Read this article to learn about: 1. Objectives of highway planning 2. Necessity of highway planning in India 3. Principle of Highway Planning 4. Highway Planning Process 5. Importance of Highway Planning.
Introduction to Highway Planning:
Planning is a prerequisite for any engineering activity or project; this is particularly true for the development of a highway network or system in a country.
The objectives of highway planning are:
(i) Planning a highway network for safe, efficient and fast movement of people and goods.
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(ii) Keeping the overall cost of construction and maintenance of the roads in the network to a minimum.
(iii) Planning for future development and anticipated traffic needs for a specific design period.
(iv) Phasing road development programmes from considerations of utility and importance as also of financial resources.
(v) Evolving a financing system compatible with the cost and benefits.
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To fulfill these objectives, the following principles have to be borne in mind:
(i) The proposed road links should be a part of the planned road network for the state/nation.
(ii) The importance of the road shall be based on the traffic demand, and hence its type should fall under the standard classification.
(iii) The maintenance needs of the roads should receive prompt attention by setting aside funds for this purpose.
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(iv) Statutory provisions for traffic regulation should be in place.
Classification of Roads:
The classification of roads depends on the criterion considered.
They may be all-weather roads if they can be used during all seasons of a year; fair-weather roads, if traffic is interrupted during monsoon at course ways where water overflows for a few hours. Based on the type of carriage-way or the road pavement, it may be a paved road with at least a water-bound macadam layer; or it may be an unpaved road. Earth roads and gravel roads fall in this category.
Superior paved roads have bituminous surface or concrete surface for the carriage-way. A bituminous road is also known as a black-top road.
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Traffic volume, load transported per day, and the location and function are important criteria for classification of roads. These criteria have been taken into account in the classification recommended by the Nagpur Plan—NH, SH, MDR, ODR and VR, as also in the one modified by the Lucknow Plan—with categories of Primary, Secondary and Tertiary roads.
Urban roads are classified based on their function and location:
(i) Expressways— for movement of heavy volume of traffic.
(ii) Arterial streets—for connecting the central area to expressways.
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(iii) Sub-arterial streets—similar to arterial roads but with less spacing.
(iv) Collector streets—for collection and distribution of traffic through local streets in residential areas.
(v) Local streets—to access private property like residences, shops and industries. Traffic originates here or ends here.
In this context, certain definitions are relevant:
(i) Road – A convenient way over which vehicles may lawfully pass for going from one place to another.
(ii) Service road – Used for servicing and as a means of access to adjacent property; constructed parallel to the main road adjacent to roadside buildings.
(iii) Street – A road within a town or a residential locality with buildings on one or both sides.
(iv) Country road – Road connecting one place to another on the country-side.
(v) Urban road – A road within a town or a city.
(vi) Bypass road – A road constructed skirting a village or a small town, taking off through a highway and joining it after bypassing the inhabited area; this helps through traffic to move fast without having to enter the village or town.
(vii) Highway – Any public road or a street may be called a highway.
(viii) Arterial road – Road passing within a city and linking the state or national highway, with limited access.
(ix) Freeway – An arterial highway with controlled access crossing other roads at different levels.
(x) Boulevard – Very wide road with avenue on its either side; generally used for ceremonial processions or considered as prestigious roads in a city.
Urban Road Patterns:
Although road patterns in a country are historically inherited, later additions can be planned bearing in mind the requirements of the day.
Road patterns are of great use in urban highway planning. The choice of a road pattern depends upon the extent of land use or the distribution of residential, industrial and business areas in a city, the nature of the terrain, and the planner’s preferences.
The main patterns in use in urban areas are:
This is also known as rectangular or block pattern and is perhaps the simplest (Fig. 1.5). The Romans preferred it, as have the Americans who adopted it in many of their cities. This is easy to set out in straight lines and rectangular co-ordinates, and is suitable for flat terrain.
The disadvantages of this pattern are monotonously long streets and the inconvenience in traffic operation. There are also certain advantages such as bypassing any road with traffic congestion and the convenience of imposing one-way traffic, if necessary, making alternate streets with one- way traffic in opposite directions.
