Improving haulage unit operation efficiency at an open-pit mine in Alto Paranaíba, MGAbstract
This article presents a study aimed at improving the haulage unit operation in a mining company located in the Alto Paranaíba region, in the state of Minas Gerais. The objective was to evaluate the effects of increasing the truck speed limit from 40 km/h to 45 km/h, combined with mine infrastructure improvements, such as: access road classification, traffic signage, geometric road design and drainage, running surface enhancements, as well as operator training and standardization through a Work Instruction (WI). The methodology compared KPIs across two equivalent periods, from May to September of 2023 and 2024, with a data integrity index of 89.9%, using the Fastmine dispatch system. The results show an 18% increase in productivity, from 211.72 to 249.87 t/h, 13.41% reduction in cycle time, 50% decrease in incidents, and an estimated reduction of 12 tons of CO2 emissions, in addition to 3% decrease in specific diesel consumption per tonne.
Keywords:
mineral haulage; mine roads; operational efficiency; Safety; Sustainability.
1. Introduction
Open-pit mining is defined by the Brazilian Mining Code as the set of activities aimed at exploiting mineral deposits, including the dispatch of ore and waste rock to the feed points of processing units and to waste dumps (Darling, 2011). The selection of loading equipment, such as hydraulic excavator, rope shovel, or wheel loader, depends on the scale of the mining face, the selectivity required to separate ore from waste, the volume to be moved, and the capacity of each machine (Newman et al., 2010; Fisonga and Mutambo, 2017). The haulage unit operation in open-pit mining is one of the most critical and costly processes, and it can account for up to 60% of the mine’s total production cost (Soofastaei, 2017; Hustrulid et al., 2013). Beyond its economic impact, this stage directly influences environmental and safety indicators due to fuel consumption, pollutant gas emissions, and the risks associated with the movement of large equipment.
Prior to hauling, fragmentation of the rock mass is essential to enable loading, when mechanical disaggregation does not meet the required size distribution, drilling and blasting with explosives are employed. The blast design must consider bench height, hole diameter and inclination, burden, spacing, type of explosive and stemming, as well as proximity to communities in order to mitigate vibrations and dust dispersion (Botelho, 2014; Racia and Peroni, 2017; Quaglio, 2020). The choice of transport mode, whether trucks, conveyor belts, rail systems, or slurry pipelines. must take into account variables, such as distance, volume, particle size distribution, topography, and geotechnical conditions. In recent decades, technological advances, such as real-time monitoring, data analytics, and autonomous vehicles have helped reduce costs and improve operational safety (Darling, 2011; Hustrulid, Kuchta and Martin, 2013).
Auxiliary activities, such as maintenance of mining faces, haul roads, and dumps, ensure the continuity of mining operations and the integrity of equipment. The geometric design of haul roads must comply with NR-22, providing for safety berms, adequate signage, grades compatible with the fleet, and road crowning/crossfall to drain stormwater (Thompson, Peroni and Visser, 2019; Coutinho, 2017).
This study aims to analyze the impacts of increasing the speed limit of haul trucks in mining operations from 40 km/h to 45 km/h at a mining company located in the Alto Paranaíba region, Minas Gerais, Brazil. The proposal involves evaluating gains in productivity, cost reduction, risk mitigation, and environmental impacts. To this end, the study considers interventions in mine infrastructure, geometric upgrades to haul roads, and training programs, such as training on operational efficiency and fuel reduction, individualized feedback, as well as updates on new technologies and systems. In this way, the research contributes to strategic decision-making in the haulage management of mining operations, offering a model that can be applied and replicated in different production contexts.
The proposed modeling framework is based on a structured, sequential set of criteria for the technical and operational evaluation of mining haul roads. This approach ensures that any change to posted speed limits is implemented only after a rigorous, evidence-based verification of roadway safety conditions, geometric design parameters, and structural capacity. In addition, it is intended to assess the effects on operational safety by identifying additional or mitigated risks, and to examine the impact on fleet sizing, in order to understand whether the change helps optimize equipment allocation and reduce cycle times. These specific objectives provide a basis for strategic decisions that reconcile productivity, sustainability, and safety in mineral haulage.
