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.