Bismarck Municipal Airport is south of the city. It has the largest passenger volume in western North Dakota and the second highest within the state. The airport is served by United Express, Allegiant Air, Delta Air Lines, American Airlines, and Frontier Airlines. A new $15 million terminal opened in May 2005. The previous terminal was built in the mid-1960s and expanded in the mid-1970s. After a windstorm collapsed part of the roof connecting the expanded terminal to the original building, officials decided to demolish the entire complex and build the new terminal.