Current tracks are still being built for roughly the same cost. Your Japanese example comes in at about $23 million/km built. I was recently looking at the co

Current tracks are still being built for roughly the same cost. Your Japanese example comes in at about $23 million/km built. I was recently looking at the costs of the Paris-Strasbourg line (opened in 2016), which cost €5.15B for 406 km of track, so about €13 million/km.