![](https://lemmy.dbzer0.com/pictrs/image/49f3a7e0-27bd-4dc2-a729-379e3a6c80e5.png)
![](https://lemmy.world/pictrs/image/0d5e3a0e-e79d-4062-a7bc-ccc1e7baacf1.png)
It doesn’t double the capacity. It’s more a 30% increase. And, double-deckers are actually old. They date from the 19th century. In 1855, the Chemin de fer de l’Ouest introduced double-deckers on suburban lines of Paris.
https://fr.wikipedia.org/wiki/Voiture_Ouest_à_impériale
Modern double-deckers date from the 1930s, with the Voiture à étage Etat:
The train in the picture is the test train of Siemens that first ran between Herrenberg and Eutingen im Gäu in 2022 for the Land BaWü.
https://vm.baden-wuerttemberg.de/de/service/presse/pressemitteilung/pid/zwischenbilanz-fuer-den-batteriezug/