Regional train service between St. Marx <---> Praterstern and Hauptbahnhof <---> Praterstern was scheduled to stop from September 7, 2026 until October 2027 due to a planned construction project to improve the lines. Unfortunately, there was a major fire late last week at Praterstern which damaged rail cables. This has resulted in an immediate implementation of this planned stoppage.
Why does this matter?
Well, if you were planning to use the CAT (City Airport Train) (honestly never recommended) or the S7 train from the airport into the city, then those trains will now only get you to Sankt Marx. From St. Marx, there will be replacement buses taking you to the closed stations. Similarly, the CAT will be operating replacement buses. EDIT - At this time, the CAT is operating replacement buses from the airport to the city, so no train at all. The S7 is terminating at Wien-Geiselbergstraße, which is one station further away from the city center.
Similarly, the Hauptbahhof <---> Praterstern corridor on the S-Bahn is a major route for many who live here (including me) and many tourists. Think of it as a subway on steriods (better seating, less stress) at the same pricepoint.
So what do I do?
If you are trying to get from the airport into the city, then that is easy - you take the Railjet direct to the Hauptbahnhof. Just expect it to be more crowded than usual. Tickets are purchased from the machines in the hall of the airport station (no need to go to the OBB counter and no need to buy them in advance). The ride take about 15 minutes. From the Hauptbahnhof, you can easily get on the U1 Subway line.
If you are trying to get somewhere on the Hauptbahnhof to the Praterstern corridor, then look for replacement buses or, better, take Tram O, which runs this entire distance.
If you have questions, just ask.
https://wien.orf.at/stories/3366762/
https://www.oebb.at/dam/jcr:f8efd7b8-2201-4868-bd53-c2bb6016e32e/sbahn-wien-core-line-english.pdf