Chandigarh city is an excellent example of this pattern. Recently developed localities in most major cities such as Bangalore City have been built on this pattern.
In this pattern, roads emanate from a central focal area, which may be a business centre or an important public building. In order to ease the congestion in the focal area, ring roads are provided; there can be several such roads—inner, intermediate and outer—depending on the requirements of the traffic.
The shape of a ring road may be round, square, or elongated. Based on this, the pattern may be star and grid, or star and circular. The star and grid pattern, or the radial and block pattern has been the basis of the Nagpur Road Plan, and it has been adopted in a number of Indian cities (Fig. 1.6).
The star and circular pattern, also known as the radial and circular pattern, has been adopted in certain cases, although in a limited way. A classic example is the Connaught Place area of New Delhi. (Fig. 1.7)
The basic figure of the road network in this case is a hexagon; each hexagon has at least one side common with an adjacent pattern, as shown in Fig. 1.8.
The hexagonal pattern can be modified by dividing the hexagon into six triangle units by link roads; this facilitates travel from one place to any other place in the area in the minimum possible time, compared to any other pattern. This, in fact, is known as a ‘minimum travel pattern’ and was used in certain cities to great advantage.
Highway Planning Studies:
Highway planning involves the assessment of the length of road required for a given area, which may be a city, district, state or a country; further, it includes the preparation of a master plan for the area taking into consideration future needs, and phasing the programme in annual or five-year plans, based on the priorities and utility.
For assessing the required road length for the area, field studies are to be carried out to collect the necessary data.
These are:
Details of the existing facilities, their utility, distribution of the existing population in the area, population growth trends, existing products in the agricultural and industrial sectors, future trends of development in these sectors, existing communication and education facilities, and the per capita income are to be collected.
Details of the existing road facilities, traffic volume in vehicles per day, traffic flow patterns, classes of traffic such as passenger cars, busses and trucks, loads carried, average speeds, anticipated future trends of traffic growth, and other traffic-related studies are to be conducted.
These include study of the topography, soil, road life and special problems, if any, relating to construction, drainage and maintenance.
Various financial aspects such as the sources of funding, estimated revenue from taxes on vehicles, toll tax, and indirect benefits of raising the living standards of the people due to the proposed road network are considered.
A systematic study of all these data will help the planner in the preparation of a Master Plan to serve the needs of the area for a specified design period of say, 20 to 25 years.
These studies also help in fixing priorities of various routes or sectors based on their utility per unit length. Based on the priorities and the maximum utility per unit length, the entire development plan for the design period will be phased in 5-year intervals, depending upon the availability of financial resources. This is known as phasing of the Master Plan for road development.
For calculating the optimum road length a system called saturation system or maximum utility system is used.
This system is based on the principle of qualifying the utility of a proposed road network based on the villages and towns of different populations it serves, as also the weight of agricultural or industrial products it carries.
For example, consider the ‘utility units’ attached to villages with certain population ranges as given below:
The total utility units for all the villages served by a proposed road may be called, based on this. Similarly, the utility unit for 1000 tonnes of agricultural products may be taken as 1.00, and that for 100 tonnes of industrial product as 10.00. If the break-up is not known, a suitable average value may be taken as the utility unit for the entire productivity.
The total utility units may be got by summing up the values from both these criteria and divided by the length of the roads, to obtain the total utility per unit length.
Thus, the value for different options under investigation may be compared and the best option with the highest total utility units chosen.
This option is supposed to be utilised to the maximum extent by traffic in all stretches of the road, reaching saturation.
This system has been used extensively in the U.S.A.
The disadvantage of this system is the element of arbitrariness of the utility coefficients assigned to the various factors; but with sound judgment and professional skill and experience, balanced weightages may be arrived at for choosing the best option.
Highway Alignment:
The laying out of the centre line of a proposed highway on the ground is called its ‘alignment’. A new road should be aligned carefully since any change in alignment may not be possible or may be expensive at a later stage, owing to increased land acquisition costs and roadside structures constructed after the road has taken shape.
