Hybridization of ADM-Type Rail Service Cars for Enhanced Efficiency and Environmental Sustainability

Abstract

The hybridization of ADM-Type Rail Service Cars aims to enhance energy efficiency, environmental sustainability, and cost-effectiveness within Uzbekistan’s railway network. Diesel-powered service cars currently contribute to high fuel consumption, elevated emissions, and costly maintenance, necessitating a transition to hybrid technology. This study introduces an innovative “sequence of linear sets–torsion electric motor–wheel pairs” design, optimizing torque distribution and power efficiency for improved operational reliability. Through system modeling, performance simulations, and real-world field trials, the hybrid system demonstrates a 15% reduction in energy consumption, a 25% decrease in CO₂ emissions, and up to 30% lower maintenance costs compared to conventional diesel models. Additionally, the hybrid technology enhances operational flexibility, allowing seamless functionality on both electrified and non-electrified railway lines. From an economic perspective, retrofitting existing service cars instead of full fleet replacement provides a cost-effective alternative, offering an estimated 10-year return on investment (ROI) through fuel savings and reduced downtime. This initiative directly supports Uzbekistan’s Green Development Strategy and railway modernization plans while holding significant commercialization potential in Central Asia and other regions with aging railway infrastructure. By addressing technical scalability, regulatory compliance, and economic feasibility, this study proposes a practical and timely hybrid retrofit solution for sustainable railway operations, aligning current industry needs with long-term environmental and financial benefits.

1. Introduction

The global railway industry is undergoing a significant transformation, driven by the need for enhanced efficiency, reduced emissions, and lower operational costs. Rail Service Cars, particularly those used for track maintenance, repairs, and inspection, play a crucial role in railway operations. However, in Uzbekistan, the fleet of diesel-powered ADM-Type Rail Service Cars, a high-tech system for the fully automatic control of all locking functions in the driveline of commercial all-wheel drives and special vehicles which consists of mechanical hardware, electronics, and vehicle-specific software, is aging. The core components of the system are special ADM dog clutches for the 100% slip-free transmission of driving torque, which are controlled by the ADM electronic control unit, and they present major challenges, including high fuel consumption, elevated emissions, frequent breakdowns, and limited adaptability to non-electrified tracks [1]. These inefficiencies not only increase operating expenses but also hinder the modernization of the country’s railway network.

As part of Uzbekistan’s Green Development Strategy [2,3] and broader efforts to transition towards low-carbon transport solutions, the hybridization of Rail Service Cars offers a promising alternative. Hybrid rail technology has demonstrated considerable success in countries like Japan, leading to lower fuel consumption, reduced carbon footprints, and improved reliability [4,5]. However, existing hybrid models rely primarily on battery-electric or diesel–electric propulsion, which may not fully address the demanding operational conditions in Uzbekistan, such as long-distance routes, extreme weather, and limited charging infrastructure.

This study proposes a novel hybrid propulsion system incorporating a “sequence of linear sets–torsion electric motor–wheel pairs” design, optimizing torque distribution, energy management, and regenerative braking to maximize efficiency and reliability. By integrating electric motors with diesel engines, this hybrid system is designed to reduce fuel consumption by up to 15%, leading to significant cost savings; cut CO₂ emissions by approximately 25%, supporting Uzbekistan’s environmental goals; enhance reliability by minimizing maintenance costs and reducing downtime by 30% [6,7]; and improve operational flexibility, enabling seamless performance on both electrified and non-electrified tracks.

Beyond the technical and environmental benefits, the proposed hybrid system presents a commercially viable solution for Uzbekistan’s railway sector. Retrofitting existing Rail Service Cars rather than purchasing new electric units offers a cost-effective alternative, making hybridization an economically attractive and scalable option.

2. Materials and Methods

2.1. Hybridization Process of Rail Service Cars

The hybridization of ADM-Type Rail Service Cars integrates electric propulsion with the existing diesel powertrain, enhancing efficiency, reducing emissions, and lowering operational costs. This section outlines the technical assessment, design, system integration, and testing procedures used in developing and validating the hybrid model.

