Trains

If you were to take all of the concrete used to build the Hoover (Boulder) Dam, there would be enough to create a 4-foot-wide sidewalk around the equator, or enough to build a two lane road from Seattle to Miami, according to the U.S. Department of the Interior. The Department also estimates that the dam weighs 6.6 million tons (13,200,000,000 pounds). So how did 1930s-era civil and industrial engineers figure out how to transport approximately 13.2 billion pounds of concrete, along with millions more tons of metal and other materials? They teamed up with another type of engineer—the railroad engineer.