Safety analysis of unsignalized intersections under erroneous road crash data influence
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Date
2016-07-01
Authors
Ashar Ahmed
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Abstract
Accident data is the backbone of any country’s transportation database.
Identification of black spots and high risk zones are based on it. Without reliable and accurate information pertinent to accident location not even a single accident could be identified on the entire transportation network. The primary flaw in the Malaysian accident data was the ambiguous location of accident sites. Although this shortcoming was highlighted in the literature by different researchers but none had taken up the task to develop a procedure for its rectification which provided the motivation for this study. The aims of this research were to develop a method that could be used for the estimation of correct location for the accidents that occurred in
the past, to conduct microscopic analysis on the sites identified and to formulate risk estimation models that can incorporate the behavioral and traffic parameters relevant to Malaysian conditions. The rectification procedure required data from two sources; therefore, field data was collected from site while accident data was acquired from MIROS (Malaysian Institute of Road Safety Research). As a result of the rectification process, which involved the use of Nested Filtered Search Algorithm (NFSA) to match the accidents with the intersections where they might have occurred, 16 sites were correctly identified that initiated the second phase of the study. In this phase traffic data on each site was collected using data loggers while simultaneous video recording was made to extract behavioural data. A unique type of turning movement termed as the Weaving Merging Right Turn (WMRT) made by the minor road vehicles was newly identified. Further analysis, using conflict technique, revealed that WMRT results into less number of serious conflicts on wider major roads than the conventional right-turn, thus reducing the chance of occurrence of a serious conflict for all types of motorized vehicles. This parameter was utilized in the model formation along with gap acceptance and vehicle type to estimate the probability of serious conflict. The model enabled the estimation of safe critical gap for motorcycles and other vehicles turning right from the minor to the major road. Another new parameter known as ‘near side to far side volume ratio’ was formulated and found to be highly related with the accidents and conflicts occurring on site. This led to the discovery of a conditional relationship between the percentage of motorcycles, the ratio and the accidents and conflicts that occurred on each site. The probability of accidents and conflicts increased with decrease in the percentage of motorcycles moving in the far side direction provided that the near side to far side volume ratio remained greater than one. The results of this study will help remove errors from the accident data and improve the safety at unsignalized intersections.