Geometric Design Of Highway

Introduction

Since the attainment of independence, Nigeria has witnessed rapid economic and social development, which has open up the need for travelling between cities which led to increase in the need for good and safe road. Highway is any public road or other public way on land; the term exists in distinction to waterway also can said to be high-speed roads designed to connect major cities. A highway is a major road for any form of motor transport which vehicles and the public in general may lawfully pass without license. A road on the other hand is a way for vehicle and other types of traffic (human or animal) which may or may not be lawfully usable to the public at large. Highways are vitally important to a country’s economic development. The construction of a high quality road network directly increases a nation’s economic output by reducing journey times and costs, making a region more attractive economically. The actual construction process will have the added effect of stimulating the construction market. Roads could be considered as a cause and the consequence of civilization, as they both precede and follow it.

1.1 Historical Background of Road

The need for road construction came up with the invention of the wheel some 5000 years ago. Prior to this invention, people and transportation beast simply moved on tracks which were only wide enough for their comfort. With the invention of the wheel, there was the need for improvement on the existing tacks to provide firmer and wider surfaces with better riding qualities to accommodate higher volume of traffic. These improvements were carried out in order to increase the safety and speed of conveying people and goods from one place to another for social and commercial purposes.

Road transport is one of the most common mode of transport. Roads in the form of track ways, human pathways etc. were used even from the pre-historic times. Since then many experiments were going on to make the riding safe and comfort. Thus road construction became an inseparable part of many civilizations and empires. The need for road construction came up with the invention of the wheel some decades ago. Prior to this invention, people and transportation beast simply moved on tracks which were only wide enough for their comfort. With the invention of the wheel, there was the need for improvement on the existing tacks to provide firmer and wider surfaces with better riding qualities to accommodate higher volume of traffic. These improvements were carried out in order to increase the safety and speed of conveying people and goods from one place to another for social and commercial purposes.

There are many different types of highways. Highways differ primarily in the amount of access control they have and, therefore, in the amount of traffic they are designed to carry. Highway with fully controlled access can handle the most traffic and are built to the highest construction standards. Inter-state highways. Vehicles that enter or exit these types of highway can do so only at certain points along the highway, generally by using special entrance and exit ramps. The ramps allow vehicle to access the road without disturbing the flow of traffic. Incoming vehicles must merge with flowing traffic, and vehicles leaving the highway use exit ramps that guide them off the highway without blocking the traffic behind. Intersections with other roads are avoided by using either bridge known as overpasses to carry one roadway under another. Finished strips called shoulders on the edges of highways allow drivers of disabled vehicles to make repairs or await assistance without blocking traffic.

1.2 The Purpose of Highway

The purpose of the highway is to provide a means of reducing the stress or pressure due to a wheel load to the minimum value which the ground under the structure can support. This is why materials of the highest strength are used for the surface. Other purposes of highway are listed below:

1. It provide a skid resistance surface
2. It provide wider riding surface to accommodate anticipated traffic volume
3. It provide a firmer riding surface ands
4. It provide a smooth riding surface
5. It provide efficient and convenient movement of people and goods from one place to another.

The intensity of the stress is greatest at the surface of the road and it is distributed in a pyramid from down the depth of the formation. As long as the stress reaching the sub grade does not exceed the resistance put forth by the sub grade, there will be no distortion or damage to the road surface.

1.3 Geometric Design

Geometric design is defined as the design or proportioning of the visible elements of the street or highway. The geometry of the roadway is of central importance since it provides the framework for the design of other highway elements. In addition, the geometric design establishes the basic nature and quality of the vehicle path, which has a primary effect upon the overall safety characteristics of the street or highway.

The design of roadway geometry must be conducted in close coordination with other design elements. These other elements include: pavement design, roadway lighting, traffic control devices, transit, drainage, and structural design. The design should consider safe roadside clear zones, bicycle and pedestrian safety accommodation, emergency response, and maintenance capabilities.