2. Materials and methods
This study is applied research with a quantitative approach and an exploratory-explanatory design, aimed at improving the haulage unit operation in open-pit mining. The selection of key performance indicators (KPIs), namely average speed, productivity (t/h), diesel consumption (L/t), and CO2 emissions enables the measurement of efficiency gains, as well as safety and sustainability outcomes. The research was carried out at a mining operation in the Alto Paranaíba region (Minas Gerais, Brazil), and two scenarios were defined:
Scenario A (pre-improvement): 40 km/h speed limit, May-September 2023.
Scenario B (post-improvement): 45 km/h speed limit, May-September 2024.
The adoption of equivalent time windows made it possible to isolate seasonal effects, demonstrating that, in the post improvement period, precipitation did not exert a statistically significant impact on the operational indicators. Therefore, the observed gains can be attributed to the interventions implemented in the haulage system. Data were extracted from the dispatch system and validated for integrity through outlier removal and data standardization procedures. In addition, speed heat maps were generated to identify operational bottlenecks (Paiva et al., 2025).
The haulage operations analyzed in this study were carried out using 8×4R haul trucks, configured with a nominal payload capacity of 40 tons, as shown in Figure 1. This type of equipment is widely employed in open pit mining operations due to its operational robustness and suitability for mine haul road conditions. The 8×4R configuration, consisting of two steerable front axles and two driven rear axles, provides enhanced stability, load carrying capacity, and ramp performance, thereby contributing to the efficiency of the haulage cycle.
Haul truck with an 8×4R configuration. Source: Adapted by the author based on the equipment technical manual.
The geometric dimensions and technical parameters of the truck, including wheelbase, front and rear overhangs, turning radius, and axle load distribution, are compatible with the design and safety criteria of the mine’s internal road network, enabling the assessment of the operational impacts of increasing the speed limit without compromising the structural integrity of either the equipment or the haul roads.
The methodological steps comprised the classification of mine haul roads, the assessment of road width in accordance with NR-22, the verification of grades and minimum curve radii, the evaluation of the roads bearing capacity (CBR), the assessment of surface drainage conditions, and the review of mining signage. Each of these steps is described below.
2.1 Haul road classification
Initially, all mining roads were mapped and classified as primary, secondary, and tertiary haul roads, with the objective of establishing prioritization criteria for maintenance activities. Primary haul roads were defined as those intended for continuous haulage traffic along the main production cycles up to the discharge point, i.e., the crushers. Secondary haul roads are those that connect the mining faces to the primary road network. Tertiary haul roads are those associated with mine development activities (e.g., roads under construction or expansion to support advancing mining operations).
2.2 Haul road width assessment in accordance with NR-22
Haul road widths were verified according to the requirements established by Brazilian Regulatory Standard NR-22 (Occupational Safety and Health in Mining). For single-lane haul roads, the minimum criterion adopted was a width of at least twice the width of the largest haul truck operating in the mine. For dual-lane haul roads, the minimum criterion was three times the width of the largest haul truck. Measurements were performed in the field through topographic surveying and systematic visual inspections. Where nonconformities were identified, road widening was implemented to achieve compliance.
2.3 Grade verification
The longitudinal grades of the mine haul roads were evaluated based on topographic surveys and longitudinal profiles. Slope values were compared with recommended limits in accordance with internal procedures for the safe and efficient operation of haul trucks, considering braking capability, uphill performance, and fuel consumption. In sections where ramps with excessive gradients were identified, corrective interventions were carried out.
For the purposes of this study, a maximum longitudinal gradient of 10% was adopted, in line with practices recommended in the technical literature for mining haulage operations. Road segments presenting gradients exceeding this limit were identified, and corrective engineering interventions were implemented in order to ensure compliance with the adopted criteria and to maintain consistent operational conditions.
2.4 Minimum curve radius verification
The analysis of curve radii was conducted considering the proposed operational speed, the type of fleet in operation, and the traction conditions of the running surface, in order to ensure compatibility between haul road geometry and equipment operational characteristics.
2.5 Haul road bearing capacity assessment
The in situ strength of the pavement layer system in mining haul roads was determined using the Dynamic Cone Penetrometer (DCP), a standardized device that estimates the bearing capacity of the material by measuring cone penetration under a controlled sequence of hammer blows. The DCP was operated using a 575 mm drop height and a 60° cone angle, and cumulative penetration was recorded at regular increments (typically every five blows) until an approximate depth of 800 mm was reached or until refusal occurred. Refusal indicates the presence of very stiff materials, such as rock or large, coarse fragments. This procedure yields a resistance-depth profile, which is essential for assessing structural uniformity and the quality of compaction in layers trafficked by mining vehicles (Thompson, R. J.; Peroni; Visser, 2019).
