Assessment of the relationship between the existing geometric design parameters, pavement conditions and accident occurrence at black spots: a cases study of Kampala-Jinja highway

Abstract

Every year more than a million people lose lives in traffic accidents, it is increasingly happening in developing countries like Uganda as the economy grows and the number of vehicles increases. Roads form the basic mode of transportation of people and freight in Uganda. However, traffic accidents are increasingly happening every year. Therefore, this study focused on assessing the relationship between geometric design parameters, pavement conditions and accident occurrence at black spots; a case study along Kampala- Jinja highway. To achieve the objectives of the study, collection of data relevant for the study was performed by beginning with the accident data, pavement conditions and later the geometric data. The accident data reports recorded was for the years 2018-2022 and it was obtained from the police stations along the case study, using accident frequency and the definition of a black spot, 17 black spots were identified at both road segments and intersections. A black spot was defined as a section of a road where 3 fatal accidents and 6 injuries occurred on a stretch of about 500m for the past 5 years. These black spots were then located onto a map in Arc-GIS 10.4. At each black spot identified, a visual assessment of the existing pavement conditions was done and it was found that there existed rutting due to overloaded trucks, cracking due to fatigue, shoulder erosion and pot holes due to poor drainage and roughness at certain road sections. For the measurement values of the existing pavement conditions, data was collected from Uganda National Road Authority (UNRA) and this included the International Roughness Index (IRI) and average rut depths. Average pothole depths were measured from the field using the straight edge method and the average depth values were considered. This data was summarized in a tabular form. At each black spot identified, the existing geometric design parameters, carriage way width, horizontal curve lengths, horizontal curve radius, vertical curve lengths, angle of deflections, longitudinal gradients, super elevations and stopping sight distance were extracted from a civil 3D survey map of Kampala-Jinja Road obtained from UNRA and design manual (MOWT, 2010). This data was summarized in a tabular form.