Baltimore-Washington International Marshall Airport is set to begin a $60 million expansion of its international terminal this spring.

The state Board of Public Works on Wednesday approved issuing the $60-million contract to Baltimore-based Whiting Turner Contracting Company.

The construction, to be completed next year, will add six new airline gates: two full-service gates with airline hold rooms and four arrival-only gates.

Maryland and airport officials say a three-level, 70,000 square foot extension to Concourse E will support growing international traffic at BWI, which in the past couple of years has grown by 40 percent.

Officials say this next phase of development at the terminal will ensure the airport remains a choice for travelers in the Washington region while it continues to see steady growth in international traffic. Last year 25.1 million passengers flew through BWI, the busiest airport in the region.

BWI’s international traffic has been a key factor in the airport’s record-setting growth. More than 1.2 million airport passengers flew nonstop to and from international destinations in 2016, according to the airport.

“BWI continues to set records and this expansion highlights the continued success of our airport, as well as Maryland’s flourishing economy,” Gov. Larry Hogan (R) said in a statement. “This expansion will create new job opportunities for hardworking Marylanders, while bringing greater ease and efficiency to international travel, tourism, and trade.”

The investment follows the opening of the new D/E Connector last November, a $125-million project that added a new security checkpoint, two new gates for international carriers, and several amenities for passengers.

That project added new food and retail concessions, a new children’s play area, an outdoor patio space with airfield views and a gallery featuring art created by regional artists.

Final finishes of that project are still ongoing and more concessions and new restrooms will be added, the airport said. Meanwhile, officials say, work will begin this spring on the terminal extension.

The new facilities will enhance the facilities for international travel. A number of airlines have added international routes from Baltimore in recent years.

British Airways upgraded its service between Baltimore and London last summer when it added the larger 787-8 Dreamliner aircraft to its daily service.  Norwegian began service to the French Caribbean in Deember 2015. And the low-fare international airline WOW Air added flights between BWI and Reykjavik, Iceland two years ago.

Southwest Airlines, the airport’s top carrier, has eight international destinations from BWI, including service to Mexico, Costa Rica and the Dominican Republic.