Salt Lake City International Airport is currently undergoing an expansion that involves includes adding 15 new gates at a cost of more than $2.9 billion. And that may not be enough.

The Salt Lake Tribune reports interim airport director Kevin Robins thinks the current project, which also involves two new concourses and should be completed in 2020, may only cover the following five years of growth at the airport.

The project will replace the airport’s existing terminal and concourses, but could end up leading to such a high demand for flights that a third or even fourth terminal might need to be built, according to Mike Williams, terminal redevelopment project director.

The airport “continues to face the good problem of growing traffic and not enough rooms at the inn to be able to accommodate,” said Williams.

Several airlines, including Delta, Southwest, United and KLM recently added new flights at SLC. The airport was originally built to accommodate 10 million passengers a year, but it sees about twice that number. SLC is the fourth-largest U.S. hub for Delta Air Lines and the 21st-busiest airport in the United States by passenger volume.