Japan: Decarbonisation is key to rail’s green transformation

Japan: Decarbonisation is key to rail’s green transformation Work is underway to develop and test a range of alternative traction technologies that can be rolled out in commercial service over the next decade as Japan looks to decarbonise its entire rail sector by 2050. Japan’s entire railway sector has been set the goal of achieving carbon neutrality by 2050, as the fundamental objective in a report issued by the Ministry of Land, Infrastructure, Transport & Tourism in September 2025. The report from the Public-Private Study Group on Green Transformation in the Railway Sector focuses on decarbonisation of rail operations as an explicit objective (Fig 1). It identifies a number of main pillars for reducing CO₂ emissions arising from energy consumption within the rail sector. • Electrified sections: establishing renewable energy as the primary power source, improving the energy efficiency of rolling stock and power facilities, and optimising the supply–demand balance. • Non-electrified sections: Replacing diesel vehicles that use fossil fuels with decarbonised vehicles, in the form of hydrogen or battery electric multiple-units, as well as hybrid diesel multiple-units using biofuel. More than 30% of all railway lines in Japan by route length are not electrified, so the introduction of decarbonised rolling stock by around 2035 is considered essential. As well as the various technical developments currently underway, work has been undertaken on a revised regulatory framework to facilitate the widespread deployment of such decarbonised railway vehicles. Well-to-wheel effects Any evaluation of the carbon impact of railway operations needs to be conducted on a well-to-wheel basis. While EMUs do not create direct emissions at the vehicle level, CO₂ is emitted at the power plants during the electricity generation process, and this also applies to the electricity used to power BEMUs. Similarly, the production of hydrogen to power HMUs can also result in CO₂ emissions, which need to be taken into account. Fig 2 presents the estimated CO₂ emissions for HMUs, BEMUs, and HDMUs using biofuel, normalised to EMU operation. When hydrogen for HMUs is produced using renewable energy (green hydrogen), the total CO₂ emissions are around one-quarter of those of EMUs using the current power generation mix and about one-eighth of conventional DMUs, offering significant decarbonisation potential. However, when so-called ‘grey hydrogen’ is produced from fossil fuels such as natural gas, overall emissions are slightly higher than those of EMUs. This means any failure to consider the upstream hydrogen production pathway may lead to incorrect conclusions regarding the decarbonisation strategy. Similarly, the deployment of BMUs does not necessarily result in lower CO₂ emissions than EMUs, due to factors such as the increased vehicle mass arising from the onboard energy storage and the charging–discharging losses associated with Li-ion batteries. In theory, HDMUs using biofuel can ideally achieve nearly net-zero CO₂ emissions, if the feedstock is plant-derived through photosynthesis and the fuel production process can be powered by renewable energy. HMU development All Japanese HMUs use fuel cells as their primary power source. A fuel cell generates electricity directly from the electro-chemical reaction between onboard hydrogen and atmospheric oxygen; in practical terms this is the reverse reaction of water electrolysis. The only reaction product is H₂O (water), and therefore no CO₂ is emitted at the vehicle level. Compared with conventional DMUs, HMUs offer a higher energy conversion efficiency, reduced vibration and noise due to fewer mechanical components, and simplified maintenance requirements. Furthermore, while BMUs are limited in their operational range by the energy density of current battery storage technologies, HMUs are considered better suited for medium- to long-distance routes because hydrogen has a higher gravimetric energy density, and the proportional mass increase associated with increased hydrogen storage is relatively small. From a CO₂ perspective, the use of green hydrogen results in substantially lower total life-cycle emissions than fossil-fuel powered DMUs. However, hydrogen gas has a very low volumetric energy density, so storing large quantities onboard requires high-pressure containment. Current vehicle designs under consideration store hydrogen at pressures of 35 or 70 MPa. Cylinders capable of safely withstanding such pressures would be excessively heavy if constructed solely from metallic materials such as steel. Consequently, composite cylinders have been developed for automotive applications, using high-strength carbon fibre shells with lightweight metallic liners. Similar pressure vessel technologies are being adopted for HMUs. Japan’s High Pressure Gas Safety Act classifies any gas that reaches a pressure of 1 MPa or higher at 35°C as a high-pressure gas. Ministerial ordinances and related regulations prescribe detailed handling procedures and cylinder structural requirements to ensure safe operation. However, many provisions of the Act were originally developed for stationary ground-based equipment, and regulatory inconsistencies arise when high-pressure gas systems are installed on moving vehicles such as automobiles or railway rolling stock. Regulatory revisions have already been implemented in stages to ensure the safe operation of automobiles under actual operating conditions. RTRI and East Japan Railway Company (JR East) are conducting test operations using prototype HMUs (Fig 3). In both cases, the hydrogen is stored onboard under special regulatory approval. However, obtaining special approval for every vehicle in commercial service would be impractical. Therefore, the ministry-led Safety Verification Review Committee was established in 2024, with RTRI serving as the secretariat. This committee brought together subject-matter experts, the relevant ministries and agencies, industry associations, and railway operators in order to evaluate the safety of HMU operations, and to propose risk mitigation measures and recommended technical standards to facilitate a widespread deployment. Based on the committee’s findings, MLIT and the Ministry of Economy, Trade & Industry revised the relevant regulations, with the updated ministerial ordinances and public notices coming into effect from April 2025. Notably, the committee introduced a new regulatory approach for Japanese railways by formally incorporating quantitative risk assessment into the process of revising such regulations and ordinances. Exemplified standards Because defects in high-pressure gas equipment or cylinders could lead to catastrophic failure, METI has