According to Colorado Unit Coal Trains, the capacity of a unit coal train depends on the capacity of the railcars used and the length of the train.
In the 1970s, 100-car unit trains carrying 100 tons per car carried 10,000 tons per train. Nowadays, 120-car trains are normal with each car carrying roughly 120 tons. Thus the capacity of a modern unit coal train is around 15,000 tons per train.
Of interest, fossil fuels—coal, natural gas, and oil—supply the vast majority of the country's energy needs, including more than two-thirds of US electricity generation. They have powered America for more than a century, but their production and use have significant health and environmental impacts, including air and water pollution, environmental degradation, and global warming.
America has vast coal reserves that provide nearly half the country’s electricity. Though abundant, coal is a dirty energy source that is responsible for more than a quarter of the nation's total global warming emissions, including 80 percent of all those from power plants.
Coal also has significant, and harmful, consequences for the environment. Coal mining degrades surrounding landscapes, burning coal releases toxins into the atmosphere, and coal-generated electricity places heavy demands on water resources. It all adds up to a huge, and costly, impact.
To learn more, visit Union of Concerned Scientists.