Widening a motorway tunnel in the presence of traffic without resorting to alternative routes or reductions in the level of service was attempted for the first time in the world in the early 2000s to widen the Nazzano Tunnel (A1 Motorway, near Rome). The completion of the project constituted without doubt a true milestone for tunneling. It demonstrated the feasibility and efficiency of the method, which by reducing land consumption to a minimum, made it possible to expand the capacity of strategic road, motorway or rail infrastructures without reducing the level of service during construction operations. The solution to widen the existing tunnel without interrupting traffic has now become a reliable and advantageous option for clients where possible alternatives (driving a third tunnel or closing traffic in the carriageway to be widened) can be more financially and socially costly than widening the existing tunnel.