established ‘exemplified standards’ that provide specific technical interpretations of the statutory requirements. Accredited inspection bodies must verify compliance with these standards, and no equipment can be used in Japan unless it conforms. At the time, no exemplified standards existed for hydrogen pressure vessels intended for railway applications or their associated components. New standards, therefore, had to be developed. Technical guidelines serving as the basis for the exemplified standards were formulated through collaboration among railway operators and related stakeholders and were then reviewed by the High Pressure Gas Container Standards Review Committee. Once approved, the guidelines could be incorporated into the appendix of the METI document ‘On the Operation of Functional Standards of the Container Safety Regulations’, giving them official status as exemplified standards. Hydrogen containers and related equipment manufactured in compliance with these standards have subsequently been authorised for use. The technical guidelines for hydrogen containers installed on HMUs and their accessories were prepared primarily by RTRI, and were formally recognised as exemplified standards in April 2025. HMUs that comply with the revised ministerial ordinances, public notices, and exemplified standards are now being manufactured for commercial deployment on JR East-operated lines in FY 2027. BMU operation limited Battery multiple-units are equipped with rechargeable onboard Li-ion batteries, which power the traction motors in the same way as electric vehicles and recharge by recovering energy during braking. Such BMUs have already entered commercial railway service in various parts of Japan. Unlike electric road vehicles, most BMUs are equipped with pantographs, allowing them to take power from overhead contact lines to recharge at electrified stations. Such battery-electric multiple-units can run as conventional EMUs on electrified lines, and transition seamlessly between electrified and non-electrified sections. Li-ion batteries have a relatively low gravimetric energy density, resulting in a high battery mass relative to the amount of usable stored energy. This limits the maximum operating range of a BMU on a single charge. Recharging also requires an extended dwell time at stations. If this charging time has to be incorporated into the timetable, existing schedules may need modification. Consequently, the commercial deployment of BMUs is currently limited to relatively short non-electrified routes (Fig 4). From diesel to biofuel Railway vehicles are typically operated for more than 30 years, and some rolling stock in Japan has remained in commercial service for more than 50 years. Replacing the diesel fuel currently used by some form of biofuel is considered an effective strategy for achieving decarbonisation and reducing the use of fossil fuel whilst continuing to make use of existing rolling stock without major modifications. Biofuel is a liquid fuel derived from plant-based feedstock. Plants synthesise hydrocarbons from CO₂ and water through photosynthesis using solar energy. When biofuel is burned in an internal combustion engine, it re-emits the CO₂ previously absorbed from the atmosphere during photosynthesis. From a global carbon cycle perspective, this process can theoretically result in net-zero CO₂ emissions (Fig 5). At present, however, the industrial processes that convert plant-based raw materials into diesel-equivalent fuels require energy inputs that are not fully carbon-neutral. Therefore, even the use of 100% biofuel does not currently achieve net-zero CO₂ emissions. If electricity and other process energy inputs used for fuel production were supplied by renewable sources in the future, net-zero life-cycle CO₂ emissions could theoretically be achieved from the use of biofuels. In other transport sectors, notably aviation, propulsion systems currently rely on gas turbine engines for their power-to-weight ratio and performance requirements, and full electrification presents substantial technical challenges. Biofuels are consequently expected to play an important transitional role because they can be used in existing jet engines with minimal modification, and pilot-scale applications are already underway. Japanese railways have also made efforts to introduce biofuels. Specifically, RTRI and the seven Japan Railway (JR) companies, jointly conducted a range of technical development activities under a publicly solicited MLIT programme. These included testing the performance of diesel engines using biofuels, as well as long-duration operational trials. Based on these results, the West Japan Railway Company (JR West) commenced commercial operation using biofuel on various routes in the Okayama area in November 2025 (Fig 6). However, challenges remain, including the cost of biofuel production, taxation policy frameworks, and supply chain capacity. Any expansion of biofuel operations to more routes would therefore have to be phased to ensure that it is economically viable. Renewables are key The primary measures for decarbonisation of the Japanese railway sector include establishing renewable energy as the primary power source, whether used directly to feed electrified lines and battery charging or to power the production of hydrogen and biofuels. At the same time, work is needed to improve system-wide energy efficiency and optimise the supply-demand balance in electrified sections. For the non-electrified network, the fundamental policy measures include the introduction of hydrogen fuel cell and battery electric vehicles as well as a transition of existing DMUs from fossil fuels to biodiesel. Well-to-wheel evaluation of CO₂ emissions by RTRI has demonstrated that the effectiveness of emissions reduction measures varies significantly, depending on the upstream electricity generation mix and the hydrogen production pathway. Effective CO₂ mitigation will therefore require an integrated portfolio of energy supply and vehicle technology measures. Achieving carbon neutrality by 2050 will require not only continued development and deployment of decarbonised vehicles in accordance with national policy, but also the adoption of comprehensive lifecycle-based decarbonisation strategies. These strategies should incorporate life-cycle assessment methodologies and circular economy principles to ensure the long-term sustainability and resilience of railway systems. This article first appeared in the August 2026 issue of Railway Gazette International See also Japan: Autonomous Operation offers flexibility with fewer staff Subscribe to gain access to all news Already have a subscription? Log in. Choose your subscription Considering a corporate subscription? Contact us to find out more.