Being a major project linking two major Essonne hubs, Massy and Évry-Courcouronnes, it offers an alternative to the private car and facilitates connections between different modes of transport (RER B, C and D, several bus lines and, in time, the Tzen 4 and metro 18). It also stimulates the region's economic and urban development.

Running both on the national rail network (between Massy and Épinay-sur-Orge) and on tramway tracks in urban areas (between Épinay-sur-Orge and Évry-Courcouronnes), the T12 combines the advantages of rail and tramway. Passengers and residents of the 12 towns it serves benefit from a mode of transport that combines comfort and performance.

With 16 stations serving 12 Essonne communes, the T12 is a new link in the public transport network. By strengthening local services, it offers an efficient alternative to the car and supports the urban transformation of the region.