RER D

RER D 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 and its suburbs. The 190-kilometre (120 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. Line D also links Gare du Nord with Gare de Lyon via Châtelet-Les Halles. Opened in stages from 1987 to 1996, it is the longest RER line by distance, and the busiest SNCF line in France, carrying up to 615,000 passengers and operating 466 trains each working day. Almost all of the line is located in the Île-de-France region, that is, within the jurisdiction of the Île-de-France Mobilités, but some of the branch lines at the north and south of the line are outside the region.