Assessment of the Effects of Road Geometric Design Elements on Traffic Safety: A Case study from Gohatsion to Dejen Town

Abstract

The rapid and extensive increase in the number of motor vehicles caused certain negative results world-wide. Mitigating traffic accident disaster is of a prime concern and through the analysis of this study attempts are made to correlate road geometric constituents with the rate of traffic accidents. Road geometric design elements and traffic compositions were taken into consideration, and explanations were given on how they affect traffic accident in the region. The Abay Gorge, along Gohatsion–Dejen alignment, in Ethiopia witnesses frequent Road traffic accident catastrophes each year. As a research objective, this study has evolved to find the correlation between accident rate and road geometric constituents through examining the feasibility of statistical analysis techniques over the indicated variables. Accordingly, nine accident locations having frequent accident occurrences have been identified based on traffic police records obtained from two police stations. Then the accident rates of these subsections were determined. Next, the values of geometric parameters about these sub-sections are obtained from as-built road design outputs. Finally, a regression analysis is made between the selected geometric parameters and accident rates. Exploratory data analyses were conducted using Microsoft Excel Software to investigate relationships and checking of assumptions underlying the use of statistical analysis techniques, specifically using correlations and regression analysis of the data. The correlation is established in the form of an equation of Accident Rate (AR) as a function of road geometric parameters by considering the effect of individual elements on traffic accident. At the end of the study, significant relationships were found between some geometric design elements and accident rates that its impact agrees with the engineering intuition as expressed by the linear relationship between Accident rate and horizontal Radius (AR = 7.3053- 0.7334*R, with R2 = 0.9395). Thus, a combination of road geometric constituents correlates better with the rate of traffic accidents than individual geometric characteristics when multiple regression analysis is used with the highest value of coefficient of determination (R 2= 0.952). Buses/ Mini Buses and Heavy vehicles like trucks are involved in a maximum no of accidents representing 48.51% and 15.18% respectively followed by Pickups (12,21%), Others (6.93%), Cars and Station Wagon (6.27%), and Motor Cycle and Cycle (2.31%). Injuries are the dominating types of accidents constituting the highest variations in accident’s degree of severity (47.1%) followed by PDO (28.9%) and Fatal (24%) crashes.