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[en] Urban rail has widely recognised potential to reduce congestion and air pollution in metropolitan areas, given its high capacity and environmental performance. Nevertheless, growing capacity demands and rising energy costs may call for significant energy efficiency improvements in such systems. Energy consumed by stabled rolling stock has been traditionally overlooked in the scientific literature in favour of analysing traction loads, which generally account for the largest share of this consumption. Thus, this paper presents the methodology and results of an experimental investigation that aimed to assess the energy use of stabled vehicles in the Tyne and Wear Metro system (UK). It is revealed that approximately 11% of the rolling stock's total energy consumption is due to the operation of on-board auxiliaries when stabled, and investigation of these loads is therefore a worthwhile exercise. Heating is responsible for the greatest portion of this energy, and an empirical correlation between ambient temperature and power drawn is given. This could prove useful for a preliminary evaluation of further energy saving measures in this area. Even though this investigation focused on a particular metro system in a relatively cold region, its methodology may also be valid for other urban and main line railways operating in different climate conditions. - Highlights: •Energy use of stabled vehicles in an actual metro system is experimentally examined. •Stabling hours account for about 11% of the vehicles' total energy consumption. •Heating is the major consumer during stabling hours. •An empirical correlation between ambient temperature and power drawn is derived. •The methodology described may also be applied to other urban and main line railways
[en] Highlights: • An insightful overview of energy usage in urban rail systems is given. • The principal measures to reduce urban rail energy consumption are appraised. • A methodology is proposed to help implement energy saving schemes in urban rail. • Regenerative braking is shown to offer the greatest energy saving potential. - Abstract: There is increasing interest in the potential of urban rail to reduce the impact of metropolitan transportation due to its high capacity, reliability and absence of local emissions. However, in a context characterised by increasing capacity demands and rising energy costs, and where other transport modes are considerably improving their environmental performance, urban rail must minimise its energy use without affecting its service quality. Urban rail energy consumption is defined by a wide range of interdependent factors; therefore, a system wide perspective is required, rather than focusing on energy savings at subsystem level. This paper contributes to the current literature by proposing an holistic approach to reduce the overall energy consumption of urban rail. Firstly, a general description of this transport mode is given, which includes an assessment of its typical energy breakdown. Secondly, a comprehensive appraisal of the main practices, strategies and technologies currently available to minimise its energy use is provided. These comprise: regenerative braking, energy-efficient driving, traction losses reduction, comfort functions optimisation, energy metering, smart power management and renewable energy micro-generation. Finally, a clear, logical methodology is described to optimally define and implement energy saving schemes in urban rail systems. This includes general guidelines for a qualitative assessment and comparison of measures alongside a discussion on the principal interdependences between them. As a hypothetical example of application, the paper concludes that the energy consumption in existing urban rail systems could be reduced by approximately 25–35% through the implementation of energy-optimised timetables, energy-efficient driving strategies, improved control of comfort functions in vehicles and wayside energy storage devices
[en] Highlights: • An overall picture of urban rail energy use is provided. • Performance indicators are developed for urban rail system energy optimisation. • A multi-level methodology for assessing energy efficiency measures is presented. - Abstract: Urban rail systems are facing increasing pressure to minimise their energy consumption and thusly reduce their operational costs and environmental impact. However, given the complexity of such systems, this can only be effectively achieved through a holistic approach which considers the numerous interdependences between subsystems (i.e. vehicles, operations and infrastructure). Such an approach requires a comprehensive set of energy consumption-related Key Performance Indicators (KEPIs) that enable: a multilevel analysis of the actual energy performance of the system; an assessment of potential energy saving strategies; and the monitoring of the results of implemented measures. This paper proposes an original, complete list of KEPIs developed through a scientific approach validated by different stakeholders. It consists of a hierarchical list of 22 indicators divided into two levels: 10 key performance indicators, to ascertain the performance of the whole system and complete subsystems; and 12 performance indicators, to evaluate the performance of single units within subsystems, for example, a single rail vehicle or station. Additionally, the paper gives a brief insight into urban rail energy usage by providing an adequate context in which to understand the proposed KEPIs, together with a methodology describing their application when optimising the energy consumption of urban rail systems
[en] Highlights: • We assessed integration of energy storage systems into hybrid system architectures. • We considered mechanical and electrical energy storage systems. • Potential of different combinations has been analyzed by standardized duty cycles. • Most promising are diesel-driven suburban, regional and shunting operations. • Double-layer capacitors and Lithium-ion batteries have the highest potential. - Abstract: The use of diesel-driven traction is an intrinsic part of the functioning of railway systems and it is expected to continue being so for the foreseeable future. The recent introduction of more restrictive greenhouse gas emission levels and other legislation aiming at the improvement of the environmental performance of railway systems has led to the need of exploring alternatives for cleaner diesel rolling stock. This paper focuses on assessing energy storage systems and the design of hybrid system architectures to determine their potential use in specific diesel-driven rail duty cycles. Hydrostatic accumulators, flywheels, Lithium-ion batteries and double-layer capacitors have been assessed and used to design hybrid system architectures. The potential of the different technology combinations has been analyzed using standardized duty cycles enhanced with gradient profiles related to suburban, regional and shunting operations. The results show that double-layer capacitors and Lithium-ion batteries have the highest potential to be successfully integrated into the system architecture of diesel-driven rail vehicles. Furthermore, the results also suggest that combining these two energy storage technologies into a single hybridisation package is a highly promising design that draws on their strengthens without any significant drawbacks.