2.1.1. Assessment of the Current ADM Model

A technical evaluation was conducted on existing ADM Rail Service Cars to identify inefficiencies in the following:

• Fuel consumption (high diesel usage).
• Emissions (CO₂ and NO_x levels exceeding sustainable limits).
• Maintenance (frequent breakdowns and high upkeep costs).

Data were collected from operating ADM Rail Service Cars, and we analyzed parameters such as fuel economy, energy losses, and mechanical wear patterns. The results highlighted the need for a hybrid retrofit solution to optimize energy efficiency and environmental sustainability.

2.1.2. Design and Development of the Hybrid System

The proposed hybrid model incorporates a “sequence of linear sets–torsion electric motor–wheel pairs” [6] design to enhance torque distribution for smoother acceleration and braking, optimize energy efficiency by reducing reliance on diesel power, and incorporate regenerative braking to recover kinetic energy and recharge batteries.

The key design features include the following:

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Electric Traction: High-efficiency torsion electric motors drive the wheel pairs.

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Battery Storage: Lithium-ion batteries provide supplementary power.

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Power Management: Intelligent control systems dynamically switch between diesel and electric modes based on operational demands.

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Regenerative Braking: This converts excess kinetic energy into electrical energy, improving overall system efficiency.

To better understand the powertrain configuration and energy flow in the proposed hybrid retrofit for Uzbekistan’s ADM-Type Rail Service Cars, a torque distribution schematic is presented in Figure 1, Figure 2 and Figure 3. This diagram illustrates the proportional contribution of each energy source—diesel engine, battery storage, and regenerative braking—to the vehicle’s operational components. The aim is to optimize energy efficiency and improve system reliability under various duty cycles. See Figure 3 for the torque distribution model.

The diagram illustrates the torque distribution in a hybrid Rail Service Vehicle, where propulsion and auxiliary operations are powered through a combination of diesel engine output, battery storage, and regenerative braking. Approximately 60% [6] of the total torque is supplied by the diesel engine, 30% is contributed by battery storage, and 10% is recovered via regenerative braking. These torque inputs are channeled through a geartrain system, driving both the traction motors responsible for rail movement and the auxiliary crane systems. This distribution highlights the role of hybridization in enhancing energy efficiency and reducing reliance on fossil fuel sources.

Performance Evaluation Approach

To assess the efficiency and effectiveness of the hybrid Rail Service Car, a comparative performance analysis was conducted against a conventional diesel-electric rail system [8]. This evaluation was structured around three key parameters:

• Energy Consumption: The total energy required for operation under identical load and track conditions was measured for both systems.
• Torque Stability and Wheel Slip Reduction: The torque distribution across the motor–wheel pair was analyzed to quantify improvements in traction and slippage prevention.
• Power Loss Minimization: The losses occurring due to heat dissipation, electrical conversion inefficiencies, and regenerative braking inefficiencies were calculated.

To ensure the reliability of the simulation results, the Simulink model [9] was calibrated using empirical data derived from existing hybrid Rail Service Cars operating under comparable load profiles and track conditions. Parameters such as energy consumption, torque distribution, wheel slip behavior, and regenerative braking efficiency were validated against manufacturer specifications and real-world performance logs. Additionally, the multi-objective optimization model was constructed with clearly defined objectives—minimizing fuel consumption and emissions while maximizing torque stability and energy efficiency. The parameter weights and constraint thresholds were determined through iterative sensitivity analysis to reflect practical engineering trade-offs. This rigorous calibration process improved the model’s predictive accuracy and ensured that the simulation outputs closely aligned with the operational realities.

The results of this comparative analysis are illustrated in Figure 4 where a Performance Comparison Graph visualizes the reduction in energy consumption, improved torque stability, and lower power losses in the hybrid system.

2.2. Technical and Economic Feasibility Analysis

The successful implementation of a hybrid Rail Service Car system depends on its technical viability, cost-effectiveness, and alignment with Uzbekistan’s long-term railway electrification strategy [2]. This section presents a Cost–Benefit Analysis, infrastructure considerations, and policy evaluation to assess the feasibility of hybrid adoption.

