Importance of Proper DESIGN STANDARDS for HIGHWAYS in India.

The geometrics of highway should be designed to provide optimum efficiency in traffic operations with maximum safety at reasonable cost.

The booming economy and exploding traffic in the country has taken road infrastructure in India to a new dimension. An efficient planning and construction of highways, expressways and high-speed corridors have become need of the day. Highways as high-speed corridors are not just functioning as means of transporting vehicles from one place to another but also they host numerous industries along the corridor making a hub of economy. The development of high-speed corridors in the developed countries has revealed the potential of such corridors to alter the economy of the region. However, all this is possible only with a mix of proper planning and using the right design parameters while designing the alignment. 

The design of a highway alignment involves great care keeping in view the construction cost, maintenance cost, vehicle operation cost and accidents. A badly aligned highway is not only a source of potential traffic hazard but also a cause for considerable increase in transportation cost and fatigue to road users. Once a highway is constructed and opened for the traffic development takes place along the adjoining land. After fixing the alignment it is not easy to revise the alignment due to increase in cost of adjoining land and construction of costly structures by roadside.

The geometric design of a highway deals with the dimensions and layout of visible features of the highway such as alignment, sight distance and intersection. The basic requirement while designing any alignment is that it should be short, easy, safe and economical. The main factors controlling the alignment fixing are

- Geometric Design

- Obligatory points

- Traffic

- Economics

- Other considerations like hydrological, political, environmental, monotony etc.

Proper investigation and planning is very much essential in finalizing the highway alignment keeping in view the present traffic and other needs as well as future development of the region. The geometrics of highway should be designed to provide optimum efficiency in traffic operations with maximum safety at reasonable cost. The designer may be exposed to either planning of new highway network or improvement of existing highways to meet the requirements of the existing and anticipated traffic. Different approaches involve in the design of alignment depending upon the situation, basically the design of alignment is required in two situations - new highway alignment and realignment of existing road.

TOPOGRAPHIC SURVEY

Topographical survey is the backbone of detailed engineering design. Accuracy of the information collected during this survey has direct bearing on almost all the design activities involved in project preparation. The survey should be carried out with GPS and total station. Currently the LiDar survey system gives more accurate three dimensional data of the ground and other features.

ELEMENTS OF DESIGN

The design standards are to provide proper guidance to the designer to arrive at effective highway designs. The standards stipulated by any country will be permitted with sufficient flexibility to encourage the application of sound principles by the knowledgeable of design professionals. All the standards from AASHTO, NAASRA, DoT & IRC, etc allows maximum & minimum values. The larger values within ranges will normally be used, where the social, economical and environmental (SEE) impacts and not critical.

The major elements of design are:

- Sight distance

- Superelevation

- Traveled way widening

- Guidelines

- Horizontal and vertical alignment

Sight Distance: The four aspects of sight distances are -

- Sight distance for stopping, which are applicable on all highways

- Sight distance for passing of every time vehicle applicable only on 2 - lane highways

- Sight distance for decisions at complex locations

- The criteria for measuring these sight distances for use in design

DESIGN LIFE

It is a moot question whether the design capacity of a highway should be based on its life expectancy. The decision is greatly influenced by economics. For example, a highway might be designed for traffic volumes 50 years hence with the expectation that the pavement structure would be restored in 20 to 25 years. However, if the added cost of a 50-year design over a design with a 25-year life expectancy is appreciable, it may be imprudent to make a further investment providing capacity that will not be needed for at least 25 years.

SPEED

Speed is one of the most important factors considered by travelers in selecting alternative routes or transportation modes. Travelers assess the value of a transportation facility in moving people and goods by its convenience and economy, which are directly related to its speed. The attractiveness of a public transportation system or a new highway are each weighed by the travelers in terms of time, convenience, and money saved. Hence, the desirability of rapid transit may well rest with how rapid it actually is. The speed of vehicles on a road or highway depends, in addition to capabilities of the drivers and their vehicles, upon five general conditions: the physical characteristics of the highway, the amount of roadside interference, the weather, the presence of other vehicles, and the speed limitations (established either by law or by traffic control devices). Although any one of these factors may govern travel speed, the effect of these general conditions is usually interrelated.

OPERATING SPEED

Operating speed is the speed at which drivers are observed operating their vehicles during free flow conditions. The 85th percentile of the distribution of observed speeds is the most frequently used measure of the operating speed associated with a particular location or geometric feature.

EFFECTS OF GRADES

On long or fairly steep grades, drivers tend to travel faster in the downgrade than in the upgrade direction. In a refined design this tendency should be recognized, and some adjustment in Superelevation rates should be made.

 The transverse inclination to the pavement surface is known as superelevation. In order to counteract the centrifugal force generated during negotiation of vehicle on curves and reduce the tendency of vehicles to overturn or skid this superelevation is provided. The pavement surface is rotated by raising the outer edge with respect to inner edge of the pavement.

Horizontal Alignment Design

All the curves having poor geometry shall be improved in case of rehabilitation projects to the acceptable design standards and also to accommodate the widening proposal within the available Row. Superelevation design shall be carried and applied to all the curves after identification of black spots and possible causes of accidents the cost effective remedial measures is suggested.

VERTICAL ALIGNMENT DESIGN

To provide adequate vertical curve length at the grade change on criterion of stopping sight distance/overtaking sight distance/ passing sight distance. In case of rehabilitation project care should be taken to avoid cutting/scraping of existing pavement and

CROSS SECTION DESIGN

The cross section details are broadly composed of carriageway, medians, raised footpath, hard shoulders, and earth shoulder and drainage provisions. In general the carriageway is 7.0 m (two lanes of each 3.5 m). Where kerbs are provided, an additional 0.25 m “shyness” is added, i.e. the carriageway is 7.25 m wide when kerb provided in one side only - 7.5 m when kerbs are present in both sides. A 3.5 m wide shoulder should be provided, of which at least 1.5 m is paved and 2 m soft shoulder. On high embankments an extra width is given to improve the safety and to allow safety barriers to be installed.

LAND ACQUISITION

As per IRC: 73 - 1980, the required Right - of - way (RoW) for National Highway / State Highway Standards is 60 mtrs.  Efforts should be made to acquire the ROW at initial stages itself.

UTILITIES

Various types of utilities may exist along the existing alignment. They are OFC, electrical lines, underground sewage pipe lines and water supply lines etc. In general during up-gradation of a highway all the utilities should be shifted and well protected. :

ROAD SAFETY

Road safety is an issue of prime importance in all motorized countries. The road accident results a serious social and economic problems. Studies focused on geometric design and safety aim to improve highway design and to eliminate hazardous locations. The effects of design elements such as horizontal and vertical curves, lane width, shoulder width, superelevation, median width, curve radius, sight distance, etc. on safety should be studied and well addressed.

CONCLUSIONS

Since the realignment of any highway is tedious due to the developments already taken place next to the existing road the care should be taken in fixing the initial alignment. All the design standards cannot be incorporated in the up-gradation and re-alignment project. Hence the design standards should be judiciously adopted with project specific and type of road so that the purpose is served with added Road safety Features.

Right of Way (ROW) should be clearly marked on the ground and well protected from any encroachments. Especially for the country like India the problem of encroachments is very high. Strict regulations should be followed in protecting the ROW of the Road.

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