The RER B is one of the five lines in the RER rapid transit system serving Paris, France.
The line runs from the northern termini Aéroport Charles de Gaulle (B3) and Mitry-Claye (B5) to the southern termini Robinson (B2) and Saint-Rémy-lès-Chevreuse (B4).
First inauguration : 9 December 1977
Length : 80.0 km (49.7 mi)
Number of stops : 47
Traffic (2004) : 165,100,000 journeys per annum (figure only for the RATP section of the line)
The southern part of the line (south of Gare du Nord) is operated by RATP, the northern part by SNCF. Trains are owned by either company. Until December 2009, drivers changed at Gare du Nord; RATP and SNCF drivers now operate their trains along the full length of the line. Trains moving from one network to the other at this station is known as the Interconnexion. Technical difficulties of the Interconnextion include the shared tunnel with RER D between Châtelet – Les Halles and Gare du Nord, and the fact that while the SNCF part in the northern suburbs use 25 kV AC current, the RATP part uses 1500 V DC, forcing the use of dual-voltage trains.