Traction: Wellington to introduce battery

Traction: Wellington to introduce battery-electric trains The introduction of new battery-electric multiple-units, together with infrastructure improvements and enhanced timetables, is expected to transform regional rail services to the north and northeast of Wellington, as Michael Dreyer explains. New Zealand is preparing for the most significant expansion of its regional passenger rail operations in decades, with the procurement of a fleet of battery-electric multiple units to operate services linking Wellington with Masterton and Palmerston North. Branded Tūhono, a Māori word meaning ‘to connect’ or ‘to unite’, the 18 BEMUs are expected to enter service from 2029, replacing locomotive-hauled trainsets on both the Wairarapa and Manawatū lines. A full timetable will be implemented in 2030 as the first large-scale fleet deployment in Australasia. The Lower North Island Rail Integrated Mobility programme combines rolling stock replacement with infrastructure modernisation, station improvements and new maintenance facilities to support increased frequencies and a fundamentally different operating model. Wellington already has a five-line 1·5 kV DC electrified suburban network, branded as Metlink, which serves as the backbone of public transport across the capital region. The Tūhono BEMUs will be able to operate under the existing overhead before continuing on battery power on the non-electrified Wairarapa and Manawatū corridors, offering a more economic approach than extending the wires for more than 140 route-km. The programme marks a notable shift in New Zealand’s approach to regional mobility. For decades, passenger rail investment has been concentrated on the Auckland and Wellington suburban services, rather than the longer-distance regional trains. In recent years, the Wairarapa Connection and Capital Connection services have been operated by ageing diesel locomotives hauling rebuilt ex-British Rail Mk II coaches. Supporting economic growth The government, regional authorities and KiwiRail view the LNIRIM programme as a means of supporting regional economic growth, encouraging modal shift from private cars and reducing greenhouse gas emissions. The Wellington region saw sustained growth in rail demand during the decade preceding the Covid-19 pandemic. Between 2009 and 2019, annual ridership increased by more than 20% to exceed 14 million passenger journeys. This was driven in part by the introduction in 2011 of the Matangi suburban EMU fleet, built by Hyundai Rotem in South Korea. Today, more than 20 000 passengers travel by train during the weekday peak periods, accounting for around 22% of all morning trips into Wellington’s central business district and more than 40% of commuter journeys from the rapidly growing Kāpiti Coast region. Without the trains, almost 5 000 additional cars would have to use the capital’s constrained road network each day. Demand is expected to continue growing. Population forecasts indicate that the lower North Island will gain around 200 000 residents and 100 000 new jobs over the next three decades, with much of the growth concentrated along the Kāpiti, Wairarapa and Horowhenua corridors. Meanwhile, Palmerston North is expanding as an education, logistics and government centre, generating demand for longer-distance travel. Between June 2024 and July 2025, there were more than 4·5 million passenger journeys on the Hutt Valley Line and more than 4 million passengers on the Kāpiti Line. By contrast, the regional trains on the Wairarapa Line carried around 500 000 passengers, and the more limited Wellington – Palmerston North service recorded just over 100 000 boardings. Surveys found that most passengers had access to private cars but chose rail because it offered an attractive alternative to the congested roads. While the suburban network has benefited from successive renewal projects, the regional services are constrained by their ageing rolling stock, limited frequencies and infrastructure bottlenecks. Forecasts indicated that capacity on the Wairarapa corridor would be exhausted in the second half of the 2020s and the Manawatū corridor shortly afterwards. Fundamental rethink The immediate driver for the investment was the ageing fleet. The second-hand Mk II coaches dating from the early 1970s were imported to New Zealand in the late 1990s. Despite extensive refurbishment, they are approaching the end of their service life, with rising maintenance costs, ageing components and increasing difficulties in sourcing spare parts. In addition, the stock no longer meets modern passenger expectations. Accessibility is limited, boarding is difficult at many stations, and the coaches lack the comfort expected of contemporary stock. At the same time, diesel traction results in relatively high operating costs and greenhouse gas emissions. Continuing to refurbish the ageing fleet would merely prolong an increasingly expensive and carbon-intensive operating model without addressing the growing demand. These challenges were examined in detail during preparation of the LNIRIM Detailed Business Case, which was completed in 2021 by Greater