Penetration measurements (mm per five blows) were converted to California Bearing Ratio, CBR (%), based on the correlation curve presented in Figure 2, which provides an empirical relationship between the DCP penetration index and the material’s bearing capacity under field conditions. According to Thompson, Peroni, and Visser (2019), the DCP-CBR relationship is specific to the standard DCP configuration. Moreover, readings obtained in wet materials or materials prone to saturation may underestimate CBR, requiring correction or careful interpretation under such conditions. Therefore, all subsequent analyses in this study adopted the experimentally recommended correlation curve for mining haul roads, ensuring methodological consistency with the procedure described in the technical literature.
Correlation between DCP penetration rate (mm per five blows) and the California Bearing Ratio (CBR, %). Source: Adapted from Thompson, R. J.; Peroni; Visser (2019).
2.6 Surface drainage condition assessment
Surface drainage conditions along the haul roads were evaluated through field inspections, cross-slope (transverse profile) assessments, and observations of roadway behavior during precipitation events. Key elements examined included the transverse crown/camber, roadside ditches, cross-drain outlets, and the overall condition of the running surface.
In segments where drainage deficiencies were identified, corrective actions were implemented, including geometric adjustments to the transverse profile, re-excavation/cleanout of side ditches, improvements to runoff conveyance and outlet structures, as well as surface regrading. These measures aimed to minimize water ponding, reduce pavement deterioration, and maintain operational safety, particularly during the rainy season.
2.7 Mine haul road signage
Mine road signage was evaluated in terms of visibility, standardization, and suitability for the operational traffic flow. A comprehensive inventory was conducted covering regulatory and warning signs, as well as vertical and horizontal markings and reflective delineation devices used to support nighttime operations.
As part of the implemented interventions, standardized signage and LED lighting were installed, and the mine signage map was updated. These actions aimed to improve visual communication with operators, reinforce operating limits, provide advance warning of curves, grades, and other critical areas, and support the increase in operating speed while maintaining high safety margins.
2.8 Fuel consumption and CO2 emission estimation
The assessment of carbon dioxide (CO2) emissions was based on a comparative analysis of the specific diesel fuel consumption associated with the hauled production over the evaluated periods. For this purpose, the relationship between fuel consumption and the mass of ore transported, expressed as liters per ton hauled (L/t), was adopted as an indicator of the energy efficiency of the haulage operation.
The conversion of diesel consumption to CO2 emissions considered only direct combustion emissions (an approach equivalent to tank-to-wheel TTW), using the widely adopted emission factor of 2.68 kg CO2 per liter. This corresponds to 10.19 kg CO2 per U.S. gallon of distillate fuel oil and is consistent with the emission coefficients published by the U.S. Energy Information Administration (EIA).
2.9 Implemented interventions
The program comprises fundamental pillars for improving mining operations. With regard to operational safety, actions were carried out through a structured management-of-change process, periodic training with mine operational teams, and a comprehensive review of work instructions applicable to all employees. Signage was also enhanced to improve night-time operations, using reflective strips on delineator posts equipped with LED lights. In addition, a road-sign inventory/map was implemented to standardize and manage road signage, promoting efficient and safe communication across all areas.
For the construction of new mining roads, the specifications of the road manual were applied starting from the subbase layer. In this layer, a coarser graded material was used and placed over the in situ material. The base layer was composed of rockfill and finer grained materials, in order to ensure structural stability and adequate bearing capacity of the roadway. Finally, the wearing course, corresponding to the upper portion of the road, was constructed using a gravel mixture. This layer plays a fundamental role in the functional performance of the roadway, directly influencing vehicle surface interaction, increased durability, surface drainage efficiency, and operational safety.
A speed map was developed based on the data collected after the haulage process improvement, and the comparison between the two analyzed periods showed an increase in travel speeds along the mining road routes. This map enabled a spatial visualization of speed variations across access roads, identifying segments with higher or lower operational flow. The analysis of the map supported the identification of bottlenecks and opportunities for further improvements in the mine’s infrastructure.
