beginning in the 1920s, many streetcar lines in queens, brooklyn, and the rest of the city began to be replaced by buses, particularly after the unification of city's three primary transit companies (including the bmt) under municipal operations in june 1940. buses began running on the line as early as 1946. on june 30, 1949, the new york city board of estimate approved the full motorization of the line with buses. the flushing–ridgewood line was officially replaced by city-owned buses on july 17, 1949, the line was designated b58 ("b" the designation for buses based in brooklyn), and the line was renamed the corona avenue line. the early fleet consisted of general motors-built buses.