I want to know the answer to the following question:
What caused the energy efficiency to go up?
All the background I'm provided with is that "Besides increased efficiency of power plants, there was an increase in efficiency (between 1950 and 1973) of the railway utilization of this electricity with energy-intensity dropping from 218 to 124 kwh/10,000 gross tonne-km (of both passenger and freight trains) or a 43% drop.". Is that enough to answer the question?
Answer: yes