The most important private operating company was the "Große Berliner Pferde-Eisenbahn" (Great Berlin Horse Railway), which called itself "Große Berliner Straßenbahn" (GBS) (Great Berlin Tramway) after commencing electrification. GBS acquired nearly all of the other companies through the years. In 1920, the GBS merged with the municipal companies BESTAG and SSB to become the "Berliner Straßenbahn" (Berlin Tramway), which was reorganized in 1929 into the newly formed municipal "Berliner Verkehrs-AG" (BVG) (Berlin Transport Company). Besides the tramway, the BVG also took over the elevated and underground rail lines and the bus routes which were previously operated primarily by the "Allgemeine Berliner Omnibus-Actien-Gesellschaft" (ABOAG) (General Berlin Bus Corporation).