The Copenhagen Metro Line expansion, including the "Cityringen" loop with Lines M3 and M4, was a major urban infrastructure project. It faced challenges due to complex geological conditions and urban proximity. Advanced geodetic and geotechnical monitoring systems detected structural deformations early. The expansion included 17 new stations, three shafts, and a maintenance center, enhancing connectivity across a 15.5-kilometer route. Operated as a driverless system, the project represented a 2 billion euro investment by the Copenhagen Ministry of Transport and Frederiksberg municipality, managed by Salini/Impregilo Tecnimont and SELI – CMT.