Context: In comparison to the principal alternative, the diesel engine, electric railways offer substantially better energy efficiency, lower emissions and lower operating costs. Electric locomotives are usually quieter, more powerful, and more responsive and reliable than diesels. They have no local emissions, an important advantage in tunnels and urban areas. Some electric traction systems provide regenerative braking that turns the train's kinetic energy back into electricity and returns it to the supply system to be used by other trains or the general utility grid. While diesel locomotives burn petroleum, electricity is generated from diverse sources including many that do not produce carbon dioxide such as nuclear power and renewable forms including hydroelectric, geothermal, wind and solar.

Question: What is the principal alternative to electric railways?
Answer: diesel engine

Question: What locomotives are usually more reliable?
Answer: Electric locomotives

Question: What do some electric traction systems provide?
Answer: regenerative braking

Question: What type of fuel do diesel locomotives use?
Answer: petroleum

Question: What is one of the sources electricity is being generated from?
Answer: geothermal

Question: What does not offer better emissions efficiency?
Answer: Unanswerable

Question: Electricity is generated from many sources that do produce carbon what?
Answer: Unanswerable

Question: electricity is generated from non-renewable forms including?
Answer: Unanswerable

Question: Which locomotives have no global emissions?
Answer: Unanswerable

Question: All electric traction systems provide what kind of braking?
Answer: Unanswerable