Sorry to tell you this but all rail locomotives are actually powered by electric motors. It is the only method which is powerful enough to provide the torque necessary at a transportable weight. The diesel engines simply turn the generators which supply electricity to the drive systems. Diesel electric locomotives are wonderfully efficient and the per mile "carbon footprint" per ton hauled is so low so as to be almost nil. The simple reason that "greenies" don't think about rail freight is that freight doesn't vote - people do. And it's all about political power, not infrastructure.