 When New York Railways began abandoning several streetcar lines in 1919, the replacement bus routes (including the current M21 and M22 routes) were picked up by the New York City Department of Plant and Structures (DP&S).The DP&S began operating several other buses (including the current M79 and M96 routes) in 1921.All of these but the M21 were acquired by Green Bus Lines in 1933; Green transferred several of these to the Comprehensive Omnibus Corporation in 1935.