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An Analysis of Expressways Accidents in Singapore
Density Maps
Density maps are produced for all the years that are considered from 1992 to 2000 with the input data as individual accident points. Density maps show the highest concentration of a particular type of accidents. They are useful for looking at patterns rather than at locations of individual features. It creates a continuous raster surface from a set of input point features representing a magnitude per unit area, in our case the number of accidents per square kilometer. Hence by density maps the places where accidents are clustered can be easily distinguished.  Fig 2. Identified Accident-Prone Areas: Singapore Expressways Identification of accident-prone areas From the density maps produced for different years, the accident-prone areas can be easily distinguished. In order to get the real locations wherein the accidents are highly clustered all through these years, the raster layers are added up together. Thus the summed up layer gives us a density map showing accident density distribution. For better localization of the potential areas the resulting layer is reclassified i.e. producing a different raster layer by modifying classification range, color coding etc. Reclassification makes it easy to understand the distributions and also to make decisions from the displaying map. Figure 2, shows areas on Singapore expressways where accidents are highly clustered. As these areas have been determined based on 5 years of data, it can be argued that these areas may have certain factors which contribute to accidents recurrence there. The accidents may be clustered over an area but these can be caused by factors in a specific location. Hence the next step after identification of high accident locations is to perform a detailed safety analysis on these areas. Usually much less thought has been given to the safety analysis stage that follows. However it will help to determine abnormal accident pattern and would lead to selection of sites for appropriate remedial measures for the improvement of safety. This analysis of collision trends of specific accident types can be flexibly done and visually displayed using GIS. |