GIS BASED DECISION SUPPORT SYSTEM FOR IDENTIFICATION OF ROUTE CORRIDORS

Abstract

The transportation problems have increased manifold worldwide. This has necessitated the search for methods and alternatives that ensure efficient, feasible and faster methods of locating the best possible route corridor. India, bearing the tremendous pressure of population growth, feels its importance. Therefore, more share of country's budget is nowallotted for the development of transport infrastructure. The construction of a highway is facilitated by proper analysis of route location. Scientific planning of transport route can reduce the cost and time of project execution and hence the operating expenses. The whole process of route-corridor identification is dependent on three groups of data - geo-engineering data, geometric design data, and cost data. Natural and man-made terrain obstructions cause spatial variation in construction cost due to changing thematic features, like types of soils, land use slope etc. Due to poor implementation of scientific methodology for best possible route location, the transportation projects are taking more time to implement. The study area in the present study is a part of intricate hilly terrain of Garhwal Himalayas, thus having very stringent requirement of fulfillment of geometric design criteria, slope gradient being the most important out of that. The objectives of the research work are (i) creation of a database in Geographical Information System (GIS) using remote sensing and ancillary data, (ii) identification of corridors for road route connecting the habitation in the region using geo-engineering parameters, (iii) development of algorithms for GIS based route alignment, and (iv) development of a Decision Support System (DSS) for identification of best route corridors. The origin and destination points for the proposed route were chosen based on the importance of the city-centers located in the area, such that the route passes through those centers. The route has been identified between Rishikesh and Devprayag, while Vyasi has been taken as intermediate obligatory point, such the proposed route always connects all these points. Also, a number of thematic data were required in order to identify the suitability of a particular ground location for lying of route, viz. land use/ land cover, elevation, 11 slope gradient, lithology, geomorphology, lineaments, drainage, slope-dip relationship, soil and aspect. Database generation for these parameters taken for route alignment was carried out, using remote sensing (RS) and GIS techniques by incorporating information from topographic maps and field data. A high-impedance layer was also created, having rivers, landslide areas and the high elevation and steep slope areas. These areas were treated as very high-impedance areas, as the route should avoid passing through it. The high-impedance layer was overlaid on all parameter layers to avoid these high-impedance areas while finding out the route for individual parameters. The weightages for these parameters were decided on the basis of opinion of thematic and engineering experts. Saaty's method of pairwise comparison was also applied to reduce the class-biasness by individuals as given in 'direct weight method' and another set of weightages were obtained. Sub-class weightages of these parameters were also decided, as per expert opinion. These served as decision rules for delineation of suitable route connecting the given origin, destination and other obligatory points. In this research work, two different methodologies have been developed and used for transport route alignment. Computer software have been developed for the approaches. In one approach, software has been developed in Visual Basic (VB) employing a metaheuristic algorithm called Dijkstra's algorithm. This algorithm although is used in electronic/electrical circuit's design, has been used here for solving the route corridor identification problem in GIS environment. The Dijkstra's algorithm has not been used earlier in Indian conditions for route alignment. The concepts for electronic-circuits design of Dijkstra's algorithm have been successfully translated and implemented for transportation engineering application, to find the most optimal route corridor satisfying the geo-engineering parameters and decision rules of conventional route alignment techniques. The algorithm's intricacies have been solved by applying VB programming, while the mapping capabilities are achieved by integrating the results obtained from VB programming with GIS. 111 In order to show the added advantage achieved by applying Dijkstra's algorithm, another methodology has been developed in GIS by writing a program in ARC/INFO GIS's Arc Marco Language (AML), using the grid properties for analysis of weights from one grid-cell to the eight neighbouring grid-cells and finding of route, as per suitability. Four routes were obtained from both the methodologies, using the two sets of parameter weights obtained by direct method and Saaty's method. The routes were overlain on Digital Elevation Model (DEM) and satellite data and were evaluated. The results were compared according to criteria of minimum length of route, crossings with drainages, connectivity with the settlements in 4 km buffer distance on either side of routes, and cost of route. It was observed that Dijkstra's algorithm gave the location of bridges in the most optimal manner, thus reducing the number of drainage crossings and cost of route. It has been concluded that the route obtained from Dijkstra's approach satisfied the defined criteria. Ten clusters of settlements were chosen in the area as per their demographic information, and the final route was connected with these settlements by feeder routes obtained usingthe developed route alignment approaches. It has been found that RS and GIS techniques are very useful in collecting the thematic data and preparing digital database which can be used for a number of purposes, including efficient identification of route corridor. ARC/INFO GIS could be combined with any graphic programming language like VB very efficiently, to fulfill the objectives of finding the optimal route. Use of this GIS tool andVB has provided a very friendly interface to the user, such that identification of route corridor could be carried out without having much knowledge of GIS software and VB programming. The combination of advanced mathematical algorithm (Dijkstra's algorithm) with GIS gave better results in terms of applicability of all decisionrules for route-alignment, and locating bridges at the most optimum place. iv