A proposed underground tunnel connecting San Antonio's airport and downtown has won initial approval from the local regional mobility authority. The board for the agency assigned to improving transportation in Bexar County -- the Alamo Regional Mobility Authority -- chose the plan for a feasibility study. Th plan is from Elon Musk's Boring Company and would use Tesla's electric cars to carry passengers between the airport and downtown. The estimated price tag is between 247-million and 289-million dollars.