Stif has approved an initial €76m allocation for the project, 53% of which will come from the Ile de France government with the French state contributing 28%, the department of Essonne 15%, and infrastructure manager SNCF Network 4%.

The first 20km phase of Tram Express South will connect Massy Palaiseau on RER lines B and C with Épinay-sur-Orge on RER Line C and Évry-Courcouronnes on Line D, serving 16 stations in Essonne. The journey time between Massy Palaiseau and Évry-Courcouronnes will be 38 minutes with services operating at 10-minute intervals at peak times.

Phase 2 will extend the line 14.6km west from Massy-Palaiseau to Versailles Chantiers after 2020. According to Stif, initial ridership is forecast to be 40,000 passengers per day on Phase 1 and 30,000 per day on Phase 2.