HIGHWAY ALIGNMENT

 HIGHWAY ALIGNMENT

Positioning or the layout of central line of highway on the ground is known as alignment. A horizontal alignment includes straight paths, horizontal deviations and curves. Vertical alignment involves changes in vertical curves of roads.

REQUIREMENTS FOR HIGHWAY ALIGNMENT

A conventional highway alignment should satisfy the following requirements to fulfil the need of an ideal alignment:

• short: A short alignment serves ground for practical applications keeping aside the fact that while designing there are certain factors which do not allow the laying down of the shortest path.
• easy: An ideal highway alignment should be easy to construct and must allow easy operation of vehicles on gradients.
• safe: The highway alignment should be safe for construction and functioning of gradients and slopes more particularly for areas with mountain slopes and embankments.
• economical: And last but not least, the alignment should be economical for construction which is only considered if the overall cost of construction is the lowest.

FACTORS CONTROLLING ALIGNMENT

The following factors are responsible for controlling the alignment of a highway:

• Obligatory points
• Traffic
• Geometric Design
• Economics 
• Others

Obligatory points: Obligatory points are referred as control points which help in governing the alignment of highways. They are broadly classified in two categories:

• Points through which the alignment is to pass
• Points through which the alignment should not pass

Traffic: The alignment should be done to satisfy the traffic conditions in that particular area. Origin and destination points should be laid down in accordance with the desired lines showing the trend of traffic flow and must also keep in mind the future trends.

Geometric design: Geometric factors play a huge role in determining the alignment of a highway. Traditionally the idea is to provide an alignment as straightforward as possible. In that case the geometric design is supposed to be as straight and simple as possible. If necessary, adjustments should be made to the horizontal alignment of the road keeping in view the minimum radius of curve and transition curves.

Economics: Alignment is finalized on the factor that the overall design is economical. Economy as a whole takes into consideration, the cost of construction, maintenance and transportation. 

Others: Other factors usually undertake drainage conditions, politics or other hydrological factors.