A number of initiatives to guard against hazardous conditions in the tunnel had already been introduced, including a ban on vehicles over 12 metres long from 7-9am and 3-6pm on weekdays.
The tunnel is now closed and scheduled to be reopened on Monday, reports NRK.
"We hope to be able to reopen Monday, pending the completion of work on signs and other technical things over the course of the weekend,” NPRA department director Nils Audun Karbø told the broadcaster.
"We hope that drivers can plan their journeys without the consequences being too great. The reason is that we to the greatest extent possible wish to avoid vehicles that experience shows have a higher risk of catching fire when in tunnels with a lot of other traffic,” Karbø said.
An engineer who previously worked on the construction of the tunnel said after a fire and closure earlier this month that two new tunnels were necessary to solve the recurring problems with it.
To reduce risk, gaps of 100 metres must be kept between heavy vehicles using the tunnel. The NPRA is now intensifying traffic control in the tunnel including through the use of signs, to ensure this, reports NRK.
“We are also taking measure to clearly mark outside of the tunnel when it is closed. Many drove into it during the last fire even though it was blocked, and now we are trying to ensure that doesn't happen again,” Karbø said.