A motorway tunnel under the North Sea Canal will cost the Dutch state €722m by the time its contracts with private sector investors have ended, the Financieele Dagblad said on Friday.

In the 15 years since the A9 Wijker tunnel opened, the state has paid ING and Commerzbank €386m in toll fees for using the tunnel, the paper says. The FD used freedom of information legislation to find out the details.

The banks paid €185m to build the tunnel, which the state could not afford to fund at the time. In return the state agreed to pay the banks a fee for every vehicle using the tunnel.

That fee averages 53 cents and has been inflated by a larger-than-expected increase in traffic, the FD said. It is also based on interest rates in 1992, which were far higher than they are now.

The contract runs until 2026, which, the paper calculates, means the total cost to the state will be €722m. This is the equivalent of an annual return of 11% for the banks, the FD says.