Fig. 1: The temporal dynamics of the number of cities with subway system and the total length of suways.
From: Global urban subway development, construction material stocks, and embodied carbon emissions
(a) The decadal increase of cities with subway system per world region; (b) The increase of total subway length per world region and the ten longest urban subway systems by July 2020. Note: No subway systems were built in the time period of 1870 to 1889 and 1940 to 1949.
