Applicability of Existing Gravel-Road Deterioration Models Questioned

Abstract

Efforts by the Provincial Government of the Western Cape in South Africa to improve all aspects of gravel-road construction and maintenance since 2001 have resulted in such good performance that existing gravel-road performance models are of limited value in predicting future needs and properly evaluating the need for upgrading to surfaced standards. The performance of several well-constructed road sections, representing different age groups, climates, material properties, and traffic spectra, has been monitored since 2003 and compared with the prediction of various internationally accepted roughness and gravel-loss deterioration models. A background summary of the improved processes, a brief summary of the experimental design, and a discussion of existing models are presented, with emphasis on the immediate and potential future impact of results that were obtained over a period of almost 3 years. Improvements to performance models are suggested, and the impact at the project level and on strategic-level analysis and decision making is highlighted. Recommendations are made on periodic maintenance strategies based on potential economic, social, and environmental benefits.

Development of Performance Prediction Models for Gravel Roads Using Markov Chains

“…In addition to the general lack of the available GRMS that are tailored to suit the needs of small local agencies, research efforts are more designated towards solving specific issues related to managing gravel roads within the premise of the developing agency [1,[4][5][6][7][8][9][10]. This explains the importance of establishing specific rules, guidelines, and models that are designated for Wyoming gravel roads rather than following the generic practices available in the literature.…”

“…Also, these kinds of roads normally serve very low traffic volumes, which explains some of the indifference when it comes to the management of gravel roads [2,9,12]. The World Bank developed software to predict the performance of these roads such as the Roads Economic Decisions Model, the Deterioration of Unpaved Roads (DETOUR) Model, Highway Development and Management model (HDM-4), and the Roads Economic Decision Model (RED) [3,4,7,21]. These models are used to run economic evaluations related to road investment projects.…”

“…However, these models require a lengthy inputs list that may supersede the capabilities of small local agencies. These inputs are related to surface roughness, terrain type, traffic conditions, crashes, fatalities, injuries, speed, and geometric features [4,7]. Also, they are more appropriate for project level analysis rather than network level analysis.…”

Unsealed road pavement management: Surface condition deterioration and sustainability modelling

“…An assessment of models for South African conditions (Van Zyl et al 2007) produced different conclusions in that traffic volumes were found to have a low impact on the roughness progression in the HDM-4 model.…”

Improving performance and sustainability of unpaved roads: Stabilization and testing

“…Gradation and plasticity have long been recognized as critical parameters for performance of unpaved road surface materials (e.g., Hudson et al 1986;Jones and Paige-Green 2015;Paige-Green 1989;Skorseth and Selim 2000;Van Zyl et al 2007). Skorseth and Selim (2000) explained that unpaved road surface materials are different from granular base materials, because the base materials usually have a larger top size and contain a very small percentage of fines.…”