This paper presents a review of research and models regarding sustainability of railway passenger services. In order to take into account all relevant aspects in terms of environmental impacts of a railway passenger service, a holistic system perspective is required, that includes a whole life cycle assessment. A life cycle approach is important since comparison of for instance only the exhaust emissions of an electric vehicle with a petrol vehicle is misleading, due to neglecting the emissions of for instance electrical energy production process. Thus, all stages in energy carrier, vehicle and infrastructure life cycles are to be considered. Existing models are analyzed, as well as possible developments, focusing on diesel and electrical traction as the most common traction options in use, and on GHG emissions, especially on CO2, which takes the greatest part in all emissions. Issues and challenges in improving the environmental impact of railway passenger services are addressed. Additionally, several areas are indicated where environmental aspects could be included in future assessment models. The main challenge is answering how the existing partial assessments can be brought together and, together with filling the identified gaps, allow to conduct a comprehensive LCA which will produce real-world emissions estimations. Results of this paper will be used as an input in developing a framework for quantifying and improving overall environmental impacts of a railway passenger service.@en

Hybridization of diesel multiple unit railway vehicles is an effective approach to reduce fuel consumption and related emissions in regional non-electrified networks. This paper is part of a bigger project realized in collaboration with Arriva, the largest regional railway undertaking in the Netherlands, to identify optimal solutions in improving trains’ energy and environmental performance. A significant problem in vehicle hybridization is determining the optimal size for the energy storage system, while incorporating an energy management strategy as well as technical and operational requirements. With the primary requirement imposed by the railway undertaking to achieve emission-free and noise-free operation within railway stations, we formalize this as a bi-level multi-objective optimization problem, including vehicle performance, the trade-off between fuel savings and hybridization cost, influence of the energy management strategy, and other constraints. By deriving a Li-ion battery parameters at the cell level, a nested coordination framework is employed, where a brute force search finds the optimal battery size using dynamic programming for full controller optimization for each feasible solution. In this way, the global minimum for fuel consumption for each battery configuration is achieved. The results from a Dutch case study demonstrated fuel savings and CO2 emission reduction of more than 34% compared to a standard vehicle. Additionally, benefits in terms of local pollutants (NOx and PM) emissions are observed. Using an alternative sub-optimal rule-based control demonstrated a significant impact of the energy management on the results, reflected in higher fuel consumption and increased battery size together with corresponding costs.@en

Non-electrified regional railway lines with typically employed diesel-electric multiple units require alternative propulsion systems to meet increasingly strict emissions regulations. With the aim to identify an optimal alternative to conventional diesel traction, this paper presents a model-based assessment of hydrogen-powered propulsion systems with an internal combustion engine or fuel cells as the prime mover, combined with different energy storage system configurations, based on lithium-ion batteries and/or double-layer capacitors. The analysis encompasses technology identification, design, modelling and assessment of alternative powertrains, explicitly considering case-related constraints imposed by the infrastructure, technical and operational requirements. Using a regional railway network in the Netherlands as a case, we investigate the possibilities in converting a conventional benchmark vehicle and provide the railway undertaking and decision-makers with valuable input for planning of future rolling stock investments. The results indicate the highest fuel-saving potential for fuel cell-based hybrid propulsion systems with lithium-ion battery or a hybrid energy storage system that combines both energy storage system technologies. The two configurations also demonstrate the highest reduction of greenhouse gas emissions compared to the benchmark diesel-driven vehicle, by about 25% for hydrogen produced by steam methane reforming, and about 19% for hydrogen obtained from electrolysis of water with grey electricity.@en

This paper presents a simulation-based analysis of hybrid and plug-in hybrid propulsion system concepts for diesel-electric multiple unit regional railway vehicles. These alternative concepts primarily aim to remove emissions in terminal stops with longer stabling periods, with additional benefits reflected in the reduction of overall fuel consumption, produced emissions, and monetary costs. The alternative systems behavior is modeled using a backward-looking quasi-static simulation approach, with the implemented energy management strategy based on a finite state machine control. A comparative assessment of alternative propulsion systems is carried out in a case study of a selected regional railway line operated by Arriva, the largest regional railway undertaking in the Netherlands. The conversion of a standard diesel-electric multiple unit vehicle, currently operating on the network, demonstrated a potential GHG reduction of 9.43–56.92% and an energy cost reduction of 9.69–55.46%, depending on the type of service (express or stopping), energy storage technology selection (lithium-ion battery or double-layer capacitor), electricity production (green or grey electricity), and charging facilities configuration (charging in terminal stations with or without additional charging possibility during short intermediate stops) used. As part of a bigger project aiming to identify optimal transitional solutions towards emissions-free trains, the outcomes of this study will help in the future fleet planning.@en

