These train codes are called mission codes.
https://fr.wikipedia.org/wiki/Ligne_B_du_RER_d%27%C3%8Ele-de-France, via Gtranslate
Meaning of first letter used regularly:
Letter | Destination |
---|---|
E | Aéroport Charles-de-Gaulle 2 TGV |
I | Mitry – Claye |
J | Denfert-Rochereau |
K | Massy – Palaiseau |
L | Orsay-Ville |
P | Saint-Rémy-lès-Chevreuse |
Q | La Plaine – Stade de France |
S | Robinson |
U | Laplace |
Meaning of first letter used exceptionally:
Letter | Destination |
---|---|
A | Gare du Nord |
G | Aulnay-sous-Bois |
H | Bourg-la-Reine |
M | Châtelet – Les Halles |
V | Lozère |
X | Parc des Expositions |
Y | Les Baconnets |
All codes from a few years ago: http://michou94.free.fr/html/missiona.html.
The 4-letters codes describe the different routes and types of trains (express or not) of the RER B line. Indeed, RER B forks at Aulnay-sous-Bois station (while traveling to the North-East part of Paris suburb) with the B3 route going to Charles-de-Gaulle airport and the B5 route going to Mitry-Claye station. It also forks in the opposite direction at Bourg-la-Reine station with the B4 route going to Saint-Remy-les-Chevreuses.
This article describes it:
The fastest trains from CDG to central Paris have route codes beginning with KA (KALE, KALI, KAPE, KARE, etc.) or JA (JAMI, JANO), or UL. Other trains make more stops.
For your return to CDG airport from central Paris, look for B3 trains with route codes beginning with E, because all trains beginning with E go to CDG. The express trains are ERIC, EROC, ERIO, ERSE, EDME [,or] EDDY.
Here is a picture from the same article (direction CDG – Central Paris)
It seems that JIBY train stops at Denfert-Rochereau and does not go all the way, in particular not stopping at Antony (near Orly airport) and KDIT stops on the B4 route at Massy-Palaiseau.
Additional details in this article
Credit:stackoverflow.com‘