Lot 853 “North Vigana Portal Area Interventions” consists of a two-bore tunnel and two caverns, one of which is partially under the highway surface. The external works consist of the trenches excavated perpendicular to the highway escarpment. The underground part starts with the 232-m-long east cavern under the highway embankment for 48 m.

The first part of excavation was performed using the jet-grouting technique. The cavern continues in rock with partial-section excavation and finally branches off into two pipes. The branch (277 m), like the east cavern, starts under the highway embankment after which it continues in rock until it becomes the west cavern (405 m).