The Südostbahn is a small private railway, i.e. jointly owned by the cantonal and federal governments as an Aktiengesellschaft (AG). At the end of 2001, the previous SOB merged with the Bodensee-Toggenburg-Bahn (BT) to form the Südostbahn (SOB).
The Schweizerische Südostbahn AG operates between Romanshorn on Lake Constance via St. Gallen, Herisau, Degersheim, Wattwil and Ebnat-Kappel to Nesslau-Neu Sankt Johann in northeast Switzerland, and from Rapperswil via Seedamm, Pfäffikon SZ and Biberbrugg to Arth-Goldau in Central Switzerland.
In all, the SOB network measures 128.9 kilometres (80.1 miles), and comprises the following lines:
- Romanshorn – St. Gallen St. Fiden (19.1 km)
- St. Gallen – Wattwil – Nesslau-Neu St. Johann (44.5 km)
- Rapperswil – Pfäffikon SZ (Seedamm) (4 km)
- Pfäffikon SZ – Arth-Goldau (34.6 km, including 6.1 km common with Wädenswil–Einsiedeln)
- Wädenswil – Einsiedeln (16.7 km)
The Voralpen Express (VAE, Pre-Alpine Express), a named train, is jointly operated by the Südostbahn and the Swiss Federal Railways (SBB). It runs every hour as an InterRegio (IR) express train from Lucerne to St. Gallen via Arth-Goldau, Pfäffikon SZ, Rapperswil and Wattwil, continuing as a regional train to Romanshorn. SBB track is between Lucerne and Arth-Goldau, and between Rapperswil and Wattwil.
The Südostbahn (SOB) ordered four two-piece NPZ sets (RBDe 566 + ABt), which were delivered from the first production series in 1995 bearing numbers RBDe 566 400-403. The SOB opted not to convert any intermediate cars for use with these trainsets. Thus, the SOB DVT's differ from those of the SBB by the addition of a first class compartment. The locomotives, however, are identical to those of the SBB. The SOB has since converted several intermediate cars, however, and these trainsets are operated with them today. After the merger of the original SOB with the Bodensee-Toggenburg-Bahn to the new SOB, these four trainsets were repainted in the new livery of the SOB in 2003. They now operate throughout the SOB network as RBDe 566 077-080. Südostbahn had a fleet of ABt for their BDe 4/4 but they will soon be fully replaced by Stadler FLIRTs. NPZ ABt exist for the two types of RBDe 566 SOB ownes (566 071-076 ex BT and 566 077-080 ex SOB of the SBB-type). Nine BDt are used for the Voralpen Express with Re 456, Re 446 or SBB-CFF-FFS Re 420.
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