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Aargauische Südbahn ("Southern railway of Aargau") is a former railway company in Switzerland. Between 1873 and 1882, the Schweizerische Centralbahn (SCB) and the Schweizerische Nordostbahn (NOB) jointly built a connecting line to the Gotthardbahn. The line was operated by the SCB and ran from Rupperswil to Immensee. Branch lines ran from Wohlen to Bremgarten and from Hendschiken to Brugg.
The routes were opened in this order:
- 23 June 1874: Rupperswil - Lenzburg - Hendschiken - Wohlen
- 1 June 1875: Wohlen - Muri
- 1 September 1876: Wohlen - Bremgarten West
- 1 December 1881: Muri - Immensee
- 1 June 1882: Hendschiken - Brugg
In 1902, the Aargauische Südbahn (together with the SCB) became part of the Swiss Federal Railways. In 1912, the line between Wohlen and Bremgarten West was permanently leased to the Bremgarten-Dietikon-Bahn and was equipped with a third rail for 1,000 mm (3 ft 3 3⁄8 in) metre gauge trains. A planned line between Brugg and the German town of Waldshut was never built.
On 26 May 1969 a line was opened near Brugg to directly connect with the Bötzberg line. Previously all trains operating between the Gotthard and the Bötzberg lines had to reverse in Brugg. During the construction of the Heitersberg Line (opened in 1975), the Rupperswil–Lenzburg–Othmarsingen section was significantly upgraded so that it could be used by most east-west trains between Zurich and Bern.
The line is 1,435 mm (4 ft 8 1⁄2 in) standard gauge and electrified at 15 kV 16.7 Hz and has two tracks throughout. The line from Brugg to Rotkreuz is the main route for freight trains between the Basel freight yard and the St Gotthard and Italy and is therefore an important rail freight route.
Between Rotkreuz and Hendschiken S26 S-Bahn services operate every half hour. Due to lack of capacity between Gexi junction (north of Henschiken) and Lenzburg, currently only one train per hour continues to (or starts from) Aarau via Lenzburg. The other half hourly S-Bahn service starts or ends at Othmarsingen, where it connects to the S3 service to Lenzburg and Aarau. The S23 S-Bahn service operates on the Aarau–Lenzburg–Brugg route hourly.
Re 420 with a replacement train service between Mühlau and Sins