On March 27, 2025, in Arquata, the final breakthrough of the Trisungo Tunnel (1.8 km) was completed. This tunnel is part of the SS4 Salaria variant, connecting the Trisungo and Valgarizia tunnels in the province of Ascoli Piceno.
The section under construction spans approximately 2.6 km, serving as an alternative route to the existing one. It includes two rock tunnels: Trisungo and Monte Castello (190 m). The road will have a 10.5-meter-wide platform, featuring one lane in each direction along with side shoulders.
The project also includes the construction of the Trisungo interchange, which will connect the new infrastructure to the existing road network and the current SS4 Salaria route, which will be repurposed as a local road. The interchange consists of a 350-meter ramp towards Trisungo (partly in a tunnel), a 210-meter ramp towards Ascoli, and a 530-meter bi-directional bypass. Several complex supporting structures are required for the ramps, including retaining walls, pile barriers with anchors, and hydraulic works.
The SS4 Salaria upgrade plan has been entrusted to the Government’s Extraordinary Commissioner, Fulvio Maria Soccodato. A total investment of €2.1 billion has been allocated to improve the route between Rome and Ascoli, with over €510 million already fully funded for the 37-km section in the Marche region.
The first phase of the Trisungo-Acquasanta Terme variant is now nearing completion following the recent tunnel breakthrough. The second and final phase, which is fully funded with €357 million, is currently in the tendering process. This phase will upgrade the remaining 5 km of the Marche section of the Salaria and will include the construction of the Favalanciata (1,828 m) and Acquasanta Terme (2,250 m) tunnels.
