After steady growth from 1901 to 1913, passenger rail ridership around Boston peaked in 1920 and began to decline due to competition from private automobiles and service cuts during World War I. In the mid-1920s, after several difficult years, the B&M discontinued service on some marginal lines and began using small self-propelled railcars on others. A second round of discontinuances occurred from 1931 to 1936 as the Great Depression reduced traffic. Ridership sharply increased during World War II; the B&M had a slower postwar decline than its contemporaries, though major frequency reductions occurred in 1949-50. The B&M began testing Budd Rail Diesel Cars (RDCs) in 1952; in 1954, the railroad decided to switch all commuter service to RDCs to cut costs.