Wellington Regional Council, Horizons Regional Council, KiwiRail and the Waka Kotahi NZ Transport Agency. The study identified four principal objectives to justify the investment: replacing the life-expired rolling stock, increasing capacity, supporting emissions reduction targets and improving operational efficiency. From tri-mode to BEMU A comprehensive assessment evaluated continued locomotive operation, diesel multiple-units, full electrification and various hybrid options. The preferred solution was a fleet of 22 four-car tri-mode multiple-units capable of operating on 1·5 kV DC, battery power or a low-emission diesel power pack. At the time, battery technology was considered insufficiently mature to operate reliably more than 80 km beyond the electrified network. The hybrid concept was seen as a pragmatic compromise, reducing diesel operation while avoiding the high capital cost of extending the wires. However, rapid advances in battery technology between 2021 and the start of the procurement process fundamentally altered the situation. Demonstration projects in Europe, Japan and elsewhere showed that BEMUs could operate reliably over significantly longer distances than had previously been considered feasible. Advances in battery energy density, charging capability and energy management systems improved operational performance substantially while reducing the life-cycle costs. These advances coincided with New Zealand’s increasingly ambitious climate policies, which sought to eliminate rather than merely reduce diesel operation. Technical modelling demonstrated that battery-electric trains, supported by strategically located facilities, could operate the services without the need for onboard combustion engines. International competition The procurement of the LNIRIM fleet became one of the largest rolling stock competitions ever undertaken in New Zealand. Rather than placing a conventional supply contract, the regional authorities favoured a Design-Build-Maintain model intended to secure long-term performance, predictable maintenance costs and life-cycle optimisation over several decades. The process began with a call for Expressions of Interest in late 2023, before progressing to a competitive dialogue with Alstom, CAF and Stadler. Each bidder was required to propose suitable rolling stock and demonstrate its capability to support long-term fleet maintenance, infrastructure integration and operational performance within the New Zealand railway environment. The 1 067 mm gauge trainsets needed to be compatible with the existing infrastructure and local loading gauge restrictions, while providing sufficient capacity to accommodate the rapidly growing commuter demand. In September 2025 the Greater Wellington Regional Council announced the selection of Alstom as preferred supplier. Valued at NZ$1 066m over 35 years, the contract covers design, manufacturing, testing, delivery and long-term maintenance of the fleet. The trains will be built at the Savli plant in Gujarat, while maintenance will be undertaken at a purpose-built depot in Masterton. Alstom will assume long-term responsibility for fleet availability, maintenance planning and asset management throughout the contract period. The company intends to use a range of predictive maintenance technologies, including the HealthHub digital monitoring platform. Designed for New Zealand Based on Alstom’s Adessia Stream B platform, the 18 five-car Tūhono BEMUs are closely related to the trains being supplied for Ireland’s DART+ programme. The five cars are connected by semi-articulated bogies, to give an overall train length of 81·6 m. Eight of the 12 axles will be motored, providing high levels of acceleration within the 18 tonne axleload limit. The trains are designed to operate seamlessly under the existing 1·5 kV DC overhead electrification before switching to battery operation beyond Waikanae and Upper Hutt. Rapid-charging installations at Masterton and Palmerston North will top up the batteries in less than 20 min during terminal layovers, while overnight charging will take place at the stabling facilities. Regenerative braking will further improve energy efficiency. The trains have been designed for a maximum of 120 km/h, although the infrastructure generally limits operating speeds to 110 km/h. Special attention has been paid to operation through the 8·9 km Remutaka Tunnel on the Wairarapa Line; the end vehicles will have full-width emergency evacuation doors, reflecting the local tunnel safety requirements. Passenger accommodation offers a substantial improvement on the Mk IIs. There will be accessible and standard toilets, wheelchair spaces, bicycle and pram areas, luggage storage, vending machines, drinking-water dispensers, passenger information systems and CCTV. Intermediate vehicles will offer near-level boarding, with retractable sliding steps to ensure accessibility at stations with varying platform heights. At this stage, there are no plans to purchase EMU-only versions of the Tūhono trains, although there is an option in the Alstom contract. There are also provisions for the BEMU design to be adapted for operation in other parts of New