It doesn’t double the capacity. It’s more a 30% increase. And, double-deckers are actually old. They date from the 19 century. In 1855, the Chemin de fer de l’Ouest introduced double-deckers on suburban lines of Paris.
fr.wikipedia.org/wiki/Voiture_Ouest_à_impériale
Modern double-deckers date from the 1930s with the Voiture à étage Etat:
Ruxias@lemmy.world 3 months ago
WOW, what will the incredible Elon come up with next!? Dude comes up with all the great stuff we should have invented like ~50-100 years ago.
/s