1921–1939 and 1952–1956 : two rail tunnels were temporarily opened to extend line 7 to Porte des Lilas between Porte des Lilas and Pré Saint-Gervais; however in the end the voie des Fêtes was never used and the station called Haxo was never opened to the public. The voie navette was also closed to passenger traffic and the southern branch of line 7 currently terminates in an anticlockwise loop to Pré Saint-Gervais instead of Porte des Lilas.
3 December 1967 : due to the very unbalanced traffic between the two branches of line 7, the southern branch Louis Blanc – Pré Saint-Gervais was isolated and became an independent line, the line 7bis.
2 April 1971 : when the line 3 was extended eastward to Gallieni, its previous final segment to the north, Gambetta – Porte des Lilas was isolated and serviced by a short shuttle, the line 3bis.
The projected new line
It would result from the merger of:
line 3bis which currently links the Gambetta station to the Porte des Lilas station, on the south-eastern part of the new line;
line 7bis which currently performs an anticlockwise loop on its eastern end from the Botzaris station to its terminus in the Pré Saint-Gervais station, via Place des Fêtes station, and would link them to the current western terminus at Louis Blanc station, on the northwestern part of the new line.
These two lines would be connected through an existing rail tunnel, la voie navette, between the Porte des Lilas station and the Pré Saint-Gervais station, to which it would be connected from the Place des Fêtes station by a short rail tunnel, la voie des Fêtes, possibly by finally opening to the public the ghost station Haxo whose surface accesses would first need to be built, and by reopening to the traffic of the secondary station Porte des Lilas – Cinéma. The line 7bis would be also extended one station to the west, to have its terminus in Château Landon. Therefore, the Louis Blanc station would no longer be the western terminus of the line; however, it would require the creation of a new tunnel and extensive works. For now, this last segment is used by the existing line 7 connection. It was originally speculated that the new line would be given the designation of Line 15. However, since the revision of the Grand Paris Express plan, the merged line would likely be given the designation of Line 19.
