The redevelopment of the Southern section of Madrid’s inner ring road, known as Calle 30, included the construction of an underground bypass that required the road to be buried using a twin-tube tunnel design, with one tunnel for each traffic direction.

Each tube comprises three 11.5-ft wide lanes, a 1.6-ft right shoulder, and a 2.6-ft left shoulder, designed to serve as an emergency passageway. This configuration ensured capacity, safety, and operational efficiency in one of the city’s most significant urban transport infrastructures.

Along the 11,811 ftof tunnel, average excavation rates of 60 ft/day were achieved, with peak advances of up to 151 ft in 24 hours. Simultaneously with excavation, the intermediate roadway slab was constructed using prefabricated panels installed on brackets built in situ, optimizing construction schedules.

To execute the tunnels, a custom-designed EPB (Earth Pressure Balance) tunnel boring machine with an excavation diameter of 49.25 ft was manufactured, setting a world record in 2004. The tunnel lining consisted of precast concrete segments measuring 24 inches in thickness and 6.56 ft in length.

The tunnels are interconnected by cross-passages that allow evacuation in the event of fire and provide access to the lower level for emergency vehicles, reinforcing the overall safety of the infrastructure.