Evaluating the Major Causes of Road Traffic Accident Occurrence Related to Geometric Design Elements of Addis Ababa -Debre Brehan Trunk Road
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Date
2023-06
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Addis Ababa University
Abstract
Road safety issue becomes a worldwide concern specially for developing countries these days since it results in a serious social and economic problems. Several Geometric design and safety research have been undertaken by aiming to improve roadway designs and providing a forgiving roads to the road users. The impact of geometric design factors such as horizontal and vertical curves, lane width, shoulder width, super elevation, median width, curve radius, sight distance, and others on safety has been investigated. However, the relationship between geometric design components and accident rates is remained complicated and unclear since there is a scarcity of data on the association between geometric design features and the accident rates.
This study's primary objective is to investigate the geometric design related factors that influence the frequency and severity of traffic accidents on the Addis Ababa–Debrebrehan Trunk Road, by considering design elements such as the average degree of curvature, average gradient, number of lanes, lane widths, shoulder widths and types, median widths and types, total surface width, rural-urban classifications, speed limits, and the presence of structures.
As-built drawings, findings from an inventory assessment of the roads, information on traffic volumes, and traffic accidents reports from six consecutive years have been collected for this investigation. Empirical and descriptive statistical analysis models have then been used to analyses the data. In order to analyses the count/discrete outcome variable of traffic accident frequency, a generalized linear model family of Negative Binomial Regression model has been used and Ordinal Logistic Regression Model with Probit link function for severity analysis, by considering geometric design features as continuous and categorical independent variables. As a result, a total of 1192 traffic incidents were recorded and used for evaluation, of which 274 resulted in fatal, 293 in serious injury, 182 in minor injury, and 443 in property damage only crashes.
Thus, the model for accident frequency analysis has demonstrated a convergence value for the segment length, average daily traffic, median width, number of lanes, outside shoulder width, average degree of curvature, average gradient, and speed limit. In addition to the frequency model, the severity analysis model has also reached at convergence for the vertical gradient, degree of curvature, availability of structures, median width, surface width, right and left shoulder widths and availability of median barrier.
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Keywords
Crash Frequency, Accident Severity, Geometric Design Elements, Negative Binomial