The system has seven branches in the west, which were originally numbered from north to south from the S 1 (to Freising) to the S 7 (Wolfratshausen). These are coupled with the five eastern branches. Operational requirements have changed several times, particularly due to line extensions, resulting in random numbering in the east. Two lines end at Munich East station ("Ostbahnhof"), these are currently S 1 and S 6. The first change was made in June 1991 when the branch to Ebersberg changed from S 4 to S 5 as a requirement to shorten the travel time to and from Herrsching. The line to Wolfratshausen was first called the S 10, but when it was connected to run over the trunk line it was changed to the S 7.