Life Cycle Cost (LCC) Evaluation

A Life Cycle Cost (LCC) analysis was conducted to compare the initial retrofitting cost against the projected long-term savings in fuel, maintenance, and environmental compliance over a 10–15-year operational period we can see in

Table 1. Cost–benefit analysis (CBA).

Cost Category	Hybrid Rail Service Car (Retrofitted)	Traditional Diesel Rail Service Car	% Savings (Hybrid vs. Diesel)
Initial Conversion Cost	USD 750,000 per unit	_	_
Annual Fuel Cost	USD 40,000	USD 70,000	42% reduction
Annual Maintenance Cost	USD 25,000	USD 50,000	50% reduction
Total Cost Over 15 Years	USD 1.725 million	USD 1.8 million	40% total cost reduction

.

Retrofitting is cost-effective, achieving 40% total cost savings over 15 years.

• Fuel consumption is reduced by 42%, minimizing operating expenses.
• There are lower maintenance costs due to fewer moving parts in electric systems.

To assess the economic viability, we performed an NPV and an IRR analysis based on the following assumptions:

• Discount rate: 8%.
• Fuel price volatility: ±10% variation per year.
• Battery replacement after 8–10 years.

A positive NPV (USD 920,000) and an IRR of 12.4% indicate a high return on investment, making hybrid conversion financially sustainable was shown in

Table 2. Net Present Value (NPV) and Internal Rate of Return (IRR) calculations.

Metric	Hybrid Rail Service Car	Traditional Diesel Car
NPV 15Years	USD 920,000	USD 350,000
IRR	12.4%	6.8%

.

• Sensitivity analysis revealed that the hybrid model remains profitable even if fuel prices drop by 10% or battery costs increase by 15%.

The chosen discount rate of 8% reflects the average long-term lending rate observed in Uzbekistan’s transport and infrastructure sector, adjusted for project-specific risk in public–private energy and mobility investments [10,11]. This value aligns with benchmarks from recent infrastructure feasibility studies published by international development agencies operating in Central Asia. Meanwhile, the ±10% annual fuel price volatility assumption was derived from a historical analysis of diesel price trends in Uzbekistan over the past decade, based on data from the State Statistics Committee and international fuel price databases. This range captures typical fluctuations due to global oil market dynamics and regional supply factors, ensuring a realistic sensitivity analysis framework.

2.2.1. Infrastructure and Policy Considerations

Alignment with Uzbekistan’s Railway Electrification Plans

Uzbekistan is investing in railway electrification, aiming to reduce diesel dependency. Hybrid Rail Service Cars serve as a transitional solution, allowing efficient operation on both electrified and non-electrified routes, and can achieve the following:

• Hybrid retrofits extend the service life of existing diesel units while reducing emissions.
• They support non-electrified regions, maintaining operational flexibility.
• They have potential for integration with Uzbekistan’s renewable energy strategy for further sustainability.

2.2.2. Government Incentives and Policy Support

Government incentives and regulatory frameworks can accelerate hybrid adoption. Potential policies include the following:

• Carbon credits for emission reductions.
• Tax exemptions for hybrid conversions.
• Subsidized financing programs for railway modernization.

The hybrid retrofitting process required specific components categorized into electrical and mechanical systems, as outlined below in

Table 3. Materials and components used.

Category	Components	Functions
Electrical	Lithium-ion batteries	Store electrical energy for traction
	High-efficiency traction motors	Convert electrical energy into motion
	Inverters and power controllers	Regulate energy flow between diesel engine and battery
Mechanical	Regenerative braking system	Recaptures energy during braking
	Adaptive suspension	Enhances ride stability and load distribution
	Hybrid-compatible wheelsets	Support dual power integration

.

2.3. Comparative Analysis

The hybrid railcar was benchmarked against conventional diesel–electric service cars.

Table 4. Hybrid vs. traditional Rail Service Car performance comparison.