This paper presents a method for estimating Well-to-Wheel (WTW) energy use and greenhouse gas (GHG) emissions attributed to the advanced railway propulsion systems implemented in conjunction with different energy carriers and their production pathways. The analysis encompasses diesel-electric multiple unit vehicles converted to their hybrid-electric, plug-in hybrid-electric, fuel cell hybrid-electric or battery-electric counterparts, combined with biodiesel or hydrotreated vegetable oil (HVO) as the first and second generation biofuels, liquefied natural gas (LNG), hydrogen and/or electricity. The method is demonstrated using non-electrified regional railway network with heterogeneous vehicle fleet in the Netherlands as a case. Battery-electric system utilizing green electricity is identified as the only configuration leading to emission-free transport while offering the highest energy use reduction by 65–71% compared to the current diesel-powered hybrid-electric system. When using grey electricity based on the EU2030 production mix, these savings are reduced to about 27–39% in WTW energy use and around 68–73% in WTW GHG emissions. Significant reductions in overall energy use and emissions are obtained for the plug-in hybrid-electric concept when combining diesel, LNG, or waste cooking oil-based HVO with electricity. The remaining configurations that reduce energy use and GHG emissions are hybrid-electric systems running on LNG or HVO from waste cooking oil. The latter led to approximately 88% lower WTW emissions than the baseline for each vehicle type. When produced from natural gas or EU2030-mix-based electrolysis, hydrogen negatively affected both aspects, irrespective of the prime mover technology. However, when produced via green electricity, it offers a GHG reduction of approximately 90% for hybrid-electric and fuel cell hybrid-electric configurations, with a further reduction of up to 92–93% if combined with green electricity in plug-in hybrid-electric systems. The results indicate that HVO from waste cooking oil could be an effective and instantly implementable transition solution towards carbon–neutral regional trains, allowing for a smooth transition and development of supporting infrastructure required for more energy-efficient and environment-friendly technologies.@en

The Netherlands have one of the highest rail electrification rates in the EU with over 75% of the railway network electrified (European Comission, 2018), offering environment-friendly trains operation. However, in order to achieve carbon neutral railway sector by 2050, significant investments are required to further improve environmental performance from trains operation, especially in regional nonelectrified networks with passenger services typically provided by diesel multiple unit (DMU) vehicles. Due to their low utilization, full electrification of such networks is often not economically viable, thus solutions are mainly sought in alternative propulsion system technologies, such as hydrogen fuel-cell multiple unit (FCMU) and battery-electric multiple unit (BEMU) vehicles (Klebsch et al., 2019). One of the main challenges in introducing BEMU trains is determining the electrification plan for the railway network, while satisfying requirements related to quality of service, maintaining current timetable, and vehicle-specific constraints. Previous research on BEMUs operation is mainly focused on continuous partial lines electrification, or eventually limited scenario analysis on intermittent electrification (Abdurahman et al., 2021), with the optimization-based methods still lacking in the literature. This study aims to fill this gap by proposing a method for developing an optimal electrification plan, while minimizing total costs and considering several electrification alternatives for each track section. @en

Hydrogen fuel cell multiple unit vehicles are acquiring a central role in the transition process towards carbon neutral trains operation in non-electrified regional railway networks. In addition to their primary role as a transport mean, these vehicles offer significant potential for applications in innovative concepts such as smart grids. Compared to the pure electric propulsion systems, fuel cell technology allows for cogeneration processes by recovering generated heat in addition to the provision of the electrical power. This paper presents the analysis of fuel cell hybrid-electric multiple unit vehicle employed in regional railway transport during regular service, and in vehicle-to-grid application during the off-service hours, where it provides the electrical and thermal energy for stationary consumers in terminal stations. The system dynamics are modelled using a backward-looking quasi-static simulation approach, with implemented real-time optimization-based control strategy for managing the power flows between different components. In a case study of selected vehicle and railway services in the Netherlands, the fuel cell system showed average hydrogen consumption of 0.4 kg/km, with the overall electrical efficiency of 38.89%. In vehicle-to-grid scenario, the system satisfied complete stationary power demand, and provided about 327 kWh of thermal energy during two-hours operation, reaching overall cogeneration efficiency of 66.81%.@en

Hydrogen fuel cell multiple unit vehicles are acquiring a central role in the transition process towards carbon neutral trains operation in non-electrified regional railway networks. In addition to their primary role as a transport mean, these vehicles offer significant potential for applications in innovative concepts such as smart grids. Compared to the pure electric propulsion systems, fuel cell technology allows for cogeneration processes by recovering generated heat in addition to the provision of the electrical power. This paper presents the analysis of fuel cell hybrid-electric multiple unit vehicle employed in regional railway transport during regular service, and in vehicle-to-grid application during the off-service hours, where it provides the electrical and thermal energy for stationary consumers in terminal stations. The system dynamics are modelled using a backward-looking quasi-static simulation approach, with implemented real-time optimization-based control strategy for managing the power flows between different components. In a case study of selected vehicle and railway services in the Netherlands, the fuel cell system showed average hydrogen consumption of 0.4 kg/km, with the overall electrical efficiency of 38.89%. In vehicle-to-grid scenario, the system satisfied complete stationary power demand, and provided about 327 kWh of thermal energy during two-hours operation, reaching overall cogeneration efficiency of 66.81%.@en

