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Optimal route analysis using GIS
Methodology
The Road Network Map of the study area is prepared using the Survey of India Guide Map of Chennai City(Scale 1:25000) and updated with the Orthophoto prepared in the year 1989. The Hospital locations and Ambulance Locations were collected from the Trauma Care Consortium. Non-spatial data such as Volume of Traffic, Type of Road, Width of Road and Speed Limit were collected from M/s. Kirloskar Consultants, prepared based on field Survey. The average time delay at road junctions and turns were obtained from the City Traffic Police Department and the time delay due to volume of traffic for 2 lane, 4 lane roads and congested traffic were based on empirical formula. The various impedance factors that cause time delay for the flow of traffic in a road network are volume of traffic, width of road, time of travel, number of signals and turns etc., The ROUTE Module available in Arc-Info, which is a path finding program used to model the movement of resources between two or more points. The path is controlled by specifying the origin, destination and any stops or nodes the route must pass through. This module evaluates the possible paths on the network from the starting point to the destination to determine which has the lowest impedance. The optimal path is determined by finding the path with the lowest total for the arc directional impedance(the value in either the from-to impedance or the to-from impedance in Arc Attribute Table) and the turn impedance (in the TRN turn table). Orgin and Destination The ambulance location is the origin and the nearest hospital is the destination, via the accident spot. Suitable landmarks (i.e. identifiable buildings, round turns, road junctions etc.) have been identified and located along each road in order to specifically reach the accident spot. The place of accident is related to the nearest landmark in the road network. A SML (Simple Macro Language) script was used to have a menu-based interface with the user. The user is prompted to select the accident spot in terms of landmark and is requested to specify whether the time of occurrence of accident is during peak hour or non-peak hour. Using buffer zones, the ambulance locations and the hospitals located within the buffer zone are selected. For these ambulance and hospital locations the optimal route having lowest impedance is selected. The analysis leads to two routes, one from the ambulance location to the accident spot and the other from accident spot to the hospital. The results are displayed graphically highlighting the route to be traversed indicating the locations of ambulance, accident spot and hospital. In order to make the output more meaningful, the highlighted route is also described with regard to details like the road to start, the roads to traversed, turns to left or right and distance of travel along each road. Results Three accident spots were considered in this study, and they are Raghavendra mandapam, U.S. Consulate and Madras Boat club. The detailed description of the route for Route No. 1, to be traversed is given in Table 01. Route No.1
The graphical output in the form of a map indicating the route to be traversed along with the distances and directions to be traversed along each road segment gives complete description of the route with least impedance. Conclusions Geographic Information System can be used to address the objectives of finding the optimal route between the given origin and destination. It can be used to find out the routes involving shortest distances as well as shortest travel time. However, in order to achieve realistic results, the volume of traffic data has to be real time. Real time transmission of volume of traffic via satellite or through internet or using local microwave transmitters it is possible to receive online volume of traffic. This information may be made available in a suitable data exchange format so that this could be automatically added as an attribute information in the road network. References
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