Highway Engineering And Construction

Highway engineering and construction includes planning, designing, and building of highways. History stands witness that good roads lead to prosperity for distant societies. If a road is well planned and then executed according to the plan, a highway can open the gates of growth and development.

Highways connect two or more places and ensure that industries, employment, and development follow. Bridges, traffic lights, pavements, bike paths, and lane dividers make up a safe highway. Modern highways are known for their high capacity, efficiency, and planned construction. Highway networks are very important for the growth of a region. Highways open new trade routes and almost every industrial region in the world is connected to the major highway network system of that particular country.

The topics collected in this guide will help you understand much of the terminology and theory of modern day highway engineering and construction. By using the links in the following sections, we will learn about different aspects of highway construction, design, and planning. We begin with the history of highway construction and the major changes highway construction has undergone up to this point.

Construction, maintenance, and management 
Highway construction is generally preceded by detailed surveys and subgrade preparation. The methods and technology for constructing highways has evolved over time and become increasingly sophisticated. This advancement in technology has raised the level of skill sets required to manage highway construction projects. This skill varies from project to project, depending on factors such as the project's complexity and nature, the contrasts between new construction and reconstruction, and differences between urban region and rural region projects. 

There are a number of elements of highway construction which can be broken up into technical and commercial elements of the system. Some examples of each are listed below: 
  • Technical Elements 
  • Materials 
  • Material quality 
  • Installation techniques 
  • Traffic 
  • Commercial Elements 
  • Contract understanding 
  • Environmental aspects 
  • Political aspects 
  • Legal aspects 
  • Public concerns 
Typically, construction begins at the lowest elevation of the site, regardless of the project type, and moves upward. By reviewing the geotechnical specifications of the project, information is given about: 
  • Existing ground conditions 
  • Required equipment for excavation, grading, and material transportation to and from the site 
  • Properties of materials to be excavated 
  • Dewatering requirements necessary for below-grade work 
  • Shoring requirements for excavation protection 
  • Water quantities for compaction and dust control 
Subbase course construction 
A subbase course is a layer designed of carefully selected materials that is located between the subgrade and base course of the pavement. The subbase thickness is generally in the range of 4 to 16 inches, and it is designed to withstand the required structural capacity of the pavement section. 

Common materials used for a highway subbase include gravel, crushed stone, or subgrade soil that is stabilized with cement, fly ash, or lime. Permeable subbase courses are becoming more prevalent because of their ability to drain infiltrating water from the surface. They also prevent subsurface water from reaching the pavement surface. 

When local material costs are excessively expensively or the material requirements to increase the structural bearing of the sub-base are not readily available, highway engineers can increase the bearing capacity of the underlying soil by mixing in Portland cement, foamed asphalt, or use polymer soil stabilization such as cross-linking styrene acrylic polymer that increases the California Bearing Ratio of in-situ materials by a factor 4 – 6. 

Base course construction 
The base course is the region of the pavement section that is located directly under the surface course. If there is a subbase course, the base course is constructed directly about this layer. Otherwise, it is built directly on top of the subgrade. Typical base course thickness ranges from 4 to 6 inches and is governed by underlying layer properties. 

Heavy loads are continuously applied to pavement surfaces, and the base layer absorbs the majority of these stresses. Generally, the base course is constructed with an untreated crushed aggregate such as crushed stone, slag, or gravel. The base course material will have stability under the construction traffic and good drainage characteristics. 

The base course materials are often treated with cement, bitumen, calcium chloride, sodium chloride, fly ash, or lime. These treatments provide improved support for heavy loads, frost susceptibility, and serves as a moisture barrier between the base and surface layers. 

Surface course construction 
There are two most commonly used types of pavement surfaces used in highway construction: hot-mix asphalt and Portland cement concrete. These pavement surface courses provide a smooth and safe riding surface, while simultaneously transferring the heavy traffic loads through the various base courses and into the underlying subgrade soils. 

Hot-mix asphalt (HMA) layers 
Hot-mix asphalt surface courses are referred to as flexible pavements. The Superpave System was developed in the late 1980s and has offered changes to the design approach, mix design, specifications, and quality testing of materials. The construction of an effective, long-lasting asphalt pavement requires an experienced construction crew, committed to their work quality and equipment control. 

