Freight trains are back and they're on a roll. After nearly going under during the 1960s, railroad companies now carry 40 percent of this nation's freight, a figure climbing steadily as shippers discover that trains are cheaper and more efficient than trucks. New equipment, computer systems and improved technology have made the difference. Engineers learn the ropes on locomotive simulators at sophisticated training centers. New locomotives are checked out at testing centers run by the rail companies. Freight trains are now part of a unified transport system capable of taking hundreds of truck trailers and scores of ship containers and zipping them from one coast to the other. The rail freight industry is alive and well and clearly on the move.