WASHINGTON — Southwest Airlines will add new service between Baltimore-Washington International Airport and several cities this summer and fall.

Southwest already dominates traffic at BWI, accounting for about 70 percent of its flights.

Starting August through November, BWI adds additional nonstop service on existing routes to Denver, Seattle, Portland, Maine, New Orleans, Minneapolis and Boston.

Last month, Southwest announced additional summer flights to a half dozen destinations.

BWI remains the Washington region’s busiest airport, setting its seventh consecutive monthly record for passengers in January.

BWI had 23.8 million passengers in 2015, topping Ronald Reagan Washington National Airport by about 800,000 passengers last year.