The old (existing) Karavanke tunnel was closed due to a malfunction of the ventilators. Problem is partially fixed and ban is now only for buses and trucks over 3.5 tons.

This is one of the reasons a second Karavanke Tunnel is being built. Not only as a second lane in each direction, but also as an alternative in such cases.

https://cdn.24ur.com/novice/slovenija/pozor-predor-karavanke-bo-predvidoma-dlje-casa-zaprt.html