RER A


RER A is one of the five lines in the Réseau Express Régional, a hybrid suburban commuter and rapid transit system serving Paris, France and its suburbs. The RER A line crosses the Paris region from east to west, with all trains serving a group of stations in central Paris, before branching out towards the ends of the line.
The initial portion of the line was built in stages between December 1969 and December 1977 by connecting two existing suburban commuter rail lines with a new tunnel under Paris: the line between Vincennes and Boissy-Saint-Léger in the east, and the line between Saint-Germain-en-Laye and Nanterre line in the west. The viaduct between Vincennes and the former Gare de la Bastille terminus was redeveloped into the Promenade plantée elevated park in 1993.
Since opening, three additional branches have been added: one in the east serving Marne-la-Vallée and Disneyland Paris and two to the west serving Poissy and Cergy.
The RER A has had a significant social impact on Paris and the surrounding region by speeding up trips across central Paris, by making far fewer stops than the Paris Métro and by bringing far-flung suburbs within easy reach of the city centre. The line has far exceeded all traffic expectations, currently serving over 1.2 million passengers per day, on about 300 million journeys per year. That makes the RER A the busiest single rail line outside of East Asia.

Popular success and responses

The line has far exceeded all traffic expectations, currently serving over 1.2 million passengers per day, on about 300 million journeys per year. That makes the RER A the busiest single rail line outside of East Asia. Ever-increasing traffic volume and the need to ward off imminent saturation have been major factors in RATP and SNCF's planning since the inauguration of the line.
Several major capital investments have been made to relive overcrowding on the line:

Branches

Line A provides two groups of services:
During off-peak hours, the Poissy – Noisy services operate every 20 minutes plus a La Défense – Noisy service every 20 minutes, and the St-Germain – Boissy and Cergy – Chessy services operate every 10 minutes.
Operations are very complex during peak periods, with an average of one train every 2 minutes on the common trunk line in the busier direction, and one train every 2 min 30 sec in the other direction. The Marne la Vallée branch has the most intensive service.

Names of services

RER trains display a "nom de mission" or "name of service", not the name of the destination station. These are invented names designating individual services, and are accompanied by a two-digit number, for example ZARA59 or DJIB72.
The first letter corresponds to the destination :
LetterToExamples of names of services
BLa DéfenseBYLL, BORA, BTON
DNoisy-le-Grand – Mont d'EstDYNO, DJIN, DOMI
NBoissy-St-LégerNELY, NAGA
OTorcyOKEY, ORKA, OFRE
QMarne-la-Vallée – ChessyQUDO, QIKY, QBIK, QAHA
RLa Varenne-ChennevièresRHIN, RUDI
TPoissyTERI, TJAC, TIKY
UCergy-le-HautUPAL, UDON, UXOL
WWQWZ
XLe Vésinet – Le PecqXUTI, XOUD
YRueil-MalmaisonYCAR, YVAN
ZSaint-Germain-en-LayeZARA, ZEUS, ZINC

The second letter corresponds to the stations served and the origin station: a letter can have different meanings, depending on the destination. For instance, second letter "E" indicates:
The third and fourth letters are used to form a pronounceable name, changed when the service number reaches the maximum. For example, successive trains to Boissy-St-Léger are called NEGE96, NEGE98, then NELY02, NELY04, etc. Each service is uniquely identifiable, as there cannot be two "NEGE" services with the same number in the same day.
Services with the same first two letters serve the same stations, e.g. ZEBU, ZEUS and ZEMA, or NEGE, NELY and NEMO. The letters ZZ generally indicate that the established service pattern was changed for an unspecified reason, generally a technical problem which disrupted operations.

Morning Peak

Every 10 minutes:
Every 10 minutes:
In both directions every 10 minutes:
In both directions every 20 minutes:
Off-peak, a train is scheduled every 3 minutes 20 seconds between La Défense and Vincennes in both directions.