Tranche 853 "Works in North Portal Vigana area" consists of a double-tube tunnel and two caverns, one of which is partially under the motorway. The external works consist of trenches dug perpendicular to the slope of the motorway. The underground part begins with the eastern cavern, 232 m long, extending for 48 m under the motorway embankment. The first part of the excavation was performed using the jet-grouting technique. The cavern continues through rock and branches into two tubes. Excavation involved partial sections. The link road (277 m), like the eastern cavern, begins under the motorway embankment, after which it continues through the rock until it becomes the western cavern (405 m).