[cesarb]

Different technologies. Judging from this article, this Maastricht tunnel seems to have been built as a "cut and cover" tunnel, while according to Wikipedia, that SR99 tunnel was built with a tunnel boring machine. AFAIK, the cut and cover method is much cheaper (but more disruptive during the construction, and can only be used for shallow tunnels like this one).

[RandallBrown]

The TBM in the SR99 tunnel is also the largest TBM in the world. It was a bit of a gamble, and it didn't pay off. Another huge problem was that it ran into a huge metal caisson that had been placed while surveying the area to build the tunnel... The contractors operating the machine "knew" about it, but still ran into it, which broke the machine for a long time. (They were given information that it was there, but they overlooked it.)

[mcv]

Boring tunnels is also hard in the muddy Dutch soil. It was used in Amsterdam for the new Noord-Zuid-lijn, which had tons of complications and went way over deadline and budget by an enormous amount.

Although if there's a part of the country that is suitable for boring, it's probably Maastricht, which is in the tiny part of the country that has actual hills.

[scarejunba]

The SF Market St plan doesn't have that and the Central Subway has got to be cut and cover since they just shut down the road.

[secabeen]

Cut and cover is just so much cheaper.