Mapping and modelling global mobility infrastructure stocks, material flows and their embodied greenhouse gas emissions

Roads and rail-based mobility infrastructures are the basis for mobility services and underpin several Sustainable Development Goals, but also induce material use and greenhouse gas emissions. To date, no stock-flow consistent study has assessed globally accumulated stocks of mobility infrastructures, associated material flows and emissions, and their spatial patterns. We present global findings on material stocks for all roads, rail-based infrastructures, incl. tunnels and bridges, and model associated material flows and their embodied emissions for the year 2021. The stock-flow consistent model combines crowd-sourced Open Street Maps data with archetypical infrastructure designs, material compositions, assumptions on lifetimes and network growth rates, incl. uncertainty ranges. We derive spatially explicit, national-level stock estimates for 180 countries and map them at a resolution of 5 arcminutes, and derive material flows and embodied emissions at the country-level. We find that 314 [218–403] Gt of materials (41 [28–53] tons/cap) have accumulated in global mobility infrastructure, the majority in roads as aggregates and asphalt. Stocks are unequally distributed between countries, from averages of 23 [16–30] tons/cap in low income countries, to 130 [89–164] tons/cap in high income countries. Spatial inequality of per capita stocks per area differs by orders of magnitude, from 101-104 between rural, suburban, and dense urban areas. We find that 8 [4–16] Gt/year of material flows are due to expansion and maintenance, amounting to 6 [3–10] % of global resource extraction. These translate into 0.36 [0.19–0.69] Gt CO2eq/year, or 1 [0.5–1.9] % of global GHG emissions in 2021. Approximately two-thirds of these flows result from maintenance and replacement of stocks, indicating an important lock-in of resource use due to already existing infrastructure stocks. These findings support the crucial role of improving spatial planning, limiting stock expansion and (sub-)urbanization, to achieve more sustainable resource use and mitigate climate change.