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If you're digging a tunnel underneath a city, you might as well make it useful by turning it into a subway system for people to use.

• dagw 7y ago
  Making tunnels that are large enough and safe enough to transport people is a much bigger and more expensive endeavor than making ~1m diameter tubes for transporting goods.
  • q3k 7y ago
    [citation needed]
    • icebraining 7y ago
      Much of the cost of the subway is the access caverns, life safety systems, etc. For example, NYC built a 2-mile water tunnel for $250M [1]. A subway tunnel costs in the ballpark of $500M-$3B per mile[2]. [1] https://jalopnik.com/meet-pat-the-drill-thatll-dig-a-new-underwater-tunnel-5903263 https://jalopnik.com/meet-pat-the-drill-thatll-dig-a-new-und... [2] https://sf.curbed.com/2018/6/18/17464616/bay-area-subway-train-rail-costs-price-bart-muni https://sf.curbed.com/2018/6/18/17464616/bay-area-subway-tra...
    • dagw 7y ago
      https://ec.europa.eu/regional_policy/sources/docgener/studies/pdf/assess_unit_cost_rail/annex_13_case_study_tunneling.pdf https://ec.europa.eu/regional_policy/sources/docgener/studie... is as good a place as any to start. It also has plenty of citations of its own if you want to dig further into any aspect. Basically. the biggest cost of building a tunnel is excavation cost and the cross sectional area of a tunnel is the biggest factor affecting excavation cost for any given ground condition. Secondly once you add people you have to add emergency escape tunnels and related systems which is just more tunnel that needs digging.
    • lawlessone 7y ago
      https://en.wikipedia.org/wiki/London_Post_Office_Railway https://en.wikipedia.org/wiki/London_Post_Office_Railway
  • tachudda 7y ago
    A tunnel would need to be large enough to be maintained by humans when all the pallets crashed into each other and someone had to unjam it. We'd have a new kind of plumber