Requirements of an Ideal Alignment:
1. Directness:
The aligned route between end points should be as direct as possible and result in the minimum possible length under the circumstances.
2. Ease of Construction, Maintenance and Operation:
The alignment should be such that it is easy to construct, maintain and operate the highway. The curves and gradients should be easy.
3. Safety:
Safety for the road-users should be the primary consideration; the stability of natural slopes and man-made slopes for embankments and cuttings should be ensured to prevent possible accidents.
4. Economy:
The overall cost of construction and maintenance of the road, as also the operation cost of the vehicles should be as low as possible.
5. Special Considerations:
Depending upon the purpose of the highway and the characteristics of the terrain, special considerations may be needed as in the case of hill roads or ghat roads.
Horizontal Alignment:
This is the alignment of the roadway in the horizontal plane; although it is ideal to have a straight route between end points, it is practically impossible owing to several constraints. A change in direction necessitates the use of horizontal curves for smooth flow of traffic.
Vertical Alignment:
Although it is ideal to have a roadway at the same elevation throughout, this is almost impractical and gradients or slopes along the length become mandatory. A change in gradient calls for curves in the vertical plane; vertical curves should be designed and constructed for smooth flow of traffic based on several criteria.
The alignment may be smoothened as shown in Fig. 2.1:
Factors Controlling Alignment:
The selection of alignment of a proposed new highway route will be based on a careful consideration of the following factors:
1. Obligatory Points:
These are the points through which the alignment has to necessarily pass for maximum utilisation of the road (Figure 2.2). While aligning a new highway route between two end points, it would be necessary to make it pass through places of importance. This may be based on the population that can be served, or places of business or industrial importance.
2. Topographical Features:
Topographical features like a lake or a hillock may require the alignment to be taken around them. In the case of a big hill the option of constructing a tunnel through it for maintaining a straight alignment can be considered. The relative costs of these options have to be studied to finalise the alignment.
Figure 2.3 shows a change in alignment around an obstruction caused by a lake and a hillock.
3. Geometric Design Aspects:
Factors such as radius of curve, longitudinal gradients, sight distances, road intersections, design speed, lateral friction, and super-elevation govern the alignment to a considerable degree; radii of horizontal curves and longitudinal gradients should facilitate easy maneuvering of vehicles.
The alignment should be such that bridges are located at right angles to the direction of flow of the stream or river (Fig. 2.4).
5. Deviations Dictated by Circumstances:
Although a straight horizontal road is the best option, it is highly monotonous for a driver; so, to divert attention on a straight road and break the monotony, a slight bend or curve may be created at least once in a kilometre or two to make the driver alert. Obstructions such as places of worship (such as established temples and churches), monuments of historical interest, public buildings such as hospitals and educational institutions and utility services like water supply and sewerage lines and overhead transmission lines may necessarily have to be bypassed.
This may dictate deviation in the alignment of the roadway, leaving sufficient margin for these hindrances. Sometimes, the alignment may have to be changed to bypass expensive private property or agricultural or industrial area.
6. Proximity to Materials and Labour:
Proximity to the sources of materials for road-making and the availability of cheap labour may be a criterion for fixing the alignment.
7. Economic Considerations:
Before an alignment is chosen, two or three alternative routes may have to be investigated and their overall cost – initial outlay and maintenance cost over a design period – compared. The route with the best economy is then selected.
8. Political Considerations:
Sometimes, political considerations may dictate the choice of alignment, setting aside even economic considerations. Of course, the other important criteria have to be necessarily borne in mind.
Highway Project Preparation:
A highway project may be an entirely new route or it may involve re-alignment and re-design of an existing road such as for upgrading its geometric design standards.
The work of a new highway project involves:
(a) Selection of the alignment.
(b) Geometric design.
(c) Testing and selection of the materials for the subgrade and the pavement.
(e) Pavement construction including surfacing.
(f) Rolling and compaction and curing, if necessary.
(g) Quality control during construction.
(h) Performance of review and appraisal under traffic.
Realignment of an Existing Road:
An existing road may have to be realigned under a variety of circumstances:
(i) Redesign and improvement of geometric design aspects owing to increased traffic needs.
