Coal in great quantity is also shipped upstream, mainly from coal fields of central and southern Illinois and western Kentucky Petroleum Products - gasoline, kerosene, fuel oil, lubricating oil upbound from the oil fields of Texas and Louisiana. The roller dam at Locks and Dam 15 is the largest in the world. It is unique because it consists of 11 hollow metal cylinders while other dams on the Upper Mississippi have a combination of roller and tainter gates. The dam was angled and erected at the narrowest part of the river to prevent frequent ice jams. Germany sued for the patent and the U.S. paid them for it.
Roller dams create some of the most dangerous undercurrents produced.
Safe distance from the dam is 600 feet above and 150 feet below. Single rollers can be raised and lowered to maintain water levels at 9 feet, which is what tows need to keep from running aground. The roller dams only purpose is navigational. It is not a flood control dam since it can not store water in flood conditions to be effective. The swingspan, weighing 2.5 million pounds, is powered by a 56 horsepower electric streetcar motor and can turn the swingspan complete 360 degree circle in either direction.