The S55 was a former regional railway service of the S-Bahn Zürich on the Zürcher Verkehrsverbund (ZVV), Zürich transportation network.
Until timetable changes in late 2015, the S55 linked Niederweningen and Oberglatt, as a short-working of the then routing of service S5. With that timetable change, service S55 was dropped altogether, and service S5 was diverted away from Niederweningen. Service on this stretch of line is now provided by service S15.
References
S55 (ZVV) Wikipedia(Text) CC BY-SA