Need a break? Play the USA TODAY Daily Crossword Puzzle. Musk's bold statements come a few months after he formed a venture called The Boring Co. to manufacture faster and more efficient tunnel-boring machines. "Just received verbal govt approval for The Boring Company to build an underground NY-Phil-Balt-DC Hyperloop," Musk said. He added that the system would ferry passengers from "city center to city center in each case, with up to a dozen or more entry/exit elevators in each city." And he urged Americans to lobby federal and state officials "if you want this to happen fast." Madeline Brozen, associate director of the Institute of Transportation Studies at the University of California Los Angeles, said the potential costs are "incomprehensible." A 120-mile above-ground stretch of the most comparable U.S. project, a high-speed rail project in California, will cost an estimated $7 billion to $10 billion, she said. But underground projects are more expensive, the hyperloop proposed by Musk is unproven technology and the innovator's system would theoretically travel five times faster than California's. Similarly, the phase one expansion of New York City's Second Avenue Subway opened for riders on Jan. 1 — nearly a century after the project was proposed. Built at an estimated cost of $4.45 billion, the expansion included three new subway stations along an underground route of no more than two miles. Winning approval for a project like the one envisioned by Musk would likely require oversight reviews and authorization from transportation authorities and other government agencies that are "territorial" and bureaucratic by nature, Brozen said. "It’s quite easy to draw up enthusiasm for a project in 140 characters when you have 10 million followers on Twitter," she said. "It’s a very different ball game when you’re trying to bring a mega-project to fruition." It was not immediately clear what Musk meant by "verbal" government approval, which carries little weight in a world in which tunneling can require navigating a byzantine thicket of regulations. However, a White House spokesman said the Trump administration has had "promising conversations" with Musk and the Boring Co. and is "committed to transformative infrastructure projects" under the premise that "our greatest solutions have often come from the ingenuity and drive of the private sector." The U.S. Department of Transportation referred questions to the White House. At the state level, some officials seemed uncertain at best about Musk's plan. J.J. Abbott, press secretary for Pennsylvania Gov. Tom Wolf, said his boss is "a big supporter of transit" who "would be interested in hearing more details on this project." "However, to date, neither our administration nor the Department of Transportation has been contacted," said Abbott. Spokespersons for the governors of Maryland, Delaware, New Jersey and New York did not respond to messages seeking comment. New York City and Philadelphia representatives said there had been no contact with Musk. A spokesperson for Amtrak, which controls much of the current rail service between New York City and Washington, had no immediate comment. A representative of New York's Metropolitan Transportation Authority pledged to look into whether the agency had had contact with Musk or The Boring Co. "The Boring Company has had a number of promising conversations with local, state and federal government officials," a company spokesman said. "With a few exceptions, feedback has been very positive and we have received verbal support from key government decision-makers for tunneling plans, including a Hyperloop route from New York to Washington DC." He said the company looks forward to future conversations with cities and states along the route and expects to secure the formal approvals necessary to break ground later this year. Brogan BamBrogan, the founder of hyperloop technology company Arrivo, applauded Musk's plan, saying "there is clearly a great interest in 21st-century transportation." But Richard Barone, transportation programs vice president for the Regional Plan Association, which studies ways to guide New York metropolitan area growth, was less certain. "Hyperloop needs to be weighed next to more conventional and proven technologies like high-speed rail, which would incrementally build off our legacy investments, including existing rights-of-way and stations," said Barone. Related: