RER B

RER B
RER B
	RER B train at Aéroport Charles de Gaulle 2 TGV
Overview
Termini	Aéroport Charles de Gaulle 2 TGV (B3), Mitry–Claye (B5); Robinson (B2), Saint-Rémy-lès-Chevreuse (B4);
Connecting lines	; ; ; ; ;
Stations	47
Service
Type	Rapid transit/commuter rail
System	Réseau Express Régional
Operator(s)	RATP/SNCF
Rolling stock	MI 79, MI 84
Ridership	165 million journeys per annum (2004)
History
Opened	8 December 1977; (last extension in 1994)
Technical
Line length	80 km (50 mi)
Track gauge	1,435 mm (4 ft 8+1⁄2 in) standard gauge
Electrification	Overhead line:; 25 kV 50 Hz AC; 1,500 V DC;
Route map
Route map
proposed extension
Rouvres
	Dammartin–Juilly
	–Saint-Mard
	↑ 25 kV AC
	↓ 1.5 kV DC
	Magenta
	Gare de l'Est

RER B is one of the five lines in the Réseau Express Régional (English: Regional Express Network), a hybrid commuter rail and rapid transit system serving Paris, France and its Île-de-France suburbs. The 80-kilometre (50 mi) RER B line crosses the region from north to south, with all trains serving a group of stations in central Paris, before branching out towards the ends of the line.

The line opened in stages starting in December 1977 by connecting two existing suburban commuter rail lines with a new tunnel under Paris: the Chemin de Fer du Nord to the north (which formerly terminated at Gare du Nord) and the Ligne de Sceaux to the south (which formerly terminated at Luxembourg station).

The RER B, along with the rest of the RER network, 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, with passengers taking 165 million journeys per year in 2004. That makes the RER B the second busiest single rail line in Europe (after RER A).

The line faces capacity challenges as a result of sharing a tunnel with RER D trains between Châtelet–Les Halles and Gare du Nord.