So far, only one tube in each tunnel has been in operation and two-way traffic has caused jams during the peaks of summer tourist seasons.
The tunnels will be closed for traffic from 10 pm Friday to 10 am Saturday for the final technical adjustments of all tubes for one-way traffic.
Transport Minister Bozidar Kalmeta is expected to attend tomorrow's inauguration ceremony.
The construction of the four tubes cost HRK 2.3 billion before Value Added Tax.
The right tube of the Mala Kapela tunnel is 5,780 metres long, and it was open for traffic in June 2005. The left tube is 5,821 metres long.
The right tube of the Sveti Rok tunnel is 5,670 meters long and has been in operation since June 2003.
This tunnel's left tube is 5,679 metres long.
Both facilities have been constructed according to New Austrian Tunneling method (NATM).
Speed limit in the tunnels is 100 kilometres per hour.