At the end of February 2012, the Regentalbahn was selected by the Zweckverband Schienenpersonennahverkehr Rheinland-Pfalz Süd (ZSPNV Süd) as the winner of the Dieselnetz Südwest - Los 2 tender. Since the 2014/2015 regular timetable change on 14 December 2014, the company has been operating the Mainz-Alzey-Kirchheimbolanden, Frankfurt-Mainz-Bad Kreuznach-Idar-Oberstein-Saarbrücken (Regional-Express services), Mainz-Bad Kreuznach-Kaiserslautern (a Regional-Express train pair during peak working hours) and Mainz-Idar-Oberstein-Baumholder/Neubrücke (Nahe) lines for 22.5 years until June 2037. In December 2016, an additional Regional-Express line was introduced on the Kaiserslautern-Bad Kreuznach-Bingen-Koblenz route, which means that 6.4 million train-kilometres per year now have to be covered. The diesel network southwest contains non-electrified main and secondary railways in Rhineland-Palatinate and connects the Rhenish Hesse, Nahe, Western Palatinate and Saarland regions in particular with the Rhine-Main region and the centres of Mainz, Rüsselsheim am Main and Frankfurt am Main as well as Frankfurt Airport.
