Decarbonizing Roads: A Life-Cycle Blueprint for Cleaner Transport Systems

The report provides a comprehensive, life-cycle assessment framework showing that most road-sector emissions stem from vehicles rather than road construction, and offers detailed tools to evaluate and reduce these emissions across Asia and the Pacific. It guides governments in adopting low-carbon policies—such as electrification, better maintenance, modal shifts, and cleaner construction practices to align road investments with climate-resilient, net-zero pathways.

In a landmark study led by the Asian Development Bank (ADB) with research support from the University of Birmingham, consultants from New Zealand, and environmental analysts at MetaMeta, experts attempt to fully quantify the climate footprint of road transport, an issue long obscured by partial data and narrow methodologies. The research stresses that while roads are vital to Asia’s economic dynamism, the majority of their carbon impact comes not from asphalt or concrete but from the tens of millions of vehicles that move across them daily. With Asia experiencing a 41% rise in transport emissions from 2010 to 2019, the authors argue that countries can no longer expand mobility without also expanding their understanding of the emissions they generate.

Moving Beyond Tailpipes

The publication’s central premise is that measuring only tailpipe emissions gives an incomplete, and often misleading, picture of transport-sector climate impacts. To correct this, ADB enhances the widely used Highway Development and Management (HDM-4) system to include emissions from vehicle manufacturing, fuel production and distribution, electricity generation for EVs, and road construction. This updated toolkit incorporates the IPCC’s latest global warming potential factors and country-level grid emission intensities, acknowledging that an electric vehicle in Mongolia’s coal-heavy grid behaves quite differently from one in Bhutan’s renewables-based grid. Such a whole-of-life approach, the authors argue, is essential if governments are to align road projects with their Paris Agreement commitments.

Where the Carbon Really Comes From

A striking finding is that more than 80% of road-related life-cycle emissions come from vehicle operations, not construction. Heavy congestion, rough road surfaces, and rapid motorization magnify tailpipe emissions, making urban and suburban corridors the most carbon-intensive. Yet the report also highlights the opposite pattern in remote and low-volume networks, such as those in Pacific Island countries, where construction and maintenance dominate the carbon profile due to low traffic volumes. This geographic contrast underscores why one-size-fits-all decarbonization strategies fall short. For megacities, electrification and congestion reduction matter most; for islands, recycling materials, using low-carbon construction technologies, and optimizing maintenance schedules may yield greater dividends.

Policies That Bend the Emissions Curve

The report catalogs a wide suite of policies that can reduce road-sector emissions, ranging from traffic demand management and optimized intersections to truck overloading enforcement, public transport expansion, cleaner electricity grids, and priority lanes for electric vehicles. Case studies demonstrate how these measures perform in real contexts. In Central and West Asia, expanding a two-lane highway to four lanes initially increases emissions due to construction and induced traffic, but targeted mitigation, recycled asphalt, optimized material sources, reduced speed limits, and roadside tree planting help offset part of the increase. Another case shows how a national network’s emissions fall sharply when maintenance funding is improved, as smoother roads significantly reduce vehicle fuel consumption. Meanwhile, South Asian analyses reveal that shifting just 20% of private car users to buses or trains cuts millions of tons of CO₂e, while a systematic shift from petrol motorbikes to electric two-wheelers delivers up to 14 million tons of emissions reduction over 25 years. These transitions also bring safety co-benefits in regions where two- and three-wheelers account for the majority of severe traffic injuries.

A Toolkit for Smarter, Low-Carbon Decisions

The annex of the publication details an Excel-based toolkit designed to work seamlessly with HDM-4, guiding users through importing data, setting scenario assumptions, modeling electric fleet transitions, and evaluating the carbon and economic implications of each investment. The tool allows annual adjustments to electricity grid factors, integrates ancillary assets such as charging stations or nonmotorized transport lanes, and incorporates social cost of carbon calculations into economic analyses. What emerges is a decision-support system that enables governments to quantify trade-offs early, when project designs can still be altered. Ultimately, the report’s narrative is clear: expanding roads across Asia and the Pacific remains essential for economic growth, but doing so sustainably requires embedding decarbonization thinking into every step, from planning to construction, from fleet policy to grid reform. With the right tools, the region can build not just more roads, but cleaner, safer, and climate-consistent ones.