Zealand. Infrastructure investment A purpose-built maintenance depot at Masterton will be the home base for the BEMUs throughout the 35-year contract. It will provide three maintenance roads, bogie exchange facilities, workshops and office accommodation, employing around 30 staff. There will also be expanded stabling facilities at Masterton and Palmerston North, which will provide overnight charging to ensure that the trains can be fully recharged before entering service each morning. Although Alstom and the regional authorities have not disclosed the battery capacity for commercial reasons, the battery system has been specified to ‘comfortably’ cover the non-electrified sections of 58·5 km between Upper Hutt and Masterton and 81 km between Waikanae and Palmerston North, while maintaining sufficient energy reserves to account for gradients, timetable resilience and long-term battery degradation over the 35-year service life. KiwiRail is delivering extensive infrastructure upgrades, including new signalling between Upper Hutt and Masterton, extra passing loops, track renewals, bridge works and level crossing improvements. More than 40 km of track has already been renewed on the Wairarapa Line, including works in the Remutaka Tunnel, which will enable higher speeds and shorter journey times. Five new traction substations will strengthen the 1·5 kV DC network and support the battery charging. The current resignalling uses conventional technology, although the BEMUs will be supplied ETCS Level 2-ready. Transforming the timetable The programme will fundamentally transform regional passenger services, allowing the introduction of a more frequent, reliable and attractive timetable on both routes. Today’s services are largely focused on peak-hour commuting. The Wairarapa Connection operates a limited number of weekday trains, while the Capital Connection between Wellington and Palmerston North has a single return service on weekdays. This has limited rail’s attractiveness despite the increasing travel demand and growing road congestion. The new operating concept offers a significant step change. Peak services on the Wairarapa Line will double from three to six trains in the peak direction, while the Manawatū Line will see a second train in both the morning and evening peaks. In addition, there will be more inter-peak, evening and weekend trips to create an all-day service. According to the LNIRIM business case, train services are expected to increase by 143% over the 30-year evaluation period compared with a minimum-investment scenario. The initial timetable alone will introduce 49 additional trains per week. Meanwhile, the infrastructure improvements will cut the current 1 h 40 min journey time between Wellington and Masterton by an estimated 15 min. The improved onboard facilities and higher service frequencies are intended to reposition regional rail as an attractive all-day mobility option, supporting mode shift, regional development and long-term patronage growth. Whereas the Capital Connection service is currently operated by KiwiRail, the Tūhono fleet is expected to be operated by Transdev Wellington, which already runs the Metlink suburban network and the Wairarapa Line under contract to Greater Wellington and Horizons Regional Councils. However, KiwiRail will continue to own and maintain the infrastructure. Strong economic benefits The 2021 LNIRIM business case estimated the infrastructure expenditure at NZ$587m or NZ$763m including risk allowances; the total has since increased to approximately NZ$800m following the decision to go for a fully battery-electric fleet. This is separate to Alstom’s NZ$1bn contract to supply and maintain the rolling stock. The package is primarily being funded by the New Zealand government through appropriations and the National Land Transport Fund, with contributions from the Greater Wellington and Horizons regional councils. The economic assessment demonstrated a benefit:cost ratio of 1·83 and a positive NPV of around NZ$218m, with quantified benefits of NZ$481m. These include shorter journey times, improved reliability, reduced road congestion, environmental gains and wider benefits from the enhanced regional connectivity. A key finding was that the modernised railway would be significantly more efficient to operate than today’s loco-hauled services. Although overall life-cycle expenditure would increase due to the expanded timetable, the operating costs per trip would fall by around 50%, supported by the reduced maintenance requirements, higher fleet utilisation and increased passenger revenue. The business case anticipated that the improved services could shift around 24 million passenger journeys from road to rail over the appraisal period, avoiding between 600 000 and 1·6 million tonnes of CO₂ emissions while reducing road congestion, improving safety and strengthening regional connectivity. These benefits position LNIRIM as a long-term investment in sustainable mobility, rather than simply a rolling stock replacement programme. This article first appeared in the August 2026 issue of Railway Gazette International 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.