The Regionalbahn line, which was also called the K-Bahn from 1989 to 1995, now runs from Koenigstein via Frankfurt-Höchst station as timetable route 646 to Frankfurt (Main) Hauptbahnhof.

This is followed by Liederbach station, which is located exactly on the border of the two districts of Oberliederbach and Niederhofheim and provides the first crossing opportunity after Höchst.

After running through fields and meadows, the railway reaches the halt of Münster, then the centre of the town of Kelkheim, where train crossings takes place.

Shortly later, the railway reaches Hornau station, where the signal box controlling the line is located.

Apart from few other steam locomotives, which were partly short time lend, the FKE switched powers to diesel engines, buying several Esslingen railbuses in 1959 and renting Class V 100 and Class V 160 from Deutsche Bundesbahn operating as push-pull trains with "Silberling"-coaches.

While the train's driver had left to take a break, the three-car diesel multiple unit, which had been waiting unattended in Kelkheim Hornau, started moving towards Frankfurt, because the parking brake had not been activated.

For unknown reasons, the twenty-two-year-old had not been able to pull the emergency brake to prevent the disaster, or at least alleviate its extent and perhaps save his life.

At the beginning of November 2014, it was announced that the Rhein-Main-Verkehrsverbund and Alstom had agreed to use new railcars with fuel cell propulsion (iLINT) on the lines of the Taunus network (12, 13, 15 and 21) from 2018 at the earliest.