Optimal route analysis using GIS

Optimal route analysis using GIS

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D. Thirumalaivasan
Senior Lecturer in Civil Engineering, Department of Civil Engineering, Anna University. 
[email protected] 

Prof. V. Guruswamy
Honorary Director,  Centre for GIS Applications, Anna University.
[email protected]

Abstract
Chennai City is the fourth largest city in India, covering an areal extent of 1167 square kilometers of which the Chennai Municipal Administration area extends over 172 Square Kilometers. The city is continuously growing in terms of population in geometric progression. The city being a hub of commercial and business activities is facing ever-increasing vehicular traffic. This has resulted in multifaceted traffic problems such as accidents, peak hour congestion etc., The road network of Chennai city is of Radial Pattern having major highways to the North, West and Southwest. The other major roads being the arterial road along the coast and the road parallel to NH4. However, the existing road network in the city is unable to accommodate the present day heavy vehicular traffic. This poses a serious problem while deploying emergency services such as Ambulance and Fire Services where Time Factor plays a crucial role. To find optimal route between two given points, either the shortest path between them or the route having minimum travel time is to be selected. For emergency services, such as Ambulance and Fire Services, route having minimum travel time is to be preferred over the route having the shortest distance. With this objective of optimizing travel time, the various Impedance Factors that play a significant role in deciding the travel time such as Volume of Traffic, type of road, road width, number of junctions, turns etc., are analyzed in determining the optimal route having the minimum travel time. The ROUTE module available in Arc-Info is used for the Road Network analysis and the resulting routes for various origin and destination points are analyzed. In order to have realistic applications, the Ambulance locations of Trauma Care Centre were assumed as starting points and the nearest hospital locations to the accident site were taken as the destinations. The results obtained for various ambulance locations and accidents spots are presented. 

Introduction
Worldwide, the transportation problems faced by various nations have increased manifold, necessitating search for methods or alternatives that ensure efficient, feasible and faster means of transport. This is all the more true in a country like India, where in the population growth in metros is increasing significantly. Various situations, particularly emergency situations demand a method that can ensure speedy transportation e.g. Ambulance Services, Fire Services etc. 

Speedy transportation in such circumstances saves valuable human lives. Remote Sensing and GIS play a vital role in transportation and urban planning applications. In this paper an attempt is made to find optimal route for ambulance and fire services based on shortest travel time using GIS. 

For a given origin and destination, one is always tempted to use the shortest distance route. But, this need not always be the best route, in emergency situations, wherein shortest travel time is to be preferred over shortest distance. A shorter route does not always translate to shorter travel time, because it may be narrow in width or it may have higher volume of traffic, or more numbers of signals and turns and so on. 

Study Area
The study area was decided, based on the ambulance service network of Trauma Care Consortium, which mainly covers the central part of Chennai city. TRAUMA CARE CONSORTIUM (TCC) is a unique not for profit, public charitable service and the first of its kind in India and makes available on demand to residents of Chennai City, fully equipped ambulances for emergency movement of road accident victims to hospitals. This service is operational effective since mid April 1996 and until date has been instrumental in assisting over 1500 road accident victims in Chennai City. The Additional Director General of Police and Commissioner of Police of Greater Chennai have granted permission to operate this service in conjunction with the Chennai City Traffic Police. They have positioned ambulances, which are wireless linked, at key locations within the city, and these ambulances are deployed to rescue the road accident victims on receiving information regarding the place of accident.

The following table illustrates the statistics like time of day during which, the accidents have occurred during the period 1996-99.

Accident Time Analysis in Chennai City (1996-99)
Time in Hours No. of Accidents Percentage
00 : 00 to 03 : 59 302 13.16 %
04 : 00 to 07 : 59 171 7.45 %
08 : 00 to 11 : 59 342 14.90 %
12 : 00 to 15 : 59 384 16.73 %
16 : 00 to 19 : 59 380 16.56 %
20 : 00 to 23 : 59 715 31.16 %
Total Calls 2294
Assisted before ambulance arrival 565

Nearly 32 percentages of the accidents, have occurred during the peak hours of traffic and necessitates the need to have optimal route analysis so as to reach the hospital in quick time from the accident spot. The study area extends from Arcot Road, Peters Road stretch in the north to Kathipara junction of G.S.T. Road, Sardar Patel Road stretch in the South. The entire east-west stretch of the city is included with in the above north – south limits. The study area is shown in fig.01. 

Figure 1

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

  • Ambulance Spot: Ashok Pillar to Raghavendra mandapam
  • Go straight to Inner Ring Road
  • Go straight in Inner Ring Road
  • Turn Right to MGR Salai
  • Turn Right to 1st Main Road 
  • Accident Spot: Raghavendra Mandapam to Hospital
  • Turn Back on to 1 st Main Road
  • Turn right to M.G.R. Salai
  • Turn right to North Usman road
  • Go Straight to South Usman Road
  • Turn right to Police Quarters Road
  • Go straight to Kothandaswami Koil Street 
  • Reach Bharathi Raja Hospital

For these accident spots, the routes to be traversed from the ambulance location to the hospital is depicted in Fig. 02. (Shown at the end of the paper)

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

  1. Adaptation of GIS for Transportation , Staff of Transport Research Board, NCHRP Journal, 1993.
  2. Integrating GIS Technology and Transport Models, Howard J. Simkowitz, TRR Journal, 1990.
  3. Exploring Route Choice Behaviour using GIS, Mohammed A Abdel, TRR Journal, 1995.
  4. Traffic Accident Analysis using GIS Oriented Data, Shigeru Morichi, 7th WCTR, Sydney, Australia.
  5. Forecasting Travel time, David B Roden, TRR Journal, 1996.

Figure 2