There are massive subway extension/construction under way in Paris.
There are currently 12 TBM boring the ground under Paris and 5 more in assembly.
There is the big Grand Paris Express project with four new lines (line 15, 16, 17, 18 and the extension of line 14, note that the line 11 further extension project is currently on hold).
Thats 200 new km of subway and 61 new stations
(A view of what is currently under construction in this project).
Outside the massive global project, there are other metro extension under construction.
Line 4 : southbound 1.5 km and 2 stations (opening in 2021)
Line 11 : northeastern bound 5.5 km and 6 stations (opening in 2023)
Line 12 : northernbound 1.5 km and 2 stations (opening in 2021)
Line 14 :northernbound 5 km and 5 stations (opening in 2020)
Line 14 has three extensions under construction.
-Saint-Lazare to Mairie de Saint Ouen (2020, nearly completed)
Two under the Grand Paris Express project contracts
-Mairie de Saint Ouen to Carrefour Pleyel (2024)
-Olympiades to Orly airport (2024)
Photos of the construction work at Villejuif institut Gustave Roussy where the southern extension of line 14 and the new line 15 will meet.
https://www.societedugrandparis.fr/g...r-allison-2814
There are also other projects like an eastern extension for line 1 but not yet under construction.
The RER E is being extended westbound (50 km) from Haussmann Saint-Lazare to Mantes la Jolie with a new km of 8 km (Haussmann Saint-Lazare to Nanterre la Folie).