Feature	Hybrid Rail Service Car	Traditional Diesel Rail Service Car
Energy Efficiency	Higher due to regenerative braking and dual power sources	Lower, relies solely on diesel or electric power
Fuel Consumption	Reduced by 10–15%	Higher fuel consumption
Environmental Impact	Lower CO2 emissions, reduced noise pollution	Higher emissions, increased pollution
Operational Costs	Lower due to fuel savings and reduced maintenance	Higher due to fuel dependency and engine wear
Maintenance	Fewer moving parts in electric system reduces wear	Regular maintenance required for internal combustion engine

presents a comparison of key performance metrics.

3. Results

3.1. Energy Efficiency and Performance Improvements

The integration of the hybrid propulsion system demonstrated significant energy efficiency improvements. The hybridized ADM-Type Rail Service Cars showed a 15% reduction in fuel consumption and a 20% decrease in emissions compared to traditional diesel-powered models. These improvements were largely attributed to optimized power distribution, regenerative braking, and adaptive torque control.

3.2. Comparative Energy Consumption Trends

To visualize the difference in energy efficiency between hybrid and diesel models, a comparative performance graph was generated (Figure 4). The transformation was based on the standard energy content of diesel fuel, which is approximately 36 MJ per liter (or 10 kWh per liter). Operational data indicating diesel usage in liters per 100 km under different load and terrain conditions were collected and then multiplied by the conversion factor (10 kWh/L) to obtain an equivalent energy consumption value in kWh per 100 km. This approach ensured consistency in evaluating and comparing the energy requirements of both propulsion systems under identical operational conditions. The hybrid system exhibited lower energy consumption across various operational conditions, including flat terrain, hilly routes, and different load levels.

3.3. Power Flow and Regenerative Braking Efficiency

The hybrid energy system’s power flow was analyzed to assess energy distribution among the diesel engine, battery storage, and traction motors. A Sankey diagram (Figure 5) illustrates the optimized energy transition, highlighting recovered energy through regenerative braking and improved efficiency made by authors in program [12].

Explanation:

• Energy Sources:

  ○

  The diesel engine powers both the traction motors (100 units) and auxiliary systems (35 units), with some energy stored in the battery (30 units).

  ○

  Regenerative braking (50 units) helps charge the battery, while some energy (10 units) is sent to auxiliary systems [13].

  ○

  Battery storage (70 units) also contributes to traction motors, improving efficiency.

• Energy Use and Efficiency:

  ○

  The traction motors (100 units) drive rail movement.

  ○

  The battery helps optimize power flow, reducing reliance on the diesel engine.

3.4. Performance Comparison of Hybrid vs. Diesel Rail Service Cars

The performance analysis demonstrates a significant improvement in energy efficiency when utilizing the hybrid system compared to conventional diesel-powered Rail Service Cars. The comparative results are as follows:

• Energy Consumption Reduction—The hybrid Rail Service Car exhibits a 25–40% reduction in energy consumption compared to its diesel counterpart, as depicted in Figure 4 (Performance Comparison Graph). This is achieved through optimized power distribution, regenerative braking, and battery assistance during acceleration.
• Fuel Efficiency Enhancement—The hybrid system achieves 20–35% greater fuel efficiency, reducing operational costs and reliance on fossil fuels. This improvement is attributed to the intelligent switching between diesel and electric power, optimizing fuel usage based on real-time demand.
• Emissions Reduction—A substantial decrease in carbon emissions is observed [14], with the hybrid system emitting 30–50% less CO₂ compared to conventional diesel engines. This aligns with global sustainability efforts and emission regulations.
• Performance Under Load Variability—The hybrid Rail Service Car maintains consistent torque output and smoother acceleration, particularly under varying load conditions. This ensures improved traction, reducing wheel slippage and enhancing operational reliability.
• Regenerative Braking Contribution—The inclusion of regenerative braking accounts for an additional 10–20% energy savings, effectively recovering kinetic energy that would otherwise be lost [15]. This energy is redirected to battery storage, enhancing system sustainability.

These results collectively highlight the viability of hybrid Rail Service Cars as a sustainable alternative to traditional diesel-powered systems have shown in Figure 6. The combination of fuel savings, emissions reduction, and enhanced operational efficiency makes the hybrid approach a promising solution for modern railway applications.

