The ÖBB 4020 electric multiple unit from Austria

S-Bahn train in the tunnel under Wien Hauptbahnhof (Vienna Main Station)

The Austrian Federal Railways (ÖBB) had electrified many railway lines at the very early days of mainline electrification choosing the then most-advanced low-frequency alternating current system with 15 kV, 16 (2/3) Hz AC voltage. The federal capital Wien was reached by electric trains in 1952 as the main area for electrification had been the mountain passes. In those years Austria was still under Allied occupation with the capital being inside the zone controlled by the Soviet Union but the city itself split up into four control zones very similarly to those of Berlin. But while Berlin and Germany gradually shifted into an Eastern and Western part Austria was jointly run by the four allies and in 1955 given independence.
After that, the development of the city sped up and required the establishment of a commuter railway network which later incorporated various rail links inside the city and became the Vienna S-Bahn. The main vehicle on the S-Bahn became the ÖBB class 4030 electric multiple unit which had almost the same features as the subject of the present article, only being different in exterior design and the electric systems.

The class 4020 used to appear at the UNESCO World Heritage Semmering Railway

The delivery of the new three-car multiple units, consisting of a motor car 4020, a trailer 7020 and a driving trailer 6020 started in 1978 and in the upcoming nine years 120 examples were built by Vienna-based Simmering-Graz-Pauker (SGP), Swiss Brown, Boveri and Cie. (BBC), and Linz-based electric engineering company ELIN. Most of the 72 class 4030 trainsets were scrapped with some being moved to provincial regional traffic where they were replaced by the CityShuttle push-pull trains until 2004. With the high number of new, class 4020 trainsets the Vienna commuter rail network could greatly be lengthened, linking more and more communities to the fast rail network.
An ÖBB 4020 trainset is 69.4 metres long, weighs 127.4 tons, has a maximum speed of 120 km/h and a power output of 1200 kW. The angular shape of the train gave it a modern look emphasized by the large windscreen, the huge side-windows and the wide doors that smoothed into the side of the car body nicely. The shape of the driver's cabs earnt the nickname "TV set" for the trains. Three trainsets can be coupled together and operated from one driver's cab but usually only two sets are used - on RegionalExpress trains requiring a greater capacity Wiesel double-decker push-pull sets are used nowadays.
The electric system of the multiple unit was cutting-edge technology not only in Austria but also worldwide. The thyristor control with pulsating current traction motors was never before used in series production but allowed for a light-weight control system that allowed smooth, step-free acceleration and rheostatic electric braking. The greatest acceleration is 0.7 m/s² which was a lot better than that of contemporary trainsets and is only slightly worse than the replacement class 4024 "Talent"'s 0.9 m/s². High accelerations are really handy on the S-Bahn where stops are close to each other and the tracks often switch with steep gradients between underground and elevated sections.
Early trainsets were delivered with two, open toilet stalls, both installed in the middle car, but later ones had one toilet operating with a closed system. The open toilets could be closed electronically in urban areas for hygienic reasons.

An elevated Vienna S-Bahn station before the changing of the Stammstrecke to right-hand side driving

The trainsets originally had benches with low backs that were soon changed to more comfortable, more standard seats. As the trains were used on slower, longer regional routes in the Tirol and Vorarlberg areas as well as on the Rudolfsbahn and Gesäusebahn branches around Selzthal it was an improvement welcomed by passengers. After the beginning of the delivery of the CityJet trainsets by Siemens in 2015, the class 4020 has soon been retreated to certain S-Bahn Wien routes and more and more of them are removed from service without having any kind of malfunction or damage. In a few years, maybe months, these iconic trains will completely disappear from the railways of Austria only to be replaced by vehicles most railfans would consider soulless plastic.

A bridge on the Danube (Donau)

Some sets have been repainted to a design similar to the livery of the CityShuttle push-pull sets (seen at Melk)

 Breitenstein am Semmering on a day of fresh snow

Two examples at Praterstern station at the Northern side of the Stammstrecke

• Additional photos of the ÖBB 4020 EMUs

Sources

• https://de.wikipedia.org/wiki/ÖBB_4020 
• https://blog.oebb.at/die-schnellbahnzuege-der-reihe-4020/ 
• Markus Inderst: Bildatlas der ÖBB-Lokomotiven