The route runs from Kiel via the towns of Preetz, Plön and Eutin to Lübeck through the Schleswig-Holstein Uplands and, on the Ascheberg–Eutin section, through Holstein Switzerland.

This region is characterized by lakes, forests and terminal moraines and is thus an important recreational area.

Thus Kiel and Neumünster were connected by rail with the Baltic port of Neustadt, but not yet with the important seaport of Lübeck.

Despite the different railway companies, passenger trains were soon working the Kiel-Lübeck route, while the other two branches - Neumünster–Ascheberg and Eutin–Neustadt - become less important.

This affected Bockholt and Kühren in 1980, Elmschenhagen, Kroog (both districts of Kiel) and Wahlstorf in 1981 and Gleschendorf Ottendorf, Timmdorf and Pansdorf in 1985.

The first stage of construction of the expansion project on the Kiel-Lübeck route had been achieved by June 2010.

The Class 648 multiple units used since 2009 are sometimes supplemented by locomotive-hauled trains in peak periods for reasons of capacity.

These trains are usually headed by DB Class 218s and comprise five to seven modernized Silberlings and double-decker coaches.