Effects Of Route And Geometric Design Deficiencies On The Road Users: A Case Study On Addis Ababa - Jimma Highway

Abstract

More proactively good road design and well-developed traffic management measures produce roads which are safer and which are less likely to develop as black spots. However, Addis Ababa - Jimma road, especially Gibe Bridge to Deneba road segment, among the roads and trails built and improved during the five years Italian occupation, at that time, considered to represent the optimum route as it was, today the road lacked most of the modern highway location, geometric design and construction features desirable for present day traffic volume, large size, heavy weight and high-speed traffic. These road segment, consists of 6m and 6.5m wide narrower road section and several narrower bridges are located in sharp horizontal curves, the curve length accounts 50.9% of the route, the existence of 56.24% of curves radii below 40m including all of the seven switch-back curves and 57.8% of the vertical alignment fall into 5%-10% grade. To alleviate these deficiencies, ERA conducted rehabilitation measures without major changes, except re-alignment of the road from station km 268+954 to 302+170 and the widening of existing 6m carriageway width to 6.5m to 7m in most parts of the route. However, still there is a traffic crash occurrence, particularly on Gibe bridge to Deneba road segment which has causing a significant human life loss with traffic crash rate of 1.57 and huge estimated property damages cost of 179,343.49 ETB/Km in five years of 2003-2007 E.F.Y for the road users as well as highway structures re-location/replacement costs of ETB 41,673,094.63 in four years of 2012-2015 G.C for the government are noticeable on the route mostly due to the initial geometric design deficiencies of the road. In order to address these problems, this research was done by reviewing traffic accident data of 11 Woredas and 3 City Administrations Police Offices, As-built Design Drawings, Tender and Final Project Reports of the existing Addis-Jimma Road Rehabilitation Project, traffic count data of the past 5 years and highway drainage crossing structures relocation cost of the past 4 years. The current ERA and AASHTO geometric design manuals as well as previous studies were also reviewed having access to the information in other countries in order to understand the existing knowledge and experiences. Comparative analysis was applied to characterize the collected data to investigate the deficiencies of geometric design attributes and highway drainage crossing structures relocation cost on the route by dividing the route into three segments, to identify the black-spot road segment by crash rate and property damages cost by dividing the route into four road segments. GIS based least cost route selection analysis was conducted by giving influence factor of 60% for slope and 40% for stream order. Finally, short-term (low-cost) and long-term (high-cost) engineering interventions including GIS based most appropriate route corridor selection (by the least cost path method using computer application of ArcGIS version 10 software) which can minimizes road traffic accident, travel time cost, vehicle operation and maintenance cost and highway structure maintenance cost has been recommended.