Factors affecting highway alignment | Requirement of Highway alignment

What is Highway alignment?

A highway alignment may be defined as a position occupied by the centerline of the road on the ground. It is just laying down the road on the ground. There are different factors that affect the highway alignment described below.

Highway alignment may be classified as,

  • Horizontal alignment
  • Vertical alignment

1) Horizontal alignment:- It is the projection of highway alignment on a horizontal plane & covers a straight path, horizontal deviation & curves.

2) Vertical alignment:- It is the projection of highway alignment on a vertical plane & covers the change in slope & vertical curves.

Requirement of Highway alignment

The basic requirements of an ideal highway alignment are as follows.

1) Short:- Highway alignment should be as short as possible.

2) Easy:-Highway alignment should be in such a way that it should be easy in construction, maintenance & vehicle operating costs.

3) Safe:- It should have safe geometric features for traffics operation and it also should be safe in construction, maintenance & vehicle operation,

4) Economical:-

  • It should be economical in construction.
  • It should be an economical in-vehicle operation cost.
  • It should be economical in maintenance (Both traffic & non-traffic).
  • It should serve the maximum community.

Factors affecting highway alignment

Factors affecting highway alignment | Requirement of Highway alignment

The shortest route is the best route but due to different factors alignment get deviated from the short route. The factors due to which alignment is to have deviated are

1) Obligatory points through which highway is to pass

2) Obligatory points through which highway is not to pass

3) Composition of traffic

4) Geometric features

5) Economy

6) Others

  • The necessity to breakdown monotony
  • Political pressure
  • Defense purpose
  • Foreign territory

Let us describe all the factors of highway alignment one by one.

1) Obligatory point through is the highway is to pass:-

  • An industrial area or mine zone to which a highway is to serve additionally.
  • Tourist spot
  • Bridge site
  • Hill pass
  • Link with the intermediate town.

2) Obligatory point through highway is not to pass:-

  • Marshy land
  • waterlogged area etc.
  • Historically & archeologically important property.
  • Restricted zone for defense, national security.
  • Costly structural elements requiring heavy compensation
  • Densely populated area.

3) Composition of traffic

For a highway with intensive heavy vehicles and a high volume of traffic, alignment yielding a minimum length of steep ascends is much more reliable than the shortest route.

Similarly, a highway leading to a recreation spot, picnic spot, or tourist spot which might have been predominant by light passenger car and few buses alignment may be chosen with a higher slope.

4) Geometric features

The permissible limit of descending slopes, sight distances requirements, degree curvature and bends, the width of the road and so many other dimensional features of the road also may b dictate alignment.

5) Economy

The alignment finalized on the basis of the above requirements should be economical i.e highway alignment can be deviated to make construction cost economical, maintenance cost economical, vehicle operation cost economical.

I hope this article on “ Factors affecting highway alignment ” remains helpful for you.

Happy Learning – Civil Concept

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