Context: In the former Soviet Union, electric traction eventually became somewhat more energy-efficient than diesel. Partly due to inefficient generation of electricity in the USSR (only 20.8% thermal efficiency in 1950 vs. 36.2% in 1975), in 1950 diesel traction was about twice as energy efficient as electric traction (in terms of net tonne-km of freight per kg of fuel). But as efficiency of electricity generation (and thus of electric traction) improved, by about 1965 electric railways became more efficient than diesel. After the mid 1970s electrics used about 25% less fuel per ton-km. However diesels were mainly used on single track lines with a fair amount of traffic  so that the lower fuel consumption of electrics may be in part due to better operating conditions on electrified lines (such as double tracking) rather than inherent energy efficiency. Nevertheless, the cost of diesel fuel was about 1.5 times more (per unit of heat energy content) than that of the fuel used in electric power plants (that generated electricity), thus making electric railways even more energy-cost effective.

Question: What type of trains became more energy-efficient in the former Soviet Union?
Answer: electric

Question: What year could be marked as year when electric railways more efficient than diesel ones?
Answer: 1965

Question: How much fuel did electric train used less than diesel in the middle of 1970 in USSR?
Answer: 25% less fuel per ton-km

Question: What could be a factor of lower energy consumption for electric trains?
Answer: better operating conditions on electrified lines

Question: How much more expensive was diesel compare to electricity per unit?
Answer: 1.5 times more (per unit of heat energy content

Question: In the US, electric traction became more energy-efficient than what?
Answer: Unanswerable

Question: When was diesel traction three times as efficient as electric traction?
Answer: Unanswerable

Question: In what decade did electrics use about 35% less fuel per ton-km.
Answer: Unanswerable

Question: The cost of diesel was 2.5 times more than what? 
Answer: Unanswerable

Question: Due to the inefficient generation of electricity in the US, diesel traction was twice as energy efficient in what year?
Answer: Unanswerable