“Everything happens underground,” Horton said. “We won’t have construction crews walking down the street. We won’t have excavators.” The tunnel depth will gradually slant down until it’s 44 feet, well beneath underground utilities. The tunnel-boring machine that will do the bulk of the work was purchased after it was used to dig a sewer line in San Francisco, Horton said. Musk has said he wants to vastly improve the efficiency of the machine to prepare for a series of Hyperloop mass-transit tunnel networks nationwide. But Horton said Tuesday that this test tunnel is relying on existing technology.