The first stage in the development of the line so that it could be integrated in the Basel trinational S-Bahn (Trinationale S-Bahn Basel) was carried out in 1999 with the opening of stations at Weil am Rhein Gartenstadt (literally “Weil on Rhine Garden City”) and Weil am Rhein Pfädlistraße.

Since 15 June 2003, SBB GmbH, a subsidiary of the Swiss Federal Railways (SBB), responsible for passenger transport operations is Germany, has operated services on the line.

Passenger services on the Weil am Rhine–Lörrach railway are now incorporated into the network as line S5 of the S-Bahn.

DB Netz AG is still responsible for maintaining the railway infrastructure.

At the timetable change of 12 December 2004, line S5 was also extended via Lörrach Hauptbahnhof to Steinen.