Question

Write paraphrase of this:

Task1:
Highway alignment is the center line of the highway or the road on the ground. The road alignment is very important because when they not prepare it carefully it will cause high building cost, high maintenance cost and also, an increase in accident. There are requirement of high alignment like safe, easy, short and economical. And there are also factors that should be considered when choosing road alignment. These factors differ and depend on the type of road and the areas through which these roads pass. In this part we will concentrate on or obligatory points which is defined the highway alignment. It is separated into two parts, negative and positve obligatory points.
positve obligatory points:
these are those points through which the alignment should pass.
Existing road: the alignment should be fixed such the newly construction road should link to the existing road.
Intermediate town: if it is possible to have a straight road between point A&B and the intermediate town located at c, then the street need to link the intermediate town reducing the change in highway alignment.

Bridge site/Existing Bridge:
This is not adivicable to cross the river in a curve position, we have to change the alignment in such a way that it crosses the river in straight line, it should locate in right angle(90o) to the river flow and not locate in curve position. There are some reasons for this, the curve position they keep changing, when you make the right angle the length of the barge it will be short. So, the cost of this construction it will be less.   

Negative obligatory points:
When I went to the site and I saw lake or water body , I have to change this aligment to avoided the lake area. From the stragth line to curve line because of the water body. So, this water body is a Negative obligatory

Answer 1

FACTORS CONTROLLING SELECTION OF ROAD ALIGNMENT

There are a number of factors which are to be considered while selecting the alignment of roads. These factors also vary according to the type of roads and the areas through which these roads pass.

1. CLASS & PURPOSE

The alignment of the road may be decided keeping in mind the class and purpose of the road. National and state highways between two stations should be aligned as straight as possible whereas in the case of other types of roads, deviation may be permitted where found necessary.

2. OBLIGATORY POINTS

The roads are basically constructed for the development of the areas. Their alignments should necessarily pass through important towns, group of villages and places of religious, social, political and commercial importance.

3. TYPE OF VEHICULAR TRAFFIC

The alignment should be provided according to the type of vehicular traffic. In case of fast moving traffic, the road alignment should be as straight as possible whereas in case of bullock carts, tongas, etc, the alignment may even have sharp bends.

4. GRADIENT

The alignment of roads should be selected so that longitudinal slopes are not steeper than ruling gradient. To achieve this, the alignment might need a deviation from straight line.

5. HORIZONTAL CURVES

The alignment of roads should be provided with flat curves wherever found necessary. In case of national and state highways, the radius of horizontal curve should not be less than 230 m. in order to have minimum radius the alignment must be changed.

6. SIGHT DISTANCE

The alignment of roads should be decided such that minimum sight distance is available for drivers of the vehicles.

7. OBSTRUCTIONS

The alignment of roads is decided keeping in mind the obstruction. For example, the alignment should be changed to avoid marshy land, ponds, wells, graveyards, historical monumental and religious sites etc.

8. CROSS DRAINAGE WORKS

The alignment should be adjusted so that minimum numbers of cross drainage work are required. To achieve this, the alignment should be chosen along the water shed line if possible.

9. BRIDGES

While crossing river, the sites should provide all the requirements needed for a good bridge construction. The alignment of the road should cross the river at 90⁰ to avoid construction of skew bridge.

10. RAILWAY CROSSING

A road alignment should cross a railway preferably at 90⁰.

11. FORMATION BED

The selected alignment should be through such areas which provide good formation bed.

12. EARTH WORK

To avoid excessive cutting and filling, the alignment should be changed where found necessary.

13. AGRICULTURAL LAND AND DENSE FORESTS

The alignment of roads should be decided so that costly agricultural land and dense forests are avoided for the acquisition of the land.

14. EXISTING RIGHT OF WAY (ROW)

In case upgrading a road, its existing right of way should be utilized for curtailing the cost of land acquisition.

15. PUBLIC DEMAND

The selected alignment of the road should meet the public demand of the area.

Highway alignment

Once the necessity of the highway is assessed, the next process is deciding the alignment. The highway alignment can be either horizontal or vertical and they are described in detail in the following sections.

