Investigating a standardised approach towards prioritisation of gravel roads upgrade to paved roads in KwaZulu-Natal

Abstract

Gravel roads are natural earth roads comprising a formation/roadbed layer and an additional top layer of gravel material, referred to as the gravel wearing course (GWC). Gravel materials used for constructing the GWC layer are obtained from local quarries or borrow-pits. The performance of gravel roads is dependent on numerous factors, which include gravel wearing course materials’ suitability as well as the geological founding materials of the roadbed layer. The major challenge with gravel roads is that they are overly sensitive to weather conditions as well as to the type and volume of traffic using them. In contrast to paved roads, gravel roads deteriorate faster and require more maintenance since they are not sealed with impermeable layers. As in most countries, South Africa has a substantial proportion of gravel roads within its road network. Gravel roads are cheap to construct when compared to paved ones, however, their maintenance costs are higher than those of a paved road over time, and that poses a challenge as the allocation of road infrastructure funds is usually lower than the gravel road network needs. This results in a maintenance backlog and a rapid rate of gravel road deterioration, as well as an increase in their maintenance costs. The KwaZulu-Natal Department of Transport, hereafter being referred to as the KZN-DoT, developed a project prioritisation model for all their project categories. This research focused on investigating the methodology that the KZN-DoT implements when prioritizing for gravel roads upgrade to paved. The investigation of the KZN-DoT’s prioritisation methodology was achieved through evaluating prioritisation factors considered, traffic baseline being used when selecting gravel roads to prioritise for upgrade as well as through investigating the right time of upgrading a gravel road to paved surface. The aim of evaluating the KZN-DoT’s prioritisation model was to enhance it by further proposing its refinements where necessary. Recommendations and conclusions were drawn from the research findings for respective research questions and objectives. This research recommends the addition of some prioritisation factors into the KZN-DoT model and a gravel road performance modelling tool to be developed and used to establish each gravel road’s deterioration pattern and in turn quantify economies of retaining it as a gravel road versus paving it to determine the right time to upgrade them. This is a large study that was conducted by the researcher for the KZN-DoT. In the context of this research, the phrase, “upgrading of gravel roads” shall mean the upgrading of gravel roads to paved surface i.e., bituminous seal surfacing or asphalt. Whereas, for the KZN-DoT’s prioritisation model for gravel roads upgrading to paved shall mean upgrading of gravel roads to blacktop surface which is the term that the KZN-DoT use interchangeably with bituminous seal surfacing. In this research, where the term unpaved and unsealed road is used, it shall mean gravel road.