Construction issues: 
  • Asphalt mix segregation 
  • Laydown 
  • Compaction 
  • Joints 
A prime coat is a low viscosity asphalt that is applied to the base course prior to laying the HMA surface course. This coat bonds loose material, creating a cohesive layer between the base course and asphalt surface. 

A tack coat is a low viscosity asphalt emulsion that is used to create a bond between an existing pavement surface and new asphalt overlay. Tack coats are typically applied on adjacent pavements (curbs) to assist the bonding of the HMA and concrete. 

Portland cement concrete (PCC) 
Portland cement concrete surface courses are referred to as rigid pavements, or concrete pavements. There are three general classifications of concrete pavements - jointed plain, jointed reinforced, and continuously reinforced. 

Traffic loadings are transferred between sections when larger aggregates in the PCC mix inter-lock together, or through load transfer devices in the transverse joints of the surface. Dowel bars are used as load-transferring devices to efficiently transfer loads across transverse joints while maintaining the joint's horizontal and vertical alignment. Tie-bars are deformed steel bars that are placed along longitudinal joints to hold adjacent pavement sections in place. 

Highway maintenance 
The overall purpose of highway maintenance is to fix defects and preserve the pavement's structure and serviceability. Defects must be defined, understood, and recorded in order to select an appropriate maintenance plan. Defects differ between flexible and rigid pavements. 

There are four main objectives of highway maintenance: 
  • repair of functional pavement defects 
  • extend the functional and structural service life of the pavement 
  • maintain road safety and signage 
  • keep road reserve in acceptable condition 
Through routine maintenance practices, highway systems and all of their components can be maintained to their original, as-built condition. 

Project management 
Project management involves the organization and structuring of project activities from inception to completion. Activities could be the construction of infrastructure such as highways and bridges or major and minor maintenance activities related to constructing such infrastructure. The entire project and involved activities must be handled in a professional manner and completed within deadlines and budget. In addition, minimizing social and environmental impacts is essential to successful project management.

History of Highways - From Dirt Tracks to Highway Bridges
Animals trails and dirt tracks were the first ever roads that human beings used to travel from one place to another. Icknield Way in England, Harrappan Roads in India, and Apian Way in Rome are examples of ancient roads, and their traces can still be seen. Gradually, human beings started moving out and the condition of roads also improved with time. Today we have highway bridges as high as 245 meters from the ground level.

Various Aspects of Designing and Constructing a Highway
Planning remains the most important part of the process of engineering construction, irrespective of the nature and type of construction. Planning works are followed by design works and once designs are completed, execution works are started. Planning is important because global population is increasing at an exponential rate; globalization and technological advancements have made things easier for people, but challenging for engineers. Planning helps in estimation of risks, capacity calculation, and it enables engineers to leave scope for any future modification or expansion of roads or bridges. In this section we find insightful articles about building roads over swamps, geometric design considerations of highways, and design aspects of constructing bridges. Articles related to highway road project management are also discussed in this section.

Highway Construction Materials
Highway construction materials are selected on the basis of the type of highway, known and projected traffic density, and the climatic conditions of the region. At some places we manage with bitumen (asphalt) only, however, at some place concrete roads are required. Modern age engineers emphasize the use of eco-friendly methods to construct roads, bridges, and pavements. Maximizing the use of recycled waste products is a smart new trend that has actually helped in making better roads and highways- without doing much damage to our environment. In this group are articles about the importance of constructing green pavements using recycled waste products, using air entrained concrete in construction works, and an interesting comparison of concrete and asphalt roads.

Highway Safety Guidelines
Highway safety is an important aspect of highway construction and engineering. Designing a highway means adopting safety measures so that not only vehicular traffic stays safe, but the pedestrians and bikers also feel safe while moving on the highway. Bott's dots, traffic lights, pedestrian marking, zebra crossings, and traffic circles are some of the important aspects of highway design safety. GPS-based road traffic monitoring systems are one of the modern age inventions that make our road travel safe and efficient. Even bike traffic is also considered while safely designing the highway. Articles related to highway safety are discussed in this section.

Wrapping Up
The articles included in this guide will provide a great information source for those interested in highway design and construction processes. These articles cover the most fundamental aspects of transportation engineering and also let you know about major design and planning considerations related to highway safety and operations. 

Are there additional topics in road construction, maintenance, and design that you would like to see covered at Bright Hub? If so, please add your suggestions in the comments section below. Please note that comments are moderated and will take some time to appear.

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