Baltimore-Washington International Marshall Airport, which has set records for passenger traffic in the past year, will undergo a major expansion during the next 18 months to accommodate future growth.

Travelers will eventually be able to glide along sidewalks that will connect concourses B and C and have more areas to go through security, buy food and wait for their flights. Airport officials announced Wednesday that the $100 million expansion will include a nine-lane security checkpoint, a secure connector between concourses B and C with two sets of moving sidewalks, additional restrooms, modernized airline gate hold rooms, and about 8,500 square feet of new food and retail space.

“We’ve had 26 of 28 months with positive growth, and 16 of the last 18 months we’ve set new records,” said Paul J. Wiedefeld, BWI’s executive director. “So because of that, we want to be proactive to position ourselves for additional growth.”

The project is scheduled to be completed by summer 2013.

The plans for the new construction come after the airport experienced a monthly record for passenger traffic in July, with 2.2 million travelers arriving at or departing from BWI.

Airport officials said the new security checkpoint will serve concourses A, B and C. The new connector will allow passengers to transfer between the 14 airline gates on concourse C and the 26 gates on concourses A and B without having to go through security again.

Wiedefeld said the designs for the project have been approved by the Maryland Board of Public Works, but the panel still has to approve the construction of the project. The board is scheduled to discuss the project at its Dec. 7 meeting.

“We’ve been talking to the members, and they know this is where we’re headed,” he said.

Wiedefeld said there will be “very minimal” disruption to travelers during the construction.

The last time the airport underwent a major expansion was in 2004, with the expansion of the A and B terminals, Wiedefeld said.

Jonathan Dean, a spokesman for BWI, said the project will be funded through fees the airport charges airlines, including landing and leasing fees.

BWI officials also announced that passengers should expect some major changes to the airport Wednesday morning as a result of the merger of AirTran Airways and Southwest Airlines.

AirTran will move its operations, including ticketing and baggage check-in, to Southwest at terminals A and B. AirTran flights will depart from concourse B.

The airport has added new concessions to terminals A and B, and officials said more food and retail options are scheduled to open soon.

The airport will add 16 new automated ticketing kiosks to terminals A and B for Southwest and AirTran travelers, a third curbside check-in location and a four-lane security checkpoint on the lower level near concourse A.

Southwest, which closed on the deal to acquire AirTran in May, is waiting for the Federal Aviation Administration to grant the airline a certificate to fully integrate operations. After the certificate is issued, which Southwest expects early next year, the AirTran fleet will fly under Southwest’s colors.

Wayne Pennell, BWI’s deputy executive director for operations and maintenance, said the new four-lane checkpoint on the lower level was added to temporarily deal with the additional growth. It is the only checkpoint on the lower level.

“It’s a different scenario for us,” Pennell said. “But we needed something to relieve the volume.”

Pennell said passengers traveling on Delta Air Lines will find the airline’s operations moved to AirTran’s location. That change is scheduled to take place Dec. 13.

The new nine-lane checkpoint, which will be the airport’s largest, will be built where Delta’s ticketing counter is now located. BWI will then close the temporary checkpoint on the lower level and the six-lane checkpoint at concourse C, which has been described by airport officials as too small and cramped for travelers. Once construction is finished, the airport will have 31 checkpoint lanes.