Gravel to paved roads in KZN

Prioritising gravel to paved routes in KwaZulu-Natal

A high percentage of South Africa’s road network is unpaved, which, given budget constraints, poses a challenge in terms of their upkeep. This is compounded by a shortage of suitable gravel sources. A more viable option would be to pave highertrafficked sections. The following KwaZulu-Natal Provincial Road Network case study supports that argument.

By Gugu Ndlovu and Professor Dhiren Allopi*

Gravel-loss survey

This is an edited version of a technical paper. The full paper and references are available from the authors. Email: gugwana84@gmail.com / allopid@dut.ac.za.

The regravelling of unpaved roads at their optimal frequency extends the life of gravel borrow pits and also results in significant savings on road infrastructure budgets. Achieving this requires an in-depth understanding of gravel material behaviour when deployed as the wearing course under prevailing conditions. This must also be supported by an effective decisionsupport system for the prioritisation of the maintenance and upgrading of unpaved roads.

Within KwaZulu-Natal, the province’s Department of Transport is responsible for more than 24 713 km of gravel roads within the provincial road network. This requires adequate annual funding to cater for new access roads, and the maintainance and upgrading of the existing unpaved network. There is a vital need to enhance the existing planning criteria, and thus the optimal utilisation of funds.

Background

To date, the department has made significant progress in capturing all declared public roads into a single geographic information system (GIS). Both the declared paved and unpaved provincial road networks have been classified in accordance with the Technical Recommendations for Highways (TRH26, 2012). Traffic count surveys and road network condition visual assessments, in line with the Technical Methods for Highways (Draft TMH22, 2013), have also been carried out.

The latter assessments were completed following a call made by the National Department of Transport for all provinces to have updated input data for use in the Rural Road Asset Management System (RRAMS). This has a direct bearing on the allocation of the Provincial Road Maintenance Grant (PRMG) for the maintenance of the unpaved road network. Among other reasons, the PRMG was also established to supplement provincial investments for routine, periodic and special maintenance (Department of Transport Conditional Grant Framework 2016).

The outcome of KwaZul-Natal’s assessments shows that the network condition has worsened compared to previous years. Many issues have contributed to this, such as the underfunding of road maintenance projects, shortage of suitable road material sources, as well as the lengthy process of obtaining environmental approvals for borrow pits.

The majority of the funds to date have been used for the provision of new gravel roads and for the upgrading of gravel roads to paved roads.

Prioritisation methodology

The developed prioritisation system for the upgrading of unpaved to paved roads in KwaZulu-Natal ranks gravel road segments using selected prioritisation factors. The baseline traffic criteria used is 200 vehicles per day (vpd). Each prioritisation factor is represented as a separate GIS shape file layer. The factors were carefully selected to ensure that the department’s project priorities align with national and provincial strategies. Much of the data comes directly from the Provincial Growth and Development Programme, as well as outputs from other national and provincial strategies (Department of These figures show the road visual assessment information that can be stored within the Gravel Road Transport Project Planning Management System (GRMS) Framework 2018).

This graph shows the gravel road maintenance programme, which can also be stored within the GRMS

Prioritisation factor presented on GIS

Investigation of traffic baseline

Literature reveals that sealing can be considered as an option in a range of 50 to 500 vpd. It is therefore clear that the traffic baseline cannot be the same for all road segments and may vary due to prevailing conditions.

In KwaZulu-Natal’s case, benefit analysis from a road authority’s and road user’s perspective will be analysed to assess and make recommendations regarding baseline traffic. As the costs of maintaining unpaved roads differs from one geographic location to the next, so too will the traffic baseline criteria.

When to upgrade unpaved roads to paved?

For a road authority to determine the right time to upgrade an unpaved road, it has to have performance management tools in place to predict deterioration patterns. Updated input data like traffic counts, complemented by a good record-keeping of road maintenance history, becomes vital for these tools to bare positive results.

The right time to upgrade is when it becomes too costly to maintain. The rate of gravel loss assists in determining regravelling frequencies and the agent’s costs of maintaining a gravel road.

Recommended approach

Setting up the targeted and intervention roughness coefficient for each road class must be undertaken so that maintenance can be programmed accordingly.

Management of gravel road performance using tools such as the Gravel Loss Prediction Model (GLPM) is critical, as it helps the responsible agent to plan accordingly and timeously. The GLPM predicts the rate at which a gravel road will lose gravel. This then determines the optimal regravelling frequency.

The GLPM and allied tools like the Gravel Road Management System (GRMS) store important information about the behaviour of gravel roads. They can also incorporate other databases such as the Material Information Management System. It is important for roads authorities to have a materials database of local borrow pits and suitable quarries. This helps in projecting associated maintenance costs. It also helps in forecasting the future deficit of borrow pit material so that future maintenance strategies can be planned well in advance. Being able to predict the future demand and supply of quarry and borrow pit material can also assist in determining future costs and the best timing for maintenance interventions.

Conclusion

Prioritising the upgrading of unpaved roads to paved must consider their historic behaviour. This can be holistically approached with ease when supported by inputs from the GLPM tool and other databases. Road asset managers then need to investigate the percentage split required to optimally distribute road funds according to costs and socioeconomic priorities.

*Gugu Ndlovu is a project manager at Sanral and Professor Dhiren Allopi works out of the Department of Civil Engineering at Durban University of Technology.

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