PAVEMENT DESIGN

With the determination of geometric design and both horizontal and vertical alignments in highway design, the designer can start working on the pavement design.

The two major types of pavement are:

1. Flexible pavement - using asphalt as surface
2. Rigid pavement - using concrete as surface

Formulae for solving thicknesses of pavements on both types are long for manual computation so AASHTO deviced a graphical solution for thickness determination through nomographs.

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VERTICAL ALIGNMENT

Vertical alignment is the rise or fall of the curves in a highway. Similar with horizontal alignment or the curving to the left or right of the highway curve, the critical parameter for this alignment is the sight distance - stopping and overtaking.

The only difference with the relation of sight distance with the length of the curve is the number of cases where

1. S>L
2. S<L where        S = sight distance and L = length of curve

The two kinds of vertical curves are:

1. Summit (aka, crest curve, and oververticals) = curve which concaves upwards

2. Valley (aka, sag curve, and underverticals)   = curve which convexes upwards.

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HORIZONTAL ALIGNMENT OF HIGHWAYS

Alignment is one of the geometric elements of a highway. The two kinds are horizontal alignment and vertical alignment. The former alignment consists of the different curves that can be laid out horizontally. The two main types of horizontal alignment and their subclasses are:

credits from Wikipedia

1. Circular curves

• Simple curve
• Compound curve
• Broken back curve
• Reverse curve

2. Easement curves

• Spiral between tangent and circular curve
• Double spiral
• Spiral between circular curves

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GEOMETRIC DESIGN OF HIGHWAYS

Highways have various geometric factors. These factors are the supplemental parameters in constructing a highway. These are:

credits from Japan Times

• Design speed
• Sight distances
• Minimum radius of curvature
• Superelevation
• Vehicle cornering
• Design volume
• Number of lanes

Apart from designing the actual curve for a highway, these factors are needed to make the curve safer for travel.

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BASIC CONCEPTS OF HIGHWAY ENGINEERING

Transportation is important for the advancement of the nation. It is essential for the general development and economic prosperity. It is also important for strategic movement in emergency for defense of the country and to maintain better law and order.

courtesy of US PIRG

Different surveying procedures to locate a highway are introduced in advanced geomatics. The working factors to locate these transportation networks are:

• The purpose of construction
• Present and future traffic volume
• Available funds
• Acquisition for road right of way

The different classifications of highways run around mobility and access. Highways are classified into three:

1. Arterials

2. Collectors

3. Local streets

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HIGHWAY ENGINEERING

Highway engineering is a subset of transportation engineering with the prerequisite subjects of basic to advanced geomatics. All of which are important components of civil engineering. The two main metrics of quality of highways are:

• Efficiency - delay, travel time, speed, other operational characteristics
• Safety - collisions, fatalities

Highway engineering is a multidisciplinary field with interconnected sudisciplines which include planning, design, operations, and safety with other related fields such as structural engineering, hydraulic engineering, and geotechnical engineering.

The course includes:

• Introduction
• Basic concepts of highway engineering
• Geometric design of highways
• Horizontal alignment
• Vertical Alignment
• Pavement analysis
• Pavement design