The year 1983 saw the stipulation of a General Agreement between the Regional authority of Lombardy, the City Council of Milan, the Italian Railway Company and the North Milan Railway Company (FNM, now LeNord).

MM designed and built the urban section, about 10 km long, with 6 underground stations and 1 surface station.
The overall length of the line is over 18 km (including the connections with the external network), half of which is underground, with 10 stations in the municipal district of Milan, of which 6 underground and 4 on the surface.