Elon Musk wants to build a tunnel connecting the San Antonio airport to the Riverwalk. His construction firm, The Boring Company, is one of five that have submitted proposals for the project. The Alamo Regional Mobility Authority plans to select a finalist early next year. Musk's company is building a transportation loop under the Las Vegas Strip. The billionaire now lives in Austin, and his electric car company Tesla is building a factory east of the city.