Wheelchair accessibility must be booked in advance. The kilometre mi 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 connects Creil in the north to Melun and Malesherbes in the south, passing through the heart of Paris. Opened in stages from to , it is the longest RER line by distance, and the busiest SNCF line in France, carrying up to , passengers and operating trains each working day. It was decided instead that each line should have its own platforms, with RER A at the Gare de Lyon having its tracks at a lower level of the underground station and the future RER D on the upper level.
Initially 19 km 12 mi long, it was equipped with bi-current Z stock trains, while newer Z stock trains were still being built. They were initially composed of 4 cars until the northβsouth interconnection was inaugurated in , when they became 5-car trains where they're coupled to make car trains. At the same time, one-man operation started on the RER D. On 11 September , the northβsouth interconnection of the RER D was put into service by building a dedicated 2.
On 29 January , the first renovated Z train was presented, the first of trains. Like all other lines of the RER system, every train is assigned a four letter code, called a name of service or a mission code. Train timetables, passenger information display systems and the front of the trains all display names of services.
The first letter corresponds to the final destination, which is essentially the train's terminus. The second letter indicates the stations served by the train in the section spanning from Gare de Lyon to Villeneuve-Saint-Georges. On 20 September , an unusual incident occurred near Villeneuve-Triage station. A southbound train stopped at on the central track near the station due to an incident.