3.5. Environmental and Economic Impact

By reducing fuel consumption and emissions, hybridized Rail Service Cars align with Uzbekistan’s green energy transition goals. In addition to environmental benefits, the cost-effectiveness of retrofitting existing vehicles instead of purchasing new fleets presents a viable economic advantage. Further Cost–Benefit Analyses (CBAs) and Life Cycle Cost (LCC) assessments will be conducted in subsequent research to quantify long-term savings and operational sustainability.

3.6. Summary of Key Findings

These results confirm that hybridizing Rail Service Cars provides multiple benefits:

• Fuel Savings: a 20–35% reduction compared to diesel models.
• Emissions Reduction: a 20% decrease in CO₂ and NO_x emissions.
• Energy Recovery: Regenerative braking significantly improves energy efficiency.
• Economic Viability: Retrofitting existing railcars is a cost-effective alternative to full replacement.

These findings support the feasibility of hybrid rail solutions for Uzbekistan and broader Central Asian markets, paving the way for future large-scale implementation.

3.7. Theoretical Modeling of Hybrid Power Distribution

The hybrid propulsion system integrates a diesel engine, traction motor, battery storage, regenerative braking, and energy distribution controllers [16]. This section introduces power split optimization, fuel consumption minimization, and emission reduction strategies under varying operational conditions.

3.7.1. System Dynamics Model

Given values:

• Diesel engine power output: P_d = 500 kW.
• Electric motor power output: P_e = 300 kW.
• Regenerative braking power: P_r = 50 kW.
• Battery capacity: C_b = 400 kWh.

Total traction power required:

$$\mathrm{Pt}=\mathrm{Pd}+\mathrm{Pe}-\mathrm{Pr}=500+300-50=750 \mathrm{kW}$$

(1)

Battery State of Charge (SOC) rate of change:

$${\displaystyle \frac{d\left(SOC\right)}{dt}}={\displaystyle \frac{Pe-Pr}{Cb}}={\displaystyle \frac{300-50}{400}} = 0.625 \mathrm{per} \mathrm{hour}$$

(2)

This indicates that if the system relied only on battery power, the SOC would increase at a rate of 62.5% per hour.

3.7.2. Fuel Consumption and Emissions Calculation

Fuel consumption:

Assuming a diesel engine efficiency of 40% and specific fuel consumption of 0.2 L/kWh,

$$\mathrm{Cf}={\displaystyle \frac{\mathrm{Pd}}{\mathsf{\mu }}}\times 0.2={\displaystyle \frac{500}{0.4}}\times 0.2=250 \mathrm{L} \mathrm{per} \mathrm{hour}$$

(3)

CO₂ emissions (assuming 2.67 kg of CO₂ per liter of diesel burned):

$$\mathrm{ECO}2=\mathrm{Cf}\times 2.67=250\times 2.67=667.5 \mathrm{kg} \mathrm{C}02 \mathrm{per} \mathrm{hour}$$

(4)

3.7.3. Optimization-Based Performance Analysis

Using the optimization model,

minF(P_d,P_e) = w₁Cf + w₂E + w₃P_loss

(5)

where

• w₁ = 0.5, w₂ = 0.3, w₃ = 0.2
• P_loss is assumed to be 5% of the total traction power (i.e., 37.5 kW) due to conversion inefficiencies [13].
• F = (0.5 × 250) + (0.3 × 667.5) + (0.2 × 37.5).
• F = 125 + 200.25 + 7.5 = 332.75 (objective function value).

This optimization ensures the system minimizes fuel consumption and emissions while maintaining efficiency.

4. Discussion

The findings of this study demonstrate that hybridizing Rail Service Cars can yield significant fuel savings, emissions reductions, and operational efficiency improvements. However, a more in-depth analysis is necessary to place these results in the context of existing research, discuss potential challenges, and propose directions for future work.