Alignment

The position or the layout of the central line of the highway on the ground is called the alignment. Horizontal alignment includes straight and curved paths. Vertical alignment includes level and gradients. Alignment decision is important because a bad alignment will enhance the construction, maintenance and vehicle operating costs. Once an alignment is fixed and constructed, it is not easy to change it due to increase in cost of adjoining land and construction of costly structures by the roadside.

Requirements

The requirements of an ideal alignment are

• The alignment between two terminal stations should be short and as far as possible be straight, but due to some practical considerations deviations may be needed.

• The alignment should be easy to construct and maintain. It should be easy for the operation of vehicles. So to the maximum extend easy gradients and curves should be provided.

• It should be safe both from the construction and operating point of view especially at slopes, embankments, and cutting. It should have safe geometric features.

• The alignment should be economical and it can be considered so only when the initial cost, maintenance cost, and operating cost are minimum.

Factors controlling alignment

We have seen the requirements of an alignment. But it is not always possible to satisfy all these requirements. Hence we have to make a judicial choice considering all the factors.

The various factors that control the alignment are as follows:

• Obligatory points: These are the control points governing the highway alignment. These points are classified into two categories. Points through which it should pass and points through which it should not pass. Some of the examples are:

– bridge site: The bridge can be located only where the river has straight and permanent path and also where the abutment and pier can be strongly founded. The road approach to the bridge should not be curved and skew crossing should be avoided as possible. Thus to locate a bridge the highway alignment may be changed.

– mountain: While the alignment passes through a mountain, the various alternatives are to either construct a tunnel or to go round the hills. The suitability of the alternative depends on factors like topography, site conditions and construction and operation cost.

– intermediate town: The alignment may be slightly deviated to connect an intermediate town or village nearby. These were some of the obligatory points through which the alignment should pass. Coming to the second category, that is the points through which the alignment should not pass are:

– religious places: These have been protected by the law from being acquired for any purpose. Therefore, these points should be avoided while aligning. – very costly structures: Acquiring such structures means heavy compensation which would result in an increase in initial cost. So the alignment may be deviated not to pass through that point.

– lakes/ponds etc: The presence of a lake or pond on the alignment path would also necessitate deviation of the alignment.

• Traffic: The alignment should suit the traffic requirements. Based on the origin-destination data of the area, the desire lines should be drawn. The new alignment should be drawn keeping in view the desire lines, traffic flow pattern etc

• Geometric design: Geometric design factors such as gradient, radius of curve, sight distance etc. also govern the alignment of the highway. To keep the radius of curve minimum, it may be required to change the alignment. The alignments should be finalized such that the obstructions to visibility do not restrict the minimum requirements of sight distance. The design standards vary with the class of road and the terrain and accordingly the highway should be aligned

• Economy:The alignment finalised should be economical. All the three costs i.e. construction, maintenance, and operating cost should be minimum. The construction cost can be decreased much if it is possible to maintain a balance between cutting and filling. Also try to avoid very high embankments and very deep cuttings as the construction cost will be very higher in these cases.

• Other considerations: various other factors that govern the alignment are drainage considerations, political factors and monotony.

– Drainage:

– Political: If a foreign territory comes across a straight alignment, we will have to deviate the alignment around the foreign land.

– Monotony: For a flat terrain it is possible to provide a straight alignment, but it will be monotonous for driving. Hence a slight bend may be provided after a few kilometres of straight road to keep the driver alert by breaking the monotony.

– Hydrological (rainfall/water table):

Special consideration for hilly areas Alignment through hilly areas is slightly different from aligning through a flat terrain. For the purpose of efficient and safe operation of vehicles through a hilly terrain special care should be taken while aligning the highway. Some of the special considerations for highway alignment through a hilly terrain is discussed below.

• Stability of the slopes: for hilly areas, the road should be aligned through the side of the hill that is stable. The common problem with hilly areas is that of landslides. Excessive cutting and filling for road constructions give way to steepening of slopes which in turn will affect the stability.

• Hill side drainage: Adequate drainage facility should be provided across the road. Attempts should be made to align the roads in such a way where the number of cross drainage structures required are minimum. This will reduce the construction cost.

• Special geometric standards: The geometric standards followed in hilly areas are different from those in flat terrain. The alignment chosen should enable the ruling gradient to be attained in minimum of the length, minimizing steep gradient, hairpin bends and needless rise and fall.

• Ineffective rise and fall : Efforts should be made to keep the ineffective rise and excessive fall minimum