(ii) Raising the level of a road subjected to flooding.
(iii) Reconstruction of weak culverts and bridges to take care of increased traffic needs.
(iv) Construction of over-bridges and under-bridges at road intersections and level crossing.
(v) Construction of a bypass near a busy town.
Project Report:
Any project should be submitted to the competent authority along with a report.
The report should contain the following:
i. Name of the project
ii. Authority for execution
iii. Necessity
iv. Summary of alignment details
v. Summary of geometric design aspects
vi. Traffic details including anticipated future needs for a chosen design period
vii. Details of important drainage and cross-drainage works
viii. Specifications for the materials
ix. Details of quantities required
x. Rate analysis
xi. Detailed and abstract estimated
xii. Total cost and duration of the project
xiii. Material sourcing, labour and equipment
xiv. Construction scheduling (using project analysis tools such as CPM and PERT)
xv. Temporary facilities like diversion roads, work-sheds, water supply and power
xvi. Signals and traffic signs
xvii. Lighting
xviii. Roadside arboriculture
Engineering Surveys:
Highway alignment and location are facilitated by a systematic step-by-step procedure of conducting ‘engineering surveys’.
These surveys include: 1. Study of Topographic Maps 2. Reconnaissance Survey 3. Preliminary Survey 4. Location Survey 5. Soil Survey 6. Construction Survey.
Topographic maps are available from the Survey of India; these are contour maps with 15 to 30 m contour intervals and show important topographic features like rivers, valleys, ridges, and hills. By a careful study of these maps, it is possible to align highways bearing in mind the obligatory points. Depending upon the elevations of the terminal points, and considering the ruling gradients and other factors, two or three alternative routes may be chosen.
The objective of reconnaissance survey is to physically examine the possible alignments observed during the study of topographical maps. This is generally carried out using simple surveying instruments such as prismatic compass, Abney level, hand level or tangent clinometer.
Details of certain features not available from the map study are collected during the reconnaissance survey.
Some of the details that may be gathered are:
(i) Approximate gradients, radii of horizontal curves necessary.
(ii) Obstructions such as permanent structures not shown in the maps.
(iii) Ponds, lakes, valleys, bridges, hillocks, and similar topographical features with relevant details.
(iv) Information relating to cross-drainage structures such as culverts, causeways and bridges required along each of the possible routes.
(v) Geological features and information on soil types along the route.
(vi) Stability of slopes in the case of hilly terrain.
(vii) Sources of construction materials – borrow areas for earth materials and quarries for stones and broken stone.
(viii) Climatic factors, hydrological information, water-table levels, water sources and maximum flood levels in the case of streams and rivers.
(ix) Availability of labour, power and water supply along the route.
The objectives of a preliminary survey are:
(i) To compare the proposed routes chosen during reconnaissance for a good alignment.
(ii) To carry out accurate field work for detailed surveys on the chosen alternative routes
(iii) To estimate the quantities of the earth work and other materials to facilitate the preparation of detailed and abstract estimates of the project cost.
(iv) To choose the best alignment from all angles.
The various kinds of detailed survey carried out are:
Traverse Survey:
Open traverse are run with the help of a theodolite and tapes, the lengths of each of the lines and the deflection angles wherever a change in direction is required are measured accurately.
Longitudinal section along the proposed route and cross-sections at intervals of 30 m to 100 m along the route are to be taken, depending upon the nature of terrain – plain or rolling.
Contouring is also done in the vicinity of the route by using either tachometry or precise levelling. Bench-marks are connected to GTS bench-marks.
Drainage, cross-drainage works, hydrological data, soil data and details of existing features like buildings, lakes, rivers, power lines and geological landmarks are collected more accurately than during reconnaissance.
Instruments used for the conventional method of surveying include the theodolite, chain, tapes, levelling instrument, prismatic compass, plane table and clinometers.
Where the area is large, modern methods involving the use of aerial photogrammetry, remote sensing and photointerpretation techniques, geographic positioning system (GPS), geographic information system (GIS), and total stations may be gainfully employed for modelling and precise determination of the topographic features.
