Investigating the effect of traffic volume and environmental factors on Bituminous road deterioration in Kampala.

Abstract

The road network is the backbone of transport systems in Uganda. Road transport is the most dominant mode of transport and it accounts for over 90% of the cargo freight and passenger movement. The entire road network in Uganda totals to 144,785 kmof this only5,100 km(4%) ispaved, the rest being gravel or earth roads. Kampala(the study area) has an estimated road network of 2,110 km of which only 578 km is paved.One of thechallenges faced by agencies responsible for the development, construction, and maintenance of these roads is axle loading control partly due to the constantly increasing traffic volumes (estimated at 6%), which causes the actual axle loading imposed on the pavementstovary from the design axle loading. When these roads are exposed to destructiveclimateand traffic loading, the pavements deteriorate faster resulting in poor road conditions duringthe time in which theroadis in service, especially when maintenance interventions are not duly scheduled. This research was conducted to determine the effect of traffic volume and environmental factors on road deterioration in order to determine at what point in time a pavement should be maintained. Traffic volumes were determined by carrying out Manual Classified Traffic Counts and the volume was converted to axle loadingusing an equation stated inRoad Design Manual Vol III, Part 1 for Flexible Pavements. Environmental conditions were incorporated into the research by using an environmental coefficient that was given in the HDM–4. Road conditions were estimated using a Road Visual Condition Assessment from the Ministry of Works and Transport. It was observed that road conditions deteriorate more under the combined effect of environmental factors and increase in axle loading that is to say, for Old Kira road when axle loading increases from 0.69 MESAL/lane/year to 3.00 MESAL/lane/year, the IRI will increase from 7.9 to 9 that isfrom fair road conditions to poor road conditions which will take approximately 2 years and for Kyebando – Kisalosalo road, when axle loading increases from 0.45 MESAL/lane/year to 3.85 MESAL/lane/year the IRI will increase from 6.6 to 9 which is from a fair to a poor road condition which will happen approximately in 4 years.