The second track construction project envisages a single track with service pipes along the longest tunnels. In order to enable the upgrade of the second track to a two-track line in the future, the Government of the Republic of Slovenia adopted a decision in June 2017 to provide the necessary foundations and projects for increasing the profile of the service pipes in the T1, T2 and T8 tunnels in the first phase, and to amend the building permit.

In February 2018, the Ministry of Infrastructure, DRSI, obtained changes to the project construction documentation, on the basis of which, in August 2018, ARSO made a decision that, due to the increase in service pipe profiles, it is not necessary to carry out a new environmental impact assessment and obtain a new environmental consent. It is also not necessary to change the building permit, which was decided by the Ministry of Environment and Spatial Planning.

DRSI is leading the process for the second track to be built as a double track in the future. However, by expanding the service pipes in the three longest tunnels of 2TDK, 61 percent of the parallel track of the second track will be ready for construction.