Highway Alignment And Its Requirements

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The position and the location of the centerline of the highway on the ground is called highway alignment. Highway alignment includes horizontal and vertical alignment.

A wrong highway alignment could result in any of the following disadvantages on its users.

  • Increase in highway construction cost
  • Increase in maintenance cost
  • Increase in vehicle operation cost.
  • Increase in accident rate

Since it is challenging to change or alter the alignment and also very costly, it is desirable to properly design the highway alignment base on investigations and analysis.

Requirements of Good Highway Alignment

  1. Short
  2. Easy
  3. Safe
  4. Economical

Short It is desirable of having the shortest route to rich the destination. It will reduce the cost of journey and more importantly the time of journey.

Easy The alignment should be easy to construct and also it should have a lower traffic congestion problem

Safe It is obvious that alignment should be safe for the road users, otherwise it will pose problems to them.

Economical The road should have minimal vehicle operation and maintenance cost.

Components Of The Horizontal Alignment

  1. Design Speed
  2. Super Elevation
  3. Horizontal Curves – This includes transition curves and change in direction of the road.
  4. Sight Distance – There are three basic types of sight distances that should be considered.
    • Stopping Sight Distance (SSD)
    • Overtaking Sight Distance (OSD)
    • Intermediate Sight Distance
  5. Width Of Carriageway

Components of Vertical Alignment

  1. The longitudinal gradient of highway
  2. Vertical curves
  3. Sight Distance

straight alignment of highway

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