3. Results
Although exogenous factors, such as climate variability, cannot be fully isolated in observational studies of this nature, the comparative analysis demonstrated that climate variability did not significantly interfere with the operational results. The consistency of the outcomes across the analyzed periods reinforces the robustness of the conclusions, as presented in Table 1.
Comparability criteria between study periods (2023 vs. 2024) and key operational variables. Source: Author’s own archive.
3.1 Haul road infrastructure and road design
The classification of access roads and the widening of running lanes, as shown in Figure 3 (single-lane roads with a width greater than or equal to twice the width of the largest haul truck, dual-lane roads with a width greater than or equal to three times that width), improved operating comfort and reduced the need for critical maneuvers.
With regard to the structural composition, the primary roads presented a subbase composed of coarse graded material with blocks of up to 50 cm, while the base layer was composed of rockfill and finer grained materials, with particle sizes of approximately 20 cm.
Superelevation and surface drainage (road crowning/crossfall) mitigated risks during the rainy season. In turn, the GC/SP criteria (gradation coefficient and shrinkage product) ensured the functional performance of the wearing course/surfacing layer (Thompson, R. J.; Peroni; Visser, 2019).
The truck speed map in mining operations is an essential tool for real-time fleet monitoring and management. In addition to supporting operational safety, it also serves as a strategic resource for improving productivity. With this information, it is possible to propose targeted interventions, such as improvements to haul-road geometry, fleet redistribution, or adjustments to haulage cycles, promoting more regular traffic flow and reducing operating costs.
Figure 4 presents the speed map after the speed-limit increase, clearly highlighting the road segments where trucks began operating above 40 km/h, together with the value corresponding to the previous speed limit, and also, segments where speeds remained constrained by operational or geometric conditions.
Ten Dynamic Cone Penetrometer (DCP) tests were conducted on the mine road on a 50 m grid, with the objective of estimating CBR values in accordance with technical recommendations. Testing followed the technical procedures and methodology proposed by Thompson, Peroni, and Visser (2019).
The coordinates of the tested points, as well as the corresponding results, were recorded and compiled in Table 2.
Six tests were randomly selected, and the results were classified according to layer depth, considering 150 mm thickness increments for each layer, as shown in Table 3.
3.2 Safety
Incidents were defined according to a standardized internal procedure, encompassing events with and without material damage or personal injury. Incidents were classified by severity level, as summarized in Table 4. In the periods analyzed, all recorded incidents resulted exclusively in property damage, with no personal injuries reported.
As illustrated in Figure 5, the technical work instruction was revised to incorporate the increase in operational speed. Following the update, all employees received specific training, ensuring the correct implementation of the new guidelines and the maintenance of safety and efficiency standards.
3.3 Integrity and operational constraints
Outliers from the mine monitoring system were excluded. System errors, such as negative speeds or extreme values as high as 200 km/h were removed, resulting in a data integrity rate of 89.9%. The boxplot presented, as shown in Figure 6, compares the distribution of the average operational haulage speed between 2023 and 2024, highlighting significant changes in data behavior. In 2024, a positive shift in the median relative to 2023 is observed, indicating a consistent increase in average speed. In addition, the interquartile range for 2024 is smaller, demonstrating reduced internal variability and greater process homogeneity.
Comparisons between periods were supported by explicit statistical evidence, including the sample size per period and comprehensive descriptive statistics for cycle time. These summaries report measures of central tendency and dispersion appropriate for different distributional shapes (e.g., mean and standard deviation, as well as median and interquartile range, including quartiles). Inference was further supported by confidence intervals and hypothesis tests for between-period comparisons, and practical relevance was characterized using effect sizes, as recommended for operational variables. Collectively, these results indicate that the cycle-time improvement observed after the speed increase remains consistent, as shown in Figure 7.
3.4 Efficiency and sustainability
These integrated actions ensured process stability and mitigated risks arising from the higher speed, demonstrating that performance gains can be achieved without compromising safety standards, provided they are supported by technical planning and preventive actions. Figure 8 shows a 10% increase in average speed (31.60 to 34.62 km/h).
