Half that drop is solely from the reduction in coal carrying by rail in the last ten years. 1/3 of the entire coal industry in the US no longer exists vs 2006. Its biggest companies have gone or are going bankrupt. Production of coal has gone from a high of near 1.2 billion tons between 2007-2008 to maybe 800-825 million for 2016.

If you follow railroad companies or railcar builders, you know how big of an impact the drop in coal has caused.