The railway sector is facing significant challenges in addressing the increasing concerns related to climate change, environmental pollution and scarcity of resources. This especially applies to often non-electrified regional railway networks, with passenger services provided by diesel-driven vehicles. Innovative propulsion system concepts offer significant improvement of energy efficiency and reduction of overall environmental impact from train operation. This study presents a life cycle assessment of greenhouse gas emissions linked to the implementation of alternative powertrain systems in conventional diesel-electric multiple-unit vehicles employed on the regional railway lines in the northern Netherlands. The analysis encompassed the retrofit of a standard vehicle to its hybrid-electric, fuel cell-electric and battery-electric counterparts, and a comparative assessment of life cycle emissions during a ten-year time horizon. Results indicated significant impact of the production pathway for alternative energy carriers to diesel, namely hydrogen and electricity. The largest reduction in total emissions (96.80%) is obtained for a fuel cell-electric vehicle running on hydrogen produced from electrolysis, with slightly lower performance shown by the battery-electric configuration using green electricity produced from wind power (95.92%). Maintaining the diesel engine in the hybrid-electric alternative leads to a potential overall emission reduction of about 27%, as a result of improved fuel economy offered by the implemented energy storage system, and could be considered as a cost-effective transition solution towards carbon-neutral trains operation.@en

Hydrogen fuel cell multiple unit vehicles are acquiring a central role in the transition process towards carbon neutral trains operation in non-electrified regional railway networks. In addition to their primary role as a transport mean, these vehicles offer significant potential for applications in innovative concepts such as smart grids. Compared to the pure electric propulsion systems, fuel cell technology allows for cogeneration processes by recovering generated heat in addition to the provision of the electrical power. This paper presents the analysis of fuel cell hybrid-electric multiple unit vehicle employed in regional railway transport during regular service, and in vehicle-to-grid application during the off-service hours, providing the electrical and thermal energy for stationary consumers in terminal stations. The system dynamics are modelled using a backward-looking quasi-static simulation approach, with implemented real-time optimization-based control strategy for managing the power flows between different components. In a case study of selected vehicle and railway services in the Netherlands, the fuel cell system showed average hydrogen consumption of 0.4 kg/km, with the overall electrical efficiency of 38.89%. In vehicle-to-grid scenario, the system satisfied complete stationary power demand, and provided about 327 kWh of thermal energy during 2-h operation, reaching the overall cogeneration efficiency of 66.81%.@en

Regional railways, often characterized by non-electrified lines and transport services provided by diesel-electric multiple units, require the identification of alternative propulsion systems to meet strict emission regulations. Hydrogen, when produced using green electricity, offers a carbon-neutral operation of trains from a well-to-wheel perspective. With the aim to identify an optimal alternative to conventional diesel traction, this paper presents a comparative assessment of hydrogen-powered propulsion systems with the internal combustion engine or fuel cells as the prime mover, in combination with different energy storage technologies, including Lithium-ion batteries and double-layer capacitors. The analysis encompasses the identification, design, modelling and assessment of alternative powertrains, with respect to the particular case-related constraints imposed by the infrastructure, technical and operational requirements. Focusing on the regional railways in the Northern Netherlands, we investigate the possibilities in converting conventional benchmark vehicles operating on the network and provide a simulation-based assessment in terms of overall energy consumption. The results indicate the highest fuel savings from the propulsion system with fuel cells and hybrid energy storage system, with negligible mass limit excess.@en

Regional non-electrified railways in Europe are facing significant challenges to improve energy efficiency and reduce greenhouse gas (GHG) emissions. In addition to GHG emission regulations, companies are also imposing voluntary emission reduction targets, not only because of corporate responsibility, but also in an attempt to improve their market share, company image, and value. Featured with low transport demand compared to the main corridors, complete electrification of regional lines is often not economically viable. The solutions are being sought in alternative energy carriers and catenary-free propulsion systems. The transition from conventional diesel traction is a complex and context-specific dynamic decision-making process that requires involvement of multiple stakeholders and consideration of numerous aspects. It requires in-depth analyses that include identification of available technology, design, modelling, and assessment of potential alternatives, with respect to the particular case-related constraints imposed by infrastructure, technical and operational characteristics (e.g., track geometry, speed, and axle load limitations, maintaining existing timetables, noise-free and emission-free operation in stations, etc.). Hence, the overarching aim of this thesis is to identify and assess potential solutions in reducing overall (Well-to-Wheel) energy use and GHG emissions from the operation of regional trains, focussing primarily on synergetic adoption of alternative propulsion systems and energy carriers. We use the case study of the Dutch Northern lines with rolling stock and train services of Arriva to undertake this research, providing several scientific and practical contributions.@en