
The line 4 of the metro is one of the busiest lines in Paris because it crosses the capital from north to south, passing through the center of the capital. Its frequentation is around 175 million passengers per year, making it the second busiest line in Paris, behind line 1. Since January 2022, line 4 has enriched with two new stations located in the southern suburbs of Paris: the Barbara and Bagneux - Lucie Aubrac stations. The total length of line 4, underground over its entire route, is 14 km. The distance from one terminus to the other is covered in 36 minutes. Line 4 has a total of 29 stations, separated by an average distance of 500 meters.
The construction of line 4 gave rise to gigantic works, in particular to allow the metro to pass under the Seine. A first section, linking Porte de Clignancourt to Châtelet, was opened to the public in April 1908, while a southern section of line 4 from Porte d'Orléans to Raspail only began to operate 9 months later, in January 1909. The junction between the southern part and the northern part of the line will be made in January 1910. However, shortly after, traffic had to be interrupted for a few months due to the flooding of the Seine which flooded line 4 to the Gare de l'Est!
The automation of line 4 is underway and should be completed in 2023. The installation of screen doors on the platforms of all stations should provide more safety for users and more regularity in the service
Subway frequency
The average time interval between trains is, on weekdays, two to four minutes during the day, five to seven minutes after 8 p.m. On Sunday, expect a waiting time of six to eight minutes between each train and ten minutes on the nights of Fridays to Saturdays, Saturdays to Sundays and the eves of holidays

List of stations on line 4 from terminus to terminus with connections to other lines on the network :
Porte de Clignancourt
Simplon
Marcadet Poissonniers

Château rouge
Barbès Rochechouart

Gare du Nord



Gare de l'Est


Château d'eau
Strasbourg Saint-Denis


Réaumur Sébastopol

Etienne Marcel
Les Halles
Châtelet




Cité
Saint-Michel
Odéon

Saint Germain des-Prés
Saint-Sulpice
Saint-Placide
Montparnasse-Bienvenüe



Vavin
Raspail

Denfert-Rochereau


Mouton Duvernet
Alésia
Porte d'Orléans
Mairie de Montrouge
Barbara
Bagneux-Lucie Aubrac