Najteži dio ove dionice bio je od Bune do Čapljine u dužini od 19 km jer je prolazio teško pristupačnim kanjonom Neretve pa je za potrebe gradnje bio izgrađen i pomoćni put.
The hardest part of this section was of Buna and Capljina in length of 19 km as he passed inaccessible canyon of the Neretva River and is for the building was built and extra time.