With a view to assess the effects of highway projects on the environment and the surrounding areas, environmental impact assessment (EIA) has been made mandatory by the government.
Environmental impact analysis deals with positive and negative effects of the project and presents cost-effective preventive measures against any possible damage due to soil erosion, submergence due to floods, loss of vegetation, forest cover and wild life ecological balance.
Economic justification needs economic analysis including cost-benefit studies with reference to IRC specification-IRC: SP: 30.
Based on these studies, the final location of the selected route is made on paper, before being translated on to the ground in the next stage of location survey.
This involves the location of the final alignment on the ground and includes pegging the centre-line; establishing bench marks, and determining levels at the pegged stations and at critical points of change in slope.
The centre-line of the final route is marked by establishing pegs on the ground. All angles are accurately measured using a transit theodolite. The recommended spacing of the pegs depends on the nature of the terrain. It is 50 m for plain terrain and 20 m for hilly terrain. The pegs should be fixed in relation to at least three reference marks, so that they may be re-established in case they are disturbed.
Cross-Sections:
Cross-sections are taken at 50-100 m intervals on plain terrain, 50 m intervals on rolling terrain and 20 m intervals on hilly terrain.
Precise Levelling:
Precise levelling has to be performed and suitable benchmarks, temporary and permanent, have to be established.
The following dates are obtained for the implementation of the project:
(i) Right of way available along the route.
(ii) Land acquisition costs.
(iii) Date required for geometric design aspects.
(iv) Data for pavement design.
(v) Cost calculation.
(vi) Construction materials, equipment, and labour.
5. Soil Survey:
The nature and extent of the soils available in and around the chosen route have to be ascertained. The purpose of soil survey is to identify and classify soil for use in the design and construction of the road.
Information is gathered on the presence of unstable strata or marshy areas, subsoil water level, and demarcation of possible borrow areas along the road in accordance with IRC recommendations.
This consists of removing all under-growths such as shrubbery, thickets, tree stumps and rubbish along the route, setting out the centre-line and the right of way by affixing pegs at appropriate intervals, cutting a narrow V- shaped cut called ‘Lockspit’ in between the pegs along the route and making the necessary preparations for implementation of the project.
The final centre-line and profile can be selected using the Digital Terrain Model (DTM).
Engineering Drawings and Implementation of a Highway Project:
Details of engineering drawings necessary for the implementation of a highway project are set out by IRC in its specification IS: SP: 19-2001.
The salient features of these drawings are given below:
Locality Map:
The location of the area, its existing roads and the alignment of the proposed road along with the important places it would connect are shown in the locality map. The recommended scale for this map is 1:25000.
This shows the general topography of the area. The scale recommended for the map is 1:50000.
Land Acquisition Plans and Schedules:
All relevant information relating to the details such as buildings, adjacent properties, agricultural and other land-use details with the probable land acquisitions costs and schedules are put forth in the land acquisition plans. The scale of these plans can vary from 1:2000 to 1:8000.
Plan and Longitudinal Section:
This should consist of 1 km length of alignment for a single sheet with all relevant details. The recommended scales are 1:2500 (horizontal scale) and 1:250 (vertical scale) for plain and rolling terrain.
Cross Sections:
Cross sections should be given at 50 m intervals indicating cuts and fills, for estimation of earthwork. The recommended scale is 1:00.
Cross-Drainage Structures:
These provide standard designs of causeways, culverts, small bridges and major bridges that are to be included along the proposed route. The recommended scale is 1:50.
Road Intersections:
These are details of intersections of the proposed road with the existing roads and road signs. The recommended scale is 1:500.
Drawings of Roadside Amenities, Retaining Structures and Sign Boards:
Relevant information regarding roadside amenities and retaining structures should be shown at appropriate places along the proposed route. A suitable scale should be chosen to show the required details clearly.
The following IRC Codes may be referred to for further information on these surveys:
(i) IRC: SP: 19-2001 for NH, SH and MDR
(ii) IRC: SP: 20-2001 for ODR and RR
(iii) IRC: SP: 13 for minor bridges (span < 6 m)
(iv) IRC: SP: 54 for bridges