https://www.researchgate.net/publication/296888725_Geology_and_the_Construction_of_the_Metro https://www.researchgate.net/publication/296888725_Geology_a... Th

https://www.researchgate.net/publication/296888725_Geology_and_the_Construction_of_the_Metro https://www.researchgate.net/publication/296888725_Geology_a... The article is in French, but geology is the key factor. Do you need to bore rock or sandy soil with tar? Is the area seismically active like in Los Angeles? This affects the cost and timeline of metro construction more than just wages.