Highway design is only one element in the overall highway development process. Historically, detailed design occurs in the middle of the process, linking the preceding phases of planning and project development with the subsequent phases of right-of-way acquisition, construction and maintenance. Now, it is during the first three stages planning, project development and design. The designers and communities, working together can have the greatest impact on the final design features of the project. In fact, the flexibility available for highway design during the detailed design phase is limited a great deal by the decisions made at the earlier stages of planning and project development.
Objectives of Highway Planning
Planning is considered as a pre requisite before attempting any development programme in the present era. This is particularly true for any engineering project, as planning is the basic requirement for any new project or an expansion programme. Thus there is a need for planned development of the road network and the links. Highway planning is of great importance when the funds available are limited whereas the total requirement is much higher. In developing countries like India it is important to utilize the available funds in the best possible manner by resorting to best planning principles. The objects of highway planning are briefly given below.
- To plan overall road network for efficient and safe traffic operation, but at minimum cost. Here the costs of construction, maintenance and resurfacing or strengthening of pavement layers and the vehicle operation cost are to be given due consideration.
- To arrive at the road system and the lengths of different categories of roads which could provide maximum utility and could be constructed within the available resources during the plan period under consideration.
- To divide the overall plan into phases and to decide priorities.
- To fix date-wise priorities for development of each road link based on utility as the main criterion for phasing the road development programme.
- To plan for future requirements and improvements of roads in view of anticipated developments.
- To work out suitable financing system phases of highway planning.
Highway planning includes the following phases.
- Assessment of road length requirement for an area (it may be a district, state or the whole country)
- Preparation of master plan showing the phasing of plan in five year plans or annual plans. (In order to plan the road system in the selected region, state or country, different studies and surveys are to be carried out to collect the data required. The data collected are to be processed and analyzed to arrive at the best possible road network and to arrive at the optimum length of the road system.)
Stages of Highway Development
Although the names may vary by State, the five basic stages in the highway development process are: planning, project development (preliminary design), final design, right of way and construction. After construction is completed, ongoing operation and maintenance activities continue throughout the life of the facility.
1) Planning
The initial definition of the need for any highway or bridge improvement project takes place during the planning stage. This problem definition occurs at the State, regional or local level, depending on the scale of the proposed improvement. This is the key time to get the public involved and provide input into the decision making process. The problems identified usually fall into one or more of the following four categories.
- The existing physical structure needs major repair/replacement (structure repair).
- Existing or projected future travel demands exceed available capacity and access to transportation and mobility need to be increased (capacity).
- The route is experiencing an inordinate number of safety and accident problems that can only be resolved through physical and geometric changes (safety).
- Developmental pressures along the route make a re-examination of the number, location and physical design of access points necessary (access).
Factors to Consider During Planning
It is important to look ahead during the planning stage and consider the potential impact that a proposed facility or improvement may have while the project is still in the conceptual phase. During planning, key decisions are made that will affect and limit the design options in subsequent phases. The important factors to be considered in planning include the following.
- Physical character
- Cost
- Safety
- Capacity
- Environmental quality
- Historic and scenic characteristics
- Multimodal consideration
- Other factors
2) Project Development
After a project has been planned and programmed for implementation, it moves into the project development phase. At this stage, the environmental analysis intensifies. The level of environmental review varies widely, depending on the scale and impact of the project. It can range from a multiyear effort to prepare an Environmental Impact Statement (a comprehensive document that analyses the potential impact of proposed alternatives) to a modest environmental review completed in a matter of weeks. Regardless of the level of detail or duration, the product of the project development process generally includes a description of the location and major design features of the recommended project that is to be further designed and constructed, while continually trying to avoid, minimize and mitigate environmental impact.
3) Final Design
After a preferred alternative has been selected and the project description agreed upon as stated in the environmental document, a project can move into the final design stage. The product of this stage is a complete set of plans, specifications and estimates of required quantities of materials ready for the solicitation of construction bids and subsequent construction. Depending on the scale and complexity of the project, the final design process may take from a few months to several years. The following concepts are important considerations of design and it includes the following.
a) Developing a Concept
A design concept gives the project a focus and helps to move it toward a specific direction. There are many elements in a highway and each involves a number of separate but interrelated design decisions. Integrating all these elements to achieve a common goal or concept helps the designer in making design decisions. Some of the many elements of highway design are
- Number and width of travel lanes, median type and width and shoulders
- Traffic barriers
- Overpasses/bridges
- Horizontal and vertical alignment and affiliated landscape
b) Considering Scale
People driving in a car see the world at a much different scale than people walking on the street. This large discrepancy in the design scale for a car versus the design scale for people has changed the overall planning of our communities. The design element with the greatest effect on the scale of the roadway is its width or cross section. The cross section can include a clear zone, shoulder, parking lanes, travel lanes and/or median. The wider the overall roadway, the larger its scale; however, there are some design techniques that can help to reduce the perceived width and thus, the perceived scale of the roadway. Limiting the width of pavement or breaking up the pavement is one option. In some instances, four lane roadways may look less imposing by designing a grass or planted median in the centre.
c) Detailing the Design
Particularly during the final design phase, it is the details associated with the project are important. Employing a multidisciplinary design team ensures that important design details are considered and those they are compatible with community values. Often it is the details of the project that are most recognizable to the public. A multidisciplinary design team can produce an aesthetic and functional product when the members work together and are flexible in applying guidelines.
4) Right-of-way
Once the final designs have been prepared and needed right-of-way is purchased, construction bid packages are made available, a contractor is selected and construction is initiated. During the right-of-way acquisition and construction stages, minor adjustments in the design may be necessary; therefore, there should be continuous involvement of the design team throughout these stages.
5) Construction and Maintenance
Construction may be simple or complex and may require a few months to several years. Once construction has been completed, the facility is ready to begin its normal sequence of operations and maintenance. Even after the completion of construction, the character of a road can be changed by inappropriate maintenance actions. For example, the replacement of sections of guardrail damaged or destroyed in crashes commonly utilizes whatever spare guardrail sections may be available to the local highway maintenance personnel at the time.
Highway Route Surveys and Location
To determine the geometric features of road design, the following surveys must be conducted after the necessity of the road is decided. A variety of survey and investigations have to be carried out by Road engineers and multidiscipline persons.
1) Transport Planning Surveys
- Traffic Surveys
- Highway inventories
- Pavement Deterioration Study
- Accident study
2) Alignment and Route location surveys Desk study Reconnaissance Preliminary Survey Final location survey
3) Drainage Studies
4) Soil Survey
- Surface run-off - Hydrologic and hydraulic
- Subsurface drainage - Ground water & Seepage
- Cross–drainage - Location and waterway area required for the cross-drainage structures.
5) Pavement Design investigation, Soil property and strength, Material Survey
6) Desk study
7) Site Reconnaissance
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