Abstract
Heavy duty road transport plays a critical role in national freight systems, yet remains one of the most challenging sectors to decarbonise due to high energy demand, long driving ranges, payload constraints, and long vehicle lifetimes. Hydrogen and battery electric vehicles (BEVs) are considered promising low emission alternatives to diesel vehicles; however, their adoption is constrained by high capital and fuel costs, limited infrastructure availability, and operational challenges that vary across vehicle classes and use cases. Using a system dynamics approach, this thesis investigates the role of hydrogen and BEVs in decarbonising New Zealand’s heavy transport sector.
The research adopts a system level perspective, recognising that vehicle uptake, fuel supply, infrastructure availability, and policy instruments interact dynamically through multiple feedback mechanisms. The analysis is conducted using the UniSyD\_NZ system dynamics model, which integrates transport demand, vehicle fleet evolution, energy supply, and infrastructure development over the period 2015–2050. Technology differentiation within the model is driven by consumer behaviour, represented through a nested multinomial logit framework that captures trade-offs between capital cost, fuel cost, operating cost, refuelling or charging convenience, and infrastructure availability. The heavy vehicle fleet is categorised into three weight classes (3.5–20 tonnes, 20–30 tonnes, and >30 tonnes) to reflect differences in duty cycles, annual travel distances, and technology suitability.
Despite growing interest in hydrogen and BEVs, several gaps remain in understanding their role in decarbonising heavy transport in the New Zealand context. First, hydrogen diesel dual fuel vehicles (DFVs) are already being deployed as a transitional option, yet their system level adoption dynamics and emissions impacts have not been explicitly modelled. Second, while refuelling infrastructure is recognised as a key barrier to vehicle uptake, limited research links vehicle adoption trajectories with the number, timing, and spatial placement of hydrogen refuelling stations. Third, the trade-offs between battery electric and hydrogen technologies, particularly those related to battery size, payload constraints, and operating conditions remain insufficiently quantified across heavy vehicle weight classes. This thesis aims to address these gaps through integrated techno economic analysis, system dynamics modelling, and infrastructure optimisation.
The first part of the thesis focuses on long haul heavy freight vehicles weighing more than 30 tonnes, examining DFVs as a transitional technology for decarbonising heavy transport. DFVs are simulated alongside hydrogen fuel cell electric vehicles (FCEVs), hydrogen internal combustion engine vehicles (HICEVs), and conventional diesel vehicles (ICEVs) under a range of policy and technology scenarios, including vehicle subsidies, infrastructure support, retrofitting strategies, and technology phase out rules. The results show that, in the absence of additional policy intervention, hydrogen vehicle uptake remains limited and emissions reductions are insufficient to meet national targets. High capital and fuel costs, together with limited refuelling infrastructure, represent the main barriers to adoption. DFVs enable earlier hydrogen uptake, reduce ownership costs, and support earlier infrastructure development. Under retrofitting policies, DFVs deliver the largest near term emissions reductions, reaching up to 18\% by 2035 (relative to 2019 levels), while enabling a hydrogen vehicle share of up to 63\% and a 32\% emissions reduction by 2050. However, the analysis also indicates that prolonged reliance on DFVs may delay the transition to fully zero emission vehicles, highlighting the importance of clearly defined phase out strategies.
The second part of the thesis focuses on optimising the spatial and temporal rollout of hydrogen refuelling infrastructure for heavy duty vehicles. Two optimisation models are developed to determine how many refuelling stations are required each year, and where they should be located, based on projected hydrogen demand. Both models aim to minimise traffic weighted travel distances while ensuring feasible station utilisation. The results demonstrate that early infrastructure placement decisions strongly influence long-term network evolution and utilisation. A purely distance minimising strategy achieves rapid geographic coverage but risks underutilisation, whereas a demand feedback approach leads to more clustered station deployment around emerging freight corridors. Distinct differences are observed between the North and South Islands, reflecting their contrasting freight patterns and geography.
The final part of the thesis extends the analysis to all heavy vehicles above 3.5 tonnes by incorporating BEVs alongside hydrogen and diesel technologies. This system level assessment examines how technology competitiveness varies across vehicle weight classes under different scenarios and policy incentives. The results show that lighter heavy vehicles, which travel shorter daily distances, are more sensitive to upfront capital costs and therefore tend to favour lower cost options, making BEVs and DFVs comparatively more attractive. In contrast, heavier long haul vehicles are more strongly influenced by fuel cost, refuelling time, daily mileage, and payload constraints. Under current New Zealand operating conditions and hydrogen prices, BEVs are generally favoured, while sensitivity analysis shows that at higher daily mileage and lower hydrogen fuel prices, hydrogen vehicles particularly FCEVs become more competitive.
Overall, the thesis shows that decarbonising New Zealand's heavy transport sector is not a single technology transition. BEVs are likely to provide the most cost effective pathway for much of the heavy vehicle fleet under current New Zealand conditions, while hydrogen technologies are more relevant for the heaviest and highest utilisation freight applications, particularly for applications required long travel daily distances, and under lower hydrogen fuel costs. Hydrogen diesel DFVs and retrofits may support early hydrogen demand and near term emissions reductions, but their role should remain transitional to avoid delaying the shift to fully zero emission vehicles.
Beyond the New Zealand context, these findings offer broader insights for freight decarbonisation internationally, particularly for countries with dispersed freight networks, developing hydrogen infrastructure, and multiple competing low emission technologies. The results demonstrate that no single technology is likely to dominate the heavy vehicle sector, and that transitional technologies, when paired with clearly defined phase out strategies, can accelerate early adoption without compromising long-term decarbonisation goals. As countries pursue heavy transport decarbonisation under considerable uncertainty regarding future costs, infrastructure availability, and vehicle performance, the modelling approach developed in this thesis provides a transferable framework for evaluating differentiated, technology and class specific decarbonisation strategies for heavy road freight.
By combining behavioural modelling, infrastructure optimisation, and system dynamics analysis, this thesis investigates how policy design, technology choice, and infrastructure deployment interact over time. The findings emphasise the importance of coordinated and adaptive policies that balance near term feasibility with long-term decarbonisation objectives, and highlight the complementary roles of battery electric, hydrogen, and transitional technologies in reducing emissions from heavy transport.