RER A
By the end of the 1980s, the RER A line had become the busiest in the system and the busiest single rail line outside of East Asia. Overcrowding on the RER A was already the main transport problem in the greater Paris area. To address this issue, several projects were launched: the SNCF started construction of the Est Ouest Liaison Express (EOLE; English: "east west express link") which would later be known as the RER E line, while the RATP started construction of the Paris Métro Line 14, both of which would both parallel the RER A in central Paris.