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 com-positions, assumptions on lifetimes and network growth rates, incl. uncertainty ranges. We derive spatially explicit, national-level stock estimates for 180 countries, map them at a resolution of 5 arcminutes, and derive material flows and their 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.