The geometric design of highways deals with the dimensions and layout of visible features like of the highway. The emphasis of the geometric design is to address the requirement of the driver and the vehicle such as safety, comfort, efficiency, etc. The features normally considered are the cross section elements, sight distance consideration, horizontal curvature, gradients, and intersection. The design of these features is to a great extend influenced by driver behavior and psychology, vehicle characteristics, traffic characteristics such as speed and volume. Proper geometric design will help in the reduction of accidents and their severity. Therefore, the objective of geometric design is to provide optimum efficiency in traffic operation and maximum safety at reasonable cost. The planning cannot be done stage wise like that of a pavement, but has to be done well in advance. The main components that will be discussed are:

Design speed

Design vehicle

Safety

Sight distance

Alignment

Capacity

The safety characteristics of the design should be given primary consideration. The initial establishment of sufficient right of way and adequate horizontal and vertical alignment is not only essential from a safety standpoint, but also necessary to allow future upgrading and expansion without exorbitant expenditure of highway funds.

1.4 Classification of Roads

Roads can be classified in many ways. The classification based on speed and accessibility is the most generic one. Note: As the accessibility of road increases, the speed reduces. Accordingly, the roads can classify as follows in the order of increased accessibility and reduced speeds.

Freeways

Expressways

Highways

Arterials

Local streets

Collector’s streets

Freeways:

Freeways are access controlled divided highways. Most freeways are four lanes, two lanes each direction, but many freeways widen to incorporate more lanes as they enter urban areas. Access is controlled through the use of interchanges, and the type of interchange depends upon the kind of intersecting road way (rural roads, another freeway etc.)

Expressways:

They are superior type of highways and are designed for high speeds (120 km/hr. is common), high traffic volume and safety. They are generally provided with grade separations at intersections. Parking, loading and unloading of goods and pedestrian traffic is not allowed on expressways.

Highways:

They represent the superior type of roads in the country. Highways are of two types – rural highways and urban highways. Rural highways are those passing through rural areas (villages) and urban highways are those passing through large cities and towns, i.e. Urban areas.

Arterials:

It is a general term denoting a street primarily meant for through traffic usually on a continuous route. They are generally divided highways with fully or partially controlled access. Parking, loading and unloading activities are usually restricted and regulated. Pedestrians are allowed to cross only at intersections/designated pedestrian crossings.

Local Streets:

A local street is the one which is primarily intended for access to residence, business or abutting property. It does not normally carry large volume of traffic and also it allows unrestricted parking and pedestrian movements.

Collector’s Streets:

These are streets intended for collecting and distributing traffic to and from local streets and also for providing access to arterial streets. Normally full access is provided on these streets. There are few parking restrictions except during peak hours.

1.5 Background and Purpose

Highway geometry should be designed for vehicle traffic safety and efficiency, particularly on the trunk roads or Expressways on which traffic function must be most important. Though the design policy was established, the prerequisites of design have been imaginary or extremely limited. For example, minimum radius of horizontal curve is defined with design speed, super elevation and side slip friction factor. The actual operating speed must correspond to something speed, but it did not work well to be used for design purpose of road geometry, or did not calibrated enough because of the difficulty of data acquisition. Such an estimation model should have a feature including driver’s perception and behavior.

1.6 Aim and Objectives of the Study

1. The aim of the study is to perform the geometric design of a selected case study road and comparison between Manual and Automated design.
2. The objectives required to achieve the above aim include:
3. Design of all vertical alignment components
4. Design of all horizontal alignment components
5. Comprehensive plan and profile detailing of the case study road.

1.7 Scope of Study

The scope of this study covers the geometric design of highway at Anka road, bukkuyum L.G.A Zamfara State. Using manual design and comparing with automated design.

1.8 Outline of Study

For a proper understanding of this project report it has been divided into five chapters. Chapter one introduced the project; chapter two discusses the relevant literature in respect to this project. Chapter three contains the design methods of highway designed detail. Chapter four contains the result and analysis and finally recommendations and conclusion based on findings is shown in chapter five.