Run an S-bahn (https://en.wikipedia.org/wiki/S-train https://en.wikipedia.org/wiki/S-train) through the tunnel for 10x the throughput of humans for a given tunn

Run an S-bahn (https://en.wikipedia.org/wiki/S-train https://en.wikipedia.org/wiki/S-train) through the tunnel for 10x the throughput of humans for a given tunneling cost. Cars are a profoundly inefficient use of space in a dense area. The only way an auto tunnel network would solve traffic is by charging a sufficiently-high toll to match supply with demand. Otherwise, in an area dense enough that traffic congestion is a problem, induced demand will lead to congestion: https://www.aeaweb.org/articles?id=10.1257/aer.101.6.2616 https://www.aeaweb.org/articles?id=10.1257/aer.101.6.2616