Complex sentence: The West Side Branch was extended northward to a temporary terminus at 221st Street and Broadway on March 12,1906 served by shuttle trains operating between 157th Street and 221st Street.
Split into simpler sentences: The West Side Branch was extended northward to a temporary terminus of 221st Street and Broadway on March 12,1906. This extension was served by shuttle trains operating between 157th Street and 221st Street.