[akiselev]

Chuo Shinkansen hasn't been completed yet so at best that's the minimum bar for what it will actually cost. Until they know for sure that they won't find any underground surprises, that estimate will continue going up.

The reality is that estimating underground rail construction costs is significantly harder and riskier than above ground [1]. According to the AACE's classification system for cost estimates, the current number is a borderline class 2/3 estimate which means the estimate could be off as little as 5% or as much as 600%. Historically tunneling projects have ended up in the upper half of that range.

[1] http://web.mst.edu/~rogersda/umrcourses/ge441/Too_Dangerous_...

[kalleboo]

Tunneling estimates can go both ways... in Sweden the Citytunneln project ended up under cost and under time due to the tunneling being less complicated than expected. The Japanese certainly have experience, all their mountains are swiss cheese of highways and shinkansen tracks. I'm not sure how much American studies apply here since there's a different culture of trying to underbid to win the contract there.