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Tunnels have frequently been in the news this year, and we’re not just talking about those sophisticated drug-smuggling tunnels U.S. officials discovered on the U.S./Mexican border. Across the United States a number of major cities have either opened new commuter tunnel projects this year, or began digging massive rail, vehicle or sewer tunnels. Many cost hundreds of millions of dollars and won’t be done for several years, but in the tunneling world, those figures don’t even raise an eyebrow — some of the tunnels on this list have been in planning or under construction for decades, cost billions, and won’t be done for many years to come. Here’s a look at some of the amazing work going on hundreds of feet beneath some of America’s biggest cities, ranked by estimated final cost.