[altacc]

One of the factors other replies haven't considered is that Norway routinely spends a lot on transport infrastructure, with cost-benefit just one of the factors. This project was relatively cheap compared to the constant building of tunnels for cars that happens across the country. A typical project costs many times more than this.

Per capita Norway is one of the highest spenders in the world, due to the size and low population density of the country. Even with all this spending, transport in some places, especially the north, is slow & inefficient. This has resulted in a high number of airports and Norwegians flying more than almost every other nationality.