Since October 2010, 100 series 423 multiple units have been running in Frankfurt am Main (third series: 301-305, 325-334, fourth / fifth series: 372-456). Since June 2006, the lines S1 (with the exception of single roundabouts), S4, S5 and S6 are complete with 423. Since the timetable change on December 9, 2006, the S2 line is also driving with the new railcars. The short commuter trains S8 and S9 from the main station to Frankfurt Airport are partially driven by 423. The line S3 is served since March 28, 2010 exclusively with 423. Initially, the new units were primarily used, which were only approved in early 2010.