Denver International Airport will grow to address surging passenger traffic after city officials approved a $1.5 billion gate-expansion project earlier this week.

The Denver City Council OK’d a series of design and construction contracts associated with the project Monday night. The 39-gate expansion across the airport’s three concourses is expected to be complete by 2021.

“I think people should know that Denver is growing and that means that their airport has to grow at the same time,” DIA spokesperson Heath Montgomery told Denver7.

DIA officials say the airport must expand to meet climbing passenger traffic. When the airport first opened more than two decades ago, it was designed to accommodate 50 million passengers a year. But DIA passenger traffic has perpetually swelled, exceeding airport capacity last year. The airport set a passenger traffic record last year with 58.3 million traveling through its gates last year.

The new gate expansion is akin to another project recently approved by the city. The $1.8 billion Great Hall Project will overhaul security screening checkpoints and concessions and boost the Jeppesen terminal’s capacity to 80 million passengers a year. Through a 34-year, private-public partnership with Spanish transportation infrastructure behemoth Ferrovial, the project was controversial, in part, because of the City Council’s loss of oversight of new concessions.

DIA’s concourses were initially designed to allow for growth and additional gates, according to the airport. In 2014, five new gates were completed on DIA’s C concourse in a $46 million expansion project to bring the airport’s current gate count to 107.