Policy approaches to decarbonising the transport sector in Aotearoa New Zealand: modelling equity, population health, and health-system effects

Background: Health co-benefits are a key potential advantage of transport decarbonisation policy. However, health effects will occur in the context of existing transport-health inequities and decarbonisation policies will themselves affect inequities. This research examines the effects of national decarbonisation pathways for transport on population health, health inequity, and health-system costs in Aotearoa New Zealand.

Methods: We modelled the health, health-system, and environmental impacts of two pathways to net zero for transport developed by the New Zealand Climate Change Commission using a proportional multistate lifetable model. The behaviour pathway emphasises a mixed approach, including reduced driving, increased cycling and use of public transport, and light vehicle electrification, and the technology pathway focuses on vehicle electrification. We used data from transport, environmental, population health, and health-care sources to populate the model. We simulated changes in health effects through the pathways of physical activity, air pollution (PM_2·5 and NO₂), and injury for the Aotearoa New Zealand population from 2018 to 2050. We modelled impacts for Māori (the Indigenous People of Aotearoa) and non-Māori. For each pathway to net zero, we calculated changes in overall health-adjusted life-years (HALYs), age-standardised HALYs, and rate ratios for Māori and non-Māori. We also calculated changes in health-system costs and transport greenhouse gas emissions. 95% uncertainty intervals (95% UIs) were derived for all model outputs by use of a Monte Carlo simulation.

Findings: Both pathways show improvements in population health, reductions in health-system costs, and reduced lifecycle greenhouse gas emissions compared with baseline, although health gains were substantially larger in the behaviour pathway. For example, an extra 2100 HALYs (95% UI 1500-3100) were gained in the behaviour scenario compared with baseline. Health gains were 20-30% larger for Māori than non-Māori in both pathways, although more HALYs were gained by Māori in the behaviour pathway. For the cohort aged 0-4 years in 2018, healthy life expectancy differences between Māori and non-Māori reduced by 0·5% in the behaviour pathway over their lifetime. HALYs gained by Māori and non-Māori were altered substantially depending on assumptions about the equity of the implemented pathway.

Interpretation: Decarbonising transport might improve overall population health, save the health system money, and reduce health inequities between Māori and non-Māori. Pathways that increase physical activity have a larger effect on population health than those that rely on low-emission vehicles. The effects on inequity between Māori and non-Māori are larger in the behaviour pathway than in the technology pathway but dependent on how equitably policies supporting decarbonisation are implemented.

Funding: Health Research Council of New Zealand and University of Otago.