Complex sentence: The Dongfeng (DF) series of locomotives, which are the series of diesel electric transmission, are the most important in Chinese rail transport, with the Dongfeng4 (DF4) being by far the most common locomotive to be seen on Chinese rails.
Split into simpler sentences: The Dongfeng (DF) series of diesel electric transmission locomotives is the most important in Chinese rail transport. The Dongfeng4 (DF4) is by far the most common locomotive to be seen on Chinese rails.