Could be. It could also be that in Norway, if you send out an RFP, the companies that respond are capable of doing the work.
In the United States, if you send out an RFP, companies will respond that are actually unable to do the work but are happy to outsource it to someone else and add some percentage to the cost for the trouble. In fact, there may be times when the only companies even considered are ones that are incapable of doing it. As part of "The Fleecing of America" series on NBC, there was this coverage regarding the Hurricane Katrina clean up effort:
Here's an example of how it worked: The Ashbritt company was paid $23 for every cubic yard of debris it removed. It in turn hired C&B Enterprises, which was paid $9 per cubic yard. That company hired Amlee Transportation, which was paid $8 per cubic yard. Amlee hired Chris Hessler Inc, which received $7 per cubic yard. Hessler, in turn, hired Les Nirdlinger, a debris hauler from New Jersey, who was paid $3 per cubic yard.
That really happened, and I believe (based solely on the greed and ineptitude I witness daily) it continues to happen on most/all large-scale public works projects in the U.S. I don't know if that happens in Norway or not. If the tunnel was built in the U.S. using the example above, given an actual cost of building the tunnel at $272M, then the amount paid by the tax payers would be over $2 Billion. So that may be why it seems so low.