numbers. Locomotive-hauled service between Hauptbahnhof and Ahrensburg was S4 (now RB 81); between Altona and Elmshorn was S5 (now RE 6 and RB 71); and, before the extension of electric services to Aumühle in 1969, the service between Bergedorf and Friedrichsruh was S6 (now RB 11 and RE 1). S3 was used for Regionalbahn services between Hauptbahnhof and Maschen and Neugraben (now RB 31 and RE 5) until the opening of the Harburg S-Bahn in 1983/1984. (Stations with names bold in the following table offer a turning option) Projected extensions Plans, currently shelved, would have the S-Bahn network dramatically increased. S-Bahn trains would go as far as Kaltenkirchen (the private AKN Eisenbahn currently connects to Kaltenkirchen from Eidelstedt). S4 Hamburg - Bad Oldesloe An expansion plan which is in proposal, is the opening (or reopening) of a line S4. Plans for this have been around since the 1960s. Whilst planning the City S-Bahn and network extensions of the 1960s, the German railway thought of building an S-Bahn line S4. This line will Altona in a north westerly direction towards Itzehoe via Elmshorn, being an Express line until Pinneberg. To the east of the city, the new line should have travelled with the current S1 and S11 to Hasselbrook and from there further to the northeast direction via Wandsbek to Ahrensburg along the existing regional train line. Only the eastern part of the line from Hauptbahnhof was implemented, as a regional railway line, which was designated a S-Bahn line, since the HVV did not offer travel with regional railways at the time, but wanted its fare system to be valid on the line. Since September 2000, a popular initiative in Stormarn has been working for the improvement of the S4, today the RB 81. The initiative is currently basing their arguments on a feasibility study which was ordered by S-Bahn Hamburg GmbH in the year 2002, and in principle dusted off the plans from the 1960s. According to the study, the extension involves upgrading the line to proper S-Bahn standards, served by EMUs and the addition of extra stations. The first step would be the improvement of the line as far as Ahrensburg, with a further intended step being the continuation to Bad Oldesloe. Dual-system trains would be necessary for the new line like those used on the extension to Stade. A third rail would be built as far as Ahrensburg,