains that water.
 The sub-drain is basically a perforated pipe near the bottom, surrounded by clean coarse-
size rock which allows rapid transportation of water.
Types of road/pavement:
1. Flexible road/pavement
2. Rigid road/pavement

7. 1. FLEXIBLE ROAD/PAVEMENT
 Flexible pavements are those which are surfaced with bituminous (or asphalt) materials.
 Its "flexible" since the total pavement structure "bends" or "deflects" due to traffic loads.
 Generally this type of pavement requires some sort of maintenance or rehabilitation every
10 to 15 years.

8. Material layers are usually arranged in order of descending load bearing capacity with the highest load
bearing capacity material (and most expensive) on the top and the lowest load bearing capacity material
(and least expensive) on the bottom.
Sub-base Course:

9.  This is the layer (or layers) under the base layer.
 A sub-base is not always needed.
 A proper sub-base consists of various sizes of crushed stone aggregate, commonly known
as “crusher run”.
 Depending on the sub soils on your site you may need 8-12 inches of various sizes of
sub-base.
 It functions primarily as structural support but it can also help:
a) Minimize the intrusion of fines from the sub-grade into the pavement structure.
b) Improve drainage.
c) Minimize frost action damage.
d) Provide a working platform for construction.
 The sub base generally consists of lower quality materials than the base course but better
than the sub-grade soils.
Base Course:
 The first coat to be placed, on top of your proper sub-base, is the base course .
 It provides additional load distribution and contributes to drainage and frost resistance.
 The base is built of clean sand or rock.
 The base layer provides uniform support to the pavement and allows water that
penetrates any joints
 After the binder is put into place with paver, it is compacted with a vibratory roller for
tighter density and added strength.
 Base courses are usually constructed out of:
i) Aggregate: Base courses are most typically constructed from durable aggregates
that will not be damaged by moisture or frost action.
ii) HMA: In certain situations where high base stiffness is desired, base courses
can be constructed using a variety of HMA mixes.

10. Crush Runer
Surface Course:
 This is the top layer which comes in contact with traffic.
 It normally contains the highest quality materials.
 It serves to prevent the entrance of excessive quantities of surface water into the
underlying base & sub-grade.
 It is sometimes subdivided into two layers:
i) Wearing Course: A layer in direct contact with traffic loads. It is meant to take the
impact of traffic wear and can be removed and replaced as it becomes worn.
ii) Intermediate/Binder Course: It's main purpose is to distribute load. It may compose of
one or several HMA sub layers.
 Hot mix asphalt (HMA) is "the black stuff" used as a pavement material.
 Its a combination of aggregate and asphalt binder mixed together at elevated temperatures
that forms a hard, strong construction material when cooled to suitable temperatures.
 Also known as "asphalt concrete" (AC), "asphalt", "blacktop" or "bitumin“.
 when it is well mixed, it is laid down on the roadway as pavement.
 The pavement must then be compacted to achieve uniform density.
 If this is not done properly, it can reduce the life time of the pavement and increase the
costs of maintaining the road.
 It usually costs less.

11.  The life expectancy of an asphalt pavement is between 15 to 20 years.
2. Rigid Pavement:
 Rigid pavement composed of a PCC surface course.
 Such pavements are "stiffer" than flexible pavements due to the high modulus of
elasticity of the PCC material.
 Further, these pavements can have reinforcing steel, which is generally used to reduce or
eliminate joints.
 Because of its relative rigidity, the pavement structure distributes loads over a wide area
with only one, or at most two, structural layers.
 This type of pavement can serve 20 to 40 years with little or no maintenance or
rehabilitation and often used in urban and high traffic areas.

12. Sub-base Course:
 This is the layer (or layers) under the base layer.
 The properties and function of this layer are similar to as in flexible roads/pavements.
 A sub-base is not always needed and therefore may often be omitted (OPTIONAL
DEPENDING ON SUBGRAGE OR SOIL).
Base Course:
 This is the layer directly below the PCC layer and generally consists of aggregate or
stabilized sub-grade.
 It provides additional load distribution, contributes to drainage, uniform support to the
pavement and a stable platform for construction equipment.
 Base courses are usually constructed out of:
a) Aggregate base.
b) Stabilized aggregate or soil.
c) Dense-graded HMA.
d) Lean concrete
Surface Course:
 The surface course is the layer in contact with traffic loads.
 It consists of the PCC slab which is the stiffest layer and provides the majority of
strength.
 The surface course can vary in thickness but is usually between 150 mm (for light
loading) and 300mm (for heavy loads and high traffic).
 Portland cement concrete is used as pavement material.
 Portland cement concrete is made by mixing portland cement with water, and coarse-
and fine-size rocks.
 It initially can be more expensive.
 The life expectancy of portland cement pavement varies, as little as 20 years or more
than 40 years.

13. FACTORS AFFECTING LIFE OF PAVEMENT :
There are several factors that affect pavement life:
 Traffic volume
 Quality of materials used
 Construction practices, and
 How well the other layers of the road perform.
ROAD FINISHES :
 Hard Shoulder:
 Continuous strips alongside pavements, which vehicles may drive during emergencies.
 Normally 3 m wide to fulfilled the functions of the slow lane.

14.  Kerbs:
 To define the limits of carriageway.
 It is the dividing line between carriageway and footpath.
 Drainage- Surface and Subsurface:
 Road Chamber – Cross falls.
 To cope with heavy water run-off during a storm.

15.  Street lamps:
 Street lamps are designed to illuminate the surrounding area at night, not only as a
deterrent to criminals but also to allow people to see where they're going.
 Road Markings:
 This furniture is any kind of device or material that is used on a road surface in order to
convey official information.
 They provide guidance and information to drivers and pedestrians.

16.  They can be used to delineate traffic lanes or serve as noise generators when run across a
road.
 Traffic Signs:
 They warn drivers of upcoming road conditions such as a "blind curve", speed limits, etc.
 Direction signs tell the reader the way to a location.

17.  Direction signs are usually mounted on poles.
 Illumination is added in order to aid nighttime users.