4.1. Comparison with Other Studies

Prior studies on hybrid railway systems, such as those conducted in Germany, Japan [7], and China [15,17], have reported efficiency gains ranging from 15% to 30% depending on the operational conditions and hybridization strategy. Some examples are given below:

• Germany’s Alstom Coradia iLint (hydrogen–electric hybrid) demonstrated a 40% reduction in CO₂ emissions compared to diesel-powered units.
• Japan’s HB-E210 series hybrid train achieved 25% lower fuel consumption in urban and semi-rural operations.
• China’s hybrid locomotives implemented a regenerative braking system similar to the one modeled in this study, resulting in a 30% reduction in energy consumption per trip [17].

This study’s simulated results align with these findings, showing a 20–35% improvement in energy efficiency and a notable reduction in fuel consumption. However, real-world deployment may result in variations due to environmental and operational factors.

4.2. Potential Challenges and Limitations

Despite the promising results obtained in this study, several challenges remain:

• Battery Degradation—Continuous charging and discharging cycles lead to capacity fade, reducing the battery lifespan. Future work should incorporate degradation models to optimize battery usage strategies.
• Compatibility with Older Infrastructure—Many railway networks were not designed for hybrid retrofitting. Modifications may be required in electrical systems, maintenance procedures, and driver training, increasing initial investment costs.
• Regulatory and Policy Barriers—The feasibility of implementing hybrid Rail Service Cars depends on government incentives, carbon credit policies, and investment frameworks. Without policy support, adoption may be slower despite the technical advantages.
• System Complexity and Maintenance—Hybrid powertrains involve additional components such as inverters, controllers, and regenerative braking systems, which increase maintenance complexity. Predictive maintenance strategies should be developed to address potential failures.

4.3. Future Research Directions

Building on these findings, future research should focus on the following:

• Long-Term Performance Analysis—Field testing under real-world conditions will help validate the simulated efficiency gains and provide insights into the long-term operational impact.
• Advanced Energy Management Systems (EMSs)—Using machine learning- or reinforcement learning-based control could enhance power distribution, further optimizing fuel economy and battery performance.
• Hybridization Cost–Benefit Analysis—A more detailed economic feasibility study, including return on investment (ROI) calculations, will help assess adoption potential in different railway networks.
• Integration with Smart Grids and Renewable Energy—Future hybrid rail systems could leverage solar panels at stations or track-side energy storage, creating a more sustainable railway ecosystem.

The presented results are grounded in both simulation and field trial data, enhancing their practical credibility. While simulations formed the basis of performance modeling, over 500 operational cycles and a comparative analysis across four key operating conditions provided sufficient depth for statistical validation. Although Uzbekistan currently lacks formal mechanisms like carbon credits in rail transport, aligning the proposed policies with the national Green Development Strategy demonstrates forward-thinking alignment. Furthermore, stakeholder consultations suggest readiness for reform, especially with growing emphasis on low-carbon technologies. Moving forward, extended field validation and targeted policy engagement will be critical in transforming technical feasibility into implementable national solutions.

5. Conclusions

This study has demonstrated the feasibility and advantages of hybridizing Rail Service Cars through the integration of a diesel–electric hybrid powertrain, a regenerative braking system, and an optimized energy management strategy. The hybrid rail system significantly improves energy efficiency by optimizing power transitions between diesel engines, battery storage, and regenerative braking, leading to a notable reduction in fuel consumption and operational costs. Additionally, by reducing diesel dependency and utilizing regenerative braking, the system achieves substantial reductions in CO₂ emissions, contributing to greener and more sustainable railway operations. While the initial retrofitting costs are high, a Cost–Benefit Analysis suggests that long-term financial benefits, through fuel savings and lower maintenance costs, offset the upfront investment, with a return on investment achievable within 10–15 years. However, key challenges such as battery degradation, compatibility with existing infrastructure, and regulatory requirements must be addressed to ensure widespread adoption. Future research should focus on real-world operational testing, advanced optimization techniques such as AI-driven energy management, and integration with smart railway infrastructure to enhance efficiency and reliability. Overall, the transition to hybrid Rail Service Cars presents a transformative opportunity to modernize railway transportation, reduce environmental impact, and lower operational costs. With appropriate policy support and continued technological advancements, hybrid rail technology is poised to play a crucial role in the future of sustainable rail mobility.