Along the stretches where the new southbound carriageway (Rome direction) follows a different route to the existing one, two important underground natural excavation works were entailed (Melarancio tunnel, L=1096 and Pozzolatico tunnel, L=2420 m); it should be noted that, when designing the underground structures and altering the size of the roadbed, great attention was paid to aspects linked to the safety of users in emergencies (special equipment and structures, such as an underground escape passage for pedestrians under the roadbed).
Besides increasing the width of the motorway roadbed, the upgrading entailed several connection and interchange works with the infrastructures and services found in the area. In particular, the connection between the new road (at the Certosa junction), Certosa station and the clearway for Siena is provided by a new stretch of direct link road which runs through three natural tunnels (Le Romite tunnel, L=264 , Poggio Secco Tunnel, L=1231 m and Del Colle Tunnel L=667 m).
Furthermore the project included several design and technological solutions to improve the quality of the environment surrounding the new stretch of motorway in order to fit the structures into the landscape and mitigate the environmental impact its use will inevitably have. The project not only reduces current levels of pollution, but also includes additional works, such as rationalization operations on the local road network and park and ride car parks, which contribute towards a more functional development of transport in general and make it easier to upgrade public transport.