Productivity increased by 18% (from 211.72 to 249.87 t/h), as illustrated in Figure 9. It is important to emphasize that this gain is not solely attributable to the higher speed, but rather to a set of improvements implemented in the operational process, including a 13.41% reduction in cycle time, an 8.58% decrease in loading time, and the mitigation of queues at loading and dumping points. Taken together, these factors indicate a systemic improvement that enhanced the overall efficiency of the operation.
Carbon dioxide (CO2) is one of the main greenhouse gases emitted by human activities, especially through the combustion of fossil fuels, such as coal, oil, and natural gas. These emissions occur primarily in sectors, such as transportation.
As shown in Figure 10, specific fuel consumption (L/t) decreased by 3% between the evaluated scenarios, corresponding to an absolute reduction of 4,452 liters of diesel over the analyzed period. This reduction avoided the emission of approximately 12 t of CO2, thereby reinforcing the commitment to sustainability in mining operations. The average haulage distance did not vary significantly between the scenarios, indicating that the observed gains were not associated with shorter transport routes, but rather with increased haulage cycle efficiency achieved through operational and infrastructural improvements.
4. Dicussion
4.1 Structural capacity of the wearing course and operational implications
According to the test results, the wearing course (top layer) achieved excellent performance: virtually all tests yielded CBR values above 80%. Only P8 recorded a value of 62%, which is still considered good for the truck model used at the mine.
4.2 Operational safety and associated risks
Safety is a non-negotiable pillar in mining environments. Increasing the speed limit, although it improves productivity and asset utilization, creates additional challenges for operational control. Higher speeds can intensify the risk of accidents, especially on curved sections, in areas with heavy pedestrian traffic, and in operations where the terrain presents irregularities.
4.3 Statistical interpretation of performance (2023 x 2024)
Although the extreme values remain similar between the two years, the wider dispersion observed in 2023 indicates a higher presence of atypical events or operational interferences. These results point to an improvement in overall performance in 2024, associated with the standardization of procedures and enhanced operating conditions, which contributed to greater stability and efficiency in the mine haulage unit operation.
4.4 Climatic constraints (rainfall seasonality)
Rainfall seasonality was observed over the analyzed periods, given that precipitation is a relevant environmental variable in operational mining studies. During the 2023 interval, cumulative rainfall reached 189 mm, whereas only 17 mm were recorded over the equivalent period in 2024, characterizing distinct climatic conditions between the analyzed scenarios. Although variations in rainfall have the potential to affect haul road trafficability and haulage efficiency, the results indicate that such climatic variability did not significantly influence the operational performance indicators analyzed in this study.
This outcome can be attributed to the infrastructure interventions implemented at the mine particularly improvements to surface drainage systems and running surface conditions which were expressly designed to mitigate rain-related impacts. As a result, stable operating conditions were maintained even during precipitation events, reinforcing the attribution of the observed performance gains to the implemented operational and infrastructural improvements rather than to exogenous climatic factors.
4.5 Integration of managerial and infrastructure measures
The infrastructure and management actions implemented covering signage, haul-road geometry and drainage, running-surface improvements, grading, and WI-based training were introduced as risk-mitigation measures to support the 5 km/h increase in the posted speed limit. The observed safety and stability indicators reported in the manuscript suggest that performance gains were achieved without a deterioration in safety outcomes under the new operating condition.
5. Conclusions
The results obtained demonstrate that the controlled increase of the speed limit from 40 km/h to 45 km/h, combined with structural and managerial interventions, delivered significant gains in the open pit mine haulage unit operation. This study contributes to the literature by proposing and demonstrating the application of a structured and replicable methodology for defining operational speed limits on mining haul roads, grounded in sequential technical and operational criteria.
Unlike approaches that assess the effect of speed-limit changes in isolation, the results indicate that the observed gains in productivity, operational safety, and environmental performance stem from the integrated adoption of measures related to haul-road geometric compliance, structural capacity, operating conditions, and management practices.
In this context, the increase in the posted speed limit should not be interpreted as an isolated causal factor, but rather as the outcome of a decision-making process based on verifiable technical criteria, which gives the model potential applicability across different open-pit mining contexts, subject to local operating conditions.
Funding information
Data availability
The data supporting the findings of this article are publicly available in the institutional repository of the authors institution at: https://repositorio.cefetmg.br/home; https://sig.cefetmg.br/sigaa/public/programa/defesas.jsf?lc=pt_BR&id=629
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